Image forming apparatus

Abstract

To provide an image forming apparatus that can satisfactorily recover toner in developing means, while reducing the influence on image quality.SOLUTION: An image forming apparatus has an image carrier, an electrifying member, electrification voltage applying means, developing means, developing voltage applying means, a transfer member, and a control unit. The image forming apparatus recovers a transfer residual toner with the developing means. The average circularity of toner is 95 or less. The control unit performs a first step of controlling the voltage applied by the electrification voltage applying means to electrify the transfer residual toner passing through a position where the electrifying member and the image carrier face each other so that the toner has a predetermined polarity, and a second step of controlling the voltage applied by the developing voltage applying means to recover the transfer residual toner electrified in the first step with the developing means. The absolute value of the voltage VC applied to the electrifying member in the first step is 900 V or more and 1200 V or less. The voltage VB (V) applied to the developing means in the second step and the surface potential VD (V) of a non-exposed part of the image carrier satisfy |VB-VD|≥|VC|×0.3-170. VD is the surface potential of the non-exposed part.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an image forming apparatus.

Background Art

[0002] In an electrophotographic image forming apparatus, it is known to charge a photoreceptor (image carrier) by a charging member such as a charging roller, supply toner to the photoreceptor by developing means, and transfer the toner on the photoreceptor to a recording medium or an intermediate transfer member.

[0003] In the conventional technology, for example, it is known to clean the toner adhering to the photoreceptor with a cleaning means such as a cleaning blade. In recent years, from the viewpoint of miniaturization of the apparatus and the like, a so-called cleanerless method has been proposed in which cleaning means dedicated to cleaning the photoreceptor is not provided.

[0004] In a cleanerless image forming apparatus, it is known to recover the transfer residual toner remaining on the photoreceptor after transfer by developing means. In such a cleanerless image forming apparatus, since the transfer residual toner is recovered by the developing means and reused, waste toner can be suppressed. Therefore, user maintenance can be simplified, a waste toner container becomes unnecessary, and waste can be reduced.

[0005] However, when the toner recovery ability of the developing means is insufficient, the transfer residual toner that could not be completely recovered by the developing means remains on the photoreceptor. In this case, when the transfer residual toner is sent to the transfer position again, the transfer residual toner is transferred to the paper and transfer residual ghost occurs, resulting in a deterioration of image quality.

[0006] The potential difference between the potential of the developing means at the time of recovering the transfer residual toner and the potential of the non-exposed portion (which may be referred to as a non-image portion) on the photoreceptor is sometimes referred to as a base potential or the like. It is considered that by appropriately setting the base potential, the toner recovery by the developing means can be improved.

[0007] In Patent Document 1, in order to improve development and recovery, it is considered important to set a large background potential, and the potential value of the non-exposed portion of the photoreceptor is set high. Since transfer failure occurs as a drawback when the potential of the non-exposed portion on the photoreceptor is set high, Patent Document 1 states that it is effective to provide pre-transfer exposure means to prevent this.

[0008] In Patent Document 2, when the rotation speed of the photoreceptor is high, an attempt is made to increase the potential of the charging member and increase the discharge amount from the charging member. Thereby, control is performed to uniformly charge the residual transfer toner to a normal polarity and prevent adhesion to the charging member. Patent Document 2 discloses a side effect that the wear and deterioration of the photoreceptor progresses as the discharge amount increases.

[0009] Patent Document 3 discloses a cleanerless type image forming apparatus in which the developing means recovers residual transfer toner, and discloses prescribing the volume average particle diameter and content of the external additive contained in the toner. According to Patent Document 3, the occurrence of abnormal images can be suppressed over a long period.

Summary of the Invention

Problems to be Solved by the Invention

[0010] In Patent Document 1, when the background potential is increased, the reverse polarity toner of the developing means tends to move to the non-exposed portion of the photoreceptor, resulting in a problem of image fogging. When image fogging occurs, toner is applied to a portion of the paper where toner should not be applied originally, and the image quality deteriorates. On the other hand, when the background potential is decreased, the image density decreases and the image quality deteriorates.

[0011] In Patent Document 2, although the potential of the charging member is considered, optimizing the base potential is not taken into account, and the recovery of residual toner by the developing means is insufficient. Patent Document 2 uses toner manufactured by the suspension polymerization method, and since it can be estimated that the shape of the toner is spherical (circularity exceeding 95), problems related to the adhesion force between the photoreceptor and the toner are not encountered. Depending on the shape of the toner, the adhesion force between the photoreceptor and the toner may become too high, making it difficult to recover the toner by the developing means, but Patent Document 2 does not consider this problem. Therefore, by increasing the potential of the charging member, the potential of the non-exposed portion of the photoreceptor becomes high, resulting in image fogging.

[0012] In Patent Document 3, in a cleanerless type image forming apparatus, the conditions of the external additive contained in the toner are defined, and the occurrence of abnormal images can be suppressed over a long period. However, it is required to further improve the toner recovery ability by the developing means, and for example, it is required to further examine from viewpoints such as the adhesion force of the toner to the photoreceptor.

[0013] Therefore, an object of the present invention is to provide an image forming apparatus that can satisfactorily recover toner by the developing means while minimizing the influence on image quality.

Means for Solving the Problems

[0014] To solve the above problems, the image forming apparatus of the present invention includes an image carrier, a charging member that charges the image carrier, exposure means that exposes the charged image carrier to form a latent image on the surface of the image carrier, charging voltage application means that applies a voltage to the charging member, developing means that applies toner to the image carrier and develops the latent image formed on the surface of the image carrier to form a toner image, developing voltage application means that applies a voltage to the developing means, a transfer member that transfers the toner image to a transfer body, A control unit that controls the applied voltages of the charging voltage application means and the developing voltage application means, An image forming apparatus that recovers transfer residual toner remaining on the image carrier after the transfer using the developing means, wherein an average circularity of the toner is 95 or less, the control unit performs a first step of controlling the applied voltage of the charging voltage application means to charge the transfer residual toner passing through a position where the charging member and the image carrier face each other to a predetermined polarity, and a second step of controlling the applied voltage of the developing voltage application means to recover the transfer residual toner charged in the first step using the developing means, when an applied voltage to the charging member in the first step is an applied voltage VC, an absolute value of the applied voltage VC is 900 V or more and 1200 V or less, when an applied voltage to the developing means in the second step is an applied voltage VB [V] and a surface potential of a non-exposed portion, which is a portion of the image carrier not exposed by the exposure means, is a surface potential VD [V], VB and VD satisfy |VB - VD| ≧ |VC| × 0.3 - 170 and are characterized in that.

Advantages of the Invention

[0015] According to the present invention, it is possible to provide an image forming apparatus capable of satisfactorily recovering toner in the developing means while reducing the influence on image quality.

Brief Description of the Drawings

[0016]

Figure 1

Figure 2

Figure 3

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Figure 5A

Figure 5B

Figure 6A

Figure 6B

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Figure 8

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Figure 10

Figure 11

Embodiments for Carrying Out the Invention

[0017] Hereinafter, the image forming apparatus according to the present invention will be described with reference to the drawings. Note that the present invention is not limited to the embodiments shown below, and can be changed within the scope that those skilled in the art can conceive, such as other embodiments, additions, modifications, deletions, etc., and is included in the scope of the present invention as long as the functions and effects of the present invention are achieved in any aspect.

[0018] The image forming apparatus of the present invention an image carrier, a charging member for charging the image carrier, exposing means for exposing the charged image carrier to form a latent image on the surface of the image carrier, charging voltage applying means for applying a voltage to the charging member, Developing means for applying toner to the image carrier and developing a latent image formed on the surface of the image carrier to form a toner image; Developing voltage application means for applying a voltage to the developing means; A transfer member for transferring the toner image to a transfer medium; A control unit for controlling the applied voltages of the charging voltage application means and the developing voltage application means; and An image forming apparatus for recovering transfer residual toner remaining on the image carrier after the transfer by the developing means, wherein the average circularity of the toner is 95 or less, and the control unit performs a first step of controlling the applied voltage of the charging voltage application means to charge the transfer residual toner passing through a position where the charging member and the image carrier face each other to a predetermined polarity, and a second step of controlling the applied voltage of the developing voltage application means to recover the transfer residual toner charged in the first step by the developing means, when the applied voltage to the charging member in the first step is defined as an applied voltage VC, the absolute value of the applied voltage VC is 900 V or more and 1200 V or less, when the applied voltage to the developing means in the second step is defined as an applied voltage VB [V] and the surface potential of a non-exposed portion, which is a portion of the image carrier not exposed by the exposure means, is defined as a surface potential VD [V], VB and VD satisfy |VB - VD| ≧ |VC| × 0.3 - 170 and is characterized by this.

[0019] The image forming apparatus may be referred to as an electrophotographic apparatus, a printing apparatus, a printer, etc. Further, the image forming apparatus of the present invention can be a cleanerless type image forming apparatus. The cleanerless method may be referred to as a cleanerless system, a cleanerless imaging system, etc.

[0020] In the following description, the magnitude of the potential refers to the absolute value. In the following description, a charging roller is taken as an example of the charging member. The developing means has, for example, a developing roller, and in the following description, the developing roller is used for the explanation. As the image carrier, a photoreceptor or a photoreceptor drum is taken as an example for the explanation. As the transfer body, for example, paper or recording paper is taken as an example for the explanation, but as the transfer body, an intermediate transfer body (for example, an intermediate transfer belt) or the like can also be used.

[0021] FIG. 1 is a schematic configuration diagram showing an example of an image forming apparatus according to the present invention. As shown here, a printer as an example of the image forming apparatus according to the present embodiment has a paper feeding means 4, a registration roller pair 6, a photoreceptor drum 10 as an image carrier, a transfer roller 62, a fixing device 12, and the like.

[0022] In addition, it is provided with a charging power supply 21 for supplying a bias voltage necessary for image formation, a developing power supply 22, a cleaning power supply 23, a transfer power supply 24, etc., and their outputs are controlled by a control unit 25.

[0023] The charging power supply 21 is an example of a charging voltage applying means, and applies a voltage to the charging roller 160. The charging roller 160 is an example of a charging member. The voltage applied to the charging roller 160 may be referred to as a charging bias voltage or the like. The developing power supply 22 is an example of a developing voltage applying means, and applies a voltage to the developing means. The developing device 61 is an example of the developing means and has, for example, a developing roller 72. Although the developing power supply 22 is described as applying a voltage to the developing means, the developing power supply 22 may be described as applying a voltage to the developing roller 72. The voltage applied to the developing roller 72 may be referred to as a developing bias voltage or the like. The cleaning power supply 23 is an example of a cleaning voltage applying means, and applies a voltage to the cleaning member. As the cleaning member, for example, a recovery brush 161 can be mentioned. The transfer power supply 24 is an example of a transfer voltage application means and applies a voltage to the transfer roller 62. The transfer roller 62 is an example of a transfer member and has a voltage applied thereto for performing transfer. The voltage applied to the transfer roller 62 may be referred to as a transfer bias voltage or the like.

[0024] The paper feeding means 4 includes a paper feeding tray 14 in which sheets P as recording paper are accommodated in a stacked state, and a paper feeding roller 15 or the like that separates and feeds out the recording paper 105 accommodated in the paper feeding tray 14 one by one in order from the topmost one. The recording paper is an example of a transfer body and may be referred to as a recording medium, a recording material, a medium, or the like.

[0025] The recording paper 105 fed out by the paper feeding roller 15 is temporarily stopped by the registration roller pair 6, and after the posture deviation is corrected, at a timing synchronized with the rotation of the photosensitive drum 10, that is, at a timing when the tip of the toner image formed on the photosensitive drum 10 coincides with a predetermined position at the leading end in the conveyance direction of the paper Pa, it is sent to the transfer site N3 by the registration roller pair 6.

[0026] Around the photosensitive drum 10, in the order of the rotation direction indicated by the arrow, a charging roller 160 as a charging means, a developing device 61 including a developing roller 72, and a transfer roller 62 are arranged. Among these, the charging roller 160 and the developing roller 72 are provided in contact with the photosensitive drum 10. Further, a recovery brush 161 (which may also be referred to as a brush roller, a cleaning brush, a cleaning member, etc.) is provided in contact with the charging roller 160. Between the charging roller 160 and the developing device 61, exposure light Lb is irradiated and scanned onto the surface of the photosensitive drum 10 from the exposure means 5. The recovery brush 161 is an example of a recovery means.

[0027] When the photoreceptor drum 10 starts to rotate, a charging bias voltage is applied from the charging power supply 21 to the charging roller 160, and the surface of the photoreceptor is uniformly charged in the charging region N1. Based on the image information, exposure light Lb is irradiated from the exposure means 5 onto the surface of the photoreceptor drum 10, and an electrostatic latent image is formed by discharging the portion of the photoreceptor surface corresponding to the image to be created. This electrostatic latent image moves to the development region N2 due to the rotation of the photoreceptor drum 10. At this time, a development bias voltage is applied from the development power supply 22 to the developing roller 72 provided in the developing device 61.

[0028] In the development region N2, the negatively charged toner held on the developing roller is supplied from the developing roller 72 to the photoreceptor drum 10 according to the potential difference between the potential of the exposed portion and the development bias voltage, and a toner image is formed on the photoreceptor drum 10. The toner image formed on the photoreceptor drum 10 moves to the transfer region N3 at a predetermined timing. At this time, a transfer bias voltage is applied from the transfer power supply 24 to the transfer roller 62, and the toner image is transferred onto the recording paper 105 that has entered the transfer region N3.

[0029] The recording paper 105 carrying the toner image is conveyed toward the fixing device 12, fixed by the fixing device 12, and then discharged and stacked on the paper discharge tray. The residual toner remaining on the photoreceptor drum 10 without being transferred to the recording paper 105 in the transfer region N3 reaches the charging region N1 as the photoreceptor drum 10 rotates. In the charging region N1, the residual toner is charged to a negative polarity by the microdischarge of the charging bias voltage applied to the charging roller 160 and is returned to the development region N2. In the development region N2, the residual toner moves onto the developing roller 72 according to the potential difference between the potential of the portion not exposed by the exposure means 5, which is the non-exposed portion, and the development bias voltage, and is recovered into the developing device 61.

[0030] In the charging area N1, it is difficult to completely align the charging of the residual toner to the negative polarity, and the toner with a positive polarity adheres to the charging roller 160 side. Therefore, it is preferable to use a recovery brush 161 for scraping off the dirt on the charging roller 160. A cleaning bias voltage is applied from the cleaning power supply 23 to the recovery brush 161, and the positive-polarity toner attached to the charging roller 160 is cleaned by the potential difference and mechanical scraping. By using the recovery brush 161, the charging roller 160 can be made cleaner.

[0031] FIG. 2(A) is a block diagram for explaining the hardware configuration of the control unit 25 in the present embodiment. The control unit 25 includes, for example, a CPU which is a central element for performing arithmetic processing, and memories such as a ROM and a RAM which are storage elements (storage units). The sensor detection results, arithmetic results, etc. are stored in the RAM, and control programs, pre-determined data tables, etc. are stored in the ROM. The control unit 25 controls, for example, the charging power supply 21, the developing power supply 22, the cleaning power supply 23, and the transfer power supply 24. The control unit 25 controls the ON / OFF of the output of each power supply and the output value. The control unit 25 controls the exposure means 5. The control unit 25 controls the charge removal lamp 64 (charge removal means) and, for example, discharges the photosensitive drum 10 in pre-charge discharge.

[0032] FIG. 2(B) is a block diagram showing an example of the hardware configuration of the control unit 25.

[0033] The control unit 25 has a CPU (Central Processing Unit) 110, a RAM (Random Access Memory) 111, a ROM (Read Only Memory) 112, and a storage unit 113 connected via a bus 117.

[0034] The CPU 110 is an arithmetic means that controls the operation of the entire image forming apparatus 100. The RAM 111 is a volatile storage medium capable of high-speed reading and writing of information. When the CPU 110 processes information, the RAM 111 is used as a work area for the CPU 110. The ROM 112 is a read-only non-volatile storage medium in which programs such as firmware are stored.

[0035] The storage unit 113 is a non-volatile storage medium capable of reading and writing information, and stores an OS (Operating System), various control programs, application programs, and the like. The storage unit 113 is, for example, an SSD (Solid State Drive), an HDD (Hard Disk Drive), or the like.

[0036] In the image forming apparatus of the present embodiment, transfer residual toner remaining on the image carrier is recovered by the developing means. The image forming apparatus of the present embodiment is configured not to use a cleaning means (for example, a cleaning blade) for cleaning the image carrier (also referred to as an electrostatic latent image carrier, a photoreceptor, etc.). In this case, there are advantages such as downsizing of the apparatus.

[0037] Hereinafter, a method that does not use a cleaning means for cleaning the image carrier may also be referred to as a cleanerless method or the like. However, a means for cleaning the charging member and a means for cleaning the intermediate transfer belt may be provided, and even when these means are provided, they are included in the cleanerless method.

[0038] The basic configuration and operation of the cleanerless image forming apparatus will be described with reference to FIG. 3. FIG. 3 is a diagram for explaining an example of a process of forming an image. Details of each means of the image forming apparatus of the present invention will be described later. As the charging member, for example, a charging roller can be used, and in the following description, the charging roller is taken as an example for explanation.

[0039] First, the charging roller 160 uniformly charges the photosensitive drum 10 as an image carrier. The charging roller 160 in this example is arranged to be in contact with the photosensitive drum 10, and for example, applies a DC voltage to the photosensitive drum 10. The charging in this example is a contact-type DC charging method. The exposure device 121 exposes the photosensitive drum 10 to the exposure light L to form an electrostatic latent image on the photosensitive drum 10. The exposure device 121 is not particularly limited, but for example, uses an LED.

[0040] The developing roller 72 is an example of a developer carrier included in the developing device 61. The developing roller 72 has a developing bias applied by a developing voltage applying means and supplies the toner 200 to the photosensitive drum 10. Thereby, a toner image (also referred to as a visible image) is formed on the photosensitive drum 10. The developing device 61 has, for example, a stirring roller 73, and may stir the toner in the developing device 61. The rotation direction of the stirring roller 73 can be appropriately selected, and it may be in contact with or non-contact with the developing roller 72. The transfer roller 62 transfers the toner image on the photosensitive drum 10 to the recording paper 105. The discharging lamp 64 discharges the potential of the photosensitive drum 10. For example, it discharges by irradiating the discharging light QL.

[0041] The charging roller 62 is an example of a charging member, is arranged in contact with the photosensitive drum 10, and charges the photosensitive drum 10. The charging roller 62 has a voltage (which may also be referred to as a charging bias, etc.) applied by a charging voltage applying means (for example, a charging power supply 21). The charging member in the present invention is not limited to a contact type such as the charging roller 62, and may be a non-contact type. A modification example of the non-contact type charging member will be described later. The exposure device 121 is an example of an exposure means and corresponds to the exposure means 5 in FIG. 1. The exposure device 121 exposes the charged photosensitive drum 10 to form a latent image on the surface of the photosensitive drum 10. The developing device 61 is an example of developing means, which applies toner to the photosensitive drum 10 and develops the latent image formed on the surface of the photosensitive drum 10 to form a toner image. The developing device 61 has a developing roller 72 which is an example of a developer carrier. A voltage (which may also be referred to as a developing bias, etc.) is applied to the developing roller 72 by a developing voltage applying means (for example, a developing power source 22). The transfer roller 62 is an example of a transfer member, and the transfer member transfers the toner image to a transfer target (for example, a recording paper 105). The transfer roller 62 in this example is arranged in contact with the photosensitive drum 10, and transfers the toner image to the transfer target passing through the contact portion with the photosensitive drum 10. A voltage (which may also be referred to as a transfer bias, etc.) is applied to the transfer roller 62 by a transfer voltage applying means (for example, a transfer power source 24) in order to perform the transfer. The transfer member in the present invention is not limited to being arranged in contact with the image carrier, and may be arranged non - contact with the image carrier. Each applying means may be simply abbreviated as an applying means, etc.

[0042] The above configuration is the basic configuration of a cleaner - less type image forming apparatus. In such an apparatus, after the transfer process, cleaning means such as a cleaning grade for cleaning the photosensitive drum 10 is not provided.

[0043] In the example shown in FIG. 3, for example, - 300V is applied to the developing roller 72 and - 1100V is applied to the charging roller 160. For example, the surface of the photosensitive drum 10 becomes about - 50V by discharging and becomes about - 500V by charging. Note that the image forming apparatus of the present embodiment may include a recovery brush 161 (recovery means) for recovering the toner on the charging roller 160. In the example shown in FIG. 3, since the recovery brush 161 is not provided, it is shown by a broken line in the figure.

[0044] Here, an example of the toner flow in the example shown in FIG. 3 will be described. For the sake of explanation, the toner symbols in the figure are changed according to the position and state of the toner. The developing roller 72 carries the toner 200, and the toner 200 carried on the developing roller 72 is supplied to the photosensitive drum 10. The toner supplied to the photosensitive drum 10 forms a toner image (visible image) according to the electrostatic latent image (toner 201). The toner 201 on the photosensitive drum 10 is transferred to the recording paper 105. The toner 202 transferred to the recording paper 105 is fixed to the recording paper 105 in a later process.

[0045] The toner that was not transferred in the transfer process remains on the photosensitive drum 10 as residual transfer toner 203. After passing through the charge elimination process, the residual transfer toner 203 adheres to the charging roller 160 at the contact point (or vicinity) between the photosensitive drum 10 and the charging roller 160. Among the residual transfer toner 203, there is also toner 206 that does not adhere to the charging roller 160, and this toner 206 remains on the photosensitive drum 10. This toner 206 is recovered by the developing roller 72.

[0046] Next, an example of a method for recovering residual transfer toner in a cleanerless type image forming apparatus will be described with reference to FIGS. 4, 5A, and 5B. FIG. 4 is a schematic diagram for explaining the state after FIG. 3, and is a diagram schematically showing the state during printing. Here, the term "during printing" means the state in which the apparatus is operating, and includes not only the process of transferring toner to the recording paper but also the process of preparing to transfer toner to the recording paper. FIG. 4 is a diagram for explaining the processes performed between the transfer to the previous recording paper and the transfer to the next recording paper.

[0047] As described with reference to FIG. 3, the toner that was not transferred in the transfer process remains on the photosensitive drum 10 as residual transfer toner 203. In FIG. 4, it is shown that the residual transfer toner 203 remains on the photosensitive drum 10 on the downstream side of the transfer roller 62. After transferring to the previous recording paper 105, the surface of the photosensitive drum 10 is discharged by the charge elimination lamp 64. As a result, the potential difference between the charging roller 160 and the photosensitive drum 10 widens, and discharge occurs between the charging roller 160 and the photosensitive drum 10 before charging. In the figure, the discharge is schematically illustrated.

[0048] Before charging, the transfer residual toner 203 is charged negatively (not shown in FIG. 4). Among the transfer residual toner 203, there are those that are charged negatively, for example, by the pre-charging discharge, and those that remain slightly positively charged. The transfer residual toner 203 that remains slightly positive adheres to the charging roller 160 at the location (or in the vicinity) where the charging roller 160 and the photosensitive drum 10 are in contact. The toner adhering to the charging roller 160 is shown as toner 204.

[0049] In the figure, arrow a schematically shows that the transfer residual toner 203 on the photosensitive drum 10 adheres to the charging roller 160. The adhesion of the transfer residual toner 203 on the photosensitive drum 10 to the charging roller 160 may also be referred to as moving, etc.

[0050] The image forming apparatus of this example has a recovery brush 161 for recovering the toner adhering to the charging roller 160. The positive toner 204 adhering to the charging roller 160 is recovered by the recovery brush 161. Arrow b in the figure schematically shows that the toner 204 on the charging roller 160 is recovered by the recovery brush 161. The recovery of the toner 204 on the charging roller 160 by the recovery brush 161 may also be referred to as moving, etc. A recovery bias is applied to the recovery brush 161. The value of the recovery bias is not particularly limited and can be appropriately selected.

[0051] Among the transfer residual toner 203 on the photosensitive drum 10, the negatively charged toner does not adhere to the charging roller 160 and remains on the photosensitive drum 10. This toner is shown as toner 206. Note that both toner 203 and toner 206 are transfer residual toner.

[0052] The toner 206 remaining on the photoreceptor drum 10 is collected by the developing roller 72. The toner collected by the developing roller 72 is illustrated as toner 208. The collection by the developing roller 72 may be referred to as moving or the like. The toner 206 passing between the photoreceptor drum 10 and the developing roller 72 moves toward the developing roller 72 due to the potential difference between the photoreceptor drum 10 and the developing roller 72. The arrow c in the figure schematically illustrates that the toner 206 on the photoreceptor drum 10 is collected by the developing roller 72.

[0053] To collect with the developing roller 72 as described above, for example, a method of adjusting the potential of each member can be mentioned. As an example, for example, the surface of the photoreceptor drum 10 after discharging is -50V, the charging roller 160 is -1100V, the recovery brush 161 is -1300V, the surface of the photoreceptor drum 10 after charging is -500V, and the developing roller 72 is -300V. In FIG. 4, the potentials are illustrated as this example, but it is not limited thereto.

[0054] In the image forming apparatus of the present invention, it is preferable to have the recovery brush 161, but the recovery brush 161 is not essential. When there is no recovery means (for example, the recovery brush 161) for collecting the toner existing on the charging roller 160, it is preferable to adjust the potential so as to reduce the toner moving to the charging roller 160.

[0055] Next, with reference to FIGS. 5A and 5B, the movement of the toner and an example of toner recovery when the apparatus is powered down will be described. As described with reference to FIG. 4, the positive transfer residual toner 203 (the same applies to the toner 206) that became negative during discharge before charging adheres to the charging roller 160 and is collected by the recovery brush 161. During printing, since this collection is repeated, the positively charged toner 207 accumulates on the recovery brush 161. Note that the time when the apparatus is powered down is a non-image forming time when the image forming operation is not performed, and is also a period when the exposure means does not expose the image carrier.

[0056] When the device is being shut down, the potential difference between the recovery brush 161 and the charging roller 160 is adjusted to move the toner 207, which is slightly positively charged, toward the charging roller 160. This is indicated by the arrow d in the figure.

[0057] The toner 205 that has moved to the charging roller 160 moves to the photosensitive drum 10 due to the potential difference between the charging roller 160 and the photosensitive drum 10. This is indicated by the arrow e in the figure. The moved toner is shown as toner 209 in the figure. When the device is being shut down, since the photosensitive drum 10 is not discharged by the discharge lamp 64, the potential difference between the charging roller 160 and the photosensitive drum 10 is adjusted in consideration of this.

[0058] The positively charged toner 209 on the photosensitive drum 10 is not recovered by the developing roller 72 and passes through the developing roller 72 as it is. Further, the toner 209 passes through the transfer roller 62. Thus, when the device is being shut down, there will be positively charged toner 209 on the photosensitive drum 10.

[0059] In FIGS. 4, 5A, and 5B, toners 203, 206, and 209 are shown on the photosensitive drum 10. All of these are considered as residual transfer toners. The toner 209 has moved onto the photosensitive drum 10 again after the residual transfer toner 203 has been recovered by the recovery brush 161, but such toner may also be included in the residual transfer toners.

[0060] To move the toner as in the example shown in FIG. 5A, for example, a method of adjusting the potential of each member can be mentioned. For example, the potential of the recovery brush 161 can be set to -150V, the potential of the charging roller 160 can be set to -350V, the surface potential of the photosensitive drum 10 can be set to 500V, and the potential of the developing roller 72 can be set to +250V. In FIG. 5A, the potential is illustrated as this example, but it is not limited to this.

[0061] Next, in the apparatus shutdown, the recovery of the toner on the photoreceptor drum 10 will be described with reference to FIG. 5B. FIG. 5B is a continuation of FIG. 5A. As shown in the figure, the photoreceptor drum 10 is discharged by the discharge lamp 64 at a predetermined timing. By discharging, the potential difference between the charging roller 160 and the photoreceptor drum 10 widens, and discharge occurs between the charging roller 160 and the photoreceptor drum 10. In the figure, the discharge is schematically illustrated. Note that the discharge shown in the figure is not the discharge for image formation but the discharge for toner recovery.

[0062] Due to the above discharge, the toner 209 becomes negatively charged. Similar to FIG. 4, among the toner 209, the toner that is not negatively charged and remains positively charged adheres to the charging roller 160 and is recovered by the recovery brush 161 (arrows g and h in the figure).

[0063] The toner 209 that has become negatively charged due to the above discharge remains on the photoreceptor drum 10 without moving to the charging roller 160. Then, the negatively charged toner 209 is recovered by the developing roller 72 to which the developing bias is applied (arrow i in the figure). The toner recovered by the developing roller 72 is shown as toner 208 in the figure.

[0064] To move the toner as in the example shown in FIG. 5B, for example, a method of adjusting the potential of each member can be mentioned. For example, the potential of the recovery brush 161 is set to -1300V, the potential of the charging roller 160 is set to -1100V, the surface of the photoreceptor drum 10 after discharge is set to -50V, the potential of the surface of the photoreceptor drum 10 is set to 500V, and the potential of the developing roller 72 is set to -300V. In FIG. 5B, the potential is illustrated as this example, but it is not limited to this.

[0065] In this embodiment, the transfer residual toner on the photoreceptor can be recovered better by the developing means as follows. In the cleanerless system, when the transfer residual toner on the photoreceptor returns to the position facing the charging roller, it passes through while discharge is occurring toward the photoreceptor side due to the potential of the charging roller, and the transfer residual toner is charged with the normal polarity. Then, the transfer residual toner is conveyed to the position facing the developing roller and is recovered by the developing means by the base potential, which is the potential difference between the potential of the developing roller at the time of toner recovery and the potential of the non-exposed portion (which may also be referred to as the non-image portion) on the photoreceptor.

[0066] Note that the statement that the transfer residual toner is charged with the normal polarity may also be described as the transfer residual toner being given an electric charge and charged with the normal polarity. The base potential is the potential difference between the potential of the developing means at the time of transfer residual toner recovery and the potential of the non-exposed portion on the photoreceptor. The potential of the developing means at the time of transfer residual toner recovery corresponds to the applied voltage to the developing means in the second step described later. The charging roller is an example of a charging member, and the potential of the charging roller corresponds to the applied voltage to the charging member by the charging voltage applying means. The developing means has, for example, a developing roller and, if necessary, other members. The potential of the developing means is, for example, the potential of the developing roller. The potential of the developing roller corresponds to the applied voltage to the developing means by the developing voltage applying means. The non-exposed portion is a part of the image carrier that has not been exposed by the exposure means.

[0067] The recovery of toner by the developing means becomes possible because the force of the electric field due to the base potential overcomes the adhesion force between the toner and the photoreceptor. Therefore, if the value of the base potential is increased, the force attracting the transfer residual toner adhering to the non-exposed portion to the developing roller side becomes stronger, making it easier to recover by the developing means. Therefore, when the adhesion force between the toner and the photoreceptor is large, there is a tendency that the transfer residual toner is difficult to be recovered by the developing means. Therefore, in order to improve the toner recoverability, it is better to reduce the adhesion force between the toner and the photoreceptor.

[0068] The adhesion force between the toner and the photoreceptor is strongly affected by the shape of the toner. Spherical toner manufactured by the polymerization method has fewer contact points with the photoreceptor, so the adhesion force can be reduced. On the other hand, toner manufactured by the pulverization method has an irregular shape, so the number of contact points with the photoreceptor increases, resulting in an increase in the adhesion force.

[0069] Toner produced by the pulverization method has the advantage of being able to keep the manufacturing cost low, so it is widely used. When using toner produced by the pulverization method in a cleanerless system, since the adhesion force between the toner and the photoreceptor is large, the background potential has to be set quite high in order to reliably recover the toner by the developing means.

[0070] On the other hand, to increase the background potential, the potential of the developing roller is decreased, or the potential of the non-exposed part of the photoreceptor is increased. To increase the potential of the non-exposed part of the photoreceptor, the potential of the charging roller is increased. However, when the potential of the developing roller is decreased, the value of the development potential, which is the potential difference from the potential of the image part (which may also be referred to as the exposed part) on the photoreceptor, becomes small. For this reason, the amount of toner to be developed (the amount of toner applied to the photoreceptor) decreases, and the image density decreases. Also, when the potential of the non-exposed part of the photoreceptor is increased, the toner of the opposite polarity on the developing roller tends to move to the non-exposed part, so image fog (which may also be referred to as fogging) occurs. Therefore, there is a limit to increasing the background potential, and there is a problem that it is difficult to completely suppress the occurrence of transfer residual ghost.

[0071] Therefore, in this embodiment, the amount of charge applied to the toner is reduced by suppressing the pre-discharge before charging during toner recovery. Thereby, the electrostatic adhesion force of the toner to the photoreceptor can be reduced, and the adhesion force between the toner and the photoreceptor can be lowered. Pre-charge discharge is a discharge phenomenon that occurs between a charged member and an image carrier. By means of pre-charge discharge, the residual transferred toner can be charged. By performing a discharge process, for example, a negative charge is injected into the residual transferred toner on the photoreceptor passing through a position facing the charged member, and the residual transferred toner can be recovered by a developing means.

[0072] Pre-charge discharge is generated by the potential difference between the surface potential VO of the photoreceptor before charging and the voltage applied to the charging roller. Therefore, in order to suppress pre-charge discharge, the voltage applied to the charging roller may be set low.

[0073] Setting the voltage applied to the charging roller low as mentioned here means setting the set voltage when performing pre-charge discharge (Fig. 6B described later), and setting the voltage applied to make the residual transferred toner have a predetermined polarity. In the above, it is described that the voltage applied to the charging roller is set low, but the voltage applied to the charging roller is not always set low.

[0074] Discharging before charging and imparting a charge to the residual transferred toner to make it have a predetermined polarity is also referred to as charging the residual transferred toner. The amount of charge imparted to the residual transferred toner may also be referred to as the charge amount.

[0075] If the charge amount is too large, the adhesion of the residual transferred toner to the photoreceptor increases, making it difficult to be recovered by the developing roller. In the prior art, this point has not been noticed. The inventors of the present invention have conducted intensive studies and arrived at the present invention. In the present invention, without making the base potential larger than necessary, by not excessively performing the charge amount in pre-charge discharge, the recovery by the developing means can be performed well.

[0076] In this embodiment, while making the absolute value of the potential of the charging roller not more than a predetermined value, the value of the base potential is set within a predetermined range. Hereinafter, the features of the image forming apparatus of this embodiment will be described. The image forming apparatus according to this embodiment recovers the transfer residual toner remaining on the image carrier after transfer by the developing means. When recovering the transfer residual toner by the developing means, the control unit performs a first step and a second step. The first step is a step of controlling the applied voltage of the charging voltage applying means to charge the transfer residual toner passing through the position where the charging member and the image carrier face each other to a predetermined polarity. The second step is a step of controlling the applied voltage of the developing voltage applying means to recover the transfer residual toner charged in the first step by the developing means. When the applied voltage to the charging member in the first step is the applied voltage VC [V], the absolute value of the applied voltage VC is 900 V or more and 1200 V or less. When the applied voltage to the developing means in the second step is the applied voltage VB [V] and the surface potential of the non-exposed portion, which is the portion of the image carrier not exposed by the exposure means, is the surface potential VD [V], VB and VD are |VB - VD| ≧ |VC| × 0.3 - 170 satisfy.

[0077] In this embodiment, toner having an average circularity of 95 or less is used. Such toner is, for example, produced by a pulverization method and can be said to be non-spherical toner. In this embodiment, even if the toner has a high adhesion to the photoreceptor, a cleanerless system can be adopted, and the transfer residual toner can be recovered well.

[0078] In this embodiment, by defining the relationship between the average circularity of the toner, the potential of the charging member in the first step, and the base potential in the second step, while reducing the influence on the image quality, the recovery by the developing means can be performed well. Examples of reducing the influence on the image quality include suppressing image fogging and reducing image density. In this embodiment, by weakening the adhesion of the transfer residual toner to the photoreceptor, the recovery by the developing means can be performed well without increasing the base potential. Here, not increasing the base potential means not increasing the absolute value of the base potential.

[0079] The base potential is the potential difference between the potential of the developing means at the time of recovering the transferred residual toner and the potential of the non-exposed portion on the photoreceptor, that is, the potential difference between the potential of the developing means in the second step and the potential of the non-exposed portion on the photoreceptor. Therefore, the potential difference between the applied voltage VB and the surface potential VD corresponds to the base potential. Hereinafter, when referred to as the base potential, unless otherwise specified, it means the potential difference between the applied voltage VB and the surface potential VD in the second step.

[0080] The surface potential VD of the non-exposed portion of the photoreceptor can also be said to be the surface potential of the photoreceptor when it is not exposed by the exposure means. The method for measuring the surface potential is obtained by a normal measurement method. The surface potential VD of the non-exposed portion of the photoreceptor is determined by, for example, the value of the applied voltage VC, the type of the photoreceptor, the film thickness, etc.

[0081] Using FIGS. 6A and 6B, the normal image forming process and the toner recovery process will be described. FIG. 6A is a schematic diagram for explaining the normal image forming process, and FIG. 6B is a schematic diagram for explaining the toner recovery process.

[0082] The normal image forming process shown in FIG. 6A is performed, for example, as follows. For the sake of explanation, the reference numerals of the toner in the figure are changed according to the position and state of the toner. The developing roller 72 carries the toner 200, and the toner 200 carried on the developing roller 72 is supplied to the photoreceptor drum 10. The toner supplied to the photoreceptor drum 10 forms a toner image (visible image) according to the electrostatic latent image (toner 201). The toner 201 on the photoreceptor drum 10 is transferred to the recording paper 105 (transfer body). The toner 202 transferred to the recording paper 105 is fixed to the recording paper 105 in a later process.

[0083] In the cleaner system, after the normal imaging process shown in FIG. 6A, a toner recovery process shown in FIG. 6B is performed. As shown in FIG. 6B, the toner that was not transferred in the transfer process remains on the photoreceptor drum 10 as the remaining transfer toner 203. The remaining transfer toner 203 adheres to the charging roller 160 at the contact point (or in the vicinity) between the photoreceptor drum 10 and the charging roller 160.

[0084] In the toner recovery process, a first step and a second step are performed. After performing the first step, the second step is performed. In the first step, in order to charge the remaining transfer toner 203 passing through the charging roller 160 to a predetermined polarity, the applied voltage of the charging voltage applying means (for example, the charging power supply 21) is controlled. In the first step, pre-charge discharge is performed by controlling the applied voltage of the charging voltage applying means. By performing pre-charge discharge, the remaining transfer toner 203 is charged to the normal charging polarity. The remaining transfer toner charged to the normal charging polarity is indicated by reference numeral 206. In FIG. 6B, the remaining transfer toner 206 charged to the normal charging polarity is indicated by a black circle, and the remaining transfer toner 206 (toner 208) recovered by the developing roller 72 is indicated by a black circle.

[0085] In the second step, in order to recover the remaining transfer toner 206 charged in the first step with the developing roller 72, the applied voltage of the developing voltage applying means (for example, the developing power supply 22) is controlled. In the second step of the present embodiment, the applied voltage of the developing voltage applying means is controlled so that the base potential satisfies the above formula. By doing so, the remaining transfer toner 206 can be satisfactorily recovered by the developing roller 72.

[0086] The features of this embodiment will be described again. One feature of this embodiment is that when the applied voltage to the charging roller 160 in the first step is the applied voltage VC [V], the absolute value of the applied voltage VC is set to 900 V or more and 1200 V or less. In order to prevent the pre-charge discharge in the first step from becoming excessive, the absolute value of the applied voltage VC is set to a low value of 1200 V or less.

[0087] In the experiments conducted by the inventors, when the absolute value of the charge amount of the residual transfer toner exceeded 30 μC / g after the residual transfer toner passed through the charging position, the electrostatic adhesion force of the toner to the photoreceptor became too high and residual transfer ghosting occurred. The absolute value of the applied voltage VC at that time exceeded 1200 V. Therefore, when the absolute value of the applied voltage VC exceeds 1200 V, the electrostatic adhesion force of the toner to the photoreceptor becomes too high and residual transfer ghosting occurs. Also, when the absolute value of the applied voltage VC is less than 900 V, the image density becomes low. This will be explained again below. The reason for defining the applied voltage VC in terms of its absolute value is that normal charging can be either positive or negative.

[0088] The second feature of this embodiment is that the background potential only needs to have a minimum value and should not be made larger than necessary. Since the applied voltage VC is set low, the surface potential VD of the non-exposed portion of the image carrier in the second step is suppressed, and the background potential also inevitably becomes small. If the absolute value of the background potential (|VB - VD|) is 0.3×|VC| - 170 or more, the occurrence of residual transfer ghosting can be suppressed to an acceptable level.

[0089] (Experiment) Experiments were conducted on the above two features. This will be further explained with reference to FIGS. 7 and 8. FIG. 7 is a diagram showing an image chart in the evaluation of the experiment. FIG. 8 is a diagram showing the results of the experiment.

[0090] The applied voltage VC to the charging roller 160 in the first step is also referred to as the charging bias voltage VC. The applied voltage VB to the developing roller 72 in the second step is also referred to as the developing bias voltage VB.

[0091] As described above, in the image forming apparatus of the present embodiment, the conditions of the charging bias voltage VC, the developing bias voltage VB, and the surface potential VD of the non-exposed portion of the photosensitive drum 10 in the second step are defined. In the present embodiment, the transfer residual toner (residual toner) remaining on the photosensitive drum 10 without being transferred is collected by the developing roller 72, and the occurrence of transfer residual ghost is suppressed. These conditions are derived based on the conditions and results of the experiments conducted by the present inventors. The experiment was conducted in the following procedures 1 to 2.

[0092] <Procedure 1> To evaluate the transfer residual ghost, the image chart of FIG. 7 was prepared. Reference numeral 300 is a solid patch, and reference numeral 301 is a frame arranged to evaluate the transfer residual ghost. In this image chart, two solid patches 300 of 48 mm × 10 mm are arranged side by side near the center. Below the solid patch 300, two frames 301 for evaluating the transfer residual ghost are arranged side by side at a position separated by the length of one circumference of the photosensitive drum.

[0093] <Procedure 2> In the experiment, the image forming apparatus of FIG. 1 was used. In the image forming apparatus of FIG. 1, the charging bias voltage VC and the developing bias voltage VB were set to predetermined values, and the image chart of FIG. 7 was printed. At this time, if the recovery ability of the developing roller 72 is insufficient, the toner remaining on the photosensitive drum 10 is carried to the transfer area and transferred onto the recording paper 105 because the operation of printing on white paper is in progress. Therefore, fog-like toner adhesion occurs in the frame 301 below the solid patch 300. In the evaluation of this experiment, if no fog-like toner adhesion was visible, it was judged as "○", if it was faintly visible in the contour portion of the solid patch shape but within the allowable range, it was judged as "△", and if it was visible throughout the solid patch shape, it was judged as "×".

[0094] The procedure 2 was repeated while changing the values of the charging bias voltage VC and the developing bias voltage VB, and the results of all the determinations are summarized in FIG. 8. FIG. 8 represents a matrix of the charging bias voltage VC and the base potential (the potential difference between the non-exposed portion potential VD of the photoreceptor drum and the developing bias voltage). As shown in the figure, the absolute value [V] of the charging bias voltage VC is taken as the horizontal axis, and the base potential [V] is taken as the vertical axis.

[0095] When the absolute value of the charging bias voltage VC is increased, the amount of discharge generated between the charging roller 160 and the photoreceptor drum 10 increases. For this reason, the negative charge of the transfer residual toner 203 becomes higher, and the electrostatic adhesion force to the surface of the photoreceptor drum 10 becomes higher. Therefore, when the absolute value of the charging bias voltage VC is increased, the transfer residual ghost tends to deteriorate. However, as shown in the figure, as a result of the experiments by the present inventors, it was found that good results can be obtained if the absolute value of the charging bias voltage VC is in the range of 1200 V or less.

[0096] However, when the absolute value of the charging bias voltage VC is made smaller than 900 V, the absolute value of the surface potential VD of the photoreceptor drum 10 becomes 300 V or less. For this reason, when the developing bias voltage VB is set so as to satisfy the above relational expression, the developing bias voltage VB becomes a small value. Therefore, the potential difference from the image portion potential VL on the photoreceptor becomes insufficient, and the image density becomes thin. Therefore, the absolute value of the charging bias voltage VC is appropriately in the range of 900 V to 1200 V.

[0097] Also, even if the charging bias voltage VC is the same, if the base potential is increased, the force of the electric field that tries to peel the transfer residual toner 203 toward the developing roller 72 side overcomes the adhesion force of the transfer residual toner 203. Therefore, since it becomes easier to suppress the generation of transfer residual ghosts, Relational expression |VB - VD| ≧ |VC| × 0.3 - 170 it was found that good results can be obtained as long as the range that satisfies this is satisfied.

[0098] Combining these results, it can be said that the conditions for suppressing the generation of transfer residual ghosts are the range surrounded by the broken line and the limit line in Fig. 8. For the boundary line, the absolute value of the charging bias voltage VC on the horizontal axis is set as x, and the absolute value of the base potential on the vertical axis is set as y. The equation of the boundary line is y = 0.3x - 170, and based on this, the above relational expression is obtained.

[0099] To more reliably prevent the generation of transfer residual ghosts, it is effective to lower the absolute value of the charge amount of the transfer residual toner 203 to suppress the electrostatic adhesion force to the surface of the photosensitive drum 10. Since the charge amount of the transfer residual toner 203 is due to the discharge between the charging roller 160 and the photosensitive drum 10, it has a weak correlation with the charging bias voltage. As a result of the study, since transfer residual ghosts occurred with a high probability when the absolute value of the charge amount of the transfer residual toner 203 exceeded 30 μC / g, it is desirable to set it to 30 μC / g or less.

[0100] However, when the absolute value of the charge amount of the toner is too low, it will not respond to the electric field due to the base potential, making it difficult to be recovered by the developing roller 72. In the experiment, transfer residual ghosts did not occur even when it was lowered to 5 μC / g.

[0101] Such a preferred form will be described again. The charge amount Q of the transfer residual toner adhering to the surface of the image carrier (for example, the photosensitive drum 10) after passing through the position facing the charging member (for example, the charging roller 160) is 5 μC / g ≤ |Q| ≤ 30 μC / g It is preferable to satisfy. The charge amount Q is obtained by using an aspirating toner charge measuring device to aspirate the toner by a pump from the nozzle portion and measuring the charge amount of the toner collected in a Faraday cage provided with a filter inside the nozzle. The measurement of the charge amount Q is performed by stopping the device after the first step.

[0102] In FIG. 8, there are portions where |VC| is less than 900V, that is, where the absolute value of the charging bias voltage VC is less than 900V, and the result of transfer residual ghost is "○" (a, b in the figure). However, as described above, when the absolute value of the charging bias voltage VC is less than 900V, the potential difference between the developing bias voltage VB and the image portion potential VL on the photoreceptor is insufficient, and the image density becomes thin, so good results cannot be obtained.

[0103] In FIG. 8, there are portions where |VC| is greater than 1200V, that is, where the absolute value of the charging bias voltage VC is greater than 1200V, and the result of transfer residual ghost is "△" (allowable level) (c, d in the figure). However, considering the aspect of surely avoiding × because the plot of e was ×, the absolute value of the charging bias voltage VC is set to 1200V or less.

[0104] The upper limit value of the absolute value of the base potential (|VB - VD|) is not particularly limited and can be appropriately selected. As described in the second feature of the present embodiment above, in the present embodiment, since the absolute value of the applied voltage VC is set low, the surface potential VD of the non-exposed portion of the image carrier in the second step is suppressed, and the base potential inevitably becomes small. Therefore, the base potential does not become excessively large. For example, as the upper limit value of the absolute value of the base potential (|VB - VD|), 400V or less is preferable, and 300V or less is more preferable.

[0105] An example of a preferred form of the present invention will be described. A first image forming mode in which the image carrier is rotated at a predetermined rotational speed to perform image formation, and a second image forming mode in which the image carrier is rotated at a rotational speed smaller than that in the first image forming mode to perform image formation, It is preferable that the control unit controls the charging voltage applying means so that the absolute value of the voltage applied to the charging member is smaller in the second image forming mode than in the first image forming mode.

[0106] By doing so, even when the conveyance speed of the recording paper is made lower than normal for the purpose of printing on cardboard or the like, pre-discharge before charging of the remaining transfer toner does not become excessive, and the electrostatic adhesion force is suppressed. Therefore, the occurrence of remaining transfer ghosts can be further prevented.

[0107] An example of the above-described embodiment will be described with reference to FIG. 9. FIG. 9 is a diagram for explaining an example of the control of an image forming apparatus when the surface speed (rotation speed) of the photosensitive drum 10 is made lower than normal. The first image forming mode is an image forming mode in which the photosensitive member is rotated at a normal rotation speed, and image formation is performed by rotating the photosensitive member at a predetermined rotation speed. The second image forming mode performs image formation by rotating the photosensitive member at a rotation speed lower than that of the first image forming mode. FIG. 9 is a diagram for explaining an example of the control in the second image forming mode.

[0108] Depending on the type of the recording paper 106, it may be necessary to lower the conveyance speed of the recording paper 106 below normal in order to increase the amount of heat when fixing the toner image by the fixing device 12. In such a case, the rotation speed of the photosensitive drum 10 may be set low. In such a case, the time during which the remaining transfer toner 203 is charged becomes longer due to the discharge generated between the charging roller 160 and the photosensitive drum 10. For this reason, the absolute value of the charge amount of the remaining transfer toner 203 becomes higher than that during normal image formation.

[0109] Therefore, the charging voltage applying means is controlled so that the absolute value of the voltage applied to the charging roller 160 is smaller in the second image forming mode than in the first image forming mode. In the example of the second image forming mode shown in FIG. 9, for example, -250 V is applied to the developing roller 72 and -1000 V is applied to the charging roller 160. Compared with the control example of the image forming apparatus in FIG. 4 (applying -1100 V to the charging roller 160), the absolute value of the charging bias voltage applied to the charging roller 160 is lower. This prevents the absolute value of the charge amount of the remaining transfer toner 203 from becoming high, and can further suppress the occurrence of remaining transfer ghosts.

[0110] The transfer member (e.g., transfer roller 62) is applied with a voltage for performing the transfer, and it is preferable that the absolute value of the current flowing through the transfer member (transfer roller) is 10 μA or more when the voltage is applied to the transfer member.

[0111] The current flowing through the transfer roller 62 is obtained by measuring the current flowing between the transfer power supply 24 and the transfer roller 62 when a transfer bias voltage is applied. The current flowing through the transfer roller 62 may be regarded as the current flowing between the image carrier and the object to be transferred when a transfer bias voltage is applied. The current flowing between the image carrier and the object to be transferred is obtained by measuring the current flowing between the transfer power supply 24 and the transfer roller 62 when a transfer bias voltage is applied.

[0112] By being 10 μA or more, the charge amount of the residual toner after passing through the transfer area can be suppressed to a low level. For this reason, the charge amount of the residual toner after passing through the charging does not become excessive, and the electrostatic adhesion force is suppressed. Thereby, the generation of transfer residual ghost can be further prevented. A voltage is applied to the transfer member by, for example, a transfer voltage applying means (e.g., transfer power supply 24).

[0113] The image forming apparatus of the present embodiment preferably has a cleaning mode as in the following example. In this example, it is as follows. The charging member is a charging roller that contacts the surface of the image carrier. It has a cleaning mode for transferring the toner attached to the charging roller to the surface of the image carrier. The control unit controls the charging voltage applying means so that the toner attached to the charging roller is transferred to the surface of the image carrier in the cleaning mode. The cleaning mode is performed during non-image formation. The non-image formation time is, for example, a period when the image carrier is not exposed.

[0114] In this way, by performing the cleaning mode during non-image formation, the toner adhering to the charging roller can be satisfactorily recovered by the developing means. As an explanation of the cleaning mode in this example, for example, the explanation of FIG. 5A (arrow e) can be cited.

[0115] The image forming apparatus according to this embodiment preferably has a cleaning member and a cleaning mode as in the following examples. In this example, it is as follows. It has a cleaning member that contacts the surface of the charging member, and a cleaning voltage applying means for applying a voltage to the cleaning member. The charging member is a charging roller that contacts the surface of the image carrier. It has a cleaning mode in which the toner adhering to the cleaning member is transferred to the charging roller and further transferred to the surface of the image carrier. The control unit controls the charging voltage applying means and the cleaning voltage applying means so that, in the cleaning mode, the toner adhering to the cleaning member is transferred to the surface of the charging roller and further transferred to the surface of the image carrier. The cleaning mode is performed during non-image formation. The non-image formation time is, for example, a period during which the image carrier is not exposed.

[0116] In this way, by having a cleaning member, the charging member can be made cleaner. Also, by performing the cleaning mode during non-image formation, the toner adhering to the charging roller can be satisfactorily recovered by the developing means. Examples of the cleaning member include a recovery brush 161. As an explanation of the cleaning mode, for example, the explanation of FIG. 5A (arrows d, e) can be cited.

[0117] Next, another embodiment according to the present invention will be described. Descriptions of matters similar to those in the above embodiment will be omitted. In this embodiment, the charging member is a non-contact charging method, and a temporary cleaning roller is installed on the photosensitive drum. The cleanerless method is to recover by the developing roller, and even if it includes a temporary cleaning roller in addition to the recovery by the developing roller, it is included in the cleanerless method.

[0118] FIG. 10 is a schematic diagram for explaining an example of the image forming apparatus of the present embodiment, and is the same as FIG. 1. In this example, as the charging member, a scorotron type charger is used. This charging member is shown as charger 163 in the figure. As shown in the figure, charger 163 is a non-contact charging method.

[0119] Further, in the rotation direction of the photoreceptor drum 10, a temporary cleaning roller 166 is provided downstream of the transfer roller 62 and upstream of the charger 163. The temporary cleaning roller 166 is, for example, a brush roller.

[0120] A voltage is applied to the temporary cleaning roller 166 by the cleaning power supply 23, and for example, a negative voltage is applied. In this case, the transfer residual toner of positive polarity is temporarily stored in the temporary cleaning roller 166. The so-called stored here means that the transfer residual toner of positive polarity moves to the temporary cleaning roller 166 side and is held by the temporary cleaning roller 166. Further, the transfer residual toner temporarily stored in the temporary cleaning roller 166 is toner charged with a polarity opposite to the normal charging. The normal charging is, for example, a negative polarity, and the toner charged with a polarity opposite to the normal charging is, for example, the transfer residual toner charged with a positive polarity as described above.

[0121] On the other hand, the transfer residual toner of negative polarity passes through the temporary cleaning roller 166, negative charges are injected by the discharge process (pre-charging discharge) by the charging roller 160, and it is recovered by the developing roller 72.

[0122] In this example, at the end of the job, a positive voltage is applied to the temporary cleaning roller 166. As a result, due to the potential difference between the temporary cleaning roller 166 and the photoreceptor drum 10, the positively charged transfer residual toner stored in the temporary cleaning roller 166 moves to the photoreceptor drum 10. This movement is also referred to as ejection or the like. The transferred residual toner is injected with negative charges by the discharge process (pre-charging discharge) of the charger 163 and is recovered by the developing roller 72. Thereby, the temporary cleaning roller 166 can be kept clean.

[0123] Also in this example, the temporary cleaning roller 166 is disposed upstream of the charger 163 in the rotation direction of the photoreceptor drum 10. For this reason, the transferred residual toner that has moved from the temporary cleaning roller 166 to the photoreceptor drum 10 is immediately injected with negative charges by the charger 163. That is, since the transferred residual toner that has moved from the temporary cleaning roller 166 to the photoreceptor drum 10 is injected with negative charges by the pre-charging discharge immediately after the movement, the distance by which the photoreceptor drum 10 is rotated until the transferred residual toner is injected with negative charges by the pre-charging discharge can be shortened.

[0124] In this example, the distance by which the photoreceptor drum 10 is rotated until the transferred residual toner is injected with negative charges by the pre-charging discharge can be shortened compared to the above-described embodiment (the embodiment using the recovery brush 161). Therefore, the deterioration of the photoreceptor drum 10 can be slowed down, and the life of the photoreceptor drum 10 can be extended.

[0125] In the case of the form using the recovery brush 161, the transferred residual toner held by the recovery brush 161 moves from the recovery brush 161 to the charging roller 160, and after passing through the positions of the developing roller 72 and the transfer roller 62, pre-discharge is performed before charging. Therefore, in the present embodiment, compared with the form using the recovery brush 161, the distance for rotating the photoreceptor drum 10 until the stored transferred residual toner is pre-discharged can be shortened. In the description here, the transferred residual toner stored in the temporary cleaning roller 166 or the transferred residual toner stored in the recovery brush 161 is referred to as the stored transferred residual toner.

[0126] This embodiment will be described again. The charging member in this embodiment is a non-contact charging member that does not contact the image carrier, is downstream of the position where the transfer member performs transfer in the rotation direction of the image carrier, and has a temporary recovery means upstream of the position where the charging member and the image carrier face each other. The temporary recovery means temporarily recovers the transferred residual toner charged with a polarity opposite to the normal charging (for example, positive) on the surface of the image carrier. The temporary recovery means is, for example, the temporary cleaning roller 166. By using a non-contact charging member as the charging member, it is possible to suppress the transferred residual toner from moving to the charging member and causing charging failure. By using the above-described temporary recovery means, the transferred residual toner on the image carrier can be temporarily stored. Further, when using a non-contact charging member and a temporary recovery means, the configuration does not use a recovery means (for example, the recovery brush 161), and the number of parts can be reduced.

[0127] The image forming apparatus of the present embodiment further includes a cleaning voltage applying means (for example, the cleaning power supply 23) for applying a voltage to the temporary recovery means, and the control unit controls the cleaning voltage applying means at the end of image formation to move the transferred residual toner recovered by the temporary recovery means to the image carrier. By doing so, it is possible to perform pre-discharge before charging on the transfer residual toner collected by the temporary collection means and ejected onto the image carrier, and it is possible to reduce the distance for rotating the image carrier. As a result, the life of the image carrier can be extended. Further, by moving the transfer residual toner collected by the temporary collection means to the image carrier, the temporary collection means can be kept clean over time.

[0128] Next, another embodiment according to the present invention will be described. Descriptions of matters similar to those in the above embodiment will be omitted. This embodiment is a form using a peeling roller. In this embodiment, the toner strongly attached (fixed) to the photoreceptor is reduced in adhesion force by the peeling roller. As a result, the transfer residual toner can be recovered well by the developing means. Further, in this embodiment, filming on the photoreceptor can be suppressed.

[0129] FIG. 11 is a schematic diagram for explaining an example of the image forming apparatus of this embodiment, and is the same figure as FIG. 1. In this example, the peeling roller 165 is disposed in contact with the photoreceptor drum 10. Further, the peeling roller 165 in this example is disposed on the downstream side of the transfer roller 62 in the rotation direction of the photoreceptor drum 10 and on the upstream side of the charging roller 160. The peeling roller 165 is made of, for example, a sponge of silicone resin.

[0130] In the present invention, it is also possible to adopt a configuration that does not use the charge elimination lamp 64 (charge elimination means), and this example is an example that does not use the charge elimination lamp.

[0131] In this example, for instance, due to the peripheral speed difference between the peeling roller 165 and the photoreceptor drum 10, it is possible to peel off the remaining transferred toner from the photoreceptor drum 10. By rubbing the surface of the photoreceptor drum 10 with the peeling roller 165, the remaining transferred toner is peeled off from the surface of the photoreceptor drum 10. Further, a negative voltage is applied to the peeling roller 165 in this example. Preferably, the voltage applied to the peeling roller 165 is smaller than the absolute value of the voltage applied to the charging roller 160 during pre-charge discharge. Therefore, preferably, the voltage applied to the peeling roller 165 is smaller than the absolute value of the voltage applied to the charging roller 160 in the first step.

[0132] By applying a voltage to the peeling roller 165 in this way, the remaining transferred toner peeled off by the peeling roller 165 is charged by the peeling roller 165 and reattaches to the surface of the photoreceptor drum 10. Then, the developing roller 72 collects the remaining transferred toner negatively charged by the discharge process (pre-charge discharge) by the charging roller 160. The peeling roller 165 peels off the remaining transferred toner from the photoreceptor drum 10 and reattaches it to the photoreceptor drum 10 with a weak adhesion force, making it easier for the developing roller 72 to collect the remaining transferred toner. Thereby, it becomes possible to suppress filming on the photoreceptor drum 10.

[0133] As described above, in this example, the toner strongly attached (fixed) to the photoreceptor drum 10 has its adhesion force reduced by the peeling roller 165. In this example, the peeling roller 165 can reduce the adhesion force between the remaining transferred toner and the surface of the photoreceptor drum 10, making it easier for the developing roller 72 to collect the remaining transferred toner.

[0134] This embodiment will be described again. In this embodiment, there is a peeling roller on the downstream side of the position where the transfer member performs transfer in the rotational direction of the image carrier and on the upstream side of the position where the charging member and the image carrier face each other. The peeling roller rotates in contact with the image carrier and peels off the remaining transferred toner attached to the surface of the image carrier due to the peripheral speed difference with the image carrier. By arranging the peeling roller in such a manner, it is possible to reduce the adhesion force of the residual transfer toner before pre-discharge, and by utilizing the peripheral speed difference, it becomes easier to peel off the residual transfer toner.

[0135] Also, in the present embodiment, it is preferable that a voltage smaller than the absolute value of the voltage applied to the charging member in the first step is applied to the peeling roller. In this case, it is possible to reduce the adhesion force of the residual transfer toner reattached to the photoreceptor drum 10.

[0136] (Toner) The toner used in the present invention has an average circularity of 95 or less and is produced, for example, by a pulverization method. A method for measuring the circularity of the toner will be described.

[0137] The average circularity of the one-component developer toner can be measured, for example, by using a flow-type particle image analyzer (「FPIA-2100」, manufactured by Sysmex Corporation) and performing analysis using analysis software (FPIA-2100 Data Processing Program for FPIA version00-10). As a specific measurement method, 0.1 ml to 0.5 ml of a surfactant, preferably an alkylbenzene sulfonate, as a dispersant is added to 100 ml to 150 ml of water from which impurities and solids have been removed in advance in a container, and further about 0.1 g to 0.5 g of a measurement sample is added. The suspension in which the sample is dispersed is subjected to a dispersion treatment using an ultrasonic disperser for about 1 minute to 3 minutes, and the particle size and shape of the toner are measured by the above apparatus with the dispersion liquid concentration being 3,000 particles / μl to 10,000 particles / μl. The average circularity is calculated using the following formula.

[0138] Average circularity = (circumference of a circle equal to the projected area of the particle) / (circumference of the particle projection image)

[0139] <External additive> The toner used in the present invention has, for example, toner base particles and an external additive. The external additive used in the present invention contains inorganic fine particles. In the particle size distribution of the primary particles, the inorganic fine particles have a plurality of peaks in the range where the particle diameter is 5 nm or more and 50 nm or less. Among these peaks, let the highest peak be n1, the second highest peak be n2, the particle diameter (nm) at the apex of the peak n1 be n1d, the particle diameter (nm) at the apex of the peak n2 be n2d, the height at the apex of the peak n1 be n1h, and the height at the apex of the peak n2 be n2h. It is preferable that all of the following formulas (1) to (3) are satisfied.

[0140] n1d > n2d Formula (1) 10 < (n1d + n2d) Formula (2) 30 ≤ {(n2h / n1h) × 100} < 100 Formula (3)

[0141] The particle size distribution of the inorganic fine particles referred to in the present invention is a number-based particle size distribution for the primary particles, and can be measured by sequentially going through the following steps (1) to (3).

[0142] (1) With inorganic fine particles attached to the toner surface, an image of the toner is obtained using a scanning electron microscope SU8200 series (Hitachi High-Technologies Corporation). (2) The obtained image is binarized with image processing software A Image-kun (Asahi Kasei Engineering Corporation), and the equivalent circle diameter of the inorganic fine particles is calculated. The equivalent circle diameter of the inorganic fine particles is measured for 1000 particles. (3) Next, the number of classes is determined according to the following formula, a histogram is created, and the particle size distribution is obtained. Number of classes = 1 + log2n (n represents the number of data of the equivalent circle diameter of the inorganic fine particles)

[0143] As the inorganic fine particles used in the present invention, n1d, which is the particle diameter (nm) at the apex of the peak n1, is preferably 15 nm to 50 nm, and more preferably 20 nm to 40 nm. Also, n2d, which is the particle diameter (nm) at the apex of the peak n2, is preferably 5 nm to 50 nm, and more preferably 10 nm to 20 nm.

[0144] Also, the difference between n1d and n2d is preferably from 10 nm to 45 nm, more preferably from 13 nm to 30 nm.

[0145] From the viewpoint of further improving the effects of the present invention, more preferred forms of the formulas (2) and (3) are represented by the following formulas (20) and (30).

[0146] 20 < (n1d + n2d) Formula (20) 40 < {(n2h / n1h) × 100} < 90 Formula (30)

[0147] In the present invention, as means for having a plurality of peaks between 5 nm and 50 nm in the particle size distribution of the primary particles of the inorganic fine particles and satisfying all of the formulas (1) to (3), for example, two or more kinds of inorganic fine particles having different average particle diameters are prepared, and means such as adjusting the blending amount so as to satisfy the conditions can be mentioned. Note that the inorganic fine particles are preferably of the same kind.

[0148] The type of the inorganic fine particles used in the present invention is not particularly limited. For example, silica, alumina, titania, barium titanate, magnesium titanate, calcium titanate, strontium titanate, iron oxide, copper oxide, zinc oxide, tin oxide, silica sand, clay, mica, wollastonite, diatomaceous earth, chromium oxide, cerium oxide, red iron oxide, antimony trioxide, magnesium oxide, zirconium oxide, barium sulfate, barium carbonate, calcium carbonate, silicon carbide, silicon nitride and the like can be mentioned. Among them, from the viewpoint of improving stress resistance, at least one selected from silica (including hydrophobic silica), alumina and titania is preferable.

[0149] The inorganic fine particles can also be subjected to a hydrophobization treatment. The hydrophobization treatment can be obtained, for example, by treating hydrophilic fine particles with a silane coupling agent such as methyltrimethoxysilane, methyltriethoxysilane, octyltrimethoxysilane. Further, the inorganic fine particles can be heat-treated with silicone oil to perform a hydrophobization treatment.

[0150] Examples of the silicone oil include dimethyl silicone oil, methylphenyl silicone oil, chlorophenyl silicone oil, methylhydrogen silicone oil, alkyl-modified silicone oil, fluorine-modified silicone oil, polyether-modified silicone oil, alcohol-modified silicone oil, amino-modified silicone oil, epoxy-modified silicone oil, epoxy-polyether-modified silicone oil, phenol-modified silicone oil, carboxyl-modified silicone oil, mercapto-modified silicone oil, methacryl-modified silicone oil, α-methylstyrene-modified silicone oil, and the like.

[0151] Commercially available inorganic fine particles can be used. Examples of silica include R972, R974, RX200, RY200, R202, R805, R812 (all manufactured by Nippon Aerosil Co., Ltd.). Examples of titania include P-25 (manufactured by Nippon Aerosil Co., Ltd.), STT-30, STT-65C-S (all manufactured by Titanium Industry Co., Ltd.), TAF-140 (manufactured by Fuji Titanium Industry Co., Ltd.), MT-150W, MT-500B, MT-600B, MT-150A (all manufactured by Teika Co., Ltd.). Examples of hydrophobized titania fine particles include T-805 (manufactured by Nippon Aerosil Co., Ltd.), STT-30A, STT-65S-S (all manufactured by Titanium Industry Co., Ltd.), TAF-500T, TAF-1500T (all manufactured by Fuji Titanium Industry Co., Ltd.), MT-100S, MT-100T (all manufactured by Teika Co., Ltd.), IT-S (manufactured by Ishihara Sangyo Co., Ltd.).

[0152] From the viewpoint of improving stress resistance, the specific surface area of the inorganic fine particles by the BET method is preferably 20 m 2 / g to 500 m 2 / g, and more preferably 30 m 2 / g to 400 m 2 / g.

[0153] In addition to the inorganic fine particles, other external additives such as fatty acid metal salts (e.g., zinc stearate, aluminum stearate, etc.) and fluoropolymers can also be used in combination. .

[0154] Also, the content of the external additive is preferably 1.8% by mass or less in the toner. Also, the volume average particle diameter of the external additive is preferably 5 nm or more and 50 nm or less.

[0155] <Toner mother particles> The toner mother particles in the present invention contain, for example, a binder resin, a colorant, a charge control agent, a release agent, etc. Known materials can be used for the toner mother particles.

[0156] [Binder resin] As the binding resin, polymers of styrene and its substituents such as polystyrene, poly-p-chlorostyrene, polyvinyltoluene, etc.; styrene copolymers such as styrene-p-chlorostyrene copolymer, styrene-propylene copolymer, styrene-vinyltoluene copolymer, styrene-vinylnaphthalene copolymer, styrene-methyl acrylate copolymer, styrene-ethyl acrylate copolymer, styrene-butyl acrylate copolymer, styrene-octyl acrylate copolymer, styrene-methyl methacrylate copolymer, styrene-ethyl methacrylate copolymer, styrene-butyl methacrylate copolymer, styrene-methyl α-chloromethacrylate copolymer, styrene-acrylonitrile copolymer, styrene-vinyl methyl ketone copolymer, styrene-butadiene copolymer, styrene-isoprene copolymer, styrene-acrylonitrile-indene copolymer, styrene-maleic acid copolymer, styrene-maleic acid ester copolymer, etc.; polymethyl methacrylate, polybutyl methacrylate, polyvinyl chloride, polyvinyl acetate, polyethylene, polypropylene, polyester, epoxy resin, epoxy polyol resin, polyurethane, polyamide, polyvinyl butyral, polyacrylic acid resin, rosin, modified rosin, terpene resin, aliphatic or alicyclic hydrocarbon resin, aromatic petroleum resin, chlorinated paraffin, paraffin wax, etc. can be mentioned and can be used alone or in combination.

[0157] [Colorant] As the colorant, all known dyes and pigments can be used. For example, carbon black, nigrosine dye, iron black, naphthol yellow S, Hansa yellow (10G, 5G, G), cadmium yellow, yellow iron oxide, loess, lead yellow, titanium yellow, polyazo yellow, oil yellow, Hansa yellow (GR, A, RN, R), pigment yellow L, benzidine yellow (G, GR), permanent yellow (NCG), Balkan fast yellow (5G, R), tartrazine lake, quinoline yellow lake, anthrazane yellow BGL, isoindolinone yellow, red lead, minium, vermilion, cadmium red, cadmium mercury red, antimony vermilion, permanent red 4R, para red, phthalein red, parachloro ortho nitroaniline red, resorcin fast scarlet G, brilliant fast scarlet, brilliant carmine BS, permanent red (F2R, F4R, FRL, FRLL, F4RH), fast scarlet VD, Balkan fast rubine B, brilliant scarlet G, resorcin rubine GX, permanent red F5R, brilliant carmine 6B, pigment scarlet 3B, Bordeaux 5B, toluidine maroon, permanent Bordeaux F2K, heliobordeaux BL, Bordeaux 10B, bon maroon light, bon maroon medium, eosin lake, rhodamine lake B, rhodamine lake Y, alizarin lake, thioindigo red B, thioindigo maroon, oil red, quinacridone red, pyrazolone red, polyazo red, chrome vermilion, benzidine orange, perinone orange, oil orange, cobalt blue, cerulean blue, alkali blue lake, peacock blue lake, victoria blue lake, metal-free phthalocyanine blue, phthalocyanine blue, fast sky blue, indanthrene blue (RS, BC), indigo, ultramarine, dark blue, anthraquinone blue, fast violet B, methyl violet lake, cobalt violet, manganese violet, dioxane violet, anthraquinone violet, chrome green, zinc green, chromium oxide, pyridine, emerald green, pigment green B, naphthol green B, green gold, acid green lake, malachite green lakePhthalocyanine green, anthraquinone green, titanium oxide, zinc white, lithopone, and mixtures thereof can be used. The amount used is generally 0.1 to 50 parts by mass with respect to 100 parts by mass of the binder resin.

[0158] [Charge control agent] Known charge control agents can also be used. For example, nigrosine dyes, triphenylmethane dyes, chromium-containing metal complex dyes, molybdate chelate pigments, rhodamine dyes, alkoxyamines, quaternary ammonium salts (including fluorine-modified quaternary ammonium salts), alkylamides, simple substances or compounds of phosphorus, simple substances or compounds of tungsten, fluorine-based activators, metal salts of salicylic acid, and metal salts of salicylic acid derivatives can be mentioned.

[0159] The amount of the charge control agent used in the present invention is determined by the type of the binder resin, the presence or absence of additives used as necessary, and the toner manufacturing method including the dispersion method, and is not uniformly determined. Preferably, it is used in the range of 0.1 to 10 parts by mass with respect to 100 parts by mass of the binder resin, and preferably in the range of 2 to 5 parts by mass. Further, if necessary, a plurality of charge control agents may be used in combination.

[0160] [Release agent] In the present invention, a release agent may be used to impart releasability to the toner. The softening point of the release agent used is preferably 70 to 100°C.

[0161] Examples of the release agent include synthetic waxes such as low molecular weight polyethylene and polypropylene and their copolymers, vegetable waxes such as candelilla wax, carnauba wax, rice wax, wood wax, and jojoba wax, animal waxes such as beeswax, lanolin, and spermaceti wax, mineral waxes such as montan wax and ozokerite, and oil waxes such as hydrogenated castor oil, hydroxystearic acid, fatty acid amide, and phenol fatty acid ester.

[0162] From the perspective of chemical structure, hydrocarbon waxes, ester waxes, amide waxes, etc. are known, but ester waxes are suitable when evaluated in terms of storage stability, image quality, fixing temperature range, etc.

[0163] The amount of the release agent is preferably 1 to 6 parts by mass with respect to the entire toner.

[0164] The method for manufacturing the toner in the present invention may be a conventionally known method, and examples thereof include a manufacturing method that passes through the steps of mixing, kneading, roll cooling, pulverizing, and classifying toner raw materials. For example, after mixing the raw materials, they are kneaded with a twin-screw kneader, cooled with a belt cooler, pulverized with a jet mill, and classified to obtain a toner.

[0165] The weight average particle diameter of the toner is preferably 4 μm to 10 μm, and more preferably 5 μm to 8 μm.

[0166] Aspects of the present invention are as follows, for example. <1> An image carrier, A charging member that charges the image carrier, Exposing means for exposing the charged image carrier to form a latent image on the surface of the image carrier, Charging voltage applying means for applying a voltage to the charging member, Developing means for applying toner to the image carrier and developing the latent image formed on the surface of the image carrier to form a toner image, Developing voltage applying means for applying a voltage to the developing means, A transfer member for transferring the toner image to a transfer body, A control unit for controlling the applied voltages of the charging voltage applying means and the developing voltage applying means, and An image forming apparatus that recovers transfer residual toner remaining on the image carrier after the transfer with the developing means, The average circularity of the toner is 95 or less, The control unit, A first step of controlling the applied voltage of the charging voltage applying means to charge the transfer residual toner passing through a position where the charging member and the image carrier face each other to a predetermined polarity; A second step of controlling the applied voltage of the developing voltage applying means to collect the transfer residual toner charged in the first step by the developing means, and when the applied voltage to the charging member in the first step is the applied voltage VC [V], the absolute value of the applied voltage VC is 900 V or more and 1200 V or less, when the applied voltage to the developing means in the second step is the applied voltage VB [V] and the surface potential of the non-exposed portion, which is a portion of the image carrier not exposed by the exposing means, is the surface potential VD [V], VB and VD are |VB - VD| ≥ |VC| × 0.3 - 170 satisfy An image forming apparatus characterized by this. <2> The charge amount Q of the transfer residual toner adhering to the surface of the image carrier after passing through the position facing the charging member is 5 μC / g ≤ |Q| ≤ 30 μC / g satisfy The image forming apparatus according to <1>, characterized by this. <3> A first image forming mode in which the image carrier is rotated at a predetermined rotational speed to form an image, and a second image forming mode in which the image carrier is rotated at a rotational speed lower than the first image forming mode to form an image, and the control unit controls the charging voltage applying means so that the absolute value of the voltage applied to the charging member is smaller in the second image forming mode than in the first image forming mode. The image forming apparatus according to <1> or <2>, characterized by this. <4> A voltage is applied to the transfer member for performing the transfer, and the absolute value of the current flowing through the transfer member when a voltage is applied to the transfer member is 10 μA or more. The image forming apparatus according to any one of <1> to <3>, characterized in that... <5> The charging member is a charging roller that contacts the surface of the image carrier, It has a cleaning mode for transferring the toner attached to the charging roller to the surface of the image carrier, In the cleaning mode, the control unit controls the charging voltage applying means so that the toner attached to the charging roller is transferred to the surface of the image carrier. The cleaning mode is performed during a period when the image carrier is not exposed by the exposure means. The image forming apparatus according to any one of <1> to <4>, characterized in that... <6> A cleaning member that contacts the surface of the charging member, And cleaning voltage applying means for applying a voltage to the cleaning member. The charging member is a charging roller that contacts the surface of the image carrier, It has a cleaning mode for transferring the toner attached to the cleaning member to the charging roller and further to the surface of the image carrier. In the cleaning mode, the control unit controls the charging voltage applying means and the cleaning voltage applying means so that the toner attached to the cleaning member is transferred to the surface of the charging roller and further to the surface of the image carrier. The cleaning mode is performed during a period when the image carrier is not exposed by the exposure means. The image forming apparatus according to any one of <1> to <4>, characterized in that... <7> It is downstream of the position where the transfer member performs transfer in the rotation direction of the image carrier, It has a peeling roller upstream of the position where the charging member and the image carrier face each other, The peeling roller rotates in contact with the image carrier and peels off the residual transferred toner attached to the surface of the image carrier by the peripheral speed difference with the image carrier. The image forming apparatus according to any one of <1> to <6>, characterized in that... <8> A voltage smaller than the absolute value of the voltage applied to the charging member in the first step is applied to the peeling roller. The image forming apparatus according to <7>, characterized in that... <9> The charging member is a non-contact charging member that does not contact the image carrier. It has a temporary recovery means on the downstream side of the position where the transfer member performs transfer in the rotation direction of the image carrier and on the upstream side of the position where the charging member and the image carrier face each other. The temporary recovery means temporarily recovers the transfer residual toner charged with a polarity opposite to the normal charging on the surface of the image carrier. The image forming apparatus according to any one of <1> to <8>, characterized in that... <10> It has a cleaning voltage application means for applying a voltage to the temporary recovery means. The control unit controls the cleaning voltage application means at the end of image formation to move the transfer residual toner recovered by the temporary recovery means to the image carrier. The image forming apparatus according to <9>, characterized in that...

Explanation of reference numerals

[0167] 10 Electrostatic latent image carrier (photoconductor drum) 28 Fixing device 61 Developing device 62 Transfer roller 64 Charge elimination lamp 72 Developing roller 73 Stirring roller 105 Recording paper 121 Exposure device 160 Charging roller 161 Recovery brush 163 Charger 165 Peeling roller 166 Temporary cleaning roller

Prior art documents

Patent Document

[0168]

Patent Document 1

Patent Document 2

Patent Document 3

Claims

1. An image carrier; a charging member for charging the image carrier; an exposure unit that exposes the charged image carrier to light to form a latent image on the surface of the image carrier; a charging voltage applying means for applying a voltage to the charging member; a developing unit that applies a toner to the image carrier and develops a latent image formed on the surface of the image carrier to form a toner image; a developing voltage applying means for applying a voltage to the developing means; A transfer member for transferring the toner image onto a transfer medium; a control unit for controlling the applied voltages of the charging voltage application means and the developing voltage application means, an image forming apparatus in which residual toner remaining on the image carrier after the transfer is collected by the developing means, the toner has an average circularity of 95 or less, The control unit is a first step of controlling an applied voltage of the charging voltage applying means in order to charge the transfer residual toner passing through a position where the charging member and the image carrier face each other to a predetermined polarity; a second step of controlling an applied voltage of the developing voltage applying means in order to recover the transfer residual toner charged in the first step by the developing means; When the voltage applied to the charging member in the first step is an applied voltage VC [V], the absolute value of the applied voltage VC is 900 V or more and 1200 V or less, When the voltage applied to the developing means in the second step is an applied voltage VB [V], and the surface potential of the non-exposed portion of the image carrier that is not exposed by the exposure means is a surface potential VD [V], VB and VD are |VB-VD|≧|VC|×0.3-170 Fulfill 1. An image forming apparatus comprising:

2. The charge amount Q of the transfer residual toner adhering to the surface of the image carrier after passing the position facing the charging member is 5μC / g≦|Q|≦30μC / g Fulfill 2. The image forming apparatus according to claim 1,

3. a first image forming mode in which an image is formed by rotating the image carrier at a predetermined rotation speed, and a second image forming mode in which an image is formed by rotating the image carrier at a rotation speed slower than that in the first image forming mode, The control section controls the charging voltage application section so that the absolute value of the voltage applied to the charging member is smaller in the second image forming mode than in the first image forming mode.

2. The image forming apparatus according to claim 1,

4. A voltage is applied to the transfer member to effect the transfer; The absolute value of a current flowing through the transfer member when a voltage is applied to the transfer member is 10 μA or more.

2. The image forming apparatus according to claim 1,

5. the charging member is a charging roller that contacts the surface of the image carrier, a cleaning mode in which the toner adhering to the charging roller is transferred to the surface of the image carrier; the control unit controls the charging voltage application unit in the cleaning mode so as to transfer the toner adhering to the charging roller to the surface of the image carrier; The cleaning mode is performed during a period when the exposure unit does not expose the image carrier.

2. The image forming apparatus according to claim 1,

6. a cleaning member that contacts the surface of the charging member; a cleaning voltage applying means for applying a voltage to the cleaning member, the charging member is a charging roller that contacts the surface of the image carrier, a cleaning mode in which the toner adhering to the cleaning member is transferred to the charging roller and then to the surface of the image carrier; the control unit controls the charging voltage application unit and the cleaning voltage application unit in the cleaning mode so as to transfer the toner adhering to the cleaning member to the surface of the charging roller and further to the surface of the image carrier; The cleaning mode is performed during a period when the exposure unit does not expose the image carrier.

2. The image forming apparatus according to claim 1,

7. the transfer member is located downstream of a position where the transfer member performs transfer in a rotation direction of the image carrier; a peeling roller is provided upstream of a position where the charging member and the image carrier face each other, The peeling roller rotates in contact with the image carrier and peels off the transfer residual toner adhering to the surface of the image carrier by a difference in peripheral speed between the peeling roller and the image carrier.

2. The image forming apparatus according to claim 1,

8. A voltage smaller in absolute value than the voltage applied to the charging member in the first step is applied to the peeling roller.

8. The image forming apparatus according to claim 7,

9. the charging member is a non-contact charging member that does not come into contact with the image carrier, a temporary recovery means that is located downstream of a position where the transfer member performs transfer in a rotation direction of the image carrier and upstream of a position where the charging member and the image carrier face each other; The temporary collecting means temporarily collects the transfer residual toner that is charged with a polarity opposite to the normal charge on the surface of the image carrier.

2. The image forming apparatus according to claim 1,

10. a cleaning voltage applying means for applying a voltage to the temporary collecting means, The control unit controls the cleaning voltage application unit to move the transfer residual toner collected by the temporary collection unit to the image carrier at the end of image formation.

10. The image forming apparatus according to claim 9,

Images