Image forming apparatus

Abstract

To provide a technique that can prevent an image defect resulting from water vapor.SOLUTION: An image forming apparatus comprises a brush member that has a base cloth and a plurality of fiber threads woven in the base cloth, in which leading ends of the plurality of fiber threads extending from the base cloth are in contact with a surface of an image carrier on the downstream side of a transfer part and on the upstream side of an electrifying part in the direction of rotation of the image carrier. When an area at a length of 1 mm from the leading ends of the plurality of fiber threads in contact with the image carrier is immersed in water at 20°C for 10 seconds, the amount of water absorption per unit area of the brush member is 2.2 mg / mm2 or more.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an image forming apparatus that utilizes an electrophotographic recording method. [Background technology]

[0002] In electrophotographic image forming devices such as laser printers, copiers, and facsimiles, a photosensitive drum serving as an image carrier is uniformly charged and then exposed to light according to an image pattern, forming an electrostatic latent image on the photosensitive drum. The electrostatic latent image on the photosensitive drum is then developed with toner to become visible and transferred to a recording material such as paper. Residual toner remaining on the photosensitive drum is then removed and collected from the photosensitive drum. Several cleaning techniques exist for removing residual toner, and cleaning techniques using a cleaning brush have also been disclosed. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2005-114754 Summary of the Invention [Problem to be solved by the invention]

[0004] However, Patent Document 1 had the following problems. When recording material was passed through the configuration disclosed in Patent Document 1, in which the cleaning brush was in contact with the photosensitive drum, image defects due to water vapor sometimes occurred. Water vapor is generated when the moisture contained in the recording material is heated inside the device and adheres to the surface of the photosensitive drum. This water vapor is not blocked by the cleaning brush but circulates around the photosensitive drum, attracting toner in the developing unit and causing image defects such as toner contamination. On the other hand, a cleaning blade method in which a blade is in contact with the photosensitive drum can block a certain amount of water vapor. However, if a large amount of water vapor is blocked by the blade, cleaning performance is significantly reduced, and large water droplets form and slip through the blade. As a result, the water droplets that slip through the blade attract toner in the developing unit, causing toner contamination.

[0005] An object of the present invention is to provide a technique capable of suppressing image defects caused by water vapor. [Means for solving the problem]

[0006] In order to achieve the above object, an image forming apparatus according to the present invention comprises: an image carrier that is driven to rotate; a charging member for charging the surface of the image carrier in a charging section; a developing member that supplies a developer to the electrostatic latent image formed on the surface of the image carrier charged by the charging member to form a developer image; a transfer member that forms a transfer portion that sandwiches a recording material between itself and the image carrier, and transfers a developer image from the image carrier to the recording material in the transfer portion; a brush member having a base fabric and a plurality of fiber threads woven into the base fabric, wherein tips of the plurality of fiber threads extending from the base fabric come into contact with a surface of the image carrier downstream of the transfer unit and upstream of the charging unit in a rotation direction of the image carrier; Equipped with The brush member has a water absorption per unit area of ​​2.2 mg / mm when a region of 1 mm from the tip of the plurality of fiber threads that contacts the image carrier is immersed in water at 20° C. for 10 seconds. 2 The present invention is characterized in that: [Effects of the Invention]

[0007] According to the present invention, image defects caused by water vapor can be suppressed. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is an explanatory diagram of an image forming apparatus according to a first embodiment of the present invention; [Figure 2] Schematic diagram of a brush member according to a first embodiment of the present invention. [Figure 3] 1 is a schematic control configuration diagram of an image forming apparatus according to a first embodiment of the present invention; [Figure 4] FIG. 1 is an explanatory diagram of measurement of water absorption of a brush member in Example 1 of the present invention. [Figure 5] FIG. 10 is an explanatory diagram of the state around the photosensitive drum during the image forming process in the second embodiment of the present invention. [Figure 6] FIG. 10 is an explanatory diagram of the state of toner primarily collected by the brush member in the second embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, with reference to the drawings, a detailed description will be given of an embodiment of the present invention. Note that the dimensions, materials, shapes, and relative positions of the components described in the embodiment may be changed as appropriate depending on the configuration of the device to which the invention is applied and various conditions. In other words, the scope of the present invention is not limited to the following embodiment.

[0010] Example 1 1. Image forming device FIG. 1 is a schematic diagram of an image forming apparatus 100 according to a first embodiment of the present invention. The image forming apparatus 100 of this embodiment is a monochrome laser beam printer employing a cleanerless system and a contact charging system. The image forming apparatus 100 has a photosensitive drum 1, which is a drum-type (cylindrical) electrophotographic photosensitive member serving as a rotatable image carrier. When an image output operation is started, the photosensitive drum 1 is driven to rotate in the direction of arrow R1 in the figure by a drive motor (not shown). The outer diameter of the photosensitive drum 1 is 24 mm, and the peripheral speed (surface speed) is 140 mm / sec.

[0011] The surface of the rotating photosensitive drum 1 is uniformly charged to a predetermined potential of normal polarity (negative polarity in this embodiment) by the charging roller 2, a roller-type charging member serving as a charging means, near a charging portion a where the photosensitive drum 1 and the charging roller 2 contact each other. More specifically, the charging roller 2 charges the surface of the photosensitive drum 1 by discharge occurring in at least one of the minute gaps formed between the charging roller 2 and the photosensitive drum 1, upstream and downstream of the contact point with the photosensitive drum 1 in the direction of rotation of the photosensitive drum 1. Here, however, the contact point between the charging roller 2 and the photosensitive drum 1 in the direction of rotation of the photosensitive drum 1 is assumed to be the charging portion. The charging roller 2 is an elastic roller having a conductive elastic layer around a core metal. It is disposed in contact with the photosensitive drum 1 and is driven to rotate in the direction of arrow R2 in the figure by a drive motor (not shown). While the charging roller 2 is driven to rotate in this embodiment, it may be configured to rotate in response to the rotation of the photosensitive drum 1. A predetermined charging voltage, which is a negative DC voltage, is applied to the charging roller 2 from a charging power source E1 (FIG. 3) serving as a charging voltage application means. In this embodiment, a negative DC voltage is applied as the charging voltage to the charging roller 2 during charging. In this embodiment, the charging voltage is set to -1200 V, for example. As a result, in this embodiment, the surface of the photosensitive drum 1 is uniformly charged to a dark potential Vd of -600 V.

[0012] The surface of the charged photosensitive drum 1 is scanned and exposed by an exposure device (laser exposure unit) 4, which serves as exposure means (electrostatic image forming means), with a laser beam L modulated according to image data. The exposure device 4 repeatedly exposes the photosensitive drum 1 with the laser beam L in the main scanning direction (direction of rotation axis) and also in the sub-scanning direction (direction of surface movement), thereby forming an electrostatic latent image on the photosensitive drum 1. In this embodiment, the absolute value of the dark area potential Vd on the surface of the photosensitive drum 1, which has been uniformly charged and formed, is reduced by exposure by the exposure device 4. This results in a bright area potential Vl of -100V. In the rotation direction of the photosensitive drum 1, the position of exposure by the exposure device 4 on the photosensitive drum 1 is the image exposure area b. The exposure device 4 is not limited to a laser scanner device, and for example, an LED array in which multiple LEDs are arranged along the longitudinal direction of the photosensitive drum 1 may be used.

[0013] The electrostatic latent image formed on the photosensitive drum 1 is developed (visualized) as a toner image (developer image) by a developing device 3 as a developing means using toner as a developer. The toner used as the developer in this embodiment is a spherical non-magnetic toner with an average particle size of 6.4 μm and an average circularity of 0.98. The average circularity of the non-magnetic toner used in this embodiment should be high, and specifically, 0.96 or higher is preferable. The average circularity in this embodiment is used as a simple method for quantitatively expressing the shape of particles. The particle shape is measured using a flow-type particle image analyzer FPIA-2100 manufactured by Toa Medical Electronics Co., Ltd., and the circularity is calculated using the following equation 1.

[0014] (Formula 1) TIFF2023090266000002.tif12170

[0015] Furthermore, as shown in the following formula 2, the average circularity is defined as the value obtained by dividing the sum of the circularities of all the measured particles by the total number of particles.

[0016] (Formula 2) TIFF2023090266000003.tif12170

[0017] The developing device 3 comprises a developing roller 31 as a developer carrier (developing member), a toner supply roller 32 as a developer supply means, a developer storage chamber 33 for storing toner, and a developing blade 34. The toner stored in the developer storage chamber 33 is stirred by a stirring member 35 and supplied to the surface of the developing roller 31 by the toner supply roller 32. The toner supplied to the surface of the developing roller 31 passes through the contact area between the developing roller 31 and the developing blade 34, where it is uniformly thinned into a thin layer and negatively charged by friction. While a one-component non-magnetic contact development method is used in this embodiment, this is not a limitation, and two-component non-magnetic contact or non-contact development methods may also be used. A magnetic development method may also be used. Although the normal polarity of the toner is negative in this embodiment, it is not limited to negative polarity. The normal polarity may also be positive, in which case the voltage relationship described below may be reversed as appropriate. The developing roller 31 is rotated counterclockwise in the direction of arrow R3 in the figure by a drive motor 110 so that the surfaces of the photosensitive drum 1 and the developing roller 31 move in the same direction at a development section c where the photosensitive drum 1 and the developing roller 31 come into contact with each other. The drive motor serving as the drive means 110 for driving the developing roller 31 may be a main motor common to the drive means 110 for the photosensitive drum 1, or separate drive motors may rotate the photosensitive drum 1 and the developing roller 31, respectively. During development, a predetermined developing voltage (developing bias) is applied to the developing roller 31 by a development power source E2 (FIG. 3) serving as developing voltage application means. In this embodiment, during development, a negative DC voltage is applied to the developing roller 31 as the developing voltage, and the developing voltage is set to -300 V. In this embodiment, toner charged with the same polarity (negative in this embodiment) as the charging polarity of the photosensitive drum 1 adheres to the exposed surface (image area), which is the image forming area on the photosensitive drum 1, where the absolute value of the potential has been reduced by exposure after being uniformly charged. This development method is called a reversal development method.

[0018] In this embodiment, the developing roller 31 is always in contact with the photosensitive drum 1 at the developing portion c. However, the developing roller 31 and the photosensitive drum 1 may be configured to be in a contact state or a separated state. In this case, a developing contact / separation mechanism may be separately provided. During the rotation operation, which is the pre-rotation step described below, the photosensitive drum 1 may be rotated with the developing roller 31 separated from the photosensitive drum 1.

[0019] The toner image formed on the photosensitive drum 1 is sent to the transfer section d, which is the contact point between the photosensitive drum 1 and the transfer roller 5, a roller-type transfer member serving as a transfer means. In this embodiment, the transfer roller 5 is a roller made of conductive NBR (nitrile butadiene rubber)-hydrin sponge rubber with an outer diameter of 12 mm and a hardness of 30° (Asker-C, 500 gf load). It is pressed against the photosensitive drum 1 with a predetermined pressure. Meanwhile, in synchronization with the toner image on the photosensitive drum 1, a recording material P, which is the transfer object, is transported from the storage section 6 to the transfer section d by a transport roller 8 or the like. Then, at the transfer section d, the toner image on the photosensitive drum 1 is transferred onto the recording material P, which is sandwiched between the photosensitive drum 1 and the transfer roller 5, by the action of the transfer roller 5. At this time, a predetermined transfer voltage, which is a DC voltage of the opposite polarity (positive polarity in this embodiment) to the normal polarity of the toner, is applied to the transfer roller 5 from the transfer power source E3 (Figure 3). As a result, an electric field is formed between the transfer roller 5 and the photosensitive drum 1, and the toner image is electrostatically transferred from the photosensitive drum 1 to the recording material P. In this embodiment, the transfer voltage during this transfer is +1000 V, for example. Then, due to the action of the electric field formed between the transfer roller 5 and the photosensitive drum 1, the toner image is electrostatically transferred from the photosensitive drum 1 to the recording material P.

[0020] The recording material P onto which the toner image has been transferred is sent to a fixing device 9 serving as a fixing means. In the fixing device 9, heat and pressure are applied to the recording material P, and the toner image is fixed to the recording material P.

[0021] On the other hand, the transfer residual toner that has not been transferred to the recording material P and remains on the photosensitive drum 1 is sent to a brush member 10 that is installed downstream of the transfer roller 5 in the rotation direction of the photosensitive drum 1. The brush member 10 used in this embodiment will be described below.

[0022] 2. Brush component structure 1, the image forming apparatus 100 in this embodiment has a brush member 10 (collection member) which is a contact member that serves as a paper dust collecting mechanism and a water vapor recovery mechanism. In this embodiment, the image forming apparatus 100 has the brush member 10 disposed so as to contact the surface of the photosensitive drum 1 downstream of a transfer unit and upstream of a charging unit in the rotation direction of the photosensitive drum 1. Here, the contact portion between the brush member 10 and the photosensitive drum 1 in the rotation direction of the photosensitive drum 1 is considered to be the brush contact portion.

[0023] Note that Figures 1 and 5 show the configuration arrangement in which the image forming device 100 is placed on a horizontal installation surface, which is the normally assumed installation state, and the left-right direction of the paper corresponds to the horizontal direction, and the up-down direction of the paper corresponds to the up-down direction of the device (gravity direction, vertical direction).

[0024] Fig. 2(a) is a schematic diagram of the brush member 10 in a standalone state, viewed along its longitudinal direction (substantially parallel to the rotational axis direction of the photosensitive drum 1). Fig. 2(b) is a schematic diagram of the brush member 10 in contact with the photosensitive drum 1, viewed along its longitudinal direction.

[0025] The brush member 10 has a brush portion made up of a fixedly disposed conductive fixed brush 11. The fixed brush 11 is configured by weaving a plurality of conductive threads (fiber threads) 11a made of conductive nylon 6 into a base fabric 11b made of synthetic fibers containing carbon as a conductive agent. In other words, the fixed brush 11 is configured so that the tips of the plurality of conductive threads 11a extending from the base fabric 11b come into contact with the surface of the photosensitive drum 1. The brush member 10 is disposed so that its longitudinal direction is parallel to the direction of the rotational axis of the photosensitive drum 1 and so comes into contact with the surface of the photosensitive drum 1.

[0026] As shown in FIG. 2(a), when the brush member 10 is in a standalone state, i.e., when no external force is being applied to bend the conductive threads 11a, L1 is the distance from the base fabric 11b to the tip of the conductive threads 11a. In this embodiment, L1 is 6.5 mm. The brush member 10 is arranged such that the base fabric 11b is fixed to a support member (not shown) installed at a predetermined position in the image forming apparatus 100 using a fixing means such as double-sided tape, and the tip of the conductive threads 11a penetrates the photosensitive drum 1. That is, when the brush member 10 and the photosensitive drum 1 are virtually overlapped in the direction of the rotation axis of the photosensitive drum 1 without considering deformation, the base fabric 11b is fixed so that the tip of the conductive threads 11a penetrates the photosensitive drum 1. In this embodiment, the clearance between the support member and the photosensitive drum 1 is fixed. The shortest distance from the base fabric 11b of the brush member 10 fixed to the support member to the photosensitive drum 1 is L2. In this embodiment, the difference between L2 and L1 is defined as the amount of penetration of the brush member 10 into the photosensitive drum 1. In this embodiment, the amount of penetration of the brush member 10 into the photosensitive drum 1 is 1 mm.

[0027] In this embodiment, as shown in Figure 2(a), when the brush member 10 is in a standalone state, the length L3 of the brush member 10 in the circumferential direction of the photosensitive drum 1 (the direction parallel to the direction of rotation) is 5 mm. In this embodiment, the length of the brush member 10 in the direction of the rotation axis of the photosensitive drum 1 (the longitudinal length of the brush member 10) is 216 mm. This allows the brush member 10 to come into contact with the entire image formation area (the area where a toner image can be formed) on the photosensitive drum 1 in the direction of the rotation axis of the photosensitive drum 1. In this embodiment, the thickness of the conductive thread 11a is 2 denier (representing the thickness of a thread such that 9000 m weighs 2 g) and the density is 240 kF / inch 2 (kF / inch 2 is a unit of brush density, indicating the number of filaments per square inch. As described above, the brush member 10 is supported by a support member (not shown), is disposed in a fixed position relative to the photosensitive drum 1, and rubs against the surface of the photosensitive drum 1 as the photosensitive drum 1 moves.

[0028] The brush member 10 collects (recovers) paper dust and other adhering matter transferred from the recording material P onto the photosensitive drum 1 at the transfer section, reducing the amount of paper dust that moves to the charging section and developing section downstream of the brush member 10 in the movement direction of the photosensitive drum 1. Furthermore, the brush member 10 collects water vapor that has adhered to the photosensitive drum 1 near the transfer section, reducing the amount of water vapor that moves to the charging section and developing section downstream of the brush member 10.

[0029] In this embodiment, the length of the brush member 10 in the circumferential direction of the photosensitive drum 1 is set to L3 = 5 mm, but this is not limited to this. For example, it may be changed as appropriate depending on the lifespan of the image forming apparatus or process cartridge. It goes without saying that the longer the length of the brush member 10 in the circumferential direction of the photosensitive drum 1, the longer it can capture paper dust and the more water vapor it can recover. However, the longer the length of L3, the longer the circumferential length of the photosensitive drum 1 must be, and as a result, the larger the image forming apparatus 100 must be. Since miniaturization of the image forming apparatus 100 is required, it is desirable for the brush member 11 to have L3 = 6 mm or less when abutting against the photosensitive drum 1 with an outer diameter of 24 mm.

[0030] In addition, although the length of the brush member 10 in the longitudinal direction in this embodiment is set to 216 mm, it is not limited to this and may be changed as appropriate depending on the maximum paper passing width of the image forming apparatus, for example.

[0031] In addition, the conductive thread 11a in this embodiment has a thickness of 2 denier and a density of 240 kF / inch 2 However, it is desirable to determine the thickness in consideration of the paper dust collecting power, the toner passing through, and the water vapor collecting power. The thinner the conductive threads 11a (the smaller the fineness), the weaker the paper dust blocking power becomes, and the paper dust passes through and interferes with the charging of the photosensitive drum 1 by the charging roller 2. This can cause image defects. Furthermore, the thicker the conductive thread 11a, the worse the toner passage becomes, causing it to become stuck, and the stuck toner can scatter and stain the inside of the machine, causing other problems. From the above, the thickness of the conductive thread 11a is preferably 1 to 10 denier, and furthermore, considering the ability of the conductive thread 11a to follow the photosensitive drum 1 in a low-temperature environment, 1 to 6 denier is preferable.

[0032] Further, the brush member 10 is connected to a brush power supply E4 (FIG. 3) as a brush voltage applying means.

[0033] 3. Image output operation In this embodiment, the image forming apparatus 100 executes an image output operation (job), which is a series of operations for forming an image on one or multiple recording materials P, in response to a single start command from an external device (not shown), such as a personal computer. A job generally includes an image formation process (printing process), a pre-rotation process, a paper-interval process when forming images on multiple recording materials P, and a post-rotation process. The image formation process is the period during which the electrostatic image is actually formed on the photosensitive drum 1, the electrostatic image is developed (formed as a toner image), the toner image is transferred, and the toner image is fixed. The image formation process refers to this period. More specifically, the timing of the image formation process differs depending on the location where the electrostatic image is formed, the toner image is formed, the toner image is transferred, and the toner image is fixed. Therefore, the image formation operation may be defined as the period up to the transfer of the toner image, or the period up to the fixation of the toner image. Even if the image forming operation performed on the photosensitive drum 1 is completed and the operation of the photosensitive drum 1 is switched from the image forming operation to the non-image forming operation, this does not have any effect on the image that has already been transferred to the recording material P, and therefore the above definition may be used. The pre-rotation process is a period in which preparatory operations are performed before the image forming process. The sheet interval process is a period corresponding to the interval between recording materials P when the image forming process is performed continuously on multiple recording materials P (during continuous image formation). The post-rotation process is a period in which an organizing operation (preparatory operation) is performed after the image forming process. The non-image formation time is a period other than the image formation time, and includes the pre-rotation process, sheet interval process, post-rotation process, and the pre-multiple rotation process, which is a preparatory operation when the image forming apparatus 100 is turned on or when it returns from a sleep state.

[0034] 4. Control mode 3 is a schematic block diagram showing the control mode of the main parts of the image forming apparatus 100 of this embodiment. The image forming apparatus 100 is provided with a control unit 150. The control unit 150 has a CPU 151 as an arithmetic control means that is a central element that performs arithmetic processing, an input / output unit (not shown) that controls the exchange of signals between the control unit 150 and various elements connected to the control unit 150, and the like.

[0035] The control unit 150 is a control unit that comprehensively controls the operation of the image forming apparatus 100. The control unit 150 controls the transmission and reception of various electrical information signals, drive timing, and the like, to execute a predetermined image formation sequence. The control unit 150 is connected to each unit of the image forming apparatus 100. For example, in relation to this embodiment, the control unit 150 is connected to a charging power supply E1, a developing power supply E2, a transfer power supply E3, a brush power supply E4, a drive motor 110, an exposure unit 4, and the like.

[0036] 5. Brush water absorption and image evaluation comparison Next, the water absorption amount of the brush member 10 in this example and image evaluation will be described in detail together with a comparative example. The water absorption amount of the brush member 10 in this example was measured by the following method. However, the measurement method is not limited to the method described here.

[0037] Water absorption measurement The fixed brush 11 is constructed by weaving a plurality of conductive threads 11a made of fibers of various materials and varying densities into a base fabric 11b as shown in Figure 2. The shape / dimensions of the fixed brush 11 are as follows: Similarly, the dimensions are L1 = 6.5 mm, L3 = 5 mm, and the longitudinal length = 216 mm.

[0038] FIG. 4 is a diagram illustrating the measurement of water absorption in this example. After measuring the initial weight (W0) of the fixed brush 11, the fixed brush 11 was brought close to the water surface at 20°C so that the contact surface of the fixed brush 11 against the photosensitive drum 1 was parallel (FIG. 4(a)). Only the tip 1 mm of the fixed brush 11 was immersed in the water for 10 seconds (FIG. 4(b)). Here, the contact surface of the fixed brush 11 against the photosensitive drum 1 is a term referring to the collection of tips of multiple conductive threads 11a, each cut to approximately the same length, as a surface. It can also be considered a virtual surface including the tips of the multiple fiber threads 11a. In other words, the fixed brush 11 (contact surface) was brought close to the water surface while maintaining the contact surface parallel to the water surface. This allows the tips of the multiple fiber threads 11a to enter the water at approximately the same time, preventing or minimizing differences in the degree of immersion among the multiple fiber threads 11a (ensuring that only the region of 1 mm from the tip of each fiber thread 11a is immersed in water). Next, the fixed brush 11 is lifted from the water surface, and the weight (W) of the sample is measured when water droplets stop falling, and calculated using the following formula. Water absorption amount (g)=W-W0

[0039] Water absorption comparison As the fiber material used for the conductive thread 11a, a comparative test of water absorption was carried out using the following conductive thread 11a materials / densities.

[0040] (Table 1) TIFF2023090266000004.tif25153

[0041] From A, B, C, and F in Table 1, we can see that, from the perspective of fiber material, MC Nylon® and Nylon 6 have higher water absorption than SFCP and Beslon®. This shows a trend that corresponds to the magnitude of the water absorption rate according to the ASTM D570 test method (the rate of change in test piece weight when immersed in water at 23°C for 24 hours), and the higher the water absorption rate of the fiber material, the greater the water absorption amount.

[0042] Furthermore, from C, D, E, F, and G in the same table, it can be seen that for the same fiber material, the higher the density of the conductive thread 11a, the greater the amount of water absorption. This is because the higher the density of the conductive thread 11a, the greater the surface area, and therefore the greater the amount of water vapor that adheres per unit area.

[0043] In this example, nylon 6 is used as the fiber material, but this is not limiting. Any fiber material that exhibits high water absorption may be used, and the water absorption rate measured by the ASTM D570 test method is preferably 0.5% or more, and more preferably 1.1% or more.

[0044] Image evaluation comparison Next, a comparative test was conducted to evaluate the image quality when multiple sheets of recording material stored in a high-temperature, high-humidity environment were passed through the printer. The recording material used for the image evaluation was Xerox Vitality Multipurpose paper, Letter size, with a basis weight of 75 g / m. 2 The paper was taken out of its packaging and left in an environment with a temperature of 30°C and humidity of 80% for two days. The moisture content of the paper was measured using a moisture meter, Moistrex MX-8000, manufactured by NDC Infrared Engineering, and was found to be 9.2%. For comparison, the moisture content was measured immediately after opening and was found to be 5.7%.

[0045] (Table 2) TIFF2023090266000005.tif54153

[0046] Table 2 shows the results of toner-stained images when 100 sheets of each of the above-mentioned recording materials were continuously fed. In Table 2, ◯ indicates no toner-stained images, △ indicates slight toner-stained images, and × indicates significant toner-stained images.

[0047] From A, B, C, and F in the table, it can be seen that SFCP and Beslon (registered trademark) caused significant toner contamination of images after 10 consecutive sheets were fed, whereas MC Nylon (registered trademark) and 6 Nylon, which have high water absorption, were able to significantly reduce this.

[0048] Furthermore, from C, D, E, F, and G in the same table, it can be seen that the timing at which toner-stained images appear varies depending on the density. In the case of nylon 6, slight toner-stained images appear on the 50th sheet at a density of 70 kF, on the 100th sheet at a density of 150 kF, and none appear even on the 100th sheet at a density of 240 kF. In other words, the higher the density, the less likely to develop toner-stained images. This is because the higher the density, the greater the water absorption capacity, and water vapor can be accumulated inside the brush member 10 even when printing material with a high moisture content is fed through.

[0049] In this embodiment, assuming that the recording material has a high moisture content, the amount of water absorption of the fixed brush 11 measured by the water absorption amount measurement described above is preferably 2.4 g or more, and the amount of water absorption per unit area is 2.2 mg / mm 2 Therefore, it is desirable that the density of the conductive thread 11a be 240 kF or more when MC nylon (registered trademark) (water absorption rate = 0.5%) is used, and that the density of the conductive thread 11a be 150 kF or more when 6 nylon (water absorption rate = 1.1%) is used.

[0050] Here, the water absorption amount per unit area is the value obtained by dividing the amount of moisture contained in the fixed brush 11 by measuring the amount of water absorption, by the contact area between the fixed brush 11 and the photosensitive drum 1. The contact area between the fixed brush 11 and the photosensitive drum 1 is the collection of contact areas between the tip ends of each of the multiple conductive threads 11a and the photosensitive drum 1. From a microscopic perspective, there may be gaps between the tip ends of adjacent conductive threads 11a that do not contact the surface of the photosensitive drum 1. Therefore, strictly speaking, it is difficult to clearly define the contact area between the fixed brush 11 and the photosensitive drum 1 as a single area. However, as an approximate contact area, for example, the gaps may be ignored and a single area may be defined by capturing the overall outline of the collection of contact areas between each of the multiple conductive threads 11a and the photosensitive drum 1, and the area of ​​that area may be used as the contact area.

[0051] In this example, the contact area was calculated as follows. That is, it is assumed that an area of ​​the conductive thread 11a having a length (L1): 6.5 mm and a length corresponding to an intrusion amount (L1-L2): 1 mm contacts the circumferential surface of the photosensitive drum 1. Also, the length (L3): 5 mm of the brush member 10 in the circumferential direction of the photosensitive drum is assumed to be the length (width) of the bundle of conductive threads 11a in the same direction. Then, It is assumed that the conductive threads 11a that contact the peripheral surface of the photosensitive drum 1 in the contact area are arranged in a row over a range of 5 mm in the peripheral direction of the photosensitive drum, and that the row extends in the longitudinal direction of the peripheral surface of the photosensitive drum 1 within a range of 216 mm, which is the longitudinal width of the brush member 10. Therefore, 1 mm x 5 mm x 216 mm = 1080 mm 2 In this example, the water absorption per unit area of ​​A to G was: A: 0.27 mg / mm 2 , B: 0.74 mg / mm 2 , C: 1.38 mg / mm 2 , D: 2.22 mg / mm 2 , E: 1.85 mg / mm 2 , F: 2.22 mg / mm 2 , G: 2.68 mg / mm 2 The method for defining the contact area is not limited to the above method, and other methods may be used.

[0052] 6. Effects of this Example As described above, according to this embodiment, the amount of water absorption per unit area is 2.2 mg / mm on the downstream side of the transfer unit and the upstream side of the charging unit in the rotation direction of the photosensitive drum. 2 The brush member described above is provided. This allows the brush member to sufficiently collect water vapor adhering to the photosensitive drum surface, even when recording materials with high moisture content are continuously fed through the device. This makes it possible to suppress image defects such as toner contamination caused by water vapor.

[0053] In this embodiment, the example is described as being applied to a DC charging type image forming apparatus, but the present invention can also be applied to an AC charging type image forming apparatus that uses an oscillating voltage in which a DC voltage (DC component) and an AC voltage (AC component) are superimposed as a charging voltage.

[0054] Furthermore, in this embodiment, only the DC component of the developing voltage has been described, but the developing voltage may be an oscillating voltage in which a DC voltage (DC component) and an AC voltage (AC component) are superimposed.

[0055] In addition, in this embodiment, toner is used as the developer, which is a non-magnetic one-component developer, but a magnetic one-component developer may also be used.

[0056] In addition, although the present embodiment uses a "cleanerless system" configuration that does not have a cleaning means for the photosensitive drum 1, the present invention is not limited to this. For example, a "blade cleaning system" may be used in which a blade is used as a cleaning means downstream of the brush member 10 and upstream of the charging roller 2 in the transport direction of the photosensitive drum 1.

[0057] In addition, in this embodiment, the density of the conductive threads 11a is determined assuming that recording materials with high moisture content are continuously fed, but this is not limited to this. Depending on the usage environment of the image forming apparatus 100, for example, in a high humidity environment, the time between sheets during continuous feeding may be made longer than the normal time between sheets. In this case, the occurrence of toner-stained images can be suppressed even if the brush member absorbs only a small amount of water, so the density of the conductive threads 11a may be appropriately determined depending on the time between sheets.

[0058] Example 2 Next, a description will be given of a second embodiment of the present invention. The basic configuration and operation of the image forming apparatus of this embodiment are the same as those of the image forming apparatus of embodiment 1. Therefore, in the image forming apparatus of this embodiment, elements having the same or corresponding functions or configurations as those of the image forming apparatus of embodiment 1 are given the same reference numerals as those of the image forming apparatus of embodiment 1, and detailed descriptions thereof will be omitted.

[0059] This embodiment is characterized in that a brush voltage is applied to the brush member 10 by the brush power supply E4 shown in Fig. 3. The control of the brush voltage in the image forming process will be described below.

[0060] 1. Brush voltage control In this embodiment, the brush member 10 is supplied with a brush power supply E4 under the control of the control unit 150. A predetermined brush voltage, which is a negative DC voltage, is applied. Here, the brush power supply E4, which serves as a brush voltage application means, may apply a voltage in which a DC component and an AC component are superimposed, for example. In this embodiment, the brush voltage during the image formation process is -300 V. Meanwhile, the surface potential of the photosensitive drum 1 after passing through the transfer unit d is approximately -50 V. As a result, among the residual toner particles sent from the transfer unit d, positively charged toner particles are primarily collected by the brush member 10 at the brush unit e due to the potential difference between the brush voltage and the surface potential of the photosensitive drum 1. Meanwhile, negatively charged toner particles are attracted to the photosensitive drum 1 at the brush unit e and pass through the brush unit e. The toner particles that have passed through the brush unit e are uniformly discharged at the charging unit a to acquire the desired negative charge and are then sent to the development unit c. Of the toner sent to the development section c, the non-image area (non-exposed area) is transferred to the development roller 31 due to the potential difference between the dark area potential (Vd) on the surface of the photosensitive drum 1 and the development bias (Vdc), and is then collected in the development device 3. As in the first embodiment, the dark area potential (Vd) in this embodiment is approximately -600 V, and the development bias (Vdc) is -300 V. On the other hand, the image area (exposed area) is not transferred to the development roller 31 due to the potential difference between the light area potential (Vl) on the surface of the photosensitive drum 1 and the development bias (Vdc), and is sent as is as the image area to the transfer section d as the photosensitive drum 1 rotates, and is transferred to the recording material P. The light area potential (Vl) in this embodiment is approximately -100 V, as in the first embodiment.

[0061] 5 shows the state around the photosensitive drum 1 during the image forming process. From this figure, it can be seen that the positive polarity toner among the transfer residual toner is primarily collected by the brush member 10, and the negative polarity toner passes through the brush portion e and the charging portion a and is transferred to the developing roller 31.

[0062] FIG. 6 shows the state of toner that has been primarily collected by the brush member 10. From this figure, it can be seen that water vapor adheres to the toner that has been primarily collected by the brush member 10. In this way, the water vapor that has adhered to the surface of the photosensitive drum 1 is not only collected by the brush member 10 together with the residual toner, but also, due to the brush voltage, can be transported along with the toner to the base fabric 11b side of the brush member 10 (the side opposite the brush tip). This allows the brush member 10 to collect more water vapor than in a configuration in which no brush voltage is applied.

[0063] 2. Image evaluation comparison A comparative test was carried out to evaluate the images when a plurality of sheets of recording material stored in a high-temperature, high-humidity environment were passed through, as in Example 1. Detailed conditions are the same as in Example 1, and therefore will not be repeated here.

[0064] (Table 3) TIFF2023090266000006.tif58153

[0065] Table 3 shows the results of toner-stained images when 200 sheets of each of the above-mentioned recording materials were continuously fed. The image ranks in this table are the same as those in Example 1.

[0066] From the table, it can be seen that the timing of the occurrence of toner-stained images is delayed for all fiber materials, that is, the occurrence of toner-stained images with an increase in the number of continuously fed sheets is suppressed. This is because the brush voltage can cause water vapor to be drawn around the base fabric side of the brush member 10 (the side opposite the brush tip) along with the toner, so more water vapor can be collected than when no brush voltage is applied.

[0067] 3. Effects of this embodiment As described above, according to this embodiment, the brush voltage is used to draw water vapor adhering to the photosensitive drum surface, together with the residual toner, around the base fabric side of the brush member 10. This allows the brush member to collect more water vapor, and suppresses the occurrence of toner-stained images that occur with an increase in the number of sheets passed continuously.

[0068] From the above results, Example 2 has the following configuration.

[0069] The brush power supply E4 serves as a brush voltage application unit that applies a brush voltage to the brush member 10. The brush member 10 is a conductive brush, and the control unit 150 controls the brush voltage applied to the brush member 10 from the brush power supply E4 so that a brush voltage of the same polarity as the toner charged to the normal polarity is applied to the brush member 10 while the image forming operation is being performed.

[0070] The control unit 150 controls the voltage applied from the brush power supply E4 to the brush member 10 so that the brush voltage applied to the brush member 10 and the surface potential of the photosensitive drum 1 have the same polarity and the absolute value of the brush voltage is greater than the absolute value of the surface potential of the photosensitive drum 1.

[0071] Furthermore, it has a transfer power supply E3 as a transfer voltage application unit that applies a transfer voltage to the transfer roller 5. The control unit 150 controls the transfer power supply E3 so that the brush voltage applied to the brush member 10 and the surface potential of the photosensitive drum 1 at the transfer portion d have the same polarity and the surface potential of the photosensitive drum 1 at the transfer portion d is smaller than the brush voltage applied to the brush member 10.

[0072] In this embodiment, the surface potential of the photosensitive drum 1 is controlled by varying the transfer voltage and brush voltage, but this is not limiting. For example, the transfer voltage and brush voltage may be varied with the photosensitive drum 1 grounded and the surface potential at ground (0 V). Alternatively, the potential relationship with the transfer roller 5 and the brush member 10 may be controlled by applying a voltage directly to the photosensitive drum 1.

[0073] In addition, although the present embodiment has been described using an example in which the present invention is applied to a DC charging type image forming apparatus, the present invention can also be applied to an AC charging type image forming apparatus that uses an oscillating voltage in which a DC voltage (DC component) and an AC voltage (AC component) are superimposed as a charging voltage.

[0074] Furthermore, in this embodiment, only the DC component of the developing voltage has been described, but the developing voltage may be an oscillating voltage in which a DC voltage (DC component) and an AC voltage (AC component) are superimposed.

[0075] In addition, in this embodiment, toner is used as the developer, which is a non-magnetic one-component developer, but a magnetic one-component developer may also be used.

[0076] In addition, although the present embodiment uses a "cleanerless system" configuration that does not have a cleaning means for the photosensitive drum 1, the present invention is not limited to this. For example, a "blade cleaning system" may be used in which a blade is used as a cleaning means downstream of the brush member 10 and upstream of the charging roller 2 in the transport direction of the photosensitive drum 1.

[0077] In this embodiment, the recording material P, which is the transfer target, is transported to the transfer section and transferred. However, a conveying belt for conveying the recording material P to the transfer portion may be provided.

[0078] Furthermore, in this embodiment, a pre-exposure unit may be provided that exposes the surface of the photosensitive drum 1 downstream of the transfer portion d and upstream of the charging portion a in the rotation direction of the photosensitive drum 1. The pre-exposure unit may be provided upstream or downstream of a contact portion e between the brush member 10 and the photosensitive drum 1. When the pre-exposure unit is provided upstream of the contact portion e, the surface potential of the photosensitive drum 1 may be controlled by the pre-exposure unit.

[0079] In addition, in this embodiment, the density of the conductive threads 11a is determined assuming that recording materials with high moisture content are continuously fed, but this is not limited to this. Depending on the usage environment of the image forming apparatus 100, for example, in a high humidity environment, the time between sheets during continuous feeding may be made longer than the time between sheets under normal conditions. In this case, the occurrence of toner-stained images can be suppressed even if the brush member absorbs only a small amount of water, so the density of the conductive threads 11a may be appropriately determined depending on the time between sheets. [Explanation of symbols]

[0080] 1... photosensitive drum, 2... charging roller, 3... developing device, 4... exposure device, 5... transfer roller 10...brush member, 31...developing roller, 150...control section

Claims

1. an image carrier that is rotated; a charging member for charging the surface of the image carrier in a charging section; a developing member for supplying a developer to the electrostatic latent image formed on the surface of the image carrier charged by the charging member to form a developer image; a transfer member that forms a transfer portion that sandwiches a recording material between the image carrier and the transfer portion and transfers a developer image from the image carrier to the recording material in the transfer portion; a brush member having a base fabric and a plurality of fiber threads woven into the base fabric, the brush member being disposed downstream of the transfer unit and upstream of the charging unit in a rotation direction of the image carrier, the brush member having tips of the fiber threads extending from the base fabric in contact with a surface of the image carrier, the surface being downstream of the transfer unit and upstream of the charging unit in a rotation direction of the image carrier; Equipped with The brush member has a water absorption per unit area of ​​2.2 mg / mm when a region of 1 mm from the tip of the plurality of fiber threads that contacts the image carrier is immersed in water at 20° C. for 10 seconds. ２ The image forming apparatus according to the present invention is characterized in that

2. The image forming apparatus according to claim 1, characterized in that the water absorption amount per unit area is a value obtained by dividing the amount of water contained in the brush member when the multiple fiber threads are brought close to the water surface at 20°C while maintaining a state in which an imaginary plane including each of the tips of the multiple fiber threads that contact the image carrier is parallel to the water surface, and only a 1 mm area from the tips of the multiple fiber threads is immersed in water for 10 seconds, by the contact area between the brush member and the image carrier.

3. 3. The image forming apparatus according to claim 1, wherein the material of the fiber yarn has a water absorption rate of 0.5% or more according to the test method of ASTM D570.

4. 4. The image forming apparatus according to claim 3, wherein the density of the plurality of fiber threads is 240 kF or more.

5. 3. The image forming apparatus according to claim 1, wherein the material of the fiber yarn has a water absorption rate of 1.1% or more according to the test method of ASTM D570.

6. 6. The image forming apparatus according to claim 5, wherein the density of the plurality of fiber threads is 150 kF or more.

7. a brush voltage application unit that applies a brush voltage to the brush member; A control unit that controls the brush voltage application unit; Further equipped with The brush member is a conductive brush, The image forming apparatus according to any one of claims 1 to 6, characterized in that the control unit controls the brush voltage application unit so that the brush voltage applied to the conductive brush by the brush voltage application unit while an image forming operation is being performed has the same polarity as the surface potential of the image carrier, and the absolute value of the brush voltage is greater than the absolute value of the surface potential of the image carrier.

8. a transfer voltage application unit that is controlled by the control unit to apply a transfer voltage to the transfer member, 8. The image forming apparatus according to claim 7, wherein the control unit controls the transfer voltage application unit so that the brush voltage and the surface potential of the image carrier in the transfer unit have the same polarity and the surface potential of the image carrier in the transfer unit is smaller than the brush voltage.

9. 9. The image forming apparatus according to claim 1, wherein the toner remaining in the transfer section and not transferred from the image carrier to the recording material is collected by the developing member.

10. 10. The image forming apparatus according to claim 1, wherein the developer is a one-component developer.

11. An image forming apparatus as described in any one of claims 1 to 10, characterized in that the charging member contacts the surface of the image carrier in the charging section to charge the surface of the image carrier.

Images