Image forming device

Abstract

An image forming apparatus is disclosed. The image forming apparatus includes a rotatable photosensitive member, an image forming portion, a cleaning device, and a controller. The cleaning device includes a scraper, a rotatable brush, and an applying portion. The controller controls the applying portion to apply a bias voltage to the brush so that the potential of the brush has a polarity opposite to the normal charge polarity of the toner. When the tensile strength of the brush is A (cn / dtex), the thickness of the brush is B (denier), and the bristle density of the brush is C (kF / inch) 2 ), when the length of the brush is D (mm) and the elastic deformation rate of the surface of the photosensitive member is E (%), the following relationship is satisfied: 48 (%) ≤ E ≤ 60 (%) and 400 ≤ {A×B 2 ×C / D 2}≤20408.

Description

Technical Field

[0001] The present invention relates to an image forming apparatus such as a copying machine, a printer, or a facsimile machine using an electrophotographic type. Background Art

[0002] Conventionally, in electrophotographic image forming devices, a toner image formed on the surface of a photosensitive member through the steps of charging, exposure, and development is transferred directly to a recording material or via an intermediate transfer member. On the surface of the photosensitive member, where the transfer process of the toner image from the photosensitive member to the recording material or intermediate transfer member ends, untransferred toner (residual toner), toner additives, and discharge products remain. For this reason, these must be removed from the surface of the photosensitive member before subsequent image formation. Various methods are used to remove residual toner from the surface of the photosensitive member, including methods using fur brushes, magnetic brushes, and cleaning blades. Among these methods, scraping off residual toner from the surface of the photosensitive member by rubbing it with a cleaning blade is widely used due to its relatively simple structure and low cost.

[0003] With the recent acceleration of image forming devices and improvements in image quality, the melting point of the toner used has decreased and its shape has become closer to a sphere, making it difficult to ensure cleaning performance using only a cleaning blade. Therefore, there is a method of using an auxiliary cleaning member to assist in removing the transfer residual toner by the cleaning blade. For example, a method has been proposed in which a brush (brush roller) that contacts the surface of the photosensitive member and can apply a bias is arranged upstream of the cleaning blade in the direction of movement relative to the surface of the photosensitive member (Japanese Patent Application (JP-A) 2009-300860). According to this method, at least a portion of the transfer residual toner before reaching the cleaning blade can be removed by the brush, so that the load on the cleaning blade can be reduced, thereby improving cleaning performance.

[0004] Furthermore, in recent years, in order to extend the life of photosensitive members, thermosetting photosensitive members have been developed, in which the surface of the photosensitive member is less susceptible to wear. Furthermore, there is a trend toward extending the replacement interval of cleaning blades in line with the photosensitive member. When the surface of a photosensitive member is less susceptible to wear, damage such as vibration or reverse rotation (curling) of the cleaning blade, or peeling or abrasion of the edge of the cleaning blade is more likely to occur.

[0005] Furthermore, when the surface of a photosensitive member is not easily abraded, a phenomenon known as "fusion" or "filming" (hereinafter, this phenomenon is simply referred to as "toner fusion"), in which components of the toner or external additives to the toner are deposited and accumulated (grown), is likely to occur. Therefore, a method has been proposed in which a brush is brought into contact with the photosensitive member upstream of a cleaning blade in the direction of movement of the surface of the photosensitive member, mechanically abrading the surface of the photosensitive member, thereby refreshing the surface layer of the photosensitive member (JP-A 2014-228849).

[0006] Therefore, in order to meet the recent acceleration and life extension, the role of the brush as an auxiliary cleaning member for improving the cleaning performance has become important.

[0007] JP-A 2009-300860 describes cleaning performance as follows: In order to increase the probability of contact between the brush and the toner, cleaning performance is improved by limiting the density of the brush bristles or by limiting the resistance value of the brush. In addition to its cleaning function, the brush also serves to wear away the surface layer of the photosensitive member. However, JP-A 2009-300860 does not describe the wear or abrasion of the surface layer of the photosensitive member. Furthermore, JP-A 2014-228849 does not describe the properties of the surface layer of the photosensitive member or the rigidity of the brush. The degree of wear on the surface layer of the photosensitive member varies depending on the hardness of the surface layer of the photosensitive member, the bristles of the brush, and the contact conditions.

[0008] As mentioned above, in recent years, there has been a trend toward increasing hardness in the surface layer of photosensitive members. Even in the case of a hard surface layer, if the amount of wear (abrasion) of the surface layer is small, toner melting may occur on the surface of the photosensitive member. On the other hand, if the amount of wear (abrasion) is large, the life of the photosensitive member becomes shorter. This is because scratches on the surface layer of the photosensitive member increase in the circumferential direction, resulting in a state of high surface roughness, which can lead to inconveniences such as improper cleaning and the like. Summary of the Invention

[0009] A main object of the present invention is to suppress the occurrence of toner melting on the surface of a photosensitive member while achieving extension of the life of the photosensitive member.

[0010] This object can be achieved by an image forming apparatus according to the present invention. According to one aspect of the present invention, there is provided an image forming apparatus comprising: a rotatable photosensitive member; an image forming portion configured to form a toner image on the photosensitive member; a cleaning device configured to clean the photosensitive member, wherein the cleaning device comprises: a scraper contacting the photosensitive member at a first contact portion and configured to clean the photosensitive member; a rotatable brush contacting the photosensitive member at a second contact portion upstream of the first contact portion relative to the rotation direction of the photosensitive member and configured to collect toner remaining on the photosensitive member; an applying portion configured to apply a bias to the brush; and a controller configured to control the applying portion, wherein when an image forming area on the surface of the photosensitive member passes through the second contact portion, the controller controls the applying portion so as to apply a bias to the brush so that the potential of the brush has a polarity opposite to the normal charge polarity of the toner, and when the tensile strength of the brush is A (cn / dtex), the thickness of the brush is B (denier), and the bristle density of the brush is C (kF / inch) 2 ), when the length of the brush is D (mm) and the elastic deformation rate of the surface of the photosensitive member is E (%), the following relationship is satisfied: 48 (%) ≤ E ≤ 60 (%) and 400 ≤ {A×B 2 ×C / D 2}≤20408.

[0011] Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 is a schematic cross-sectional view of an image forming apparatus.

[0013] Figure 2 is a schematic cross-sectional view of an image forming portion.

[0014] Figure 3 is a graph of an output graph of FISCHERSCOPE H100V (manufactured by FISCHER INSTRUMENTS K.).

[0015] Figure 4 This is a diagram showing an example of an output graph of the FISCHERSCOPE H100V.

[0016] Figure 5 is a schematic cross-sectional view of the cleaning device and its periphery in Example 1.

[0017] Figure 6 is a schematic diagram for illustrating the occurrence process of toner fusion.

[0018] Figure 7It is a schematic diagram for illustrating the toner melting suppression effect.

[0019] Figure 8A and Figure 8B A table showing evaluation results regarding Example 1 is included.

[0020] Figure 9 2 is a schematic cross-sectional view of the cleaning device and its periphery in Example 2.

[0021] Figure 10 is a graph showing the evaluation results regarding Example 2. DETAILED DESCRIPTION

[0022] Hereinafter, the image forming apparatus according to the present invention will be described in detail with reference to the accompanying drawings.

[0023] [Example 1]

[0024] 1. Overall Structure and Operation of Image Forming Apparatus

[0025] Figure 1 is a schematic cross-sectional view of an image forming apparatus 100 of Embodiment 1. The image forming apparatus 100 of this embodiment is a tandem-type four-color-based full-color printer in which a full-color image can be formed by using an electrophotographic process and in which an intermediate transfer type is employed.

[0026] The image forming apparatus 100 includes four image forming sections 10Y, 10M, 10C, and 10K as a plurality of image forming sections (stations) for forming yellow (Y), magenta (M), cyan (C), and black (K), respectively. These image forming sections 10Y, 10M, 10C, and 10K are arranged in a straight line along the direction of movement of a substantially horizontal image transfer surface of an intermediate transfer belt 7, which will be described later. Regarding elements having the same or corresponding functions or configurations in the respective image forming sections 10Y, 10M, 10C, and 10K, these elements are collectively described in some examples by omitting the suffixes Y, M, C, and K of the reference numerals or symbols representing the corresponding colors. Figure 2 1 is a schematic cross-sectional view showing a representative single image forming section 10. In this embodiment, the image forming section 10 is configured by including photosensitive drums 1 (1Y, 1M, 1C, 1K), charging rollers 4 (4Y, 4M, 4C, 4K), exposure devices 3 (3Y, 3M, 3C, 3K), developing devices 8 (8Y, 8M, 8C, 8K), primary transfer rollers 5 (5Y, 5M, 5C, 5K), cleaning devices 6 (6Y, 6M, 6C, 6K), and the like, which will be described later.

[0027] The image forming apparatus includes a photosensitive drum 1 of a rotatable drum-type (cylindrical) photosensitive member (electrophotographic photosensitive member) as a first image bearing member for bearing a toner image. The photosensitive drum 1 is driven by a drum drive motor (not shown) as a driving source. Figure 1 The photosensitive drum 1 rotates (is driven) in the direction of arrow R1 (counterclockwise) at a predetermined peripheral speed (process speed). The surface of the rotating photosensitive drum 1 is uniformly charged to a predetermined polarity (negative in this embodiment) and a predetermined potential by a charging device 2 serving as a charging member. During the charging process, a charging bias (charging voltage) is applied to the charging device 2 by a charging power supply (high-voltage power supply) E1.

[0028] The charged surface of the photosensitive drum 1 is subjected to scanning exposure based on an image signal by an exposure device 3, which serves as an exposure component, to form an electrostatic latent image (electrostatic image) on the photosensitive drum 1. The electrostatic latent image formed on the photosensitive drum 1 is developed (visualized) by a toner supplied as a developer by a developing device 4, which serves as a developing component, to form a toner image (developer image) on the photosensitive drum 1. In this embodiment, toner charged to the same polarity as the charge polarity of the photosensitive drum 1 (negative in this embodiment) is deposited on the exposed portion (image portion) of the photosensitive drum 1, whose absolute value of potential has been reduced by exposure after uniform charging (reversal development type). During development, a predetermined development bias (development voltage) is applied to the developing sleeve 41 of the developing device 4 by a development power source (high-voltage power source) E2. In this embodiment, the normal charge polarity of the toner, which serves as the charge polarity of the toner during development, is negative (-).

[0029] An intermediate transfer belt 7, a rotatable intermediate transfer member formed of an endless belt and serving as a second image bearing member for carrying toner images, is positioned opposite the four photosensitive drums 1Y, 1M, 1C, and 1K. The intermediate transfer belt 7 is stretched around a drive roller 71, a tension roller 72, and a secondary transfer counter roller 73, serving as a plurality of stretching rollers, and is stretched with a predetermined tension. A driving force is transmitted to the intermediate transfer belt 7 from a belt drive motor (not shown), serving as a drive source, and the drive roller 71 is rotationally driven, causing the intermediate transfer belt 7 to rotate (circulate and move) in the direction of arrow R2 (clockwise) at a predetermined circumferential speed (process speed) corresponding to the circumferential speed of the photosensitive drums 1. Primary transfer rollers 5Y, 5M, 5C, and 5K are provided on the inner circumferential surface of the intermediate transfer belt 7, corresponding to the photosensitive drums 1Y, 1M, 1C, and 1K, respectively. These rollers 5Y, 5M, 5C, and 5K are roller-shaped primary transfer members (transfer devices) serving as primary transfer components. The primary transfer roller 5 is pressed against the photosensitive drum 1 and contacts the photosensitive drum 1 via the intermediate transfer belt 7, forming a primary transfer portion (primary transfer nip) T1, which is the contact portion between the photosensitive drum 1 and the intermediate transfer belt 7. The stretching rollers excluding the drive roller 71 among the plurality of stretching rollers and each of the primary transfer rollers 5 rotate as the intermediate transfer belt 7 rotates. The toner image formed on the photosensitive drum 1 is transferred (primarily transferred) to the rotating intermediate transfer belt 7 in the primary transfer nip T1 by the action of the primary transfer roller 5. During the primary transfer, a predetermined primary transfer bias (primary transfer voltage) is applied to the primary transfer roller 5 by a primary transfer power supply (high-voltage power supply) E3. This primary transfer bias is a DC voltage of a polarity opposite to the normal charge polarity of the toner (positive in this embodiment). For example, during full-color image formation, yellow, magenta, cyan, and black toner images formed on the photosensitive drum 1 are primarily transferred onto the intermediate transfer belt 7 in sequence and superimposed in the same image position (image forming area).

[0030] On the outer peripheral surface side, at a position opposing the secondary transfer opposing roller 73, a secondary transfer roller 8, which is a roller-shaped secondary transfer member and serves as a secondary transfer component, is provided. The secondary transfer roller 8 is pressed toward the secondary transfer opposing roller 73 and contacts the secondary transfer opposing roller 73 via the intermediate transfer belt 7, forming a secondary transfer portion (secondary transfer nip) T2, which is the contact portion between the intermediate transfer belt 7 and the secondary transfer roller 8. In the secondary transfer portion T2, the toner image formed on the intermediate transfer belt 7 is transferred (secondary transferred) by the action of the secondary transfer roller 8 onto the recording material P, which is sandwiched and fed between the intermediate transfer belt 7 and the secondary transfer roller 8. During the secondary transfer, a predetermined secondary transfer bias (secondary transfer voltage) is applied to the secondary transfer roller 8 by the secondary transfer power supply 26. This secondary transfer bias is a DC voltage of a polarity opposite to the normal charge polarity of the toner (positive in this embodiment). The secondary transfer opposing roller 73 is electrically grounded (connected to the ground). Incidentally, in this embodiment, the roller corresponding to the secondary transfer opposing roller 73 can be used as a secondary transfer member, and a secondary transfer voltage having the same polarity as the normal charge polarity of the toner can be applied to the roller. In this case, it is only necessary for the roller corresponding to the secondary transfer roller 8 to be used as an opposing electrode and electrically grounded. Recording materials (transfer materials, recording media, sheets) P ​​such as paper or plastic sheets are accommodated in a recording material box 11 as a recording material accommodating portion. The recording materials P accommodated in the recording material box 11 are separated and fed one by one from the box 11 by the feeding roller 12 or the like as a feeding component. The recording material P is conveyed by the conveying roller pair 13 as a conveying component toward the alignment roller pair 14 as a conveying component. Then, the recording material P is synchronized with the toner image on the intermediate transfer belt 7 and is conveyed toward the secondary transfer portion T2 by the alignment roller pair 14.

[0031] The recording material P to which the toner image has been transferred is conveyed to a fixing device 9 serving as a fixing member. The fixing device 9 heats and pressurizes the recording material P by pinching and conveying the recording material P carrying the unfixed toner image with a rotatable fixing member pair, thereby fixing (melting, adhering) the toner image to the surface of the recording material P. The recording material P to which the toner image has been fixed is discharged (output) by a discharge roller pair 15 serving as a discharge member onto a discharge tray (not shown) or the like provided outside the apparatus main assembly of the image forming apparatus 100.

[0032] On the other hand, deposited matter such as toner (primary transfer residual toner) remaining on the photosensitive drum 1 after the primary transfer is removed and collected from the surface of the photosensitive drum 1 by a cleaning device 6 as a cleaning member. Deposited matter such as toner (secondary transfer residual toner) remaining on the intermediate transfer belt 7 after the secondary transfer is removed and collected from the surface of the intermediate transfer belt 7 by a belt cleaning device 74 as an intermediate transfer member cleaning member.

[0033] The position on the photosensitive drum 1 at which charging is performed by the charging device 2 relative to the rotational direction of the photosensitive drum 1 is the charging position Pa. Furthermore, the position on the photosensitive drum at which the photosensitive drum surface is illuminated with light emitted by the exposure device 3 relative to the rotational direction of the photosensitive drum 1 is the exposure position Pb. Furthermore, the position on the photosensitive drum 1 at which toner is supplied by the developing device 4 relative to the rotational direction of the photosensitive drum 1 (the portion opposing the developing sleeve 41) is the developing position Pc. Furthermore, the position on the photosensitive drum 1 at which the primary transfer of the toner image onto the intermediate transfer belt 7 is performed relative to the rotational direction of the photosensitive drum 1 (corresponding to the aforementioned primary transfer portion T1, which is the contact portion with the intermediate transfer belt 7) is the primary transfer position Pd. Furthermore, the position on the photosensitive drum 1 at which transfer residual toner is removed by the fur brush 62 of the cleaning device 6 (described later) relative to the rotational direction of the photosensitive drum 1 (the contact portion with the fur brush 62) is the brush cleaning position Pe. In addition, with respect to the rotation direction of the photosensitive drum 1, the position on the photosensitive drum 1 where the transfer residual toner is removed by the cleaning blade 61 of the cleaning device 6 described later (the contact portion with the cleaning blade 61) is the blade cleaning portion Pf. With respect to the rotation direction of the photosensitive drum 1, the charging position Pa, the exposure position Pb, the development position Pc, the primary transfer position Pd, the brush cleaning position Pe, and the blade cleaning position Pf are arranged in the order specified from the upstream side toward the downstream side when viewed from the charging position Pa.

[0034] The image forming apparatus 100 includes a CPU 201 as a control unit (controller) for controlling the image forming apparatus 100. A RAM 202 as a storage unit serving as a memory for operation and a ROM 203 as a storage unit storing programs executed by the CPU 201 and various data are connected to the CPU 201. Furthermore, a video controller 204 for processing image forming information input to the image forming apparatus 100 is connected to the CPU 201. The video controller 204 for processing image forming information processes image forming information input from an external device (not shown) such as a personal computer (PC) or an image reader connected to the image forming apparatus 100. The CPU 201 controls the various components of the image forming apparatus 100 based on the image information processed and generated by the video controller 204. That is, the image forming apparatus 100 forms and outputs a toner image (printout) corresponding to the image information input to the CPU 201 on a recording material P.

[0035] 2. Detailed composition of each part

[0036] Next, description will be made on the detailed configuration of each portion of the image forming apparatus 100. Incidentally, the cleaning device 6 will be specifically described later.

[0037] <Charging equipment>

[0038] In this embodiment, a corona charging type charging device 2 is used as a charging component. The corona charging type charging device 2 includes a discharge electrode and a grid electrode, and a high voltage is applied to the discharge electrode so that the surface of the photosensitive drum 1 is uniformly charged by utilizing the discharge phenomenon. In this embodiment, for example, a voltage is applied to the discharge electrode by the charging power supply E1 so that a current of -1000μA flows, and a voltage of -600V is applied to the grid electrode. Thus, the surface of the rotating photosensitive drum 1 is uniformly charged to a charge potential of about -500V. In this embodiment, the charge potential of the photosensitive drum 1 has a negative polarity, and the surface of the photosensitive drum 1 is charged to the negative polarity side. Incidentally, based on the environment, the state of the image forming apparatus 100, etc., the charge potential of the photosensitive drum 1 can be changed in accordance with the value of the development bias.

[0039] Incidentally, the charging component is not limited to a charging device of a corona charging type. For example, as a charging component, a contact-type charging roller capable of contacting the surface of the photosensitive drum 1 can be used. In this case, the surface of the photosensitive drum 1 is charged by utilizing the discharge phenomenon generated in the small gap between the photosensitive drum 1 and the charging roller. In addition, in this case, a charging bias under predetermined conditions is applied to the core metal of the charging roller. As the charging bias, an oscillating voltage in the form of a superposition of a DC component (DC bias) and an AC component (AC bias) can be used. For example, by setting the DC bias to -500V and setting the AC bias to a peak-to-peak voltage value that is not less than twice the discharge starting voltage when a DC voltage is applied in the environment, the photosensitive drum 1 can be uniformly charged to about -500V.

[0040] <Exposure Equipment>

[0041] In this embodiment, a laser scanner is used as the exposure device 3. The exposure device 3 includes a semiconductor laser and subjects the photosensitive drum 1, whose surface is uniformly charged by the charging device 2, to image exposure based on image information. The exposure potential of the photosensitive drum 1 formed by irradiating the photosensitive drum surface with laser light by the exposure device 3 is approximately -200 V.

[0042] Incidentally, in this embodiment, an example in which a semiconductor laser is used as an exposure component will be described, but other components such as an LED may also be used.

[0043] In addition, a potential measuring member capable of measuring the surface potential of the photosensitive drum 1 after exposure is disposed, and it can be made possible to check whether the charge potential and the exposure potential actually become predetermined potentials.

[0044] <Developing Equipment>

[0045] In this embodiment, a reversal development type developing device 4 using a two-component developer is used as the developing unit. The developing device 4 includes a developing container 42 containing a two-component developer primarily composed of a mixture of non-magnetic toner particles (toner) and magnetic carrier particles (carrier). Furthermore, the developing device 4 includes a developing sleeve 41 rotatably disposed at the opening of the developing container 42, serving as a developer carrying member (developing member). In this embodiment, negatively charged toner (negative toner) is used as the toner. In this embodiment, the length of the developing sleeve 41 relative to the rotational axis is 325 mm. The developing sleeve 41 magnetically retains the developer in the developing container 42 via a magnet (not shown) fixed and disposed within the developing sleeve 41, and transports the developer to the developing portion, which serves as the gap between the developing sleeve 41 and the photosensitive drum 1. In this embodiment, an oscillating voltage, a superposition of a DC component (DC bias) and an AC component (AC bias), is applied to the developing sleeve 41 as a developing bias by a developing power source E2. For example, a development bias is applied in the form of a superposition of an AC bias of 1600 V in Vpp and a DC bias of -400 V. This development bias causes development to proceed by deposition of toner on the electrostatic latent image. Incidentally, the setting value of the development bias is an example and can be set to an appropriate adjusted value depending on the charge potential or exposure potential of the photosensitive drum 1.

[0046] <Intermediate Transfer Belt>

[0047] In this embodiment, an endless intermediate transfer belt 7 is used as the intermediate transfer member. In this embodiment, the intermediate transfer belt 7 includes three layers, which are composed of a resin layer, an elastic layer, and a surface layer, in the order specified from the back side (inner peripheral surface side) toward the front side (outer peripheral surface side). A material such as polyimide or polycarbonate is used as the resin material constituting the resin layer. The thickness of the resin layer can preferably be greater than 70 μm and less than 100 μm. In addition, a material such as polyurethane rubber or chloroprene rubber is used as the elastic material constituting the elastic layer. The thickness of the elastic layer can preferably be greater than 200 μm and less than 250 μm.

[0048] In addition, a material that can improve the secondary transfer performance by reducing the deposition force of the colorant on the surface of the intermediate transfer belt 7 can be preferably used as the material constituting the surface layer. For example, one of resin materials such as polyurethane, polyester or epoxy resin, or two or more of elastic materials such as elastic material rubber, elastomer, butyl rubber, etc. are used as the base material. In addition, in the base material, one or two or more materials such as particles or powders of fluorine-containing resins for enhancing lubrication performance by reducing surface energy or materials with different particle sizes can be dispersed and used. The thickness of the surface layer can preferably be not less than 5 μm and not more than 10 μm. In this embodiment, a conductive agent such as carbon black is added for adjusting the resistance value and thus the volume resistivity is 1×10 8 Ω.cm or more and 1×10 14 An intermediate transfer belt with a thickness of Ω·cm or less is used as the intermediate transfer belt 7 .

[0049] <Primary Transfer Roller>

[0050] In this embodiment, a primary transfer roller 5, a roller made by molding a polyepichlorohydrin rubber elastic layer with adjusted electrical resistance around a metal shaft, is used as the primary transfer member. The primary transfer roller 5 is positioned approximately 2 mm downstream from the rotational center of the photoreceptor drum 1 relative to the direction of movement of the intermediate transfer belt 7 and is pressed against the photoreceptor drum 1 with a predetermined pressure. A primary transfer bias is applied to the primary transfer roller 5, causing the toner image to be transferred from the photoreceptor drum 1 to the intermediate transfer belt 7. At this time, in some cases, not only toner but also a small amount of carrier may be present on the photoreceptor drum 1. As described above, providing the elastic layer in the intermediate transfer belt 7 reduces damage to the photoreceptor drum 1 in the primary transfer section T1, even when hard materials such as carrier are trapped in the primary transfer section T1.

[0051] <Toner>

[0052] In this embodiment, the toner is frictionally charged to a negative polarity by friction with a carrier. In this embodiment, a carrier containing ferrite and having an average particle size of about 40 μm is used as the carrier. In addition, in this embodiment, a toner having an average particle size of about 6 μm obtained by subjecting a kneaded product of a pigment and a wax component in a resin binder mainly comprising polyester to pulverization and classification is used as the toner. In addition, in this embodiment, a variety of external additive components (external additives) are deposited on the surface layer of the toner for the purposes of charge control, imparting fluidity, improving transfer performance, etc. In this embodiment, the external additive is frictionally charged to a positive polarity, which is a polarity opposite to the normal charge polarity of the toner. In this embodiment, as an external additive component, in addition to silicon dioxide and titanium oxide, inorganic fine particles having an average particle size of primary particles of 30 nm or more and 300 mm or less, having at least one of a cubic particle shape and a rectangular parallelepiped particle shape, and including perovskite crystals are externally added. In this embodiment, strontium titanate fine powder is externally added as the inorganic fine particles including perovskite crystals. Before the external additive component is added to the toner particles, the external additive component may preferably be added to the toner particles in an amount of 0.05 parts by weight or more and 2.00 parts by weight or less per 100 parts by weight of the (final) toner particles, and in this embodiment, strontium titanate fine powder is externally added in an amount of 0.5 parts by weight. The strontium titanate fine powder used as the inorganic fine particles may more preferably be particles that have not undergone a sintering step.

[0053] The strontium titanate fine powder includes at least one of a cubic particle shape and a rectangular parallelepiped particle shape, and when supplied to the cleaning portion of the photosensitive drum 1 by the cleaning device 6 described later, plays a role in polishing the surface of the photosensitive drum 1. The material of the inorganic fine particles may be barium titanate fine powder, calcium titanate fine powder, or the like in addition to the strontium titanate fine powder.

[0054] The average particle size of the primary particles of the inorganic fine powder of perovskite crystals is 30 nm to 300 nm, preferably 40 nm to 300 nm, and more preferably 40 nm to 250 nm. If the average particle size is less than 30 nm, there is a possibility that the polishing (abrasion) effect of the particles by the cleaning device 6 in the cleaning portion of the photosensitive drum 1 may become insufficient. On the other hand, if the average particle size exceeds 300 nm, there is a possibility that the polishing effect is too strong, resulting in scratches on the surface of the photosensitive drum 1.

[0055] Furthermore, the inorganic fine powder of perovskite crystals is not always limited to that present as primary particles on the surface of the toner particles, but rather exists as aggregates. Even in this case, good results can be obtained when the content of aggregates having a particle size of 600 nm or greater is 1% (particle) or less.

[0056] In the case where the inorganic fine powder contains particles and aggregates of 600 mm or more in an amount exceeding 1%, there is a possibility that scratches may occur on the surface layer of the photosensitive drum 1 even when the primary particle size is less than 300 nm.

[0057] Incidentally, the cleaning portion of the cleaning device 6 for the photosensitive drum 1 includes a blade cleaning position Pf which is a contact portion between the photosensitive drum 1 and the cleaning blade 61 and a brush cleaning position Pe which is a contact portion between the photosensitive drum 1 and the fur brush 62 .

[0058] Here, the average particle size (number average particle size) of the primary particles of the above-mentioned inorganic fine particles (external additives) can be obtained by observing the inorganic fine particles present on the surface of the toner particles using a scanning electron microscope. An ultra-high resolution field emission scanning electron microscope ("S-4800", manufactured by Hitachi, Ltd.) can be used as a scanning electron microscope. Incidentally, a basic analysis of an energy dispersive X-ray analyzer (manufactured by EDAX) is performed in advance, and then the material of the relevant particles is checked so that the measurement can be performed. For example, in a magnified field of view with a maximum magnification of 50,000 times, the long diameters of 100 primary particles of the inorganic fine particles are randomly measured so that the number average particle size can be obtained. The observation magnification can be appropriately adjusted depending on the size of the inorganic fine particles.

[0059] In addition, the particle size of the toner can be measured by using a precise particle size distribution measuring device according to the small hole resistance method ("Multisizer 3 Coulter Counter" (registered trademark) manufactured by Beckman Coulter Co., Ltd.) equipped with a 100 μm aperture tube and dedicated software included in the measuring device for measurement condition setting and measurement data analysis ("Beckman Coulter Multisizer 3 Version 3.51" manufactured by Beckman Coulter Co., Ltd.) and then calculating the average particle size (weight average particle size) of the above-mentioned toner by performing measurement data analysis. Incidentally, it can be said that a toner having an average diameter of about 4 μm or more and about 8 μm or less is a small particle size toner.

[0060] <Photosensitive drum>

[0061] In this embodiment, a photosensitive drum 1 is used as a photosensitive member. The photosensitive drum 1 is a negatively chargeable organic photoconductor (OPC) and has a length of 360 mm and an outer diameter of 84 mm relative to the rotation axis direction. In this embodiment, the photosensitive drum 1 is composed of a conductive substrate and a photosensitive layer, which is formed on the conductive substrate and includes a photoconductive layer mainly composed of an organic photoconductor. The OPC is generally composed of a charge generating layer, a charge transport layer, and a surface protective layer each formed of an organic material, stacked in a specified order on a metal substrate as a conductive substrate. For example, a photosensitive drum in which the above-mentioned layers are formed of the materials disclosed in JP-A2005-43806 is used as the photosensitive drum 1 in this embodiment. In addition, in this embodiment, a type of photosensitive drum 1 is used in which the surface of the top layer is cured by using, for example, the provided electron beam irradiation ("EC150 / 45 / 40mA", manufactured by IWASAKI ELECTRIC Co., Ltd.).

[0062] The elastic deformation rate of the surface of the photosensitive drum 1 (for example, the photosensitive drum 1 of the type in which the topmost surface is cured by the above-mentioned electron beam) may preferably be 48% or more and 65% or less. In addition, the universal hardness value (HU) of the surface of the photosensitive drum 1 may preferably be 150 N / mm 2 Above and 220N / mm 2 If the elastic deformation rate is less than the above range, or if the universal hardness value (HU) is less than the above range, scratches are likely to appear on the surface of the photosensitive drum 1, making it difficult to extend the life. If the elastic deformation rate is greater than the above range, or if the universal hardness value (HU) is greater than the above range, the amount of wear on the surface of the photosensitive drum 1 becomes too small, making it easy for the toner on the surface of the photosensitive drum 1 to melt.

[0063] Additionally, in this embodiment, during image formation, the photosensitive drum 1 is rotationally driven by a driving device (not shown) normally at a process speed (peripheral speed) of 400 mm / s.

[0064] Here, the universal hardness value (HU) and elastic deformation rate of the surface of the above-mentioned photosensitive drum 1 are values ​​measured (obtained by performing a hardness test) using a microhardness measuring device ("FISCHERSCOPE H100V", manufactured by FISCHERINSTRUMENTS KK) in an environment with a temperature of 23°C and a relative humidity of 50% RH. The FISCHERSCOPE H100V is a device in which an indenter is in contact with a measurement object (the peripheral surface of the photosensitive drum 1) and a load is continuously applied to the indenter, and the hardness is continuously obtained by directly reading the indentation depth under the load. A Vickers square pyramid diamond indenter with an angle of 6° between the opposing faces is used as the indenter, and the indenter is pressed against the peripheral surface of the photosensitive drum 1. The final load continuously applied to the indenter is set to 6 mN, and the time (holding time) for maintaining the state in which the final load of 6 mN is applied to the indenter is 0.1 seconds. In addition, the number of measurement points is 273 points.

[0065] Figure 3 This is a diagram showing the outline of the FISCHERSCOPE H100V. Figure 4 : is a graph showing an example of an output graph of FISCHERSCOPE H100V when the photosensitive drum 1 in this embodiment is the measurement object. Figure 3 and Figure 4 In FIG. 1 , the ordinate represents the load F [mN] applied to the indenter, and the abscissa represents the indentation depth [μm] of the indenter. Figure 3 Results are shown when the load applied to the indenter is made maximum by increasing the load stepwise (A→B) and then is decreased stepwise (B→C). Figure 4 Results are shown when the load applied to the indenter is increased stepwise to a final value of 6 mN and then the load is decreased stepwise.

[0066] In addition, the universal hardness value (HU) can be obtained from the above-mentioned indentation depth when the final load of 6 mN is applied to the indenter by the formula shown below. Incidentally, in the formula shown below, "HU" represents the universal hardness value, "Ft" represents the final load, "St" represents the surface area of ​​the portion into which the indenter is pressed when the final load is applied to the indenter, and "hf" represents the indentation depth of the indenter when the final load is applied to the indenter.

[0067] HU=Ff(N) / Sf(mm 2 )

[0068] =6×10 -3 / {26.43×(hf×10 -3 ) 2}

[0069] In addition, the elastic deformation rate can be obtained from the workload (energy) of the indenter on the measurement object (the peripheral surface of the photosensitive drum 1), that is, from the change in energy due to the increase and decrease in the load of the indenter on the measurement object (the peripheral surface of the photosensitive drum 1). Specifically, the value obtained by dividing the elastic deformation workload We by the total workload Wt (We / Wt) is the elastic deformation rate. Incidentally, the total workload Wt is Figure 3 The area of ​​the region surrounded by ABDA in , and the elastic deformation workload We is the area of ​​the region surrounded by CBDC. These surface layer characteristics of the photosensitive drum 1 can be represented by measurement results of the photosensitive drum 1 at the initial stage of use (in a fresh state).

[0070] 3. Cleaning Equipment

[0071] <Overall Structure and Operation of Cleaning Equipment>

[0072] Next, the cleaning device 6 in this embodiment will be described in further detail. Figure 5 is a schematic cross-sectional view of the cleaning device 6 and its periphery in this embodiment.

[0073] The cleaning device 6 includes a housing 66. In addition, the cleaning device 6 includes a fur brush (conductive brush roller) 62 which is a rotatable roller-shaped brush having conductivity. The fur brush 62 is used not only as a toner scraping component (cleaning member) for scraping toner from the photosensitive drum 1, but also as a recording material polishing component (polishing member) for polishing (grinding) the surface of the photosensitive drum 1. In addition, the fur brush 62 constitutes an auxiliary cleaning component (auxiliary cleaning member) for assisting in removing toner from the surface of the photosensitive drum 1 by the cleaning blade 61 described later. The fur brush 62 is rotatably supported by the housing 66. The direction of the rotation axis of the fur brush 62 is substantially parallel to the direction of the rotation axis of the photosensitive drum 1. The fur brush 62 is arranged to contact the surface of the photosensitive drum 1. In this embodiment, the fur brush 62 is deployed so that the amount of intrusion into the surface of the photosensitive drum 1 is 0.7 mm. Here, the intrusion amount can be expressed by a value obtained by subtracting the distance (shortest distance) between the base material on the rotation axis of the bristle brush 62 described later and the photosensitive drum 1 from the length of the brush fiber described later. When the bristle brush 62 contacts the surface layer of the photosensitive drum 1, a driving force is transmitted from a driving motor as a driving source to the bristle brush 62, so that the bristle brush 62 is Figure 5, and is rotationally driven in the direction of arrow R3 (clockwise) at a predetermined rotational speed (the peripheral speed when the brush fibers are not deformed due to external force). That is, the brush 62 is rotationally driven so as to move in the same direction as the photosensitive drum 1 in the contact portion between itself and the photosensitive drum 1. Incidentally, the driving force may be transmitted to the brush 62 from a dedicated driving source, or may be branched and then transmitted to the brush 62 from a driving source for other rotatable components such as a driving source for the photosensitive drum 1. In addition, in this embodiment, the brush 62 is rotationally driven at a peripheral speed faster than the peripheral speed (surface movement speed) of the photosensitive drum 1. In this embodiment, the brush 62 is rotationally driven at a peripheral speed that is 110% of the peripheral speed of the photosensitive drum 1.

[0074] In addition, the cleaning device 6 includes a cleaning blade (elastic cleaning blade) 61, which is a plate-shaped (scraper-shaped) member formed of an elastic material. The cleaning blade 61 not only serves as a toner scraping member (cleaning member) for scraping toner from the photosensitive drum 1, but also serves as a photosensitive member polishing member (polishing member) for polishing (grinding) the surface of the photosensitive drum 1. The cleaning blade 61 is fixed to a supporting member 61a formed of a metal plate or the like by adhesive bonding or the like, and the supporting member 61a is fixed to the housing 66 so that the cleaning blade 61 is supported by the housing 66. The longitudinal direction of the cleaning blade 61 is substantially parallel to the direction of the rotation axis of the photosensitive drum 1. The cleaning blade 61 is arranged to contact the surface of the photosensitive drum 1 at a contact portion (scraper cleaning position Pf) downstream of the contact portion (brush cleaning position Pe) between the fur brush 62 and the photosensitive drum 1. The cleaning blade 61 is disposed so that an edge portion of its free end portion (on the photosensitive drum 1 side), which is one end portion with respect to the width direction substantially perpendicular to the longitudinal direction, contacts the photosensitive drum 1 with a predetermined pressure. Furthermore, the cleaning blade 61 contacts the photosensitive drum 1 in a direction opposite to the rotational direction of the photosensitive drum 1, such that a fixed end portion, which is the other end portion with respect to the width direction, is positioned upstream of the above-mentioned free end portion with respect to the rotational direction of the photosensitive drum 1.

[0075] In addition, the cleaning device 6 includes a collecting roller 63 as a rotatable roller-shaped member having conductivity. The collecting roller 63 serves not only as a collecting component (collecting component) for collecting toner from the brush 62, but also as a voltage applying component (voltage applying component, conductive component) for applying voltage to the brush 62. The collecting roller 63 is rotatably supported by the housing 66. The direction of the rotation axis of the collecting roller 63 is substantially parallel to the direction of the rotation axis of the brush 62. The collecting roller 63 is disposed to contact the brush 62 on the downstream side of the contact portion between the brush 62 and the photosensitive drum 1 relative to the rotation direction of the brush 62. The contact portion between the brush 62 and the collecting roller 63 relative to the rotation direction of the collecting roller 63 is the collecting position Pg. When the collecting roller 63 contacts the brush 62, a driving force is transmitted from the drive motor as a driving source to the collecting roller 63, so that the collecting roller 63 is Figure 5 63 is rotationally driven in the direction of arrow R4 (counterclockwise) at a predetermined rotational speed. That is, the collecting roller 63 is rotationally driven so as to move in the same direction as the brush 62 in the contact portion between itself and the brush 62. Incidentally, the driving force may be transmitted to the collecting roller 63 from a dedicated driving source, or may be branched and then transmitted to the collecting roller 63 from a driving source for other rotatable components such as a driving source for the collecting drum 63. In addition, in this embodiment, the collecting roller 63 is rotationally driven at a circumferential speed faster than the circumferential speed of the brush 62. In this embodiment, the collecting roller 63 is rotationally driven at a circumferential speed that is 105% of the circumferential speed of the brush 62.

[0076] In addition, the cleaning device 6 includes a scraper member 64, which is a plate-shaped (scraper-shaped) member formed of an elastic material. The scraper member 64 serves as a removal component (removal member) for removing the toner on the collection roller 63. The collection roller 63 is supported by a housing 66. Incidentally, similar to the cleaning blade 61, the scraper member 64 can be supported by the housing 66 via a supporting member. The longitudinal direction of the scraper member 64 is substantially parallel to the direction of the rotation axis of the collection roller 63. The scraper member 64 is arranged to contact the surface of the collection roller 63 on the downstream side of the contact portion (collection position Pg) between the collection roller 63 and the brush 62. The contact portion between the collection roller 63 and the scraper member 64 relative to the rotation direction of the collection roller 63 is the removal position Ph. The scraper member 64 is arranged so that the edge portion of its free end portion (on the collection roller 63 side) contacts the photosensitive drum 63 with a predetermined pressure, and the free end portion is one end portion relative to the width direction substantially perpendicular to the longitudinal direction. In addition, the scraper member 64 contacts the collection roller 63 in the direction opposite to the rotation direction of the collection roller 63, so that the fixed end portion as the other end portion thereof with respect to the width direction is arranged on the upstream side of the above-mentioned free end portion with respect to the rotation direction of the collection roller 63.

[0077] In addition, the cleaning device 6 includes a feed screw 65 as a feed member. The feed screw 65 is provided below the scraper member 64 relative to the direction of gravity. The feed screw 65 is rotated in the direction of the rotation axis of the photosensitive drum 1, for example, from Figure 5 The toner collected in the housing 66 is fed from the front side in the figure toward the rear side.

[0078] A cleaning power source E5, which is an applying component constituting a potential switching component for the fur brush 62, is connected to the collecting roller 63. In addition, a cleaning bias (cleaning voltage) can be applied to the collecting roller 63 by means of the cleaning power source E5. It can be considered that the cleaning power source E5 also constitutes the cleaning device 6. The cleaning power source E5 is connected to the CPU 201 for controlling the timing of bias application and the bias value (potential) to be applied. In this embodiment, during the removal of toner from the surface of the photosensitive drum 1, a cleaning bias which is a DC voltage of positive polarity (+) opposite to the normal charge polarity of the toner is applied to the collecting roller 63 by means of the cleaning power source E5. The period of toner removal refers to the period during which the image forming area (the area capable of forming a toner image) on the surface of the photosensitive drum 1 defined corresponding to the recording material P and relative to the surface movement direction of the photosensitive drum 1 passes through the brush cleaning position Pe. As will be described in detail later, a conductive material such as conductive fiber is used as the material of the fur brush 62.

[0079] Furthermore, the fur brush 62 contacts the collection roller 63, to which a cleaning bias is applied, causing its potential to become slightly smaller in absolute value than the cleaning bias applied to the collection roller 63. Consequently, the fur brush 62's potential becomes positive, opposite to the toner's normal charge polarity. Consequently, the fur brush 62 rubs against the surface of the photosensitive drum 1, trapping the toner on the surface of the photosensitive drum 1 both mechanically and electrostatically. This further improves cleaning efficiency. Consequently, at least a portion of the toner on the surface of the photosensitive drum 1 is collected by the fur brush 62 before reaching the cleaning blade 61.

[0080] Toner that has moved from the surface of the photosensitive drum 1 to the fur brush 62 in the contact portion between the photosensitive drum 1 and the fur brush 62 is then transferred to the collection roller 63 in the contact portion between the fur brush 62 and the collection roller 63 due to the potential difference between the fur brush 62 and the collection roller 63. Specifically, the potential of the collection roller 63 is slightly greater in absolute value than the potential of the fur brush 62 on the side opposite to the normal charge polarity. Consequently, at least a portion of the toner collected by the fur brush 62 is electrostatically transferred to the collection roller 63. The toner that has moved from the surface of the collection roller 63 in the contact portion between the fur brush 62 and the collection roller 63 is scraped off by the scraper member 64 in the contact portion between the collection roller 63 and the scraper member 64. The toner scraped off the surface of the collection roller 63 by the scraper member 64 falls due to gravity.

[0081] In addition, the toner on the surface of the photosensitive drum 1 that is not collected by the fur brush 62 is scraped off from the surface of the photosensitive drum 1 by the cleaning blade 61 and is stored in the housing 66 .

[0082] The toner thus collected in the housing 66 is fed by the feed screw 65 disposed at the lower portion (bottom) of the housing 66 , and is discharged to the outside of the housing 66 .

[0083] Then, the toner is conveyed toward a collection container (not shown) provided inside the apparatus main assembly or the like of the image forming apparatus 100 .

[0084] Incidentally, in this embodiment, application of the cleaning bias to the collecting roller 63 is started in synchronization with the timing at which the charging device 2 starts driving (charging process of the surface of the photosensitive drum 1 ) after the photosensitive drum 1 starts rotating.

[0085] <Cleaning Scraper>

[0086] In this embodiment, the cleaning blade 61 is made of polyurethane rubber and has a length of 340 mm with respect to the longitudinal direction, and contacts the photosensitive drum 1 with a predetermined pressure. From the viewpoint of cleaning performance, preferred physical properties of the cleaning blade 61 are as follows. The hardness (IRHD) may preferably be in the range of 65° or more and 85° or less. In addition, the rebound elastic coefficient in an environment of 25°C may preferably be in the range of 15% or more and 60% or less. In addition, the elongation at break in a tensile test may be 300% or less. In addition, the Young's modulus may preferably be in the range of 50 kg / cm 2 Above and 200kg / cm 2 In addition, the 100% modulus may preferably be in the range of 4.0 MPa or more and 9.0 MPa or less.

[0087] Incidentally, it is more preferable that the hardness (IRHD) is 70° or more and 80° or less, the elongation at break is 250% or less, and the rebound elastic coefficient at 25° C. is 15% or more and 35% or less.

[0088] The measurement method of the above-mentioned physical properties is as follows. The hardness (IRHD) of the cleaning blade 61 prepared was measured based on JIS K6253 by using a hardness tester manufactured by HW Mallace & Co., Ltd. The 100% modulus of the cleaning blade 61 prepared was measured based on JIS K6251 by using a tensile testing machine ("UNITRON TS-3013", manufactured by Ueshima Seisakusho Co., Ltd.). In addition, the elongation at break in the tensile test of the cleaning blade 61 prepared was measured based on JIS K6251 by using a tensile testing machine ("UNITRON TS-3013", manufactured by Ueshima Seisakusho Co., Ltd.).

[0089] The rebound elasticity of the cleaning blade 61 prepared was measured based on JIS K6255 in an environment of 25° C. by using a Lupke rebound elasticity tester manufactured by Ueshima Seisakusho Co., Ltd. In addition, the Young's modulus of the cleaning blade 61 prepared was measured based on JIS K 6251 by using a tensile testing machine (“UNITRON TS-3013”, manufactured by Ueshima Seisakusho Co., Ltd.).

[0090] <Brush>

[0091] The brush 62, which is a rotatable member, is constructed by implanting fibers on a rotating shaft. In this embodiment, the brush 62 is prepared by winding a fiber-implanted cloth material (base material) around a metal rotating shaft having a diameter of 12.1 mm. As an example, the fibers (brush fibers) of the brush 62 are obtained by spinning acrylic tow having a thickness of 6 denier at a speed of 70 kF / inch. 2The fiber is prepared by implanting a bristle (brush) density (bristle density per filament) on a base material. In addition, as an example, the outer diameter of the entire brush 62 (the outer diameter when the brush fiber is not deformed by an external force) is 21.4 mm. In addition, the length of the brush fiber obtained by subtracting the diameter of the core metal (12.1 mm) and the thickness of the base material (0.15 mm × 2) from the outer diameter is 4.5 mm. In addition, in this embodiment, a conductive fiber whose resistance is adjusted by dispersing a certain amount of carbon black in the base material of the fiber is used as the brush fiber. From the viewpoint of cleaning performance, etc., the preferred physical property of the filament tensile strength of the brush fiber in an environment of a temperature of 23°C and a relative humidity of 50% RH (herein, the tensile strength is simply referred to as "brush fiber tensile strength") may preferably be 40 cn / dtex or more and 80 cn / dtex or less. When the brush fiber tensile strength is less than 40 cn / dtex, there is a possibility that the toner cannot be collected by the brush 62 due to the early bristle falling of the fiber and thus improper cleaning occurs. In addition, when the brush fiber tensile strength exceeds 80 cn / dtex, the surface of the photosensitive drum 1 is damaged with respect to the circumferential direction of the photosensitive drum 1, so that image defects occur. In addition, in an environment with a temperature of 23°C and a relative humidity of 50% RH, the resistance of the brush 62 may preferably be greater than 10 LogΩ and less than 12 LogΩ. When the resistance is less than 10 LogΩ, there is a possibility that excessive current flows from the brush 62 into the photosensitive drum 1 and thus image defects occur due to drum memory (a phenomenon in which the potential history is not eliminated but remains). In addition, when the resistance exceeds 12 LogΩ, there is a possibility that insufficient current flows through the brush 62 and thus the toner cannot be collected by the brush 62.

[0092] The measurement method of the above-mentioned physical properties is as follows. The filament tensile strength of the brush fiber in an environment of 23°C and 50% RH is measured in accordance with "Test methods for woven and knitted fabrics" (JIS L1096:2010). In addition, the resistance of the brush 62 is measured in the following manner by using a homemade measuring device (manufactured by Canon Corporation). That is, under the condition of an intrusion depth of 1 mm, the brush 62 is in contact with the metal roller, and the current flowing through the brush 62 when the brush 62 rotates under an applied voltage of 400 V is detected, so that the resistance value of the brush 62 is measured.

[0093] Incidentally, the conditions of the fur brush 62 capable of suppressing the occurrence of toner fusion on the surface of the photosensitive drum 1 while achieving extension of the life of the photosensitive drum 1 will be described further specifically later.

[0094] <Collecting Roller>

[0095] In this embodiment, a As the collecting roller 63, a solid metal roller made of SUS (stainless steel) is used.

[0096] <Scraper Component>

[0097] As the material of the scraper member 64 , there can be cited a nylon-based sheet material, a polyurethane rubber blade, etc. In this embodiment, substantially the same material as that of the above-described cleaning blade 61 is used.

[0098] 4. The rigidity of the brush and the surface characteristics of the photosensitive drum

[0099] Next, the relationship between the condition of the fur brush and the surface layer of the photosensitive drum 1 and the following configuration will be described: extending the life of the photosensitive drum 1 by suppressing the occurrence of scratches on the surface of the photosensitive drum 1 while suppressing toner melting by appropriately wearing the surface of the photosensitive drum 1 will be described.

[0100] <Occurrence of Toner Fusion and Suppression thereof>

[0101] First, the toner melting suppressing effect by the fur brush 62 capable of applying a bias in this embodiment will be described. Figure 6 is a schematic diagram for illustrating the occurrence process of toner fusion. Figure 7 This is a schematic diagram for illustrating the toner melting suppression effect by the fur brush 62 capable of applying a bias in this embodiment.

[0102] like Figure 6 As shown in FIG, the photosensitive drum 1 rubs (wears) against the cleaning blade 61 in contact with the photosensitive drum 1, thereby increasing the temperature near the contact portion between the cleaning blade 61 and the photosensitive drum 1 (hereinafter, this contact portion is also referred to as the "blade nip"). As a result, the toner present in the vicinity melts and adheres to the photosensitive drum 1. Toner melting is a phenomenon that occurs in this manner.

[0103] Initially, in the vicinity of the doctor blade nip, a deposited substance of the external additive of the toner (hereinafter, also referred to as an external additive blocking layer) is formed ( Figure 7 ), so that the toner is suppressed from entering the doctor blade nip. As a result, the temperature rise of the toner is suppressed, so the toner melting does not occur.

[0104] However, the fluidity of small-sized toners due to the recent improvement in quality is high, and thus the external additive blocking layer is easily disconnected ( Figure 6 ) In addition, as the processing speed is increased, the frictional heat generated by the cleaning blade 61 is also likely to increase, so that there is a tendency for toner to be easily melted.

[0105] Therefore, in this embodiment, if Figure 7As shown in , by disposing a bias-applicable brush 62 upstream of the cleaning blade 61 in the moving direction relative to the surface of the photosensitive drum 1, the toner is collected before the toner reaches the external additive blocking layer. As a result, the external additive blocking layer is stably maintained, so that the occurrence of toner melting is suppressed. In this embodiment, the toner is collected by the brush 62 by applying a cleaning bias of +300V of a polarity opposite to the normal charge polarity of the toner to the conductive brush 62. Therefore, by providing the bias-applicable brush 62, the occurrence of toner melting can be suppressed as much as possible. However, even in the case of providing the bias-applicable brush 62, in the long-term use of the photosensitive drum 1 with an extended life, it becomes important to appropriately suppress the growth (accumulation) of toner melting in the event of its occurrence.

[0106] Conventionally, a fur brush is positioned upstream of a cleaning blade relative to the direction of movement of the photosensitive drum surface so that it contacts the drum and mechanically polishes the drum surface along with the deposited material. This method has been used. However, increasing the rigidity of the fur brush to improve its polishing force can lead to excessive wear of the drum, although this suppresses toner melting, causing problems such as shortened drum life.

[0107] Therefore, by enhancing the colorant collecting performance of the brush 62 when a bias voltage is applied, the external additive blocking layer is stably maintained, thereby suppressing the occurrence of colorant melting itself, and enabling the surface of the photosensitive drum 1 to be properly polished without making the rigidity of the brush 62 too high, so that it is expected that the growth of colorant melting is suppressed by suppressing the shortening of the life of the photosensitive drum 1.

[0108] <Relationship between Brush Conditions and the Surface Layer of the Photosensitive Drum>

[0109] It was confirmed that the amount of wear of the surface layer of the photosensitive drum 1 and the occurrence or non-occurrence of toner fusion were affected by the condition of the fur brush 62 .

[0110] First, the wear of the surface layer of the photosensitive drum 1 and the polishing of the deposited substances on the surface of the photosensitive drum 1 vary depending on the specification of the bristle brush 62. Therefore, the bristle brushes 62 having different tensile strength, thickness, length, and bristle density of the brush fibers were prepared, and their relationship with the wear of the surface layer of the photosensitive drum 1 was examined. Incidentally, the intrusion amount of the bristle brush 62 into the photosensitive drum 1 was made constant.

[0111] Here, the tensile strength of the brush fiber A [cn / dtex], the thickness of the brush fiber B [denier], the bristle density of the brush fiber C [kF / inch], and the 2] and the length D [mm] of the brush fibers are used to calculate the brush rigidity index as an indicator of the hardness of the brush 62 relative to the photosensitive drum 1. The brush rigidity index [unitless] is specifically represented by the following formula (1).

[0112] (Brush rigidity index) = A × B 2 ×C / D 2 ...(1)

[0113] The brush rigidity index of formula (1) is calculated by multiplying the strength of the brush fiber by the contact area of ​​the brush fiber. Regarding the rigidity of the brush fiber itself, it can be checked that when the rigidity is checked while changing the brush fiber thickness and the brush fiber length, the rigidity increases as the brush fiber length becomes shorter and the brush fiber thickness becomes larger. It can be said that in the case where the brush rigidity index of the above formula (1) is large, a harder brush 62 appears on the photosensitive drum 1, and therefore the wear ratio of the surface layer of the photosensitive drum 1 becomes larger. In addition, in the case where the brush rigidity index of the above formula (1) is large, it can be said that the ability to remove deposited substances on the surface of the photosensitive drum 1 is high.

[0114] On the other hand, also with respect to the photosensitive drum 1 in contact with the fur brush 62, photosensitive drums 1 having different elastic deformation rates E and hardness of the surface layer were prepared, and under a plurality of conditions, the wear of the surface layer when each of the photosensitive drums 1 was in contact with the fur brush 62 was examined. As a result, it was confirmed that the elastic deformation rate was largely correlated with the wear of the surface layer and the melting of the toner.

[0115] It can be said that the brush rigidity index (=A×B 2 ×C / D 2 ) and the elastic deformation rate (=E) are both indicators of hardness. For this reason, when this ratio falls within a certain range, the wear of the surface layer of the photosensitive drum 1 can be kept within an appropriate range when a brush 62 having a certain degree of rigidity is deployed. In other words, it is possible to suppress toner melting due to insufficient wear of the surface layer of the photosensitive drum 1, and to suppress excessive wear of the surface of the photosensitive drum 1 due to excessive wear, thereby preventing the life of the photosensitive drum 1 from being shortened.

[0116] <Experimental Example>

[0117] By changing the brush stiffness index (=A×B 2 ×C / D 2), the elastic deformation rate (=E) of the photosensitive drum 1, and the voltage applied to the brush (brush application voltage) (cleaning bias) were tested. Specifically, when forming images on 500,000 sheets in a high-temperature / high-relative-humidity environment (30°C / 80% RH), the surface condition of the photosensitive drum 1, such as surface wear and surface roughness, and the occurrence of image defects due to toner fusion were examined. Incidentally, in this case, the evaluation was performed using the image forming unit 10K for black.

[0118] As the surface wear of the photosensitive drum 1 progresses, black streaks appear on the sheet (paper) on which an image is formed. The case where black streaks appear on the sheet during image formation on 500,000 sheets is evaluated as "poor (x)", and the case where no black streaks appear is evaluated as "good (o)". In addition, as toner melting progresses, white void portions (white voids) appear on the solid black image on the sheet during image formation on 500,000 sheets. The case where white voids having a size (maximum diameter) of 2 mm or more appear on the solid black image on the sheet during image formation on 500,000 sheets is evaluated as "poor (x)", and the case where no white voids appear is evaluated as "good (o)".

[0119] exist Figure 8A and Figure 8B As an example, the brush application voltage = 0V, the brush fiber tensile strength A = 80cn / dtex, the brush fiber thickness B = 6 denier, and the brush fiber bristle density C = 75kF / inch will be described. 2 and the brush fiber length D = 4.5 mm, the elastic deformation rate E of the photosensitive drum 1 was changed to 5 results of 45%, 48%, 55%, 60% and 62% (experiment numbers 1 to 5). Images were formed on 500,000 sheets for each photosensitive drum having each elastic deformation rate, and then the wear of the surface layer of the photosensitive drum 1 and the presence or absence of toner melting were checked. As a result, in the case where the elastic deformation rate of the photosensitive drum 1 was 45%, image defects occurred when more than about 480,000 sheets were formed. This is considered to be because the rigidity of the photosensitive drum 1 is small and the surface layer of the photosensitive drum 1 is excessively worn. In addition, in the case where the elastic deformation rate of the photosensitive drum 1 is 48% or more, toner melting occurs. This is considered to be because the rigidity of the photosensitive drum 1 is large and the amount of polishing (wear) of the surface layer of the photosensitive drum 1 becomes small.

[0120] Next, similar experiments were conducted (Experiments 6 to 25) while varying the brush stiffness index by changing the brush fiber thickness B, brush fiber bristle density C, and brush fiber length D, while applying a brush voltage of 0 V. The results demonstrated that while increasing the brush stiffness index prevented toner melting when the brush voltage was 0 V, wear of the surface layer of the photosensitive drum 1 occurred early. In other words, it was not possible to establish conditions that could simultaneously suppress image defects caused by excessive wear and toner melting.

[0121] On the other hand, by applying a cleaning bias (in this embodiment, +300V) to the fur brush 62 (Experiments 26 to 41), it became possible to suppress toner melting without increasing the brush stiffness index (e.g., Experiments 27 to 29). Furthermore, by applying a cleaning bias (in this embodiment, +300V) to the fur brush 62 (Experiments 26 to 41), the brush stiffness index was sufficiently reduced, thereby suppressing the occurrence of image defects due to excessive wear of the surface layer of the photosensitive drum 1. In other words, it became possible to achieve both suppression of toner melting and extension of the life of the photosensitive drum 1 (e.g., Experiments 27 to 29).

[0122] Incidentally, in Experiments No. 31 to 34, the brush rigidity index was changed within the range of 3.6 mm to 4.5 mm of the brush fiber length D. In these experiments, good results were obtained within the range of 4.2 mm to 4.5 mm of the brush fiber length D. In addition, in Experiments No. 35 to 38, the brush rigidity index was changed by setting the brush fiber tensile strength to 40 cn / dtex and by changing the brush thickness B within the range of 6 to 18 deniers. In these experiments, good results were obtained within the range of 6 to 15 deniers of the brush fiber thickness B. In addition, in Experiments No. 39 to 41, the brush rigidity index was changed by setting the brush fiber tensile strength to 40 cn / dtex and by changing the brush thickness B within the range of 30 to 75 kF / inch. 2 The brush stiffness index was changed by changing the brush bristle density C within a range of 30 to 45 kF / inch. 2 Incidentally, in Experiments Nos. 31 to 41, evaluation was performed under the conditions such that the elastic deformation rate E of the photosensitive drum 1 was 48% and thus the photosensitive drum 1 was relatively easily worn.

[0123] In addition, when the brush rigidity index is too small, the bristles of the brush 62 fall off and cannot properly contact the photosensitive drum 1, and as a result, it is understood that the toner cannot be collected before it reaches the cleaning blade 61. Through the research of the present inventors, it is understood that such a problem can be sufficiently solved when the brush rigidity index is 400 or more.

[0124] from Figure 8A and Figure 8B The results shown in the formula are obtained by satisfying the following conditions:

[0125] 48(%)≤E≤60(%), and

[0126] 400≤{A×B 2 ×C / D 2}≤20408,

[0127] It is understood that the following effects can be obtained. That is, while suppressing the shortening of the life of the photosensitive drum 1 due to excessive wear of the surface layer of the photosensitive drum 1, the occurrence of toner melting due to excessive wear of the surface layer of the photosensitive drum 1 can also be suppressed. In addition, in order to achieve the suppression of the shortening of the life of the photosensitive drum 1 and the suppression of the occurrence of toner melting, it is preferable to satisfy 400≤{A×B 2 ×C / D 2}≤14000, and more preferably, satisfying 400≤{A×B 2 ×C / D 2}≤10000.

[0128] Therefore, in the case where a cleaning bias is applied to the fur brush 62, by determining the elastic deformation rate (=E) of the photosensitive drum 1 and the brush rigidity index (=A×B 2 ×C / D 2 ) so as to satisfy the above-mentioned conditional expression, shortening of the life of the photosensitive drum 1 and occurrence of inconveniences such as toner melting can be suppressed. That is, the fur brush 62, under appropriate conditions that match the surface hardness of the photosensitive drum 1, contacts the photosensitive drum 1, thereby suppressing the occurrence of image defects such as toner melting on the surface of the photosensitive drum 1 without excessively abrading the surface of the photosensitive drum 1. In other words, according to this embodiment, by enhancing the toner cleaning performance of the fur brush 62 when a bias voltage is applied, the external additive blocking layer is stably maintained, thereby suppressing the occurrence of toner melting itself, and enabling appropriate polishing of the surface of the photosensitive drum 1 without making the rigidity of the fur brush 62 excessively large, making it possible to suppress the growth of toner melting while suppressing shortening of the life of the photosensitive drum 1.

[0129] As described above, in this embodiment, the image forming device 100 includes a rotatable photosensitive member 1, a charging device 2 for charging the surface of the photosensitive member 1, a developing device 4 for supplying colorant to the surface of the photosensitive member 1, a transfer device 5 for transferring the colorant (image) from the surface of the photosensitive member 1 to the transfer receiving member 7 in the transfer position Pd; and a cleaning device 6 for removing the colorant from the surface of the photosensitive member 1, and the cleaning device 6 includes: a cleaning scraper 61, which contacts the surface of the photosensitive member 1 in the scraper cleaning position Pf downstream of the transfer position Pd and upstream of the charging position Pa with respect to the rotation direction of the photosensitive member 1; a rotatable roller brush 62, which contacts the surface of the photosensitive member 1 in the brush cleaning position Pe downstream of the transfer position Pd and upstream of the scraper cleaning position Pf with respect to the rotation direction of the photosensitive member 1; and an applying portion E5, which is used to apply a bias to the brush 62. In addition, in this embodiment, when the brush fiber tensile strength is A (cn / dtex), the brush fiber thickness is B (denier), and the bristle density of each brush fiber is C (kF / inch) in an environment with a temperature of 23°C and a humidity of 50% RH, 2 ) and the brush fiber length is D (mm) and the elastic deformation rate is E (%) when the hardness test is performed using a Vickers square pyramid diamond indenter in an environment with a temperature of 23° C. and a humidity of 50% RH, the image forming apparatus 100 satisfies the following: 48 (%) ≤ E ≤ 60 (%) and 400 ≤ {A×B 2 ×C / D 2}≤20408. In this embodiment, when the image forming area on the surface of the photosensitive member 1 passes through the brush cleaning position Pe, the applying portion E1 applies a bias to the brush 62, causing the potential of the brush 62 to have a polarity opposite to the normal charge polarity of the toner. Furthermore, in this embodiment, the resistance of the brush 62 is 10 LogΩ or more and 12 LogΩ or less in an environment of a temperature of 23°C and a humidity of 50% RH. Furthermore, in this embodiment, the cleaning device 6 includes a conductive member 63 that contacts the brush 62 and a removal member 64 for removing toner from the conductive member 63, and the applying portion E5 applies a bias to the brush 62 via the conductive member 63. Furthermore, in this embodiment, the brush 62 rotates in the contact portion with the photosensitive member 1 in the same direction as the surface of the photosensitive member 1, with a speed difference between itself and the surface of the photosensitive member 1.

[0130] In addition, according to this embodiment, it is possible to suppress the occurrence of toner fusion on the surface of the photosensitive drum 1 while achieving extension of the life of the photosensitive drum 1 .

[0131] [Example 2]

[0132] Next, another embodiment of the present invention will be described. The basic configuration and operation of the image forming apparatus 100 of this embodiment are the same as those of the image forming apparatus 100 of Embodiment 1. Therefore, in the image forming apparatus 100 of this embodiment, elements having the same or corresponding functions and configurations as those of the image forming apparatus 100 of Embodiment 1 are denoted by the same reference numerals or symbols as those of Embodiment 1, and detailed description thereof will be omitted.

[0133] Figure 9 Figure 1 is a schematic cross-sectional view of the cleaning device 6 and its surroundings in this embodiment. In Embodiment 1, the image forming apparatus 100 includes a charge removal device (pre-cleaning charge removal device) 16 as a charge removal component. This device removes charge from the photosensitive drum 1 downstream of the primary transfer portion T1 and upstream of the fur brush 62 relative to the rotational direction of the photosensitive drum 1. In this embodiment, the charge removal device 16 removes charge from the surface of the photosensitive drum 1 by irradiating the surface of the photosensitive drum 1 with light. The position of the photosensitive drum 1 where the charge is removed by the charge removal device 16 (the photosensitive drum surface is irradiated with light) relative to the rotational direction of the photosensitive drum 1 is the charge removal position Pi. Specifically, the charge removal position Pi is located downstream of the primary transfer position Pd and upstream of the brush cleaning position Pe relative to the rotational direction of the photosensitive drum 1. In this embodiment, the charge removal device 16 uses an LED as the charge removal light source, but other components such as semiconductor lasers may also be used. Furthermore, in this embodiment, the charge removal device 16 uses constant current control, with the current set to 50 mA. This charge removal device 16 removes the surface potential of the photosensitive drum 1 by emitting light toward the surface of the photosensitive drum 1 (pre-cleaning exposure). Before the toner is electrostatically collected by the fur brush 62, the surface potential of the photosensitive drum 1 (at least the surface potential in the image forming area relative to the rotational axis) is uniformly removed by the charge removal device 16 to a value of approximately -100 V to approximately 0 V. Incidentally, in this embodiment, similar to Embodiment 1, the charge potential of the photosensitive drum 1 is approximately -500 V, and the exposure potential of the photosensitive drum 1 is approximately -200 V. Charge removal refers to the removal of at least a portion of the charge.

[0134] Here, when the voltage applied to fur brush 62 has a polarity opposite to the normal charge polarity of the toner and the absolute value of the potential difference between fur brush 62 and photosensitive drum 1 is preferably 250V or greater, the toner is electrostatically collected. On the other hand, when the absolute value of the potential difference between fur brush 62 and photosensitive drum 1 reaches the discharge start voltage (e.g., 650V) or greater, the charge polarity of the toner on photosensitive drum 1 reverses (inverted polarization), preventing the toner from being electrostatically collected from photosensitive drum 1 to fur brush 62. Specifically, the absolute value of the potential difference between fur brush 62 and photosensitive drum 1 is preferably 50V or greater, more preferably 250V or greater and less than the discharge start voltage. Incidentally, the discharge start voltage can be measured using the following measurement method. While forming a solid white image, the current flowing from fur brush 62 to photosensitive drum 1 is measured while increasing the voltage applied to fur brush 62 from 0V. At this point, the current flows from a certain threshold voltage. Herein, a voltage at which a current of 10 μA or more starts to flow is defined as a discharge starting voltage.

[0135] Without the charge removal device 16, the potential difference between the fur brush 62 and the photosensitive drum 1 differs between the solid black image portion and the solid white image portion (non-image portion), preventing the fur brush 62 from collecting toner. Consequently, toner melting may occur in some cases. This is because, for example, the absolute value of the potential difference between the photosensitive drum 1 and the fur brush 62 becomes equal to or greater than the discharge start voltage at the solid white image portion, and the charge polarity of the toner on the photosensitive drum 1 is reversed by the discharge. Specifically, as described in Example 1, in order to achieve an extended lifespan of the photosensitive drum 1 by suppressing the brush stiffness index to a certain value or less, it is important to stably maintain the external additive blocking layer by more appropriately collecting toner before it reaches the external additive blocking layer, thereby suppressing the occurrence of toner melting.

[0136] On the other hand, as in this embodiment, by providing the charge removal device 16, the potential difference between the fur brush 62 and the photosensitive drum 1 is appropriately maintained, so that the toner can be appropriately collected by the fur brush 62. In addition, in this embodiment, the external additive blocking layer can be more stably maintained by more appropriately collecting the toner before the toner reaches the external additive blocking layer, thereby suppressing the occurrence of toner melting, and therefore, in order to achieve an extension in the life of the photosensitive drum 1, it becomes easy to suppress the brush rigidity index to a certain value or less.

[0137] Here, an experiment similar to the experimental example in Example 1 was conducted for each of a configuration without and a configuration with the charge-removing device 16 by varying the voltage applied to the brush (brush application voltage). Specifically, when images were formed on 500,000 sheets in a high-temperature / high-humidity environment (30°C / 80% RH), the surface condition of the photosensitive drum 1, such as surface wear and surface roughness, and the occurrence of image defects due to toner fusion, were examined. Incidentally, in this example, evaluation was performed using the image forming unit 10K for black. The evaluation criteria were the same as those of the experimental example in Example 1.

[0138] exist Figure 10 The results are shown in . Figure 10 From the results shown in FIG1 , it can be understood that, when the charge-eliminating device 16 is provided, the potential difference between the fur brush 62 and the photosensitive drum 1 is uniformly maintained in the direction of the rotational axis of the photosensitive drum 1. This allows the external additive blocking layer to be more stably maintained by more appropriately collecting toner before it reaches the external additive blocking layer, thereby suppressing toner melting. Furthermore, when the charge-eliminating device 16 is provided, the potential difference between the fur brush 62 and the photosensitive drum 1 is appropriately set, thereby increasing the range (margin) of the brush applied voltage within which toner can be appropriately collected, compared to when the charge-eliminating device 16 is not provided.

[0139] As described above, in this embodiment, the image forming apparatus 100 includes the charge removal device 16 for removing charge from the surface of the photosensitive drum 1 at the charge removal position Pi, which is located downstream of the transfer position Pd and upstream of the brush cleaning position Pe with respect to the rotational direction of the photosensitive drum 1. In this embodiment, the charge removal device 16 removes charge from the surface of the photosensitive drum 1 by irradiating the surface of the photosensitive drum 1 with light. Furthermore, in this embodiment, when the image forming area on the surface of the photosensitive drum 1 passes through the brush cleaning position Pe, the applying section E5 applies a bias voltage to the brush 62 such that the potential of the brush 62 becomes opposite to the normal charge polarity of the toner, and the absolute value of the potential difference between the surface of the photosensitive drum 1 from which charge has been removed at the charge removal position Pi and the brush 62 becomes smaller than the discharge start voltage.

[0140] In addition, according to this embodiment, it is possible to suppress the occurrence of toner fusion on the surface of the photosensitive drum 1 while achieving extension of the life of the photosensitive drum 1 .

[0141] [Other embodiments]

[0142] As described above, the present invention has been described based on specific embodiments, but is not limited to the above embodiments.

[0143] For example, in the above-described embodiment, the rotatable roller-shaped brush is rotationally driven so as to move in the same direction as the photosensitive member in the contact portion with the photosensitive member, but the present invention is not limited thereto.

[0144] For example, a configuration may be employed in which a rotatable roller-shaped brush is rotationally driven so as to move in a direction opposite to the rotation direction of the photosensitive drum 1 in a portion in contact with the photosensitive member, and rotates at a speed difference with the photosensitive member. Similarly, in the above-described embodiment, the collecting member (conductive member) is rotationally driven so as to move in the same direction as the brush in a portion in contact with the brush, but may also be rotationally driven so as to move in a direction opposite to the rotation direction of the brush.

[0145] In Example 2, a configuration in which charges are removed by light is used as the charge removal member. However, the present invention is not limited thereto. For example, a configuration in which charges are removed by AC discharge using a charger or by allowing charges to escape into a conductive member in contact with a photosensitive member may also be employed.

[0146] Furthermore, while the image forming apparatus in the above-described embodiment employs an intermediate transfer type, the present invention is also applicable to a direct transfer type. As known to those skilled in the art, a tandem image forming apparatus employing direct transfer may include a recording material carrying member such as an endless belt, in place of the intermediate transfer member in the above-described embodiment. Furthermore, similar to the primary transfer process in an intermediate transfer type image forming apparatus, the toner image formed on the photosensitive member of the image forming portion is directly transferred to a recording material carried and transported by the recording material carrying member. Furthermore, in such an image forming apparatus, by applying the present invention according to the above-described embodiment, effects similar to those of the above-described embodiment can be achieved.

[0147] Furthermore, in the above embodiment, the number of image forming sections is four, but the present invention is not limited to this. The present invention is also applicable to an image forming apparatus including five or more (e.g., six) image forming sections. Furthermore, in the above embodiment, the image forming apparatus has a configuration using toners of four colors: Y, M, C, and K, but the present invention is not limited to such an embodiment. The image forming apparatus may also have a configuration that uses a transparent toner, a metallic toner, or the like in addition to or in place of any of Y, M, C, and K.

[0148] In addition, in the above-described embodiment, the image forming apparatus is a color image forming apparatus including a plurality of image forming portions, but the present invention is also applicable to, for example, a monochrome (single color) image forming apparatus including only one image forming portion.

[0149] According to the present invention, while achieving extension of the life of the photosensitive member, the occurrence of toner fusion on the surface of the photosensitive member can be suppressed.

[0150] While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments.The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.

Claims

1. An image forming apparatus, comprising: a rotatable photosensitive member; an image forming portion configured to form a toner image on the photosensitive member; a cleaning device configured to clean the photosensitive member, Wherein, the cleaning equipment includes: a scraper that contacts the photosensitive member at a first contact portion and is configured to clean the photosensitive member; a rotatable brush that contacts the photosensitive member at a second contact portion upstream of the first contact portion with respect to a rotational direction of the photosensitive member and is configured to collect toner remaining on the photosensitive member; and an applying portion configured to apply a bias voltage to the brush; and a controller configured to control the applying portion, wherein, when the image forming area of ​​the surface of the photosensitive member passes through the second contact portion, the controller controls the applying portion to apply a bias voltage to the brush so that the potential of the brush has a polarity opposite to the normal charge polarity of the toner, and When the tensile strength of the brush is A (cn / dtex), the thickness of the brush is B (denier), and the bristle density of the brush is C (kF / inch 2 ), when the length of the brush is D (mm) and the elastic deformation rate of the surface of the photosensitive member is E (%), the following relationship is satisfied: 48(%)≤E≤60(%), and 400≤{A×B 2 ×C / D 2 }≤20408。 2. The image forming apparatus according to claim 1 , further comprising: a transfer device configured to transfer the toner image from the photosensitive member onto a transfer-receiving material in a transfer position; as well as A charge-removing device is provided downstream of the transfer position and upstream of the second contact portion with respect to the rotational direction of the photosensitive member and is configured to remove charge from the photosensitive member.

3. The image forming apparatus according to claim 2, wherein: The charge-removing device removes charge from a surface of the photosensitive member by irradiating the surface of the photosensitive member with light.

4. The image forming apparatus according to claim 3, wherein When an image forming area of ​​the photosensitive member passes a brush cleaning position, the controller controls the charge removing device so that a potential difference between the photosensitive member and the brush is 250 V or more and less than a discharge start voltage.

5. The image forming apparatus according to claim 1, wherein When the image forming portion of the photosensitive member passes through a brush cleaning position, the controller controls the applying portion so that a potential difference between the photosensitive member and the brush becomes smaller than a discharge start voltage.

6. The image forming apparatus according to claim 1, wherein In an environment of a temperature of 23° C. and a relative humidity of 50%, the brush has a resistance of 10 LogΩ or more and 12 LogΩ or less.

7. The image forming apparatus according to claim 1, wherein The cleaning device further includes a conductive member in contact with the brush and a removing member configured to remove toner from the conductive member, and The applying portion applies a bias voltage to the brush through the conductive member.

8. The image forming apparatus according to claim 1, wherein The brush rotates in the second contact portion in the same direction as a moving direction of the surface of the photosensitive member and rotates with a speed difference with respect to the surface of the photosensitive member.

9. The image forming apparatus according to claim 1, wherein The image forming portion includes a developing device configured to develop an electrostatic image into a toner image on the photosensitive member, and Here, the developing device includes a developing sleeve for carrying a developer containing toner and an external additive, and supplies the external additive to the cleaning portion during image formation.

10. The image forming apparatus according to claim 9, wherein The external additive is charged to a polarity opposite to the normal charge polarity of the toner.

11. The image forming apparatus according to claim 10, wherein The external additive is inorganic fine powder of perovskite type crystals.

12. The image forming apparatus according to claim 10, wherein The external additive includes silicon dioxide or titanium oxide.

13. The image forming apparatus according to claim 10, wherein The external additive is strontium titanate.

14. The image forming apparatus according to claim 1, wherein The following relations are satisfied: 400≤{A×B 2 ×C / D 2 }≤14000。 15. The image forming apparatus according to claim 1, wherein The following relations are satisfied: 400≤{A×B 2 ×C / D 2 }≤10000。

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