Image forming apparatus

Abstract

To prevent the fusion of toner to a photoconductor drum of an image forming apparatus to obtain satisfactory image quality.SOLUTION: An image forming apparatus is used which comprises: a rotatable image carrier; an exposure unit that forms an electrostatic latent image on a surface of the image carrier through exposure; a developing member that supplies developer to the surface of the image carrier at a developing part in contact with the image carrier and can rotate at a rotation speed different from that of the image carrier; a developer supply member that supplies developer to a surface of the developing member; a developing voltage application part that applies developing voltage to the developing member; a supply voltage application unit that applies supply voltage to the developer supply member; and a control unit. The control unit controls, in an executable manner, an image forming operation of supplying the developer to the electrostatic latent image on the surface of the image carrier from the developing member to form a developer image and a scraping operation being an operation other than the image forming operation and of removing a deposit on the surface of the image carrier with the developing member, and controls at least any one of the developing voltage application unit and the supply voltage application unit so as to increase a force of the developing member to scrape off the deposit on the surface of the image carrier during the execution of the scraping operation as compared with that during the execution of the image forming operation.SELECTED DRAWING: Figure 3

Description

Technical Field

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

Background Art

[0002] In an image forming apparatus, an electrostatic latent image formed on the surface of an image carrier is developed with a developer on a developer carrier to form an image. At this time, a contact development method configuration in which development is performed in a state where the developer carrier is in contact with the image carrier is known. As the developer carrier in such a configuration, generally, a developing roller having an elastic layer on the outer peripheral surface of an axially rotated body is used.

[0003] On the other hand, in order to reduce the size of the image forming apparatus and reduce costs by reducing the number of components, an image forming apparatus of a so-called image carrier cleanerless method that does not provide cleaning means for removing and recovering toner remaining on the image carrier has been proposed.

[0004] In a cleanerless method image forming apparatus, transfer residual toner and fogged toner directly enter between the photosensitive drum and the charging roller, so stress is applied between the photosensitive drum and the charging roller, and toner may fuse to the photosensitive drum. When the toner fuses, it may inhibit exposure and cause the image to have white spots. Further, if the fused portion continues in the circumferential direction of the photosensitive drum, a white streak-like image defect occurs.

[0005] In the cleanerless method, toner that has not been formed into an image needs to be recovered in the developing unit, but toner that has fused to the photosensitive drum cannot be removed and recovered unless a strong force is applied to the developing unit. Usually, the developing roller is covered with a toner layer, but by exposing the surface layer of the developing roller from the toner layer, it is possible to rub the photosensitive drum more strongly and remove the toner on the photosensitive drum.

[0006] Patent Document 1 discloses a device that includes a reset mode to change the amount of toner on the developing roller when not image forming, by reducing the voltage difference between the developing roller and the toner supply roller to a smaller value than during printing. The device in Patent Document 1 reduces the amount of toner on the developing roller by reducing the voltage difference between the developer carrier and the toner supply roller in the reset mode, so that problems such as fogging do not occur when the amount of toner on the developing roller increases. This ensures that the amount of toner on the developing roller remains constant over a long period of time. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Patent No. 4669557 [Overview of the project] [Problems that the invention aims to solve]

[0008] However, Patent Document 1 does not disclose the difference in peripheral speed between the developing roller and the photosensitive drum, and is not intended to scrape off toner fused onto the photosensitive drum. Therefore, directly applying the method of Patent Document 1 may result in insufficient removal of toner fused onto the photosensitive drum, or conversely, excessive friction of the photosensitive drum with the developing roller, potentially accelerating the deterioration of the developer.

[0009] This invention has been made in view of the aforementioned problems. The purpose of this invention is to suppress the fusion of toner to the photosensitive drum of an image forming apparatus and to obtain good image quality. [Means for solving the problem]

[0010] This invention employs the following configuration: A rotatable image carrier, An exposure unit for exposing the surface of the image carrier in order to form an electrostatic latent image on the surface of the image carrier, A rotatable developing member that contacts the image carrier to form a developing section and supplies a developer to the surface of the image carrier in the developing section, wherein the developing member rotates at a rotational speed different from the rotational speed of the image carrier, A developer supply member that supplies developer to the surface of the developing member, A developing voltage application unit that applies a developing voltage to the developing member, A supply voltage application unit that applies a supply voltage to the developer supply member, An image forming apparatus comprising a developing voltage application unit and a control unit for controlling the supply voltage application unit, The control unit controls the execution of an image forming operation in which a developer image is formed on the surface of the image carrier by supplying the developer from the developing member to the electrostatic latent image formed on the surface of the image carrier, and a scraping operation other than the image forming operation in which a deposit attached to the surface of the image carrier is removed by the developing member. The control unit, when the scraping operation is performed, ensures that the scraping force of the developing member against the surface of the image carrier is stronger than when the image forming operation is performed, by applying at least one of the developing voltage application unit and the supply voltage application unit. This is an image forming apparatus characterized by controlling either one of the two. [Effects of the Invention]

[0011] According to the present invention, good image quality can be obtained by suppressing the fusion of toner to the photosensitive drum of an image forming apparatus. [Brief explanation of the drawing]

[0012] [Figure 1] Schematic diagram showing an example of the image forming apparatus in Example 1. [Figure 2] This figure shows an example of a developing roller and scraping operation used in the image forming apparatus of Example 1. [Figure 3] Diagram showing the fusion scraping control used in the image forming apparatus of Example 1. [Figure 4] Diagram showing the control block of the image forming apparatus in Example 1.

Best Mode for Carrying Out the Invention

[0013] Hereinafter, with reference to the drawings, exemplary embodiments for carrying out the present invention will be described in detail based on examples. However, dimensions, materials, shapes, relative arrangements, etc. of the components described in this embodiment are to be appropriately changed according to the configuration and various conditions of the apparatus to which the invention is applied. That is, the scope of the present invention is not intended to be limited to the following embodiments.

[0014] [Example 1] [Outline of Image Forming Apparatus] Referring to FIG. , the overall configuration and image forming operation of an electrophotographic image forming apparatus (hereinafter, image forming apparatus) according to Example 1 of the present invention will be described. FIG. 1 is a schematic cross-sectional view showing the schematic configuration of an image forming apparatus 100 according to an embodiment of the present invention.

[0015] In this embodiment, on the drawing, four image forming stations (image forming units) of yellow, magenta, cyan, and black are provided side by side from left to right. Each image forming station is an electrophotographic image forming mechanism having the same configuration except that the color of the developer (hereinafter, referred to as toner) 90 accommodated in each developing device is different. In the following description, when no particular distinction is required, subscripts Y (yellow), M (magenta), C (cyan), and K (black) given to the reference numerals to indicate that they are elements provided for any one of the colors are omitted and a general description is given. The subscripts Y (yellow), M (magenta), C (cyan), and K (black) are omitted and a general description is given.

[0016] Each image forming station primarily comprises a photosensitive drum 1 as an image carrier, a charging roller 2 as a charging means, a developing device 4, a primary transfer device 51, etc. The exposure device 3 may be common to all image forming stations, or it may be provided for each image forming station. In this embodiment, the photosensitive drum 1, the charging roller 2, and the developing device 4 are integrated as a process cartridge 8 and are configured to be detachable from the image forming apparatus body (the part of the image forming apparatus 100 excluding the process cartridge 8). However, the process cartridge in this invention may include at least the photosensitive drum 1 and the developing device 4, and may be configured to be detachable from the apparatus body as a whole. Alternatively, the developing device 4 may be configured to be detachable from the apparatus body or the process cartridge 8 independently. Furthermore, the photosensitive drum 1 and the developing device 4 may be attached to the image forming apparatus body, eliminating the need for user replacement.

[0017] The photosensitive drum 1 is a rotatable cylindrical photoreceptor that rotates around its axis in the direction of the arrow (counterclockwise on the paper). In this embodiment, the outer surface is driven to rotate at a rotational speed of 180 mm / sec. As an example, as shown in Figure 4, the photosensitive drum 1 rotates by receiving rotational driving force from a motor 15 controlled by a control unit 25. The surface of the photosensitive drum 1 is uniformly charged by a charging roller 2. In this embodiment, the charging roller 2 is a conductive roller with a conductive rubber layer on a metal core, and is arranged parallel to the photosensitive drum 1 and in contact with it at a predetermined pressure, and rotates in conjunction with the rotation of the photosensitive drum 1. A charging voltage can be applied to the charging roller 2 from a power supply unit 67 (power supply means). In this embodiment, the photosensitive drum 1 is charged by applying a DC voltage of -1150V to the charging roller 2, and the surface potential of the photosensitive drum 1 at that time is approximately -500V.

[0018] The exposure device 3 as an exposure unit acquires an image signal from the control unit 65 and scans a laser beam corresponding to the image signal on the surface of the photosensitive drum 1. As a result, an electrostatic latent image corresponding to the image signal is formed on the charged photosensitive drum 1. The image signal may be acquired from an external information processing device (not shown). As the control unit 65, for example, an information processing device such as a control circuit including arithmetic resources such as a processor and a memory can be used.

[0019] The developing device 4 supplies toner 90 to the electrostatic latent image on the photosensitive drum 1 and visualizes it as a toner image (developer image). In this embodiment, the developing device 4 is a contact developing type reversal developing device that contains toner 90 as a one-component developer having a negative normal charging polarity (charging polarity for developing an electrostatic latent image).

[0020] The developing device 4 is provided with a rotatable developing roller 42 as a developing member, a toner supply roller 43 as a developer supply member, and a regulating blade 44 as a developer regulating member. The toner supply roller 43 is an elastic sponge roller having a foam formed on the outer periphery of a conductive core metal. The toner supply roller 43 is disposed so as to contact the developing roller 42 with a predetermined penetration amount. The toner 90 supplied by the toner supply roller 43 and held by the developing roller 42 is regulated in thickness by the regulating blade 44 to be thinned and used for development. Here, the regulating blade 44 has a function of regulating the layer thickness of the toner 90 on the developing roller 42, and at the same time, has a function as a developer charging means for imparting a predetermined charge to the toner 90 on the developing roller 42.

[0021] Note that the power supply device 67 can function as a developing voltage application unit 671 that applies a developing voltage to the developing roller 42 included in the developing device 4, a supply voltage application unit 672 that applies a supply voltage to the toner supply roller 43, and a regulating voltage application unit that applies a regulating voltage to the regulating blade 44. Yes. Figure 4 shows an example of the control system of the power supply unit 67 that controls the control unit 25. The power supply unit 67 may be provided separately for the charging power supply for the charging roller and the developing power supply for the developing device. In that case, the charging power supply and the developing power supply can be considered together as the power supply means. Furthermore, the developing power supply for the developing roller and the supply power supply for the toner supply roller may be separate. In that case, the charging power supply, developing power supply and supply power supply can be considered together as the power supply means. The power supply unit 67 may also be used to apply voltage during image transfer. In addition, a transfer power supply may be provided separately from the power supply unit 67. In this embodiment, the power supply unit 67 changes the voltage applied to each component according to the control of the control unit 65.

[0022] The developing roller 42 is driven to rotate in the direction of the arrow in the figure (clockwise on the paper), so that its surface moves in the same direction as the photosensitive drum 1. As an example, the developing roller 42 and the toner supply roller 43 rotate under the rotational driving force of the motor 16 controlled by the control unit 25, as shown in Figure 4. The developing roller 42 can rotate at a different rotational speed than the photosensitive drum 1. In this embodiment, in order to obtain an appropriate image density, the developing roller 42 is driven to rotate so that the surface movement speed of the developing roller 42 is greater than the surface movement speed of the photosensitive drum 1. In addition, the developing device 4 is pressed toward the photosensitive drum 1 by a biasing means (not shown), and as a result, the developing roller 42 is pressed against the photosensitive drum 1. This deforms the surface of the developing roller 42, forming a developing nip (developing section), which allows for stable development in a stable contact state.

[0023] As shown in Figure 2(a), the developing roller 42 has a base layer 422 and a surface layer 423 formed on the outer circumference of the shaft body 421. Also, as shown in Figure 2(b), the surface layer 423 has a structure in which rough particles 423b are dispersed in a surface binder resin 423a. As a result, the surface of the surface layer 423 has multiple irregularities, including multiple recesses for toner transport and multiple protrusions. The ten-point average roughness Rzjis of the protrusions is larger than the volume average particle size of the toner 90. In this embodiment, the volume average particle size of the toner is 7 μm, and the Rzjis of the surface layer 423 is 10 μm. A range of approximately 8 μm to 30 μm is suitable for the Rzjis of the developing roller surface.

[0024] For measuring the ten-point average roughness Rzjis of the developing roller 42 in this invention, for example, a contact-type surface roughness meter, SurfCorder SE3500 (manufactured by Kosaka Laboratory), can be used. The measurement conditions were a cutoff value of 0.8 mm, a measurement length of 2.5 mm, and a feed speed of 0.1 mm / sec. Three arbitrary locations with different longitudinal positions were measured for each developing roller, and the average of the obtained measurements was taken as the Rzjis of the developing roller 42.

[0025] The volume-average particle size of Toner 90 can be determined using the measurement method described below. The measuring device used is a Coulter Multisizer IV (manufactured by Beckman Coulter). The electrolyte is prepared by dissolving high-grade sodium chloride in deionized water to a concentration of approximately 1% by mass, such as ISOTON II (manufactured by Beckman Coulter). ) can be used. For the measurement method, 0.5 ml of alkylbenzene sulfonate is added as a dispersant to 100 ml of electrolytic aqueous solution, and then 10 mg of the sample to be measured is added. The electrolyte in which the sample to be measured is suspended is dispersed in an ultrasonic disperser for 1 minute, and the volume particle size distribution is measured using a 30 μm aperture with a measuring device, and the measured median diameter (D50) is taken as the volume average particle size.

[0026] The toner image formed on the photosensitive drum 1 is electrostatically transferred to the intermediate transfer belt 53 by a primary transfer device 51, which is one of the transfer members. The toner images of each color are sequentially superimposed and transferred onto the intermediate transfer belt 53 to form a full-color toner image. The full-color toner image is then transferred to the recording material, which is the transfer target, by a secondary transfer device 52, which is a different transfer member from the primary transfer device 51. After that, the toner image on the recording material is pressed and heated by a fixing device 6 to fix it to the recording material, and the image formed product is discharged.

[0027] Furthermore, a belt cleaning device 7 is provided downstream of the secondary transfer device 52 in the direction of movement of the intermediate transfer belt 53 to remove and recover any toner 90 remaining on the intermediate transfer belt 53.

[0028] In this embodiment, a cleanerless image carrier system is employed, in which a dedicated cleaning device is not provided for the photosensitive drum 1, and the toner 90 remaining on the surface of the photosensitive drum without being transferred is recovered by the developing device 4. There are no members in contact with the surface of the photosensitive drum 1 from the position opposite the primary transfer device 51 (primary transfer position) until it reaches the contact position with the charging roller 2 (charging position). This makes it possible for the toner 90 remaining on the photosensitive drum 1 after image formation to be recovered by the developing device 4 when the developing roller 42 of the developing device 4 comes into contact with the photosensitive drum 1. When such a cleanerless system is adopted, it is also preferable to use a non-magnetic one-component developer as the toner 90. However, the present invention is not limited to the above configuration in order to obtain its effects.

[0029] Furthermore, the image forming apparatus 100 is equipped with a detection device (not shown) that detects the printing state and printing environment. The control unit 65 can perform image forming operations or, as an operation other than image forming operations, a scraping operation as described later, depending on the detected printing state and printing environment.

[0030] <Control> The operation of the image forming apparatus according to the present invention will now be described. During image formation, -300V is applied to the developing roller 42. -400V is applied to the regulating blade 44, and -400V is also applied to the toner supply roller 43. Since the charging polarity of the toner 90 of the present invention is negative, this makes it easier for toner to be supplied from the toner supply roller 43 to the developing roller 42.

[0031] In the photosensitive drum 1, the surface potential of the image printing area where the toner image is formed is controlled so that its absolute value is lower than the voltage applied to the developing roller 42 on the side of the toner 90's normal charging polarity. On the other hand, in the non-image printing area where no toner image is formed, the surface potential is controlled to the drum potential of -500V. As a result, the toner charged by the potential difference with the developing roller 42 in the image printing area is developed.

[0032] The toner image developed on the photosensitive drum is transferred to the intermediate transfer belt 53 in the primary transfer section formed by the primary transfer device 51. However, toner with a low charge or toner charged with the opposite polarity to normal charge is not transferred and instead enters the space between the charging roller 2 and the photosensitive drum 1. Similarly, any fouled toner also enters the charging roller 2.

[0033] As a result, stress is placed on the toner between the charging roller 2 and the photosensitive drum 1, causing it to deform and adhere to the photosensitive drum 1 as a deposit. In the areas on the photosensitive drum where toner has adhered (indicated by the symbol X), the transferability is reduced during the next image formation, making it easier for residual toner to be generated and causing the fused deposits on the photosensitive drum to grow.

[0034] In the fused areas on the photosensitive drum, the laser light emitted from the exposure device 3 is blocked, preventing the surface potential of the photosensitive drum 1 from reaching a predetermined potential, resulting in low image density in the solid print areas. In particular, if the fused material is continuous in the direction of rotation of the photosensitive drum, white streaks will appear on the image. Therefore, it is necessary to remove the toner remaining on the photosensitive drum.

[0035] <Fusion scraping operation> This section describes the process of suppressing the growth of fused material on the drum in this book. The voltages used during image formation are as follows: Applied voltage V_DEV of developing roller 42: -300V Applied voltage V_S of toner supply roller 43: -400V In other words, the absolute value of the development voltage during the image formation operation is smaller than the absolute value of the supply voltage. Therefore, the difference in the applied voltage between the toner supply roller 43 and the development roller 42 is -100V. In this embodiment, the normal charging polarity of the toner is negative, so the potential difference V_DIFF formed as the driving force for supplying toner from the toner supply roller 43 to the development roller 42 is as follows. Potential difference V_DIFF:+100V

[0036] When the image formation operation on the intermediate transfer belt 53 is completed in each print job, the control unit 65 changes the applied voltage V_S to the toner supply roller 43 from -400V during image formation to -350V and rotates it for a predetermined time. As a result, the potential difference V_DIFF changes from 100V to 50V, the force of toner pressing from the toner supply roller 43 to the developing roller 42 becomes weaker than during image formation, and the amount of toner on the developing roller becomes less than during image formation. In other words, the potential difference during the scraping operation is smaller than during the image formation operation. Hereinafter, this control, which reduces the potential difference V_DIFF to less than during image formation and causes the developing roller 42 and the photosensitive drum 1 to come into contact and rotate, will be referred to as the scraping operation.

[0037] Alternatively, during scraping, the applied voltage to the toner supply roller 43 may be set to -250V, and the potential difference V_DIFF to -50V, creating a potential relationship that returns toner from the developing roller 42 to the supply roller 43. Furthermore, during image formation, the absolute value of the developing voltage may be set to be less than the absolute value of the supply voltage, and during the scraping operation, the potential difference between the developing voltage and the supply voltage may be set to 0. Alternatively, during image formation, the absolute value of the developing voltage may be set to be less than or equal to the absolute value of the supply voltage, and during the scraping operation, the absolute value of the developing voltage may be set to be greater than the absolute value of the supply voltage.

[0038] Furthermore, if the normal charging polarity of the toner is positive, for example, the applied voltage to the developing roller 42 can be changed to +300V during image formation, the applied voltage to the toner supply roller 43 to +400V, and the applied voltage to the toner supply roller 43 to +350V during scraping.

[0039] Furthermore, the completion of the image formation operation on the intermediate transfer belt 53 refers to the timing when the trailing edge of the image from each image formation station is transferred to the intermediate transfer belt. In this embodiment, for the sake of simplifying control, the scraping operation is started simultaneously at all image formation stations Y, M, C, and K. Therefore, the timing of the change is when the trailing edge of the image from the downstream image formation station K is transferred to the intermediate transfer belt 53. However, the scraping operation may be initiated sequentially, starting with the image formation stations located upstream that have completed image formation first.

[0040] Figure 3 is a time chart showing the case where the scraping operation at each image forming station is started simultaneously. The horizontal axis shows the passage of time. The vertical axis shows the absolute value of the voltage, and represents the applied voltage V_DEV of the developing roller 42, the applied voltage V_S1 of the toner supply roller 43 during image forming, and the applied voltage VS_2 of the toner supply roller 43 during scraping.

[0041] At timing t1, the image forming operation begins, and the applied voltage to the toner supply roller 43 is set to V_S1. Subsequently, at timings t2_1 to t2_4, the formation of the Y image, M image, C image, and K image is completed sequentially. At timing t2_4, the scraping operation begins simultaneously at each image forming station, and the applied voltage to the toner supply roller 43 is changed to VS_2. The scraping operation ends at timing t3, after a predetermined scraping time has elapsed. After that, the print termination operation begins and ends at timing t4.

[0042] Here, we will explain the meaning of the scraping operation. In this embodiment, when the applied voltage V_S of the toner supply roller 43 during image formation is on the supply side (when the applied voltage difference V_DIFF > 0), When the voltage V_S applied to the toner supply roller 43 during the scraping operation approaches the voltage applied to the developing roller 42 compared to the voltage V_S applied during image formation, toner is less likely to be supplied to the developing roller 42, and the amount supplied decreases. As a result, the amount of toner on the developing roller decreases, and the surface irregularities of the developing roller 42 are more likely to come into direct contact with the photosensitive drum 1.

[0043] For example, when the voltage V_S applied to the toner supply roller 43 is changed from -400V to -350V, the amount of toner on the developing roller decreases, causing a portion of the developing roller surface to be exposed from the toner coat on the developing roller 42 after passing through the regulating blade 44. Figure 2(b) shows the state just before the exposed portion of the toner coat on the protruding part of the developing roller surface (shown as exposed portion P in the figure) scrapes off the fused material X on the photosensitive drum. Figure 2(c) shows the state immediately after the exposed portion P has scraped off most of the fused material X. Here, if the peripheral speed of the developing roller 42 is V1 and the peripheral speed of the photosensitive drum 1 is V2, there is a peripheral speed difference between V1 and V2, and in this embodiment, V1 > V2. In this way, the portion of the developing roller surface exposed from the toner coat comes into contact with the photosensitive drum 1 and rotates with a peripheral speed difference, thereby scraping off the fused material on the photosensitive drum. Thus, the operation in which the developing roller 42 writes off and removes the toner 90 on the photosensitive drum 1 is called the scraping operation. Hereafter, the ability of the photosensitive drum 1 to scrape off the toner 90 during the scraping operation will also be called the scraping force. The control unit can increase the amount of toner scraped off by increasing the scraping force, or decrease the amount of toner scraped off by decreasing the scraping force, by controlling the voltage applied to each component, as will be described later.

[0044] In this embodiment, the voltage V_S applied to the toner supply roller 43 is uniformly changed to -350V at all image forming stations during scraping, but the applied voltage V_S may be controlled for each image forming station.

[0045] Furthermore, in this embodiment, the applied voltage V_S of the toner supply roller is changed from -400V during image formation to -350V during scraping. However, this is not limited to this, and control should be performed to reduce the potential difference V_DIFF to the extent that the exposed area P is formed. For example, the applied voltage V_S of the toner supply roller 43 may be fixed and the applied voltage V_DEV of the developing roller 42 may be changed, or both the applied voltage V_S of the toner supply roller 43 and the applied voltage V_DEV of the developing roller 42 may be changed.

[0046] A scraping operation is performed for a predetermined time in which the toner supply roller 43 is rotated in contact with the toner supply roller 43 while the applied voltage V_S is lower than during image formation. After that, the developing roller 42 is separated from the photosensitive drum 1, and the printing completion operation is performed.

[0047] <Details of Example 1> As shown in Table 1, in Examples 1-1 to 1-5 and Comparative Examples 1-1 to 1-3, a total of 6,000 prints were performed using various printing conditions as described below, and the all-black images were evaluated. The difference in peripheral speed between the peripheral speed V1 of the developing roller surface and the peripheral speed V2 of the photosensitive drum surface was 70 mm / s. Printing environment (temperature): 15℃~30℃ Number of pages printed per job: 1 / 2 Applied voltage V_S of toner supply roller 43: -400V / -350V Voltage change time (scraping time after each job): 1.1s~6s

[0048] Regarding image quality, the results of the assessment of the degree of white streaks due to fusion are shown in Table 1, "Fusion White Streak Results." ○ indicates no problem, △ indicates minor white streaks that do not pose a practical problem, and × indicates a problem with the white streaks. Furthermore, while the scraping force can be increased by extending the scraping time, extending the scraping time indefinitely leads to toner degradation at the contact points between the regulating blade 44, the developing roller 42, and the photosensitive drum 1, resulting in unevenness in the all-black image during the latter half of the durability test. This occurs. The results are shown in Table 1 under "Development Degradation Results". ○ indicates no problem, and × indicates development degradation. [Table 1]

[0049] <Explanation of Examples 1-1 to 1-3> In Example 1-1, the number of prints per job was 1, the applied voltage V_S to the toner supply roller 43 was -350V, and the scraping time was 1.8 seconds. In Example 1-2, the number of prints per job was 2, and the scraping time was 2.5 seconds. In Example 1-3, the number of prints per job was 2, and the scraping time was 1.8 seconds. The printing environment for Examples 1-1 to 1-3 was a room temperature of 15°C.

[0050] Comparing Examples 1-1 and 1-3, even with the same scraping time, minor white spots occur when the number of sheets per job is large. This is because the scraping interval becomes longer, causing the fused material to accumulate. Therefore, as in Example 1-2, the growth of the fused material can be suppressed by increasing the scraping time to 2.5 seconds or more for a two-sheet job.

[0051] <Explanation of Examples 1-4 to 1-5> Next, we will consider the case where the printing environment is relatively high temperature. Example 1-4 was conducted in an environment with a room temperature of 23°C and an applied voltage change time of 1.6 seconds. Example 1-5 was conducted in an environment with a room temperature of 30°C. In Example 1-5, during scraping after image formation, the applied voltage V_S to the toner supply roller 43 was not changed from that used during image formation, and the scraping time was set to 1.1 seconds to maintain contact rotation.

[0052] A comparison of Examples 1-3 to 1-5 shows that when the printing environment is at a low temperature, the scraping time required to suppress fusion increases. This is because, in a low-temperature environment, the deformation-following ability of the electrostatic roller decreases, resulting in stronger stress acting on the toner, causing the toner to deform and making it more prone to fusion. On the other hand, in Example 1-5, where the temperature is particularly high, white streaks can be suppressed with a short scraping time without changing the voltage V_S applied to the toner supply roller 43.

[0053] <Explanation of Comparative Example 1-1> The following describes each comparative example. In Comparative Examples 1-1 to 1-3, the printing environment is at room temperature of 15°C. Comparative Example 1-1 is the same as Example 1-1, but with a scraping time of 1.5 seconds. From the comparison between Example 1-1 and Comparative Example 1-1, it can be seen that increasing the scraping time can suppress the occurrence of fusion. This is because, with a small applied voltage difference V_DIFF between the developing roller 42 and the toner supply roller 43, the distance over which the developing roller 42 and the photosensitive drum 1 rub against each other increases, thereby increasing the effect of scraping off fused material on the photosensitive drum. Note that in order to scrape off each part in the circumferential direction of the photosensitive drum 1, the scraping time per pass must be longer than the time it takes for the photosensitive drum 1 to complete one rotation.

[0054] <Explanation of Comparative Example 1-2> Comparative Example 1-2 involved printing two sheets per job, keeping the applied voltage V_S of the toner supply roller 43 the same as during image formation, and using the same 2.5-second scraping time as in Example 1-2. Comparing Example 1-2 and Comparative Example 1-2, it can be seen that when the applied voltage V_S of the toner supply roller 43 during scraping is not changed compared to image formation, white streaks due to fusion occur.

[0055] <Explanation of Comparative Example 1-3> Comparative Examples 1-3 involved printing two sheets per job and a scraping time of 6 seconds. In Comparative Examples 1-3, the scraping time was set to 6 seconds. Although the scraping force was sufficient, the development rotation time per job was increased, resulting in a longer time for the toner to be rubbed inside the developing machine and at the contact point between the developing roller 42 and the photosensitive drum 1. As a result, the toner deteriorated, and the all-black image became uneven.

[0056] As described above, with a difference in peripheral speed between the photosensitive drum 1 and the developing roller 42, the scraping operation can be performed by setting conditions such as the voltage applied to the developing roller 42 and the toner supply roller 43, the scraping time (contact rotation time), etc., according to the printing environment and the conditions of the printing job, thereby removing the fused material from the surface of the photosensitive drum from the exposed portion of the toner coating on the surface of the developing roller.

[0057] [Example 2] Example 2 will now be described. The same parts as in Example 1 will be omitted from the explanation. In this example, when the number of print jobs is large, the voltage V_S applied to the toner supply roller 43 is changed as a way to increase the scraping force. Specifically, the potential difference V_DIFF between the voltage applied to the developing roller 42 and the toner supply roller 43 in the direction that presses the toner from the supply roller 43 to the developing roller 42 during the scraping operation is made smaller as the number of print jobs increases. For example, if the potential difference V_DIFF during image formation is +100V, V_DIFF is set to +50V when there are 2 print jobs and 0V when there are 3 print jobs. When the potential difference V_DIFF decreases, the amount of toner on the developing roller decreases, the surface irregularities of the developing roller 42 are more exposed, and the scraping force increases.

[0058] The test results for this embodiment are shown in Table 2. In this embodiment, the scraping time was kept constant at 1.8 seconds. The peripheral speed difference between the surface of the developing roller and the surface of the photosensitive drum was 70 mm / s. Printing was performed in a room temperature environment of 15°C. [Table 2]

[0059] <Details of Example 2> Example 2-1 involved printing 2 sheets per job, applying a voltage of -350V to the toner supply roller 43 during scraping, and performing a scraping operation for 1.8 seconds at the end of each job (same conditions as Example 1-3). Example 2-2 involved applying a voltage of -300V to the toner supply roller during scraping. Example 2-3 also involved printing 2 sheets per job. The number of printed sheets per unit is 3, and the applied voltage during scraping is -300V.

[0060] <Details of Comparative Example 2> Comparative Example 2-1 is a case where the number of prints per job is 3, and the voltage applied to the toner supply roller 43 during scraping is -350V. Compared to Example 2-1, the number of prints per job has increased.

[0061] <Examination of Example 2 and Comparative Example 2> Comparing Example 2-1 and Example 2-2, a slight fusion image is produced when V_S = -350V (potential difference V_DIFF = +50V), but no fusion image is produced when V_S = -300V (potential difference V_DIFF = 0V). In this way, by making the potential difference V_DIFF formed between the developing roller 42 and the toner supply roller 43 smaller, the scraping force can be increased.

[0062] A comparison of Example 2-1 and Example 2-3 shows that by changing the applied voltage V_S of the toner supply roller 43 during scraping from -350V to -300V, thereby increasing the scraping force, it is possible to maintain a state of minor fusion image even when increasing the number of sheets per job from two to three.

[0063] On the other hand, comparing Example 2-1 with Comparative Example 2-1, it can be seen that if the applied voltage V_S to the toner supply roller 43 during scraping remains at -350V, the white streak image due to fusion deteriorates when the number of printed sheets per job is increased from 2 to 3.

[0064] [Example 3] Example 3 will now be described. The same parts as in the above examples will be omitted from the explanation. In this example, as a method to increase the scraping force when the number of prints per job is large, the difference in peripheral speed between the developing roller 42 and the surface of the photosensitive drum is increased compared to the image formation stage, thereby increasing the scraping distance. Specifically, the greater the number of prints per job, the greater the difference in peripheral speed between the developing roller 42 and the photosensitive drum 1 during the scraping operation.

[0065] The test results for this embodiment are shown in Table 3. The scraping time was kept constant at 1.8 seconds, and the applied voltage V_S to the toner supply roller 43 during scraping was uniformly set to -350V. Printing was performed in a room temperature environment of 15°C. [Table 3]

[0066] <Details of Example 3> Example 3-1 shows the result of fused white streaks when printing 2 sheets per job and rotating the developing roller 42 and photosensitive drum 1 at a peripheral speed difference of 70 mm / s (developing roller rotating faster) during scraping. The image shows only minor white streaks that do not pose a practical problem. Example 3-2 shows the result of fused white streaks when the peripheral speed difference is 120 mm / s. No white streaks occurred in Example 3-2. Example 3-3 shows the result when printing 3 sheets per job with a peripheral speed difference of 120 mm / s. In Example 3-3, the fusion was at a minor level. That was the case.

[0067] <Details of Comparative Example 3> Comparative Example 3-1 used a peripheral speed difference of 70 mm / s between the developing roller 42 and the photosensitive drum 1, and printed 3 sheets per job (same as Comparative Example 2-1). In Comparative Example 3-1, white streaks occurred due to fusion.

[0068] <Examination of Example 3 and Comparative Example 3> A comparison of Example 3-1 and Example 3-2 shows that increasing the peripheral speed difference can increase the scraping force. Furthermore, a comparison of Example 3-1 and Example 3-3, and a comparison of Example 3-1 and Comparative Example 3-1, shows that as the number of printed sheets per job increases, it becomes necessary to increase the peripheral speed difference to increase the scraping force.

[0069] [Example 4] The present invention is preferably implemented by having the control unit 65 set appropriate operating conditions according to preconditions such as the printing environment and print job settings, and then operating each component of the image forming apparatus. For this purpose, it is preferable to prepare in advance a table or formula that associates preconditions such as the printing environment and print job settings with operating conditions such as applied voltage, scraping time, and peripheral speed difference, and store it in memory or the like. The control unit 65 obtains the print job settings based on the print job instructed by the user, and uses those print job settings as a key to refer to the memory and set appropriate operating conditions.

[0070] More preferably, the image forming apparatus may include an environmental information acquisition unit 69. The control unit 65 uses the printing environment information detected by the environmental information acquisition unit 69 as a key to refer to the memory and set appropriate operating conditions. The environmental information acquisition unit 69 may include a thermometer.

[0071] As described above, according to each embodiment of the present invention, by setting operating conditions such as the voltage applied to the developing roller 42 and the toner supply roller 43, the scraping time (contact rotation time), and the peripheral speed difference between the photosensitive drum 1 and the developing roller 42, according to the preconditions (printing conditions) such as the printing environment (temperature) and the print job settings (number of prints per job), an exposed area P is formed on the surface of the developing roller, and fused material on the surface of the photosensitive drum can be removed. In particular, in cleanerless image forming apparatuses, since there is no cleaning blade to remove toner 90 remaining on the photosensitive drum 1, the effect of removing the attached material by performing the scraping operation described in this embodiment is significant. As long as the fused material is removed, the combination of conditions to be set is not limited to the above embodiments, and any combination may be performed. [Explanation of Symbols]

[0072] 1: Photosensitive drum, 42: Developing roller, 423: Developing roller surface, 43: Toner supply roller, 65: Control unit, 90: Toner, 100: Image forming apparatus

Claims

1. a rotatable image carrier; an exposure unit that exposes the surface of the image carrier to light in order to form an electrostatic latent image on the surface of the image carrier; a rotatable developing member that contacts the image carrier to form a developing section and supplies a developer to a surface of the image carrier in the developing section, the developing member rotating at a rotational speed different from a rotational speed of the image carrier; a developer supplying member for supplying developer to a surface of the developing member; a developing voltage applying section that applies a developing voltage to the developing member; a supply voltage applying section that applies a supply voltage to the developer supply member; a control unit that controls the developing voltage application unit and the supply voltage application unit, the control unit controls to execute an image forming operation in which a developer image is formed on the surface of the image carrier by supplying the developer from the developing member to the electrostatic latent image formed on the surface of the image carrier, and a scraping operation, which is an operation other than the image forming operation, in which deposits attached to the surface of the image carrier are removed by the developing member; The image forming apparatus is characterized in that the control unit controls at least one of the development voltage application unit and the supply voltage application unit so that when the scraping operation is performed, the force with which the developing member scrapes off the adhesions adhering to the surface of the image carrier is stronger than when the image forming operation is performed.

2. The stronger the force with which the control unit scrapes off the deposits from the surface of the image carrier by the developing member, the more the amount of the deposits that are scraped off can be increased.

2. The image forming apparatus according to claim 1, wherein the image forming apparatus is a recording medium.

3. When the scraping operation is performed, the control unit controls at least one of the developing voltage application unit and the supply voltage application unit so that an exposed portion exposed from the developer is formed, and causes the developing member on which the exposed portion is formed to rub against the image carrier.

3. The image forming apparatus according to claim 2, wherein the image forming apparatus is a recording medium.

4. The control unit controls at least one of the developing voltage application unit and the supply voltage application unit so that an amount of the developer supplied from the developer supply member to the developing member is reduced during the scraping operation compared to during the image forming operation.

4. The image forming apparatus according to claim 2, wherein the image forming apparatus is a recording medium.

5. In the potential difference between the developer supply member and the developing member, when the direction in which the normally charged developer is supplied from the developer supply member to the developing member is defined as positive, and the direction in which the developer is collected from the developing member to the developer supply member is defined as negative, The control unit controls at least one of the developing voltage application unit and the supply voltage application unit so that, during the scraping operation, the potential difference becomes smaller in a positive direction than during the image forming operation, the potential difference becomes zero, or the potential difference becomes negative.

5. The image forming apparatus according to claim 4.

6. The control unit sets the supply voltage and the developing voltage to the same polarity as that of the normal charging of the developer, and makes the absolute value of the developing voltage smaller than the absolute value of the supply voltage during the image forming operation, and makes the potential difference between the developing voltage and the supply voltage smaller during the scraping operation than during the image forming operation.

5. The image forming apparatus according to claim 4.

7. the control section sets the supply voltage and the developing voltage to the same polarity as that of the normal charging of the developer, and sets the absolute value of the developing voltage to be smaller than the absolute value of the supply voltage during an image forming operation; The control unit sets the potential difference between the developing voltage and the supply voltage to 0 during the scraping operation.

5. The image forming apparatus according to claim 4.

8. the control section sets the supply voltage and the developing voltage to the same polarity as that of the normal charging of the developer, and sets the absolute value of the developing voltage to be equal to or less than that of the supply voltage during an image forming operation; The control unit sets the absolute value of the developing voltage to be greater than the absolute value of the supply voltage during the scraping operation.

5. The image forming apparatus according to claim 4.

9. The control unit is capable of changing the scraping force in the scraping operation.

9. The image forming apparatus according to claim 1, wherein the image forming apparatus is a recording medium.

10. The control unit increases the scraping force by lengthening the time of the scraping operation.

10. The image forming apparatus according to claim 9,

11. The control unit increases the scraping force by increasing the difference in peripheral speed between the image carrier and the developing member.

11. The image forming apparatus according to claim 9, wherein the image forming apparatus is a recording medium.

12. The control unit can change the scraping force in the scraping operation, When the control unit performs control to make the potential difference between the supply voltage and the developing voltage smaller during the scraping operation than during the image forming operation, the control unit makes the potential difference smaller or zero, thereby increasing the scraping force, and when the control unit performs control to make the potential difference negative during the scraping operation, the control unit makes the potential difference in the negative direction, thereby increasing the scraping force.

10. The image forming apparatus according to claim 9,

13. The control unit performs control such that the scraping force increases as the number of prints per job in the image forming operation increases.

13. The image forming apparatus according to claim 9, wherein the image forming apparatus is a recording medium.

14. an environmental information acquisition unit that detects printing environmental information of the image forming apparatus; The control unit controls the scraping force in accordance with the printing environment information.

14. The image forming apparatus according to claim 9, wherein the image forming apparatus is a recording medium.

15. the environmental information acquisition unit acquires a temperature as the printing environmental information, The control unit increases the scraping force as the temperature decreases.

15. The image forming apparatus according to claim 14.

16. a transfer member that transfers the developer on the image carrier to a transfer target; The developer remaining on the surface of the image carrier without being transferred by the transfer member is collected by the developing member.

16. The image forming apparatus according to claim 1, wherein the image forming apparatus is a recording medium.

17. The developer is a non-magnetic one-component developer.

17. The image forming apparatus according to claim 1, wherein the image forming apparatus is a recording medium.

18. the developing member has a surface layer formed with a plurality of projections and recesses for transporting the developer, When the scraping operation is performed, the control unit controls the developer so that at least the protrusions of the irregularities are exposed from the developer.

18. The image forming apparatus according to claim 1, wherein the image forming apparatus is a recording medium.

19. The ten-point average roughness of the convex portions of the surface layer of the developing member is larger than the volume average particle size of the developer.

19. The image forming apparatus according to claim 18.

20. The ten-point average roughness of the protrusions on the surface of the developing member is in the range of 8 μm to 30 μm.

20. The image forming apparatus according to claim 18 or 19.

Images