Image forming apparatus

Abstract

The present invention relates to an image forming apparatus capable of satisfactorily collecting toner by a developing means while reducing influence on image quality, the image forming apparatus including an image carrier, a charging member, a charging voltage applying means, a developing means, a developing voltage applying means, a transfer member, and a control unit. The transfer residual toner is collected by a developing means. The toner has an average roundness of 95 or less. The control unit performs: a first step of controlling the applied voltage of the charging voltage applying means in order to charge the residual transfer toner at a position facing the image carrier by the charging member to a predetermined polarity; and a second step of recovering the residual transfer toner charged in the first step by the developing means. And a second step of controlling the applied voltage of the developing voltage applying means. The absolute value of the voltage VC applied to the charging member in the first step is 900 V or more and 1200 V or less. In the second step, the voltage VB [V] applied to the developing means and the surface potential VD [V] of the non-exposed portion of the image carrier satisfy VB-VD > = VC * 0.3-170. VD is a surface potential of the non-exposed portion.

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 that a photoreceptor (image carrier) is charged by a charging member such as a charging roller, and toner is supplied to the photoreceptor by a developing means, and the toner on the photoreceptor is transferred to a recording medium or an intermediate transfer member.

[0003] In the prior art, it is known to clean the toner adhering to the photoreceptor by a cleaning means such as a cleaning blade. In recent years, from the viewpoint of miniaturization of the apparatus, etc., a so-called cleanerless method has been proposed in which a cleaning means for specifically cleaning the photoreceptor is not provided.

[0004] In a cleanerless image forming apparatus, an image forming apparatus is known that recovers transfer residual toner remaining on the photoreceptor after transfer by a 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, and a waste toner container is not required, and waste can be reduced.

[0005] However, when the toner recovery ability in the developing means is insufficient, transfer residual toner not 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, resulting in transfer residual ghosting and reducing the image quality.

[0006] The potential difference between the potential of the developing means at the time of recovering transfer residual toner and the potential of the non-exposed portion (which may also be referred to as a non-image portion) on the photoreceptor is sometimes called the bottom surface potential or the like. By appropriately setting the bottom surface potential, the toner recovery of the developing means can be made good.

[0007] In Patent Document 1, it is important to set the bottom surface potential to be large for better development recovery, and the value of the potential of the non-exposed portion of the photoreceptor is set to be high. Since transfer failure occurs as a drawback when the potential of the non-exposed portion on the photoreceptor is set to be high, in Patent Document 1, it is effective to provide a pre-transfer exposure means to prevent this situation.

[0008] In Patent Document 2, when the rotation speed of the photoreceptor is high, an attempt is made to increase the discharge amount from the charging member by increasing the potential of the charging member. Thus, control is performed to uniformly charge the transfer residual toner to a regular polarity and prevent adhesion to the charging member. Patent Document 2 discloses a side effect that the wear and deterioration of the photoreceptor are aggravated due to the increase in the discharge amount.

[0009] Patent Document 3 discloses an image forming apparatus of a cleanerless type that recovers transfer residual toner by a developing means, and discloses defining the volume average particle diameter and content of an additive contained in the toner. According to Patent Document 3, generation of abnormal images can be suppressed for a long time.

[0010] In Patent Document 1, when the bottom surface potential is increased, the toner of the opposite polarity of the developing means is likely to be transferred to the non-exposed portion of the photoreceptor, thus causing a problem of image fogging. When image fogging occurs, the toner is applied to a portion of the paper where the toner should not be applied, resulting in a decrease in image quality. On the other hand, when the bottom surface 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 investigated, appropriate adjustment of the bottom surface potential is not considered, which is insufficient for recovering transfer residual toner by the developing means. In Patent Document 2, a toner manufactured by suspension polymerization is used. Since it can be presumed that the shape of the toner is spherical (roundness exceeding 95), problems related to the adhesion between the photoreceptor and the toner are not noticed. Depending on the shape of the toner, if the adhesion between the photoreceptor and the toner is too high, it becomes difficult to recover the toner by the developing means, but this problem is not considered in Patent Document 2. Therefore, by increasing the potential of the charging member, the potential of the non-exposed portion of the photoreceptor becomes high, and image fogging occurs.

[0012] In Patent Document 3, in an image forming apparatus of a cleanerless type, conditions of an additive contained in the toner are specified, and generation of abnormal images can be suppressed for a long time. However, further improvement in the toner recovery ability of the developing means is required. For example, from the viewpoint of the adhesion of the toner to the photoreceptor and the like, further investigation is required.

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

[0014]

Patent Document 1

[0015]

Patent Document 2

[0016]

Patent Document 3

[0017] In order to solve the above problems, an image forming apparatus according to the present invention includes: an image carrier; a charging member that charges the image carrier; an exposure unit that exposes the charged image carrier and forms a latent image on the surface of the image carrier; a charging voltage application unit that applies a voltage to the charging member; a developing unit that supplies toner to the image carrier and develops the latent image formed on the surface of the image carrier to form a toner image; a developing voltage application unit that applies a voltage to the developing unit; a transfer member that transfers the toner image to a transfer body; and a control unit that controls the applied voltages of the charging voltage application unit and the developing voltage application unit, and recovers transfer residual toner remaining on the image carrier after transfer through the developing unit. The image forming apparatus is characterized in that the average roundness of the toner is 95 or less, and the control unit executes a first process of controlling the applied voltage of the charging voltage application unit by charging the transfer residual toner at a position facing the image carrier through the charging member to a specified polarity, and a second process of controlling the applied voltage of the developing voltage application unit in order to recover the transfer residual toner charged in the first process through the developing unit. When the applied voltage to the charging member in the first process 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 unit in the second process is the applied voltage VB [V] and the surface potential of a portion of the image carrier not exposed by the exposure unit, i.e., the non-exposed portion, is the surface potential VD [V], VB and VD satisfy the following formula: |VB - VD| ≥ |VC| × 0.3 - 170.

[0018] According to the present invention, it is possible to provide an image forming apparatus that can satisfactorily recover toner by a developing means while reducing the influence on image quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 The figure is an explanatory diagram for explaining an embodiment of the image forming apparatus according to the present invention.

[0020] Figure 2 The figures are block diagrams (A) and (B) for explaining an example of the hardware configuration of the control unit.

[0021] Figure 3 The figure is a schematic diagram for explaining another embodiment of the image forming apparatus according to the present invention.

[0022] Figure 4 The figure is a schematic diagram for explaining another embodiment of the image forming apparatus according to the present invention.

[0023] Figure 5AThe figure shown is an explanatory diagram for explaining another embodiment of the image forming apparatus of the present invention.

[0024] Figure 5B The figure shown is an explanatory diagram for explaining another embodiment of the image forming apparatus of the present invention.

[0025] Figure 6A The figure shown is an explanatory diagram for explaining another embodiment of the image forming apparatus of the present invention.

[0026] Figure 6B The figure shown is an explanatory diagram for explaining another embodiment of the image forming apparatus of the present invention.

[0027] Figure 7 The figure shown is an image chart for experimental evaluation.

[0028] Figure 8 The figure shown is the evaluation result of transfer residual ghosting in the experimental results.

[0029] Figure 9 The figure shown is a schematic diagram for explaining another embodiment of the image forming apparatus of the present invention.

[0030] Figure 10 The figure shown is a schematic diagram for explaining another embodiment of the image forming apparatus of the present invention.

[0031] Figure 11 The figure shown is a schematic diagram for explaining another embodiment of the image forming apparatus of the present invention. Detailed Embodiment

[0032] 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 for other embodiments, additions, corrections, deletions, etc., can be changed within the scope that can be conceived by those skilled in the art. No matter what the method is, as long as it achieves the functions and effects of the present invention, it is within the scope of the present invention.

[0033] The image forming apparatus of the present invention includes: an image carrier; a charging member that charges the image carrier; an exposure unit that exposes the charged image carrier and forms a latent image on the surface of the image carrier; a charging voltage application unit that applies a voltage to the charging member; a developing unit that supplies toner to the image carrier and develops the latent image formed on the surface of the image carrier to form a toner image; a developing voltage application unit that applies a voltage to the developing unit; a transfer member that transfers the toner image to a transfer target; and a control unit that controls the applied voltages of the charging voltage application unit and the developing voltage application unit, and recovers the transfer residual toner remaining on the image carrier after transfer by the developing unit. The image forming apparatus is characterized in that the average roundness 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 so as to charge the transfer residual toner at a position facing the image carrier through the charging member to a prescribed polarity, and a second step of controlling the applied voltage of the developing voltage application means in order 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 a portion of the image carrier that is not exposed by the exposure means, i.e., the non-exposed portion, is the surface potential VD [V], VB and VD satisfy the following formula: |VB - VD| ≥ |VC| × 0.3 - 170.

[0034] The image forming apparatus may also be referred to as an electrophotographic apparatus, a printing apparatus, a printer, etc. In addition, the image forming apparatus of the present invention may be an image forming apparatus of a non-cleaner type. The non-cleaner type may also be referred to as a non-cleaner system, a non-cleaner image forming system, etc.

[0035] In addition, in the following description, the magnitude of the potential refers to the absolute value. In the following description, for example, a charging roller is described as the charging member. The developing means has, for example, a developing roller, and in the following description, the developing roller is used for the description. As the image carrier, a photoreceptor and a photosensitive drum are described as examples. As the transfer target, for example, paper or recording paper is cited, but as the transfer target, an intermediate transfer body (for example, an intermediate transfer belt) etc. may also be used in addition to these.

[0036] Figure 1The figure shows a schematic configuration example of an image forming apparatus according to the present invention. As shown in the figure, 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 photosensitive drum 10 as an image carrier, a transfer roller 62, a fixing device 12, and the like.

[0037] In addition, it also includes a charging power source 21, a developing power source 22, a cleaning power source 23, a transfer power source 24, etc. for supplying biases required for image formation, and their outputs are controlled by a control unit 25.

[0038] The charging power source 21 is an example of a charging voltage application means, and applies a voltage to a 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 or the like.

[0039] The developing power source 22 is an example of a developing voltage application means, and applies a voltage to a developing means. A developing device 61 is an example of a developing means, and has, for example, a developing roller 72. The developing power source 22 applies a voltage to the developing means, but the developing power source 22 may also apply a voltage to the developing roller 72. The voltage applied to the developing roller 72 may be referred to as a developing bias or the like.

[0040] The cleaning power source 23 is an example of a cleaning voltage application means, and applies a voltage to a cleaning member. As the cleaning member, for example, a recovery brush 161 can be cited.

[0041] The transfer power source 24 is an example of a transfer voltage application means, and applies a voltage to a transfer roller 62. The transfer roller 62 is an example of a transfer member, and a voltage is applied to it for transfer. The voltage applied to the transfer roller 62 may be referred to as a transfer bias voltage or the like.

[0042] The paper feeding means 4 includes a paper feeding tray 14 in which a recording paper P is stored in a stacked state, a paper feeding roller 15 for sequentially separating and feeding one sheet of the topmost paper of the recording paper 105 stored in the paper feeding tray 14, and the like. The recording paper is an example of a transfer body, and may also be referred to as a recording medium, a recording material, a medium, etc.

[0043] The recording paper 105 sent out by the paper feeding roller 15 stops at the registration roller 6 once, and after correcting the deviation of the posture, at a timing synchronized with the rotation of the photosensitive drum 10, that is, at a timing when the leading end of the toner image formed on the photosensitive drum 10 coincides with the specified position of the leading end of the paper Pa in the conveyance direction, it is conveyed to the transfer section N3 through the registration roller pair 6.

[0044] Around the photosensitive drum 10, a charging roller 160 as a charging means, a developing device 61 having a developing roller 72, and a transfer roller 62 are arranged in the order of the rotation direction shown by the arrow. Among them, the charging roller 160 and the developing roller 72 are arranged to be in contact with the photosensitive drum 10. In addition, a recovery brush 161 (which can also be called a brush roller, a cleaning brush, a cleaning component, etc.) is contact - provided on the charging roller 160. Between the charging roller 160 and the developing device 61, exposure light Lb is irradiated onto the surface of the photosensitive drum 10 from the exposure means 5 and scanned. The recovery brush 161 is an example of a recovery means.

[0045] When the photosensitive 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 photosensitive drum is uniformly charged in the charging area N1. According to the image information, exposure light Lb is irradiated onto the surface of the photosensitive drum 10 from the exposure means 5, and the electrostatic latent image is formed by discharging the parts of the photosensitive body surface corresponding to the image to be generated. This electrostatic latent image moves to the developing area N2 by the rotation of the photosensitive drum 10. At this time, a developing bias voltage is applied from the developing power supply 22 to the developing roller 72 provided on the developing device 61.

[0046] In the developing area N2, the negatively charged toner held on the developing roller is supplied from the developing roller 72 to the photosensitive drum 10 according to the potential difference between the potential of the exposed part and the potential of the developing bias voltage, and a toner image is formed on the photosensitive drum 10. The toner image formed on the photosensitive drum 10 moves to the transfer area N3 at a specified 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 to the recording paper 105 that has entered the transfer area N3.

[0047] The recording paper 105 carrying the toner image is conveyed toward the fixing device 12, and after being fixed in the fixing device 12, it is discharged and stacked on the paper discharge tray. The residual toner remaining on the photosensitive drum 10 without being transferred to the recording paper 105 in the transfer area N3 reaches the charging area N1 as the photosensitive drum 10 rotates. In the charging area N1, the residual toner is negatively charged by the micro - discharge of the charging bias voltage applied to the charging roller 160 and returns to the developing area N2.

[0048] In the developing area N2, according to the potential difference between the potential of the part not exposed by the exposure means 5 as a non - exposed part and the potential of the developing bias voltage, the residual toner moves onto the developing roller 72 and is recovered into the developing device 61.

[0049] In the charging area N1, it is difficult to completely align the charging of the residual toner to the negative polarity, and the positively charged toner will adhere 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 positively charged toner adhering 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.

[0050] Figure 2 (A) shows a block diagram for explaining the hardware configuration of the control unit 25 in the present embodiment. The control unit 25 has, for example, a CPU as a central element for performing arithmetic processing, and memories such as a ROM and a RAM as storage elements (storage units). The detection results of sensors, arithmetic results, etc. are stored in the RAM, and control programs, pre-obtained 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 or output value of the output of each power supply. The control unit 25 controls the exposure means 5. The control unit 25 controls the charge removal lamp 64 (charge removal means), for example, to charge-remove the photosensitive drum 10 during pre-charge discharge.

[0051] Figure 2 (B) shows a module diagram example of the hardware configuration of the control unit 25.

[0052] The control unit 25 is connected to a CPU (Central Processing Unit) 110, a RAM (Random Access Memory) 111, a ROM (Read Only Memory) 112, and a storage unit 113 via a bus 117.

[0053] The CPU 110 is a computing device for controlling 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 the working area of the CPU 110. The ROM 112 is a read-only non-volatile storage medium storing programs such as firmware.

[0054] The storage unit 113 is a non-volatile storage medium capable of reading and writing information, storing an OS (Operating System), various control programs, application programs, etc. The storage unit 113 is, for example, an SSD (Solid State Drive), an HDD (Hard Disk Drive), etc.

[0055] In the image forming apparatus according to the present embodiment, the transfer residual toner remaining on the image carrier is recovered by the developing means. The image forming apparatus according to 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 miniaturization of the apparatus.

[0056] Hereinafter, the method of not using the cleaning means for cleaning the image carrier may 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 the case including these means is also included in the cleanerless method.

[0057] Use Figure 3 to describe the basic configuration and operation of the image forming apparatus of the cleanerless method.

[0058] Figure 3 The figure shows an example of the process of forming an image. In addition, the details of each unit of the image forming apparatus of the present invention will be described later. Further, as the charging member, for example, a charging roller can be used, and in the following description, the charging roller will be described as an example.

[0059] First, the charging roller 160 uniformly charges the photosensitive drum 10 as the image carrier. The charging roller 160 in this example is configured to be in contact with the photosensitive drum 10, and for example, a DC voltage is applied 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, and an electrostatic latent image is formed on the photosensitive drum 10. There is no particular limitation on the exposure device 121, and for example, an LED is used.

[0060] The developing roller 72 is an example of a developer carrier included in the developing device 61. The developing roller 72 is applied with a developing bias by the developing voltage applying means, and the toner 200 is supplied to the photosensitive drum 10. Thereby, a toner image (also referred to as a visible image) is formed on the photosensitive drum 10.

[0061] The developing device 61 has, for example, a stirring roller 73, and the toner can be stirred in the developing device 61. The rotation direction of the stirring roller 73 can be appropriately selected, and it can be in contact with the developing roller 72 or not.

[0062] The transfer roller 62 transfers the toner image on the photosensitive drum 10 to the recording paper 105.

[0063] The charge lamp 64 discharges the potential of the photosensitive drum 10. For example, discharge light QL is irradiated for discharging.

[0064] The charging roller 62 is an example of a charging component, which is arranged in contact with the photosensitive drum 10 and charges the photosensitive drum 10. The charging roller 62 is applied with a voltage (also referred to as a charging bias, etc.) by a charging voltage application means (for example, a charging power supply 21). The charging component in the present invention is not limited to a contact type such as the charging roller 62, and can also be a non-contact type. A modification example of the non-contact charging component will be described later.

[0065] The exposure device 121 is an example of an exposure means, corresponding to Figure 1 the exposure means 5. The exposure device 121 exposes the charged photosensitive drum 10 to form a latent image on the surface of the photosensitive drum 10.

[0066] The developing device 61 is an example of a developing means, which supplies 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 as an example of a developer carrier.

[0067] The developing roller 72 is applied with a voltage (also referred to as a developing bias, etc.) by a developing voltage application means (for example, a developing power supply 22).

[0068] The transfer roller 62 is an example of a transfer component, which transfers the toner image to a transfer body (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 body through the contact portion with the photosensitive drum 10. The transfer roller 62 is applied with a voltage (which can also be referred to as a transfer bias, etc.) by a transfer voltage application means (for example, a transfer power supply 24) for transfer. The transfer component of the present invention is not limited to being arranged in contact with the image carrier, and can also be arranged non-contact with the image carrier.

[0069] Each application means is sometimes simply referred to as an application means, etc.

[0070] The above configuration is the basic configuration of an image forming apparatus without a cleaner. In such an apparatus, after the transfer process, there is no cleaning means such as a cleaning blade for cleaning the photosensitive drum 10.

[0071] In Figure 3 the example shown, 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 through discharging and about -500V through charging.

[0072] In addition, the image forming apparatus of the present embodiment may also have a recovery brush 161 (recovery means) for recovering the toner on the charging roller 160. In Figure 3 the example shown, since the recovery brush 161 is not provided, it is shown by a dotted line in the figure.

[0073] Here, an explanation Figure 3 An example of the flow of the toner in the illustrated example. For the sake of explanation, the symbol of the toner in the figure will be changed according to the position and state of the toner.

[0074] The developing roller 72 carries the toner 200, and the toner 200 carried by 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) (toner 201) according to the electrostatic latent image. 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 subsequent process.

[0075] In the transfer process, the toner that is not transferred remains on the photosensitive drum 10 as transfer residual toner 203. After the charge removal process, the transfer residual toner 203 adheres to the charging roller 160 at the contact portion (or vicinity) between the photosensitive drum 10 and the charging roller 160. Among the transfer residual toner 203, there is still 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.

[0076] Next, use Figure 4 , Figure 5A , Figure 5B To illustrate an example of a method for recovering transfer residual toner in an image forming apparatus without a cleaner.

[0077] Figure 4 Is a schematic diagram for explaining the state after Figure 3 , and is a diagram schematically showing the state during printing. The printing here refers to 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 for transferring toner to the recording paper. Figure 4 Is a diagram for explaining the process performed between the transfer to the previous recording paper and the transfer to the next recording paper.

[0078] As Figure 3 Explained, the toner that is not transferred in the transfer process remains on the photosensitive drum 10 as transfer residual toner 203. Figure 4 In, on the downstream side of the transfer roller 62, it is illustrated that transfer residual toner 203 remains on the photosensitive drum 10. After transferring to the previous recording paper 105, the surface of the photosensitive drum 10 is discharged by the charge removal lamp 64. As a result, the potential difference between the charging roller 160 and the photosensitive drum 10 is enlarged, and discharge occurs between the charging roller 160 and the photosensitive drum 10 before charging. In the figure, the discharge is schematically illustrated.

[0079] By discharging before charging, the transfer residual toner 203 becomes negatively charged ( Figure 4 not shown in the figure). In the transfer residual toner 203, by discharging before charging, for example, there are negatively charged toner and slightly positively charged toner. The slightly positively charged transfer residual toner 203 attaches to the charging roller 160 at the portion (or near) where the charging roller 160 abuts against the photosensitive drum 10. The toner attached to the charging roller 160 is illustrated as toner 204.

[0080] In addition, the arrow a in the figure schematically shows that the transfer residual toner 203 on the photosensitive drum 10 attaches to the charging roller 160. It can also be called movement or the like that the transfer residual toner 203 on the photosensitive drum 10 attaches to the charging roller 160.

[0081] The image forming apparatus of this example has a recovery brush 161 to recover the toner attached to the charging roller 160. The positively charged toner 204 attached to the charging roller 160 is recovered by the recovery brush 161. The arrow b in the figure schematically shows that the toner 204 on the charging roller 160 is recovered by the recovery brush 161. It can also be called movement or the like that the toner 204 on the charging roller 160 is recovered by the recovery brush 161. 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.

[0082] The negatively charged toner in the transfer residual toner 203 on the photosensitive drum 10 does not attach to the charging roller 160 but remains on the photosensitive drum 10. This toner is illustrated as toner 206. Also, both toner 203 and 206 are transfer residual toner.

[0083] The toner 206 remaining on the photosensitive drum 10 is recovered by the developing roller 72. The toner recovered by the developing roller 72 is illustrated as toner 208. It can also be called movement or the like that the toner recovered by the developing roller 72. Through the toner 206 between the photosensitive drum 10 and the developing roller 72, it moves toward the developing roller 72 due to the potential difference between the photosensitive drum 10 and the developing roller 72. The arrow c in the figure schematically shows that the toner 206 on the photosensitive drum 10 is recovered by the developing roller 72.

[0084] As described above, for the recovery using the developing roller 72, for example, a method of adjusting the potentials of the respective components can be cited. As an example, for example, it can be listed that the surface of the photosensitive drum 10 after discharging is set to -50V, the charging roller 160 is set to -1100V, the recovery brush 161 is set to -1300V, the surface of the photosensitive drum 10 after charging is set to -500V, and the developing roller 72 is set to -300V. In Figure 4 the figure, the potentials are illustrated as this example, but it is not limited thereto.

[0085] In the image forming apparatus of the present invention, it is preferable to have a recovery brush 161, but the recovery brush 161 is not essential. When there is no recovery means (e.g., recovery brush 161) for recovering the toner present on the charging roller 160, it is preferable to perform potential adjustment to reduce the toner moving to the charging roller 160.

[0086] Next, Figure 5A and Figure 5B will be used to illustrate an example of the operation of the toner and toner recovery when the apparatus is shut down. As Figure 4 described, during the discharge before charging, the positive transfer residual toner 203 (the same applies to toner 206) that has not become negative adheres to the charging roller 160 and is recovered by the recovery brush 161. Since this recovery is repeated during printing, the positively charged toner 207 accumulates on the recovery brush 161.

[0087] In addition, the so-called shutdown of the apparatus refers to the non-image forming time when the image forming operation is not performed, and it is also the period when the exposure means does not expose the image carrier.

[0088] When the apparatus is shut down, the potential difference between the recovery brush 161 and the charging roller 160 is adjusted so that a small amount of positively charged toner 207 moves to the charging roller 160 side. This is indicated by the arrow d in the figure.

[0089] 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 moving toner is shown as toner 209 in the figure. In addition, when the apparatus is shut down, since the photosensitive drum 10 is not discharged by the erasing lamp 64, the potential difference between the charging roller 160 and the photosensitive drum 10 is adjusted in consideration of this.

[0090] The positively charged toner 209 on the photosensitive drum 10 is not recovered by the developing roller 72 but directly passes through the developing roller 72. Further, the toner 209 passes through the transfer roller 62. Thus, when the apparatus is shut down, there is positively charged toner 209 on the photosensitive drum 10.

[0091] In Figure 4 , Figure 5A and Figure 5B , the toners 203, 206, and 209 are shown on the photosensitive drum 10. These are all considered to be transfer residual toners. The toner 209 is the toner that has moved back to the photosensitive drum 10 after the transfer residual toner 203 has been recovered by the recovery brush 161, and such toners can also be included in the transfer residual toners.

[0092] As Figure 5AAs in the example shown, in the movement of the toner, for example, a method of adjusting the potentials of the respective components can be cited. For example, the potential of the recovery brush 161 can be -150 V, the potential of the charging roller 160 can be -350 V, the potential of the surface of the photosensitive drum 10 can be 500 V, and the potential of the developing roller 72 can be +250 V. In Figure 5A the potentials are illustrated as an example, but are not limited thereto.

[0093] Next, Figure 5B is used to explain the situation where the toner on the photosensitive drum 10 is recovered during the shutdown of the apparatus. Figure 5B is Figure 5A a continuation of. As shown in the figure, at a prescribed timing, the photosensitive drum 10 is discharged by the erasing lamp 64. By discharging, the potential difference between the charging roller 160 and the photosensitive drum 10 is enlarged, and discharge occurs between the charging roller 160 and the photosensitive drum 10. In the figure, the discharge is schematically illustrated. In addition, the erasing shown in the figure is not the erasing for image formation, but the erasing for recovering the toner.

[0094] Due to the above discharge, the toner 209 becomes negatively charged. In addition, Figure 4 similar to, the toner in the toner 209 that is not negatively charged but positively charged adheres to the charging roller 160 and is recovered by the recovery brush 161 (arrows g and h in the figure).

[0095] The toner 209 that has become negatively charged due to the above discharge does not move to the charging roller 160 and remains on the photosensitive drum 10. Then, the negatively charged toner 209 is recovered by the developing roller 72 to which a developing bias is applied (arrow i in the figure). In the figure, the toner recovered by the developing roller 72 is illustrated as the toner 208.

[0096] As Figure 5B in the example shown, in the movement of the toner, for example, a method of adjusting the potentials of the respective components can be cited. For example, the potential of the recovery brush 161 is -1300 V, the potential of the charging roller 160 is -1100 V, the surface of the photosensitive drum 10 after erasing is -50 V, the potential of the surface of the photosensitive drum 10 is 500 V, and the potential of the developing roller 72 is -300 V. In Figure 5B the potentials are illustrated as an example, but are not limited thereto.

[0097] In the present embodiment, as described below, the transfer residual toner on the photoreceptor can be recovered more favorably by the developing means. In a cleanerless system, when the transfer residual toner on the photoreceptor returns to the position facing the charging roller, during the discharge period generated on the photoreceptor side by the potential of the charging roller, the transfer residual toner is charged to the normal polarity. Thereafter, the transfer residual toner is conveyed to the position facing the developing roller, and is recovered by the developing means through the bottom surface potential which is the potential difference between the potential of the developing roller as the developing means during toner recovery and the potential of the non-exposed portion (which may also be referred to as the non-image portion) on the photoreceptor.

[0098] In addition, the fact that the transfer residual toner is charged to the normal polarity can also be referred to as the transfer residual toner being charged with electricity to the normal polarity, etc.

[0099] The bottom surface potential is the potential difference between the potential of the developing means during transfer residual toner recovery and the potential of the non-exposed portion on the photoreceptor. The potential of the developing means during transfer residual toner recovery corresponds to the voltage applied to the developing device in the second process described later.

[0100] The charging roller is an example of a charging member, and the potential of the charging roller corresponds to the voltage applied to the charging member by the charging voltage applying means.

[0101] The developing means includes, for example, a developing roller, and may include other components as needed. The potential of the developing means is, for example, the potential of the developing roller. The potential of the developing roller corresponds to the voltage applied to the developing means by the developing voltage applying means.

[0102] The non-exposed portion is the portion of the image carrier that has not been exposed by the exposing means.

[0103] If the force of the electric field generated by the bottom surface potential is greater than the adhesion force between the toner and the photoreceptor, the toner can be recovered by the developing means. Therefore, if the value of the bottom surface potential is increased, the force pulling the transfer residual toner adhering to the non-exposed portion to the developing roller side becomes stronger, and thus it is easier to be recovered 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 recoverability of the toner, it is preferable to reduce the adhesion force between the toner and the photoreceptor.

[0104] The adhesion force between the toner and the photoreceptor is strongly affected by the shape of the toner. The spherical toner prepared by the polymerization method has fewer contact points with the photoreceptor, so the adhesion force can be reduced. On the other hand, the toner prepared by the pulverization method has an irregular shape and many contact points with the photoreceptor, so the adhesion force becomes larger.

[0105] The toner obtained by the pulverization method has the advantage of easily reducing the manufacturing cost, and thus is widely used. When using the toner obtained by the pulverization method in a cleanerless system, since the adhesion between the toner and the photoreceptor is large, in order to effectively recover the toner by the developing means, the bottom surface potential must be set to a considerably large value.

[0106] On the other hand, in order to increase the bottom surface potential, or decrease the potential of the developing roller, or increase the potential of the non-exposed portion of the photoreceptor. In order to increase the potential of the non-exposed portion 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 developing potential of the potential difference from the potential of the image portion (also referred to as the exposed portion) on the photoreceptor becomes smaller. Therefore, the amount of toner to be developed (the amount of toner applied to the photoreceptor) decreases, and the image density decreases. In addition, when the potential of the non-exposed portion of the photoreceptor is increased, the toner of the opposite polarity on the developing roller is easily transferred to the non-exposed portion, and thus image fog (sometimes also referred to as fogging) occurs. Therefore, there is a limit to increasing the bottom surface potential, and there is a problem that it is difficult to completely suppress the generation of transfer residual ghosting.

[0107] Thus, in the present embodiment, pre-charge discharge during toner recovery is somewhat suppressed to reduce the amount of charge applied to the toner. Thereby, the electrostatic adhesion of the toner to the photoreceptor can be reduced, and the adhesion between the toner and the photoreceptor can be decreased.

[0108] Pre-charge discharge is a discharge phenomenon that occurs between the charging member and the image carrier. Through pre-charge discharge, the transfer residual toner can be charged. By performing the discharge treatment, for example, negative charges can be injected into the transfer residual toner on the photoreceptor at the position facing the charging member, and the transfer residual toner can be recovered by the developing means.

[0109] Pre-charge discharge is generated by the potential difference between the surface potential VO of the photoreceptor before charging and the applied voltage to the charging roller. Therefore, in order to suppress pre-charge discharge, it is only necessary to set the applied voltage to the charging roller to be lower.

[0110] Here, setting the voltage applied to the charging roller to be lower means setting the set voltage when performing pre-charge discharge (described later Figure 6B ), and setting the voltage applied to make the transfer residual toner have a specified polarity. In the above, it is described that the applied voltage to the charging roller is set to be lower, but the applied voltage to the charging roller is not always set to be lower.

[0111] Discharging before charging and applying a charge to the transfer residual toner to become a specified polarity is also referred to as charging the transfer residual toner or the like. Sometimes the amount of charge given to the transfer residual toner is also referred to as the amount of charge applied, etc.

[0112] If the amount of charge is excessive during charging, the adhesion of the transferred residual toner to the photoreceptor increases, making it difficult to recover with the developing roller. In the prior art, this point has not been taken into consideration. The inventors of the present invention conducted in-depth research and thus completed the present invention. In the present invention, by not increasing the bottom surface potential to more than necessary and not excessively charging the amount of charge during pre-charging discharge, the recovery of the developing means can be performed well.

[0113] In the present embodiment, the absolute value of the potential of the charging roller is below a specified value, and at the same time, the value of the bottom surface potential is set within a specified range. Hereinafter, the features of the image forming apparatus of the present embodiment will be described.

[0114] The image forming apparatus of the present embodiment recovers the transferred residual toner remaining on the image carrier after transfer by the developing means. When recovering the transferred residual toner by the developing means, the control unit performs a first process and a second process.

[0115] The first process is a process of controlling the applied voltage of the charging voltage application means so as to charge the transferred residual toner at the position facing the image carrier by the charging member to a specified polarity.

[0116] The second process is a process of controlling the applied voltage of the developing voltage application means so as to recover the transferred residual toner charged in the first process by the developing means.

[0117] When the voltage applied to the charging member in the first process is the applied voltage VC [V], the absolute value of the applied voltage VC is 900 V or more and 1200 V or less.

[0118] When the applied voltage to the developing means in the second process is the 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 the surface potential VD [V], VB and VD satisfy |VB - VD|≥|VC|×0.3 - 170.

[0119] In the present embodiment, a toner having an average roundness of 95 or less is used. Such a toner is produced, for example, by a pulverization method and can also be said to be a non-spherical toner. In the present embodiment, even for a toner having a high adhesion to the photoreceptor, a cleanerless method can be adopted and the recovery of the transferred residual toner can be performed well.

[0120] In the present embodiment, by defining the relational expressions of the average roundness of the toner, the potential of the charging member in the first step, and the bottom surface potential in the second step, while reducing the influence on the image quality, the recovery of the developing means can be performed well. Examples of reducing the influence on the image quality include suppressing image fogging and image density reduction. In the present embodiment, by weakening the adhesion of the transfer residual toner to the photoreceptor, the recovery of the developing means can be performed well without increasing the bottom surface potential. In addition, the meaning of not increasing the bottom surface potential as described herein is not to increase the absolute value of the bottom surface potential.

[0121] The bottom surface potential is 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 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 is equivalent to the bottom surface potential. Hereinafter, when referred to as the bottom surface potential, unless otherwise specified, it represents the potential difference between the applied voltage VB and the surface potential VD in the second step.

[0122] The surface potential VD of the non-exposed portion of the photoreceptor can also be said to be the surface potential of the photoreceptor in a state where it is not exposed by the exposure means. The measurement method of the surface potential is obtained by a usual 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 or film thickness of the photoreceptor, etc.

[0123] Use Figure 6A 、 Figure 6B to explain the normal imaging process and the toner recovery process.

[0124] Figure 6A is a schematic diagram for explaining the normal imaging process, Figure 6B is a schematic diagram for explaining the toner recovery process.

[0125] Figure 6A The normal imaging process shown, for example, proceeds as follows. For the sake of explanation, the symbol of the toner in the figure will be changed according to the position and state of the toner.

[0126] The developing roller 72 carries the toner 200, and the toner 200 carried by 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) (toner 201) according to the electrostatic latent image. The toner 201 on the photosensitive 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 subsequent process.

[0127] In a no-cleaner system, in Figure 6AAfter the normal imaging process shown, the following Figure 6B toner recovery process shown is performed. As Figure 6B shown, the toner not transferred in the transfer process remains on the photosensitive drum 10 as transfer residual toner 203. The transfer residual toner 203 adheres to the charging roller 160 at the contact portion (or vicinity) of the photosensitive drum 10 and the charging roller 160.

[0128] In the toner recovery process, a first process and a second process are performed. After the first process is performed, the second process is performed. In the first process, in order to charge the transfer residual toner 203 passing through the charging roller 160 to a specified polarity, the applied voltage of the voltage application means (for example, the charging power supply 21) is controlled. In the first process, pre-charge discharge is performed by controlling the applied voltage of the voltage application means. By performing pre-charge discharge, the transfer residual toner 203 is charged to the normal charging polarity. The transfer residual toner charged to the normal charging polarity is denoted by the symbol 206. In Figure 6B , the transfer residual toner 206 charged to the normal charging polarity is indicated by a black circle, and the transfer residual toner 206 (toner 208) recovered by the developing roller 72 is also indicated by a black circle.

[0129] In the second process, in order to recover the transfer residual toner 206 charged in the first process by the developing roller 72, the applied voltage of the developing voltage application means (for example, the developing power supply 22) is controlled. In the second process of the present embodiment, the applied voltage of the developing voltage application means is controlled so that the bottom surface potential satisfies the above formula. In this way, the transfer residual toner 206 can be recovered well by the developing roller 72.

[0130] The features of the present embodiment will be described again.

[0131] The first feature of the present embodiment is that when the applied voltage applied to the charging roller 160 in the first process is set to 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 process from becoming excessive, the absolute value of the applied voltage VC is set to a lower value of 1200 V or less.

[0132] In the experiments conducted by the workers of the present invention, after the transfer residual toner passes through the charging position, when the absolute value of the charge amount of the transfer residual toner is greater than 30 μC / g, the electrostatic adhesion force of the toner to the photoreceptor becomes too high, resulting in transfer residual ghosting. At this time, the absolute value of the above-mentioned applied voltage VC exceeds 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 transfer residual ghosting will occur. In addition, when the absolute value of the above-mentioned applied voltage VC is less than 900 V, the image density will decrease. This will be described again below. The above-mentioned applied voltage VC is specified by its absolute value because normal charging can be positive or negative.

[0133] The second feature of this embodiment is that the bottom surface potential only needs to have a minimum value and not be greater than necessary. Since the above-mentioned applied voltage VC is set to be low, the surface potential VD of the non-exposed portion of the image carrier in the second process is suppressed, and the bottom surface potential will necessarily become smaller. When the absolute value of the bottom surface potential (|VB - VD|) is 0.3 - 170 or more of |VC|, the generation of transfer residual ghosting can be suppressed to an acceptable level.

[0134] (Experiment)

[0135] Experiments were conducted on the above two features. Using Figure 7 、 Figure 8 will be further described. Figure 7 Shown is a diagram of the image chart in the experimental evaluation. Figure 8 Shown is a diagram of the experimental results.

[0136] The voltage VC applied to the charging roller 160 in the first process is also called the charging bias voltage VC. The voltage VB applied to the developing roller 72 in the second process is also called the developing bias voltage VB.

[0137] 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 process are specified. In the present embodiment, the transfer residual toner (residual toner) remaining on the photosensitive drum 10 without being transferred is recovered by the developing roller 72, and the generation of transfer residual ghosting is suppressed. These conditions are derived based on the conditions and results of the experiments conducted by the workers of the present invention.

[0138] The experiment is carried out in the following steps 1 to 2.

[0139] <Step 1>

[0140] To evaluate the transfer residual ghosting, Figure 7Reference numeral 300 denotes a solid patch, and reference numeral 301 denotes a frame configured for evaluating a transfer residual ghost.

[0141] In this image chart, two 48 mm x 10 mm solid patches 300 are arranged near the center. Below the solid patches 300, two transfer residual ghost image evaluation frames 301 are arranged side by side at a distance of one lap from the photosensitive drum.

[0142] <Step 2>

[0143] Used in experiments Figure 1 An image forming device. Figure 1 In an image forming apparatus, a charging bias voltage VC and a developing bias voltage VB are set to predetermined values, and printing is performed. Figure 7 At this time, if the recovery capacity of the developing roller 72 is insufficient, the toner remaining on the photosensitive drum 10 is transported to the transfer area, and because it is in the white paper printing operation, it is transferred to the recording paper 105. Therefore, gray fog-like toner adhesion occurs in the frame 301 below the solid patch 300.

[0144] In the evaluation of this experiment, if no foggy toner adhesion was seen at all, it was judged as "○", if the outline of the solid patch shape was thin but within the allowable range, it was judged as "△", and if the entire solid patch shape was seen, it was judged as "×".

[0145] Figure 8 The figure shows the result of changing the values ​​of the charging bias voltage VC and the developing bias voltage VB, repeating step 2, and arranging all the determination results. Figure 8 The charge bias voltage VC and the bottom surface potential (the potential difference between the non-exposed portion potential VD of the photosensitive drum and the developing bias voltage) are represented in a matrix. As shown in the figure, the horizontal axis is the absolute value [V] of the charge bias voltage VC, and the vertical axis is the bottom surface potential [V].

[0146] When the absolute value of the charging bias voltage VC increases, the amount of discharge generated between the charging roller 160 and the photosensitive drum 10 increases. Therefore, the negative charge of the transfer residual toner 203 becomes higher, and the electrostatic adhesion to the surface of the photosensitive drum 10 becomes higher. Therefore, when the absolute value of the charging bias voltage VC increases, the transfer residual ghost tends to worsen. However, as shown in the figure, the experimental results of the workers of the present invention show that when the absolute value of the charging bias voltage VC is within the range of 1200V or less, good results can be obtained.

[0147] However, when the absolute value of the charging bias voltage VC is less than 900 V, the absolute value of the surface potential VD of the photosensitive drum 10 becomes 300 V or less. Therefore, if the developing bias voltage VB is set to satisfy the above relational expression, the developing bias voltage VB will become a small value. As a result, the potential difference from the potential VL of the image portion on the photoreceptor is insufficient, and the image density becomes light. Therefore, the absolute value of the charging bias voltage VC is appropriately in the range of 900 V to 1200 V.

[0148] In addition, even if the charging bias voltage VC is the same, as long as the bottom surface potential is increased, the force of the electric field pulling toward the developing roller 72 to peel off will overcome the adhesion force of the transfer residual toner 203. Therefore, it is easy to suppress the occurrence of transfer residual ghosting. Therefore, it can be understood that good results can be obtained as long as it is within the range that satisfies the relational expression |VB - VD| ≥ |VC| × 0.3 - 170.

[0149] Combining these results, it can be said that the condition for suppressing the generation of transfer residual ghosting is Figure 8 the range surrounded by the dotted line and the boundary line of. In the boundary line, let the absolute value of the charging bias voltage VC as the horizontal axis be x, and the absolute value of the bottom surface potential as the vertical axis be y. The formula of the boundary line is y = 0.3x - 170, and based on this, it becomes the above relational expression.

[0150] In order to more effectively prevent the generation of transfer residual ghosting, it is effective to reduce the absolute value of the charge amount of the transfer residual toner 203 and suppress the electrostatic adhesion force to the surface of the photosensitive drum 10. The charge amount of the transfer residual toner 203 is caused by the discharge between the charging roller 160 and the photosensitive drum 10, so there is a weak correlation with the charging bias voltage. As a result of investigation and research, if the absolute value of the charge amount of the transfer residual toner 203 exceeds 30 μC / g, transfer residual ghosting occurs with a high probability. Therefore, it is preferably 30 μC / g or less.

[0151] However, when the absolute value of the charge amount of the toner is too low, since it no longer responds to the electric field generated by the bottom surface potential, it is difficult to be recovered by the developing roller 72. In the experiment, even when it was reduced to 5 μC / g, no transfer residual ghosting occurred.

[0152] The preferred method will be described again.

[0153] After the position facing the charging member (for example, the charging roller 160), the charge amount Q of the transfer residual toner attached to the surface of the image carrier (for example, the photosensitive drum 10) preferably satisfies the following formula:

[0154] 5 μC / g ≤ |Q| ≤ 30 μC / g.

[0155] The above-mentioned charge amount Q is obtained by using an attractive toner charge amount measuring device to suck toner from the nozzle portion by a pump and measuring the charge amount of the toner trapped in a Faraday cage provided with a filter inside the nozzle. The measurement of the charge amount Q is performed after the first process by stopping the device.

[0156] In Figure 8 there are portions (a and b in the figure) where the result of transfer residual ghosting is "○" at positions where |VC| is less than 900V, that is, where the absolute value of the charging bias voltage VC is less than 900V. 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 potential VL of the image portion on the photoreceptor is insufficient, and the image density becomes light, so good results cannot be obtained.

[0157] In Figure 8 there are portions (c and d in the figure) where the result of transfer residual ghosting is "△" (allowable level) at positions where |VC| is greater than 1200V, that is, where the absolute value of the charging bias voltage VC is greater than 1200V. However, since the plotting point of e is ×, considering the view of being able to surely avoid ×, the absolute value of the charging bias voltage VC is set to 1200V or less.

[0158] The upper limit value of the absolute value (|VB - VD|) of the bottom surface potential is not particularly limited and can be appropriately selected. As described in the second feature of the present embodiment, in the present embodiment, since the absolute value of the above-mentioned applied voltage VC is set low, the surface potential VD of the non-exposed portion of the image carrier in the second process is suppressed, and the bottom surface potential also necessarily becomes small. Therefore, the bottom surface potential does not become too large. However, for example, as the upper limit value of the absolute value (|VB - VD|) of the bottom surface potential, it is preferably 400V or less, and more preferably 300V or less.

[0159] An example of a preferred embodiment of the present invention will be described.

[0160] Preferably, it includes: a first image forming mode in which the image carrier is rotated at a prescribed rotational speed to form an image, and a second image forming mode in which the image carrier is rotated at a rotational speed smaller than that of the first image forming mode to form an image, and the control unit controls the charging voltage application unit such 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.

[0161] By doing so, even when the conveyance speed of the recording paper is lower than normal for the purpose of printing on thick paper or the like, the pre-discharge before charging the transfer residual toner is not excessive, and the electrostatic adhesion force is suppressed. Therefore, the occurrence of transfer residual ghosting can be further prevented.

[0162] Use Figure 9 Illustrate an example of the above method.

[0163] Figure 9 This is an example of the control of an image forming apparatus when the surface speed (rotation speed) of the photosensitive drum 10 is lower than the normal speed. The first image forming mode is an image forming mode in which the photosensitive member rotates at a normal rotation speed, and image formation is performed by rotating the photosensitive member at a specified rotation speed. The second image forming mode performs image formation by rotating the photosensitive member at a rotation speed smaller than that of the first image forming mode. Figure 9 This is a diagram illustrating an example of the control in the second image forming mode.

[0164] Depending on the type of the recording paper 106, in order to increase the heat when fixing the toner image by the fixing device 12, it is sometimes necessary to make the conveyance speed of the recording paper 106 lower than normal. In this case, the rotation speed of the photosensitive drum 10 is sometimes set lower. In this case, the time during which the transfer residual toner 203 is charged becomes longer due to the discharge generated between the charging roller 160 and the photosensitive drum 10. Therefore, the absolute value of the charge amount of the transfer residual toner 203 becomes higher than that during normal image formation.

[0165] Therefore, the charging voltage application means is controlled so that the absolute value of the voltage applied to the charging roller 160 in the second image forming mode is smaller than the absolute value in the first image forming mode. In Figure 9 In the example of the second image forming mode shown, for example, -250V is applied to the developing roller 72 and -1000V is applied to the charging roller 160. Compared with Figure 4 the control example of the image forming apparatus (applying -1100V to the charging roller 160), the absolute value of the charging bias voltage applied to the charging roller 160 becomes lower. Thereby, it is possible to prevent the absolute value of the charge amount of the transfer residual toner 203 from becoming high and further suppress the occurrence of transfer residual ghosting.

[0166] Preferably, the transfer member (e.g., the transfer roller 62) is applied with a voltage for the transfer, and by applying a voltage to the transfer member (transfer roller), the absolute value of the current flowing in the transfer member is 10 μA or more.

[0167] The current flowing in the transfer roller 62 is obtained by measuring the current flowing between the transfer power source 24 and the transfer roller 62 when the transfer bias voltage is applied. The current flowing in the transfer roller 62 may also be the current flowing between the image carrier and the transfer member when the transfer bias voltage is applied. The current flowing between the image carrier and the transfer member is obtained by measuring the current flowing between the transfer power source 24 and the transfer roller 62 when the transfer bias voltage is applied.

[0168] By making it 10 μA or more, the charge amount of the transferred residual toner after passing through the transfer area can be suppressed to a low level. Therefore, the charge amount of the transferred residual toner after charging will not be excessive, and the electrostatic adhesion force is suppressed. As a result, the occurrence of transferred residual ghosting can be further prevented.

[0169] For example, a voltage is applied to the transfer member by a transfer voltage application means (for example, the transfer power supply 24).

[0170] The image forming apparatus of the present embodiment preferably has a cleaning mode as shown in the following examples. In this example, it is as follows.

[0171] The charging member is a charging roller that contacts the surface of the image carrier. There is 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 application means to transfer the toner attached to the charging roller to the surface of the image carrier. The cleaning mode is executed during non-image formation. The non-image formation time is, for example, a period during which the image carrier is not exposed.

[0172] In this way, by executing the cleaning mode during non-image formation, the toner attached to the charging roller can be recovered well by the developing means. As an explanation of the cleaning mode of this example, for example, Figure 5A is explained (arrow e).

[0173] The image forming apparatus of the present embodiment preferably has a cleaning member and a cleaning mode as shown in the following examples. In this example, it is as follows.

[0174] There is a cleaning member that contacts the surface of the charging member, and a cleaning voltage application means for applying a voltage to the cleaning member. The charging member is a charging roller that contacts the surface of the image carrier. There is a cleaning mode for transferring the toner attached to the cleaning member to the charging member and further to the surface of the image carrier. In the cleaning mode, the control unit controls the charging voltage application means and the cleaning voltage application 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 executed during non-image formation. The non-image formation time is, for example, a period during which the image carrier is not exposed.

[0175] In this way, by having a cleaning member, the charging member can be made cleaner. In addition, by executing the cleaning mode during non-image formation, the toner attached to the charging roller can be recovered well by the developing means. As the cleaning member, for example, a recovery brush 161 can be cited. As an explanation of the cleaning mode, for example, Figure 5A(Explanation of (arrows d and e).)

[0176] Next, other embodiments of the present invention will be described. Descriptions of the same matters as those in the above embodiments will be omitted.

[0177] The configuration of this embodiment is such that the charging member is a non-contact charging method, and a temporary cleaning roller is provided on the photosensitive drum.

[0178] The non-cleaner method uses the developing roller for recovery. Except for the recovery by the developing roller, even if a temporary cleaning roller is included, it belongs to the non-cleaner method.

[0179] Figure 10 Shown is a schematic diagram for explaining an example of the image forming apparatus of this embodiment, which is the same as Figure 1 the same figure. In this example, a corona tube type charger is used as the charging member. This charging member is represented as charger 163 in the figure. As shown in the figure, charger 163 is a non-contact charging method.

[0180] Further, in the rotation direction of the photosensitive drum 10, a temporary cleaning roller 166 is provided on the downstream side of the transfer roller 62 and the upstream side of the charger 163. The temporary cleaning roller 166 is, for example, a brush roller.

[0181] A voltage is applied to the temporary cleaning roller 166 by the cleaning power supply 23, for example, a negative voltage is applied. In this case, the positively charged transfer residual toner is temporarily stored by the temporary cleaning roller 166. The storage here means that the positively charged transfer residual toner moves to the side of the temporary cleaning roller 166 and is held by the temporary cleaning roller 166. In addition, 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, negative polarity, and the toner charged with a polarity opposite to the normal charging is, as described above, for example, the transfer residual toner charged with positive polarity.

[0182] On the other hand, the negatively charged transfer residual toner passes through the temporary cleaning roller 166, and negative charges are injected through the discharge process (pre-charging discharge) of the charging roller 160, and are recovered by the developing roller 72.

[0183] In this example, at the end of the operation, 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 photosensitive drum 10, the positively charged transfer residual toner stored in the temporary cleaning roller 166 moves to the photosensitive drum 10. This movement is also called discharging, etc. Negative charges are injected into the transferred residual toner after the movement through the discharge process (pre-charging discharge) of the charger 163, and are recovered by the developing roller 72. Thus, the temporary cleaning roller 166 can be kept clean.

[0184] Further, in this example, the temporary cleaning roller 166 is disposed upstream of the charger 163 in the rotational direction of the photosensitive drum 10. Therefore, the transfer residual toner that has moved from the temporary cleaning roller 166 to the photosensitive drum 10 is immediately injected with negative charges by the charger 163. That is, the transfer residual toner that has moved from the temporary cleaning roller 166 to the photosensitive drum 10 is injected with negative charges by pre-charge discharge immediately after the movement. Therefore, the distance that the photosensitive drum 10 rotates before injecting negative charges into the transfer residual toner by pre-charge discharge can be shortened.

[0185] In this example, compared with the above-described embodiment (the method using the recovery brush 161), the distance that the photosensitive drum 10 rotates before injecting negative charges into the transfer residual toner by pre-charge discharge can be shortened. Therefore, the deterioration of the photosensitive drum 10 can be delayed, and the life of the photosensitive drum 10 can be extended.

[0186] Further, in the case of using the recovery brush 161, the transfer residual toner held on the recovery brush 161 moves from the recovery brush 161 to the charging roller 160, and then pre-charge discharge is performed again through the positions of the developing roller 72 and the transfer roller 62. Therefore, in this embodiment, compared with the method using the recovery brush 161, the distance that the photosensitive drum 10 rotates before the stored transfer residual toner is pre-charge discharged can be shortened. In the description herein, the transfer residual toner stored in the temporary cleaning roller 166 or the transfer residual toner stored in the recovery brush 161 is referred to as the stored transfer residual toner.

[0187] The present embodiment will be described again.

[0188] The charging member in the present embodiment is a non-contact charging member that does not contact the image carrier, and has a temporary recovery unit on the downstream side of the position where the transfer member performs transfer and on the upstream side of the position where the charging member faces the image carrier in the rotational direction of the image carrier. The temporary recovery unit temporarily recovers the transfer residual toner on the surface of the image carrier that is charged with a polarity (e.g., positive) opposite to the normal charge.

[0189] The temporary recovery means is, for example, the temporary cleaning roller 166.

[0190] By setting the charging member as a non-contact charging member, charging failure caused by the movement of the transfer residual toner to the charging member can be suppressed. By using the temporary recovery means configured as described above, the transfer residual toner on the image carrier can be temporarily stored. In addition, in the case of using a non-contact charging member and a temporary recovery means, a configuration that does not use a recovery means (such as the recovery brush 161) can be adopted, thereby reducing the number of parts.

[0191] In addition, the image forming apparatus according to the present embodiment further includes a cleaning voltage applying means (e.g., a cleaning power supply 23) for applying a voltage to the temporary recovery means. When the image formation is completed, the control unit controls the cleaning voltage applying means to move the transfer residual toner recovered by the temporary recovery means to the image carrier.

[0192] By doing so, for the transfer residual toner recovered by the temporary recovery mechanism and discharged onto the image carrier, pre-discharge before charging can be performed immediately after the discharge, and the distance for rotating the image carrier can be reduced. Therefore, the life of the image carrier can be extended. In addition, by moving the transfer residual toner recovered by the temporary recovery unit to the image carrier, the temporary recovery unit can be kept clean even after a period of time.

[0193] Next, other embodiments of the present invention will be described. Descriptions of the same matters as those in the above embodiments will be omitted.

[0194] This embodiment is a method using a stripping roller. In this embodiment, the stripping roller is used to reduce the adhesion force of the toner strongly adhered (fixed) to the photoreceptor. Thereby, the transfer residual toner can be recovered well by the developing means. In addition, in this embodiment, film formation on the photoreceptor can be suppressed.

[0195] Figure 11 The figure shown is a schematic diagram for explaining an example of the image forming apparatus according to this embodiment, and is the same as Figure 1 the same figure. In this embodiment, the stripping roller 165 is arranged to be in contact with the photosensitive drum 10. In addition, the stripping roller 165 in this example is arranged on the downstream side of the transfer roller 62 and on the upstream side of the charging roller 160 in the rotation direction of the photosensitive drum 10.

[0196] The stripping roller 165 is made of, for example, a silicone resin sponge.

[0197] In addition, in the present invention, a configuration that does not use the charge removal lamp 64 (charge removal means) may also be adopted, and this example is an example that does not use the charge removal lamp.

[0198] In this embodiment, for example, through the circumferential speed difference between the stripping roller 165 and the photosensitive drum 10, the transfer residual toner can be peeled off from the photosensitive drum 10. By scraping the surface of the photosensitive drum 10 with the stripping roller 165, the transfer residual toner is peeled off from the surface of the photosensitive drum 10. Further, a negative voltage is applied to the stripping roller 165 in this example. The stripping roller 165 is preferably applied with a voltage having an absolute value smaller than the voltage applied to the charging roller 160 during pre-discharge before charging. Therefore, preferably, the stripping roller 165 is applied with a voltage having an absolute value smaller than the voltage applied to the charging roller 160 in the first step.

[0199] By applying a voltage to the peeling roller 165 in this way, the transferred residual toner peeled off by the peeling roller 165 is charged by the peeling roller 165 and reattached to the surface of the photosensitive drum 10. Then, the developing roller 72 recovers the transferred residual toner that has been negatively charged by the discharge process (pre-charge discharge) of the charging roller 160. Through the peeling roller 165, the transferred residual toner is peeled off from the photosensitive drum 10 and reattached to the photosensitive drum 10 with a weak adhesion force, making it easier for the developing roller 72 to recover the transferred residual toner. Thus, the film formation on the photosensitive drum 10 can be suppressed.

[0200] In this way, in this example, the adhesion force of the toner strongly adhered (fixed) to the photosensitive drum 10 is reduced by the peeling roller 165. In this example, the adhesion force between the transferred residual toner and the surface of the photosensitive drum 10 can be reduced by the peeling roller 165, making it easier for the developing roller 72 to recover the transferred residual toner.

[0201] The present embodiment will be described again.

[0202] In the present embodiment, in the rotation direction of the image carrier, a peeling roller is provided on the downstream side of the position where the transfer member performs transfer and on the upstream side of the position where the charging member faces the image carrier. The peeling roller contacts and rotates with the image carrier, and peels off the transferred residual toner attached to the surface of the image carrier by the circumferential speed difference with the image carrier.

[0203] By configuring the peeling roller in this way, the adhesion force of the transferred residual toner before the pre-charge discharge can be reduced, and the transferred residual toner can be easily peeled off by using the circumferential speed difference.

[0204] In addition, in the present embodiment, it is preferable to apply a voltage to the peeling roller that is smaller in absolute value than the voltage applied to the charging member in the first step.

[0205] In this case, the adhesion force of the transferred residual toner reattached to the photosensitive drum 10 can be reduced.

[0206] (Toner)

[0207] The average roundness of the toner used in the present invention is 95 or less, and it is produced by, for example, a pulverization method. The method for measuring the roundness of the toner will be described.

[0208] The average roundness of the one-component developing toner can be measured, for example, by using a flow particle image analysis device (“FPIA-2100”, manufactured by Sysmex Corporation) and analyzing it using analysis software (FPIA-2100 Data Processing Program for FPIA version 00-10).

[0209] The specific measurement method is as follows: in 100 - 150 ml of water from which impure solids have been previously removed in a container, an interfacial activator as a dispersant is added. Preferably, 0.1 - 0.5 ml of alkylbenzene sulfonate is added, and then about 0.1 - 0.5 g of the measurement sample is added. The suspension in which the sample is dispersed is subjected to a dispersion treatment with an ultrasonic disperser for about 1 minute to 3 minutes, and the concentration of the dispersion is made 3000 particles / μl - 10,000 particles / μl. The particle size and shape of the toner are measured by the said device. The average roundness is calculated using the following formula.

[0210] Average roundness = (circumference of a circle equal to the projected area of the particle) / (circumference of the particle projection image)

[0211] <Additive>

[0212] The toner used in the present invention has, for example, a toner masterbatch and an additive.

[0213] The additive used in the present invention contains inorganic fine particles. In the particle size distribution of the primary particle size of the inorganic fine particles contained in the additive, there are multiple peaks in the particle size range of 5 nm or more and 50 nm or less. Among the peaks, when the highest peak is set as n1, the second highest peak is set as n2, the particle size (nm) of the apex of the peak n1 is set as n1d, the particle size (nm) of the apex of the peak n2 is set as n2d, the height of the apex of the peak n1 is set as n1h, and the height of the apex of the peak n2 is set as n2h, it is preferably satisfied that all of the following formulas (1) to (3) are satisfied.

[0214] n1d > n2d Formula (1)

[0215] 10 < (n1d + n2d) Formula (2)

[0216] 30 ≤ {(n2h / n1h) × 100} < 100 Formula (3)

[0217] The particle size distribution of the inorganic fine particles referred to in the present invention is a particle number - based particle size distribution of its primary particles, and can be measured by successively going through the following steps (1) to (3).

[0218] (1) In the state where the inorganic fine particles are attached to the surface of the toner, 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 King (Asahi Kasei Engineering Co., Ltd.), 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) Then, according to the following formula, the number of grades is determined, a histogram is made, and the particle size distribution is obtained.

[0219] Number of levels = 1 + log2n (where n represents the number of data points of the equivalent circle diameter of the inorganic particles)

[0220] Regarding the inorganic particles used in the present invention, the particle diameter (nm) at the apex of the peak n1, i.e., n1d, is preferably 15 nm to 50 nm, more preferably 20 nm to 40 nm. Additionally, the particle diameter (nm) at the apex of the peak n2, i.e., n2d, is preferably 5 nm to 50 nm, more preferably 10 nm to 20 nm.

[0221] Furthermore, the difference between n1d and n2d is preferably 10 nm to 45 nm, more preferably 13 nm to 30 nm.

[0222] Moreover, from the perspective of enhancing the effects of the present invention, more preferred forms of the above formulas (2) and (3) are represented by the following formulas (20) and (30).

[0223] 20 < (n1d + n2d) (Formula 20)

[0224] 40 < {(n2h / n1h) × 100} < 90 (Formula 30)

[0225] In the particle size distribution of the primary particles of the inorganic particles of the present invention, there are multiple peaks between 5 nm and 50 nm. As methods that all satisfy the above formulas (1) to (3), for example, methods such as preparing two or more types of inorganic particles with different average particle diameters and adjusting their blending amounts to meet this condition can be cited. Additionally, the inorganic particles are preferably of the same type.

[0226] There is no particular limitation on the type of inorganic particles used in the present invention. For example, silica, alumina, titanium dioxide, barium titanate, magnesium titanate, calcium titanate, strontium titanate, iron oxide, copper oxide, zinc oxide, tin oxide, quartz 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, etc. can be cited. Among them, from the perspective of enhancing stress resistance, at least one selected from silica (including hydrophobic silica), alumina, and titanium dioxide is preferred.

[0227] The inorganic particles can also be subjected to a hydrophobization treatment. The hydrophobization treatment can be obtained, for example, by treating hydrophilic particles with a silane coupling agent such as methyltrimethoxysilane, methyltriethoxysilane, octyltrimethoxysilane, etc. Additionally, the inorganic particles can also be heat-treated with silicone oil and subjected to a hydrophobization treatment.

[0228] As the silicone oil, for example, 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, methacryloyl-modified silicone oil, α-methylstyrene-modified silicone oil, etc. can be cited.

[0229] As the inorganic fine particles, commercially available inorganic fine particles can be used. For example, as the silica, R972, R974, RX200, RY200, R202, R805, R812 (all manufactured by Nippon Aerosil Co., Ltd.) etc. can be cited. In addition, as the titanium dioxide, for example, P-25 (manufactured by Nippon Aerosil Co., Ltd.), STT-30, STT-65C-S (both manufactured by Titanium Industry Co., Ltd.), TAF-140 (manufactured by Fuji Titanium Industry Co., Ltd.), MT-150W, MT-500B, MT-600B and MT-150A (all manufactured by TAYCA Corporation) can be cited. As the hydrophobized titanium dioxide fine particles, for example, T-805 (manufactured by Nippon Aerosil Co., Ltd.), STT-30A, STT-65S-S (both manufactured by Titanium Industry Co., Ltd.), TAF-500T, TAF-1500T (both manufactured by Fuji Titanium Industry Co., Ltd.), MT-100S, MT-100T (both manufactured by TAYCA Corporation), IT-S (manufactured by Ishihara Sangyo Co., Ltd.) etc. can be cited.

[0230] From the viewpoint of improving stress resistance, the specific surface area of the inorganic fine particles obtained by the BET method is preferably 20 m 2 / g to 500 m 2 / g, more preferably 30 m 2 / g to 400 m 2 / g.

[0231] In addition, as the external additive, in addition to the above-mentioned inorganic fine particles, fatty acid metal salts (such as zinc stearate, aluminum stearate, etc.), fluorine-containing polymers, etc. can also be used in combination.

[0232] In addition, the content of the external additive in the toner is preferably 1.8% by mass or less.

[0233] In addition, the volume average particle diameter of the external additive is preferably 5 nm or more to 50 nm or less.

[0234] <Toner masterbatch>

[0235] The toner masterbatch in the present invention contains, for example, a binder resin, a colorant, a charge control agent, a release agent, etc. As the materials for the toner masterbatch, known materials can be used.

[0236] [Adhesive resin]

[0237] Examples of the adhesive resin include polymers of styrene and its substituents such as polystyrene, poly(p-chlorostyrene), and poly(vinyltoluene); styrene copolymers such as styrene-p-chlorostyrene copolymer, styrene-acrylene copolymer, styrene-vinyltoluene copolymer, styrene-vinylnaphthalene copolymer, styrene-methyl acrylate copolymer, styrene-ethyl acrylate copolymer, styrene-butyl acrylate copolymer, styrene-n-octyl acrylate copolymer, styrene-methyl methacrylate copolymer, styrene-ethyl methacrylate copolymer, styrene-butyl methacrylate copolymer, styrene-α-chloromethyl methacrylate copolymer, styrene-acrylonitrile copolymer, styrene-vinyl methyl ketone copolymer, styrene-butadiene copolymer, styrene-isoprene copolymer, styrene-acrylonitrile-indene copolymer, styrene-maleic acid copolymer, and styrene-maleic acid ester copolymer; polymethyl methacrylate, polybutyl methacrylate, polyvinyl chloride, polyvinyl acetate, polyethylene, polypropylene, polyester, epoxy resin, epoxy polyol resin, polyurethane, polyamide, polyvinyl butyral, polyacrylic resin, rosin, modified rosin, terpene resin, aliphatic or alicyclic hydrocarbon resin, aromatic petroleum resin, chlorinated paraffin, and solid paraffin, and they can be used alone or in combination.

[0238] (Colorant)

[0239] As colorants, all known colorants and pigments can be used, for example carbon black, aniline black, iron black, naphthol yellow S, Hansa yellow (10G, 5G, G), cadmium yellow, yellow iron oxide, yellow ochre, chrome 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), lemon yellow lake, quinoline yellow lake, Anthracene Yellow BGL, Isoindolinone Yellow, Red Iron Oxide, Red Lead, Cinnabar, Cadmium Red, Cadmium Mercury Red, Antimony Vermilion, Permanent Red 4R, Para Red, Fire Red, 2-Nitro-4-Chloroaniline Red, Lithol Fast Scarlet G, Bright Fast Scarlet, Bright Magenta BS, Permanent Red (F2R, F4R, FRL, FRLL, F4RH), Fast Scarlet VD, Urcon Fast Ruby B, Bright Scarlet G, Lithol Ruby GX, Permanent Red F5R, Bright Carmine 6B, Pigment Scarlet 3B, Bordeaux 5B, Toluidine Purple, Permanent Bordeaux F2K, Hellyer Bordeaux BL, Bordeaux 10B, Light Maroon, Medium Maroon, Aurora Lake, Rhodamine Lake B, Rhodamine Lake Y, Alizarin Lake, Thioindigo B, Thioindigo Maroon, Oil Red, Quinacridone Red, Pyrazolone Red, Polyazo Red, Chrome Vermilion, Benzidine Orange, Violinone Orange, Oil Orange, Azure Blue, Basic 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 purple red, chrome green, zinc green, chromium oxide, emerald green, emerald green, pigment green B, naphthol green B, green gold, acid green lake, malachite green lake, phthalocyanine green, anthraquinone green, titanium oxide, zinc white, lithopone and mixtures thereof. The amount used is usually 0.1 to 50 parts by mass relative to 100 parts by mass of the binder resin.

[0240] (Charge Control Agent)

[0241] As the 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, alkoxy amines, quaternary ammonium salts (including fluorine-modified quaternary ammonium salts), alkyl amides, phosphorus elements or compounds, tungsten elements or compounds, fluorine-based active agents, salicylic acid metal salts and metal salts of salicylic acid derivatives, etc.

[0242] The amount of the charge control agent used in the present invention is determined by the type of binder resin, the presence or absence of additives used as needed, and the toner manufacturing method including the dispersion method, and is therefore not determined uniformly, but is preferably used in the range of 0.1 to 10 parts by mass, preferably 2 to 5 parts by mass, relative to 100 parts by mass of the binder resin. In addition, multiple charge control agents may be used in combination as needed.

[0243] [Release agent]

[0244] In the present invention, in order to impart mold release properties to the toner, a mold release agent may also be used. The softening point of the mold release agent used is preferably 70 to 100°C.

[0245] Examples of the mold release agent include synthetic waxes such as low molecular weight polyethylene, polypropylene, and their copolymers; vegetable waxes such as candelilla wax, carnauba wax, rice bran wax, wood wax, and jojoba wax; animal waxes such as beeswax, lanolin, and spermaceti wax; mineral waxes such as montan wax and ozokerite wax; and fatty waxes such as hardened castor oil, hydroxy stearic acid, fatty acid amide, and phenol fatty acid ester.

[0246] From the viewpoint of the chemical structure of wax, known waxes include hydrocarbon waxes, ester waxes, amide waxes, etc. Evaluated from the viewpoints of storage stability, image quality, fixing temperature range, etc., ester waxes are suitable.

[0247] The amount of the mold release agent is preferably 1 to 6 parts by mass based on the total amount of the toner.

[0248] The method for manufacturing the toner in the present invention may be a conventionally well-known method, and a manufacturing method including steps of mixing, kneading, roll cooling, pulverizing, and classifying toner raw materials can be cited. For example, after mixing the raw materials, they are kneaded with a twin-screw kneader, cooled by a belt cooler, pulverized with a jet mill, and classified to obtain the toner.

[0249] The weight average particle diameter of the toner is preferably 4 μm to 10 μm, more preferably 5 μm to 8 μm.

[0250] The mode of the present invention is as described below, for example.

[0251] <1>

[0252] An image forming apparatus includes: an image carrier; a charging member that charges the image carrier; an exposure unit that exposes the charged image carrier and forms a latent image on the surface of the image carrier; a charging voltage application unit that applies a voltage to the charging member; a developing unit that supplies toner to the image carrier and develops the latent image formed on the surface of the image carrier to form a toner image; a developing voltage application unit that applies a voltage to the developing unit; a transfer member that transfers the toner image to a transfer target; and a control unit that controls the applied voltages of the charging voltage application unit and the developing voltage application unit, and recovers transfer residual toner remaining on the image carrier after transfer by the developing unit. The image forming apparatus is characterized in that the average roundness of the toner is 95 or less, and the control unit executes a first process of controlling the applied voltage of the charging voltage application unit so as to charge the transfer residual toner at a position facing the image carrier through the charging member to a prescribed polarity, and a second process of controlling the applied voltage of the developing voltage application unit in order to recover the transfer residual toner charged in the first process by the developing unit. When the applied voltage to the charging member in the first process 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 unit in the second process is the 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 unit, is the surface potential VD [V], VB and VD satisfy the following formula:

[0253] |VB - VD| ≥ |VC| × 0.3 - 170.

[0254] <2>

[0255] The image forming apparatus according to <1>, characterized in that the charge amount Q of the transfer residual toner attached to the surface of the image carrier after facing the charging member is

[0256] 5 μC / g ≤ |Q| ≤ 30 μC / g.

[0257] <3>

[0258] The image forming apparatus according to <1> or <2>, characterized in that it includes: a first image forming mode in which the image carrier is rotated at a prescribed rotational speed to form an image, and a second image forming mode in which the image carrier is rotated at a rotational speed smaller than that of the first image forming mode to form an image, and the control unit controls the charging voltage application unit such 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.

[0259] <4>

[0260] The image forming apparatus according to any one of <1> to <3>, characterized in that: a voltage is applied to the transfer member for the transfer, and by applying a voltage to the transfer member, the absolute value of the current flowing through the transfer member is 10 μA or more.

[0261] <5>

[0262] The image forming apparatus according to any one of <1> to <4>, characterized in that: the charging member is a charging roller that contacts the surface of the image carrier, and has a cleaning mode for transferring the toner adhering to the charging roller to the surface of the image carrier, and the control unit controls the charging voltage application unit in the cleaning mode to transfer the toner adhering to the charging roller to the surface of the image carrier, and the cleaning mode is executed during a period when the exposure unit does not expose the image carrier.

[0263] <6>

[0264] The image forming apparatus according to any one of <1> to <4>, characterized in that it includes: a cleaning member that contacts the surface of the charging member, and a cleaning voltage application unit that applies a voltage to the cleaning member, and the charging member is a charging roller that contacts the surface of the image carrier, and has a cleaning mode for transferring the toner adhering to the cleaning member to the charging roller and further to the surface of the image carrier, and the control unit controls the charging voltage application unit and the cleaning voltage application unit in the cleaning mode 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, and the cleaning mode is executed during a period when the exposure unit does not expose the image carrier.

[0265] <7>

[0266] The image forming apparatus according to any one of <1> to <6>, characterized in that: in the rotational direction of the image carrier, a peeling roller is provided on the downstream side of the position where the transfer member performs transfer and on the upstream side of the position where the charging member and the image carrier face each other. The peeling roller contacts and rotates with the image carrier, and peels off the transferred residual toner adhering to the surface of the image carrier by means of the circumferential speed difference with the image carrier.

[0267] <8>

[0268] The image forming apparatus according to <7>, characterized in that: a voltage smaller in absolute value than the voltage applied to the charging member in the first step is applied to the peeling roller.

[0269] <9>

[0270] The image forming apparatus according to any one of <1> to <8>, characterized in that: the charging member is a non-contact charging member that does not contact the image carrier. In the rotational direction of the image carrier, a temporary recovery unit is provided on the downstream side of the position where the transfer member performs transfer and on the upstream side of the position where the charging member and the image carrier face each other. The temporary recovery unit temporarily recovers the transferred residual toner having a polarity opposite to the normal charge on the surface of the image carrier.

[0271] <10>

[0272] The image forming apparatus according to <9>, characterized in that: a cleaning voltage application unit for applying a voltage to the temporary recovery unit is provided, and when the image formation ends, the control unit controls the cleaning voltage application unit to move the transferred residual toner recovered by the temporary recovery unit to the image carrier.

Claims

1. An image forming device, comprising: Image carrier; a charging member for charging the image bearing body; an exposure unit for exposing the charged image carrier to form a latent image on a surface of the image carrier; a charging voltage applying unit that applies a voltage to the charging member; a developing unit that applies toner to the image bearing member and develops the latent image formed on the surface of the image bearing member to form a toner image; a developing voltage applying unit that applies a voltage to the developing unit; a transfer member for transferring the toner image to a transfer object, and a control unit that controls the applied voltages of the charging voltage applying unit and the developing voltage applying unit, and The developing unit collects the transfer residual toner remaining on the image bearing member after the transfer. The image forming apparatus is characterized in that the average circularity of the toner is 95 or less, The control section executes a first step of controlling the applied voltage of the charging voltage applying unit so as to charge the transfer residual toner passing through a position where the charging member faces the image bearing member to a predetermined polarity, and a second step of controlling the applied voltage of the development voltage applying unit so that the transfer residual toner charged in the first step is recovered by the developing unit, 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 unit in the second step is the applied voltage VB [V], and the surface potential of the portion of the image carrier that is not exposed by the exposure unit, i.e., the non-exposed portion, is the surface potential VD [V], VB and VD satisfy the following equation: |VB-VD|≥|VC|×0.3-170.

2. The image forming device according to claim 1, wherein: The charge amount Q of the transfer residual toner attached to the surface of the image bearing member after passing through the position facing the charging member is, 5μC / g≤|Q|≤30μC / g.

3. The image forming device according to claim 1, characterized in that include: a first image forming mode in which the image bearing member is rotated at a predetermined rotation speed to form an image, and a second image forming mode in which the image carrier is rotated at a rotation speed lower than that in the first image forming mode to perform image formation; The control section controls the charging voltage applying unit 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.

4. The image forming apparatus according to claim 1, wherein: A voltage is applied to the transfer member to perform the transfer, By applying a voltage to the transfer member, an absolute value of a current flowing in the transfer member is 10 μA or more.

5. The image forming apparatus according to claim 1, wherein: The charging member is a charging roller that contacts the surface of the image carrier, and The cleaning mode is provided to transfer the toner attached to the charging roller to the surface of the image bearing member. The control unit controls the charging voltage applying unit in the cleaning mode so that the toner attached to the charging roller is transferred to the surface of the image bearing member. The cleaning mode is executed while the exposure unit is not exposing the image carrier.

6. The image forming apparatus according to claim 1, characterized in that include: a cleaning member in contact with a surface of the charging member, and a cleaning voltage applying unit for applying a voltage to the cleaning member, and The charging member is a charging roller in contact with the surface of the image carrier. The cleaning device has a cleaning mode in which the toner attached to the cleaning member is transferred to the charging roller and further transferred to the surface of the image bearing member. The control unit controls the charging voltage applying unit and the cleaning voltage applying unit in the cleaning mode 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 bearing member. The cleaning mode is executed while the exposure unit is not exposing the image carrier.

7. The image forming apparatus according to claim 1, wherein: A peeling roller is provided on the downstream side of the position where the transfer member performs transfer and on the upstream side of the position where the charging member and the image bearing member face each other in the rotation direction of the image bearing member. The peeling roller rotates in contact with the image carrier, and peels off the transfer residual toner attached to the surface of the image carrier due to a peripheral speed difference between the roller and the image carrier.

8. The image forming apparatus according to claim 7, wherein: A voltage having an absolute value smaller than that of a voltage applied to the charging member in the first step is applied to the peeling roller.

9. The image forming apparatus according to claim 1, wherein: The charging member is a non-contact charging member that does not come into contact with the image bearing member. A temporary recovery unit is provided downstream of a position where the transfer member performs transfer and upstream of a position where the charging member and the image bearing member face each other in the rotation direction of the image bearing member. The temporary recovery unit temporarily recovers the transfer residual toner on the surface of the image bearing member that is charged to a polarity opposite to the normal charge.

10. The image forming apparatus according to claim 9, wherein: A cleaning voltage applying unit for applying a voltage to the temporary recovery unit is provided, The control section controls the cleaning voltage applying unit to move the transfer residual toner collected by the temporary collecting unit to the image bearing member when image formation is completed.

Images