Image forming apparatus

Abstract

To prevent fusion of toner to a developing blade to prevent scattering of toner into an image forming apparatus body.SOLUTION: A developing opening 46c is installed above a rotation shaft of a supply roller 43, a stirring shaft 45a is installed above the developing opening 46c, and the absolute value of the quantity of airflow in a central part in a longitudinal direction is larger than the absolute value of the quantity of airflow at both ends in the supply roller 43. The image forming apparatus comprises a control unit 200 that performs a toner developing sequence (toner discharge at developing ends) of discharging toner to end areas in the longitudinal direction of a photoconductor drum 1, with toner carried on the developing roller 41 (S103).SELECTED DRAWING: Figure 9

Description

[Technical Field]

[0001] The present invention relates to an image forming apparatus, and more particularly to a developing device, a process cartridge, and an image forming apparatus used in an image forming apparatus such as a copying machine, a printer, or a facsimile machine that uses an electrophotographic system or an electrostatic recording system. [Background technology]

[0002] Conventionally, electrophotographic image forming apparatuses are equipped with a developing device that supplies a developer to an electrostatic latent image formed on an electrophotographic photosensitive member (image carrier) to form a developer image. This type of development method uses, for example, a single-component developer consisting only of toner. In this development method, the developing device is primarily composed of two spaces: a toner storage chamber that stores toner and a development chamber where the development process takes place. The toner is supplied to the development chamber through a development opening located at the boundary between the toner storage chamber and the development chamber by the rotation of an agitator in the toner storage chamber. The development chamber is composed of a developing roller, a supply roller, and a development blade. The developing roller is a developer carrier that transports toner to the photosensitive drum and develops the toner image on the photosensitive drum. The supply roller is a developer supplying member with a sponge structure that is arranged around the developing roller and supplies toner to the developing roller and removes it from the developing roller. The development blade is a regulating member arranged around the developing roller that regulates the toner layer formed by the toner supplied from the supply roller to the developing roller. The supply roller achieves the above-mentioned effect by contacting and penetrating a desired, specified amount of the supply roller with the surface of the developing roller using a fixed shaft method or the like. The toner transported to the developing chamber is supplied onto the developing roller by the supply roller and regulated by the developing blade. After passing through the contact area between the developing roller and the developing blade, the toner is transported to the developing area, which is the area adjacent to the photosensitive drum, where the electrostatic latent image is visualized as a toner image.

[0003] When toner is transported from the toner storage chamber to the developing chamber, if the development opening is located vertically below the agitator and the center of the supply roller is located even further below the development opening, the rotation of the agitator may repeatedly push the toner into the developing chamber. In this case, the toner may easily clog the developing chamber, potentially reducing toner movement. Meanwhile, the rotation of the agitator increases the powder pressure of the toner at the center compared to the edges. Therefore, from the perspective of toner circulation, this phenomenon is particularly evident in the image center, i.e., the center of the photosensitive drum in the axial direction. When toner movement in the developing chamber decreases, the supply roller is unable to properly supply and discharge toner. Specifically, because toner movement is reduced at the center compared to the longitudinal edges, the supply roller is unable to adequately retain toner in its sponge layer and is therefore unable to supply toner to the developing roller. This can result in image defects known as toner tracking failure, i.e., insufficient density due to a lack of toner supplied from the supply roller, occurring at the center of the image at certain rotational intervals of the supply roller or developing roller.

[0004] One way to solve this problem is to increase the supply roller's airflow, with the aim of improving toner circulation within the developing chamber and activating the supply roller. Airflow is a parameter expressed in units of L / min (liters per minute) that indicates the amount of air that passes through the supply roller when a specified volume and pressure of air is passed through it. The supply roller has a foam sponge structure, and the cell diameter and interconnectivity are controlled by the polymer viscosity of the material, the amount of carbon dioxide, and the foaming conditions. Interconnectivity is the degree to which the cells are interconnected. Adjusting the cell diameter and interconnectivity allows for control of the supply roller's airflow.

[0005] On the other hand, increasing the supply roller's air permeability can cause image defects such as horizontal bands on the developing roller or between the supply rollers (hereafter referred to as the supply roller set). Increasing the air permeability strengthens the foaming of the sponge structure, i.e., suppresses the cross-linked structure, making the supply roller softer and more susceptible to deformation. This can cause permanent deformation when the supply roller is stored for a long period of time, resulting in fluctuations in peripheral speed at the contact point with the developing roller, especially at the longitudinal ends, causing image defects. One way to address the supply roller set problem is to reduce the supply roller's air permeability. In addition, in order to improve the supply roller's ability to scrape off residual toner after development, a manufacturing method has been disclosed in which the density of the elastic layer (sponge portion) is made higher in the center of the supply roller than at both ends in the longitudinal direction (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2014-170028 A Summary of the Invention [Problem to be solved by the invention]

[0007] However, in developing devices and image forming apparatuses using supply rollers with altered longitudinal ventilation, toner scattering can occur with continued use of the developing device. This is because reducing the ventilation rate of the supply roller in response to a supply roller set suppresses foaming of the sponge structure, i.e., strengthens the cross-linking structure, making the supply roller harder and less susceptible to deformation. In particular, toner circulation in the longitudinal and lateral directions tends to be unfavorable in the longitudinal end regions, resulting in strong friction at the contact point with the developing roller, accelerating toner degradation compared to the image center. As a result, the movement of deteriorated toner within the developing chamber is further reduced, making it more likely to remain in the toner regulating section between the developing blade and the developing roller. This makes the accumulated toner more likely to adhere to the blade surface. The toner adhering to the developing blade surface fuses with the developing roller due to friction and heat, growing into a fused mass. As a result, a small gap forms between the developing blade and the developing roller, causing toner to fly out of the developing chamber. Furthermore, the formation of fused material on the developing blade makes it impossible to form a uniform toner coat on the developing roller in the longitudinal direction, resulting in uneven thickness of the toner coat on the developing roller. This causes centrifugal force generated by the rotation of the developing roller to cause toner to peel off from the toner coat and scatter in areas on the developing roller where the toner coat is thicker than the appropriate thickness. That is, toner leaks from the gap between the developing roller and the developing blade and scatters, and toner peels off from the developing roller and scatters due to the fused material on the developing blade. The scattered toner may contaminate the longitudinal ends of the developing device, the drive gear, and even the inside of the image forming apparatus and the edges of the recording material being transported.

[0008] The present invention has been made under these circumstances, and has as its object to suppress toner fusion to the developing blade and toner scattering into the main body of the image forming apparatus. [Means for solving the problem]

[0009] In order to solve the above-mentioned problems, the present invention has the following configuration.

[0010] (1) An image forming apparatus for forming an image on a recording material, comprising: an image carrier for carrying an electrostatic latent image; a developer carrier for carrying a developer and for developing the electrostatic latent image with the developer to form a developer image; a supply roller for contacting the developer carrier and supplying the developer to the developer carrier; a regulating member for regulating the developer carried on the developer carrier; a storage chamber for holding the developer; a developing chamber having the developer carrier, the supply roller, and the regulating member; a developing opening for separating the developing chamber from the storage chamber; an agitator shaft disposed in a direction perpendicular to the developer carrier; and an agitator member rotating around the agitator shaft in the storage chamber to agitate the developer, wherein the developer opening is disposed above the rotation axis of the supply roller, the agitator shaft is disposed above the developer opening, the supply roller has an absolute value of air permeability at a central portion in a longitudinal direction that is greater than the absolute values ​​of air permeability at both end portions, and the image forming apparatus is equipped with a control means for controlling the developer carried on the developer carrier to discharge toner to end regions in the longitudinal direction of the image carrier. [Effects of the Invention]

[0011] According to the present invention, it is possible to suppress toner fusion to the developing blade and toner scattering into the main body of the image forming apparatus. [Brief explanation of the drawings]

[0012] [Figure 1] Schematic cross-sectional view of an image forming apparatus according to Examples 1 to 4 [Figure 2] Schematic cross-sectional views of process cartridges of Examples 1 to 41 to 4 [Figure 3] Schematic cross-sectional view of the developing device of Examples 1 to 4 [Figure 4] Schematic cross-sectional views of supply rollers in Examples 1 to 4, and a diagram showing a method for measuring the air permeability of the supply rollers. [Figure 5] FIG. 10 is a diagram showing the relationship between the amount of airflow through the supply roller and the amount of toner contained in the black toner in Examples 1 to 4, and FIG. 11 is a diagram showing the relationship between the amount of airflow through the supply roller and the amount of deformation after being left in a harsh environment. [Figure 6]FIG. 1 shows a method 1 for changing the ventilation amount in the longitudinal direction in Examples 1 to 4. [Figure 7] FIG. 10 shows a method 2 (crushing process) for changing the ventilation amount in the longitudinal direction in Examples 1 to 4. [Figure 8] Schematic diagram showing the vicinity of one end in the longitudinal direction of the developing device of Example 1. [Figure 9] Flowchart showing a process for suppressing toner scattering in the first embodiment [Figure 10] Flowchart showing a process for suppressing toner edge scattering in the second embodiment [Figure 11] Flowchart showing a process for suppressing toner edge scattering in the third embodiment [Figure 12] Flowchart showing a process for suppressing toner edge scattering in the fourth embodiment DETAILED DESCRIPTION OF THE INVENTION

[0013] A developing device, a process cartridge, and an image forming apparatus according to the present invention will be described in detail with reference to the drawings. Hereinafter, a detailed description of an embodiment of the present invention will be given by way of example with reference to the drawings. However, the dimensions, materials, shapes, and relative positions of the components described in the embodiments may be changed as appropriate depending on the configuration and various conditions of the apparatus to which the invention is applied. In other words, the scope of the present invention is not limited to the following embodiments. [Example]

[0014] In the first embodiment, when the developing device is continuously used, toner is discharged before toner deterioration is accelerated in the longitudinal end regions of the developing roller, etc., depending on the usage conditions of the user. This makes it possible to prevent toner from fusing to the developing blade and toner scattering.

[0015] (Overall configuration and operation of the image forming apparatus) FIG. 1 is a schematic cross-sectional view of an image forming apparatus according to an embodiment. The image forming apparatus 100 is a laser beam printer that forms images using an electrophotographic system. The image forming apparatus 100 employs a cartridge system, with a process cartridge 120 being detachably attached to an apparatus main body 110. An external host device such as a personal computer or image reading device is connected to the image forming apparatus 100. The image forming apparatus 100 receives image information from the host device, and forms and outputs (prints) an image on a recording material (recording medium, transfer material) according to the received image information. A sheet material such as paper is preferably used as the recording material.

[0016] The image forming apparatus 100 has a photosensitive drum 1, which is a drum-type (cylindrical) electrophotographic photosensitive member (photoconductor) serving as an image carrier. Around the photosensitive drum 1, the following members are arranged in order along the rotation direction (X1) of the photosensitive drum 1. First, a charging roller 2, which is a roller-shaped charging member serving as charging means, is arranged. Next, an exposure device (laser scanner unit) 3, which serves as exposure means, is arranged. Next, a developing device 4, which serves as developing means, is arranged. Next, a transfer roller 5, which is a roller-shaped transfer member serving as transfer means, is arranged. Next, a cleaning device 6, which serves as cleaning means, is arranged.

[0017] When a print start signal is input to the image forming apparatus 100 and image formation begins, a driving force is transmitted to the photosensitive drum 1 from a drive motor (not shown) serving as a driving means provided in the apparatus main body 110. This causes the photosensitive drum 1 to rotate in the direction indicated by arrow X1 in FIG. 1 at a predetermined peripheral speed (e.g., 300 mm / s) (process speed). In this embodiment, the photosensitive drum 1 has an aluminum drum base and an OPC photosensitive layer provided on the drum base. The charging roller 2 is disposed in contact with the photosensitive drum 1 and rotates in response to the rotation of the photosensitive drum 1. The surface (outer periphery) of the rotating photosensitive drum 1 is substantially uniformly charged to a predetermined potential of a predetermined polarity (negative in this embodiment) by the charging roller 2. At this time, a predetermined charging voltage is applied to the charging roller 2 from a charging power source (high-voltage power source) (not shown) provided in the apparatus main body 110.

[0018] The charged surface of the photosensitive drum 1 is exposed to laser light L corresponding to image information from an exposure device 3. The exposure device 3 outputs, from a laser output unit 3a, laser light (exposure beam) L modulated in accordance with a time-series electric digital image signal of image information input to a video controller 19 from a personal computer 20 or the like. The laser light L output from the exposure device 3 enters a process cartridge 120 and is irradiated onto the surface of the photosensitive drum 1. The substantially uniformly charged surface of the photosensitive drum 1 is scanned and exposed by the laser light L, thereby forming an electrostatic latent image (electrostatic image) corresponding to the image information on the surface of the photosensitive drum 1. The electrostatic latent image formed on the surface of the photosensitive drum 1 is developed by a developing device 4 with toner T (see FIG. 3) as a developer. Details of the developing device 4 will be described later.

[0019] Meanwhile, a pickup roller 8 serving as a conveying means is driven at a predetermined controlled timing to separate and feed recording materials P, such as recording paper, stacked and stored in a tray 7 serving as a recording material storage unit, one by one. As a result, the recording materials P are conveyed to a transfer unit N at a predetermined controlled timing by a conveying means (not shown). A transfer roller 5 contacts the surface of the photosensitive drum 1 with a predetermined pressing force to form a transfer unit (transfer nip) N. The recording material P is conveyed to the transfer unit N via a transfer guide 9 serving as a guide member. As the recording material P is conveyed between the photosensitive drum 1 and the transfer roller 5, the toner image, serving as a developer image on the surface of the photosensitive drum 1, is electrostatically transferred onto the surface of the recording material P during the process of passing through the transfer unit N. At this time, a transfer voltage, which is a DC voltage of a polarity opposite to the charge polarity (negative in this embodiment) of the toner during development, is applied to the transfer roller 5 from a transfer power source (high-voltage power source) (not shown) provided in the apparatus main body 110.

[0020] The recording material P with the transferred toner image is separated from the photosensitive drum 1 and transported to a fixing device 10, which serves as a fixing means and is located downstream of the transfer portion N in the transport direction of the recording material P. The recording material P is heated and pressurized in the fixing device 10 to fix the unfixed toner image. In this embodiment, the fixing device 10 includes a heating roller with an internal halogen heater and a pressure roller pressed against the heating roller. The fixing device 10 then heats and pressurizes the toner image transferred to the surface of the recording material P while nipping and transporting the recording material P in the fixing nip between the fixing roller and the pressure roller. This melts the toner image and fixes it to the surface of the recording material P. The recording material P is then discharged to a discharge tray 11 located at the top of the apparatus main body 110 in FIG. 1.

[0021] After the recording material P is separated, the surface of the photosensitive drum 1 is cleaned by the cleaning device 6 and is then repeatedly used for the image formation process starting from the charging described above. The cleaning device 6 uses a cleaning blade 61 as a cleaning member arranged in contact with the photosensitive drum 1 to remove deposits such as toner that remains untransferred during transfer from the surface of the rotating photosensitive drum 1 and collects the toner in a recovered toner container 62.

[0022] The image forming apparatus 100 includes a control unit 200 as a control means. The control unit 200 controls the overall image forming operation described above, and includes a CPU 201, a ROM 202, a RAM 203, and a timer 204. The CPU 201 executes a program stored in advance using various parameters stored in advance in the ROM 202, thereby performing control related to the image formation described above, while using the RAM 203 as a temporary work area. The CPU 201 manages time using the timer 204 for timing control when performing various controls.

[0023] (Process cartridge) 2 is a schematic cross-sectional view of the process cartridge 120. In this embodiment, the photosensitive drum 1, the charging roller 2 as a process means acting on the photosensitive drum 1, the developing device 4, and the cleaning device 6 are integrated into a cartridge to form the process cartridge 120 that is detachable from the apparatus main body 110. The process cartridge 120 is configured by connecting a cleaning unit 12 to a developing device 4 (also referred to as a developing unit) that is separate from the cleaning unit 12. The cleaning unit 12 has the photosensitive drum 1, the charging roller 2, and the cleaning device 6. The cleaning unit 12 also forms a collected toner container 62 and has a cleaning frame 60 for supporting the photosensitive drum 1, the charging roller 2, and the cleaning blade 61. The developing device 4 will be described in detail later.

[0024] A process cartridge generally refers to a cartridge in which an image carrier such as a photosensitive member and a process means that acts on the image carrier are integrated into one cartridge, and which is detachable from the main body of an image forming apparatus. Examples of the process means include a charging means, a developing means, a cleaning means, and a toner charging means that charges residual toner after transfer. Here, a process cartridge is defined as a cartridge in which at least a developer container or a developing device and an image carrier are integrated into one cartridge, and which is detachable from the main body of an image forming apparatus.

[0025] The process cartridge 120 or the developing device 4 also has a nonvolatile memory 127. The RAM 203 and / or the nonvolatile memory 127 stores information about the process cartridge 120 or the developing device 4. For example, the RAM 203 and / or the nonvolatile memory 127 stores information such as whether the process cartridge 120 is new or not, the model number, the amount of toner T consumed or remaining, the total number of prints since the cartridge was new, the total number of rotations of the rotating body, the total travel distance converted from the number of rotations, the average print rate, etc. The RAM 203 and / or the nonvolatile memory 127 also stores the toner consumption amount Xo per dot, which is used to convert the number of dots of an image formed on the photosensitive drum 1 into the toner consumption amount.

[0026] The developing roller 41 of this embodiment can be in contact with the photosensitive drum 1 (contact state) or separated from the photosensitive drum 1 (separated state). The image forming apparatus 100 is equipped with a contact / separation mechanism 125, and the control unit 200 performs the contact / separation operation by displacing the position (relative position and posture) of the developing device 4, which is a developing unit, with respect to the cleaning unit 12 using the contact / separation mechanism 125. The control unit 200 places the developing device 4 in the contact state when the developing roller 41 supplies toner to the photosensitive drum 1, and places the developing device 4 in the separated state when toner is not being supplied to the photosensitive drum 1. This reduces deformation of the developing roller 41 and the photosensitive drum 1 due to their contact, even when there is no need to supply toner to the photosensitive drum 1. FIG. 2 shows the contact state.

[0027] (developing device) FIG. 3 is a schematic cross-sectional view of the developing device 4 of this embodiment. The developing device 4 of this embodiment has a developing chamber 46a, a toner storage chamber 46b that stores developer, and a developing frame 40 that supports each element described below. The toner used as the developer in this embodiment is toner T, a one-component developer containing a magnetic substance inside. The toner storage chamber 46b has an agitating unit 45 that has an agitating shaft 45a and an agitating sheet 45b that serves as an agitating member. The agitating unit 45 rotates in the X4 direction in FIG. 3 to transport the toner T to the developing chamber 46a.

[0028] The developing chamber 46a has a developing opening 46c (developing opening) at the boundary with the toner storage chamber 46b. The developing chamber 46a also has a developing roller 41, which is a cylindrical member serving as a developer carrier. Both ends of the developing roller 41 in the longitudinal direction (direction of the rotation axis) are rotatably supported by the developing frame 40. The developing roller 41 is disposed in contact with the photosensitive drum 1. A rotational driving force is transmitted to the developing roller 41 from a driving motor (not shown) provided in the apparatus main body 110, and the developing roller 41 is driven to rotate in the direction of arrow X2 in FIG. 3. A developing voltage required to develop the electrostatic latent image into a toner image is applied to the developing roller 41 from a developing voltage application unit 49b serving as a developing voltage application means.

[0029] A supply roller 43 is disposed on the periphery of the developing roller 41, rotating in the X3 direction in FIG. 3 in contact with the developing roller 41. A desired voltage is applied to the supply roller 43 as a supply member from a supply voltage application unit 49a as a supply voltage application means. In addition, a developing blade 42, which is a regulating member made of an elastic member, is disposed in the developing chamber 46a so as to abut against the outer peripheral surface of the developing roller 41. The developing blade 42 is supported by the developing frame 40.

[0030] Next, the developing roller 41, supply roller 43, and developing blade 42 will be described. The developing roller 41 has a conductive core metal with a silicone rubber base layer and a urethane rubber surface layer. Coarse particles are present on the surface layer of the developing roller 41, optimizing the amount of toner adhesion. The supply roller 43 is a conductive sponge roller with a urethane sponge structure in which a foamed layer is formed on a conductive core metal. The developing blade 42 is made of a metal SUS sheet metal, and the long side that contacts the developing roller 41 and is the free end is coated with a resin laminate. The developing roller 41 and supply roller 43 are supported (fixed) at both longitudinal ends by the frame (not shown) of the image forming apparatus 100.

[0031] The developing roller 41 and the photosensitive drum 1 rotate so that their surfaces move in the same direction at the opposing portion (contact portion, developing area). In this embodiment, the developing roller 41 is arranged in contact with the photosensitive drum 1, but the developing roller 41 may also be arranged in close proximity to the photosensitive drum 1 with a predetermined gap therebetween.

[0032] The photosensitive drum 1 is electrically grounded, and a developing voltage applied to the developing roller 41 generates an electric field in the region between the photosensitive drum 1 and the developing roller 41. The charged toner T transported to the developing region is transferred to the surface of the photosensitive drum 1 by the action of this electric field in accordance with the electrostatic latent image on the surface of the photosensitive drum 1. In this way, the electrostatic latent image on the photosensitive drum 1 is developed with the toner T. In this embodiment, the photosensitive drum 1 is uniformly charged and then exposed to light, and toner T charged to the same polarity (negative polarity) as the charging polarity of the photosensitive drum 1 is attached to the exposed portion (image portion) on the photosensitive drum 1 where the absolute value of the potential has attenuated. In this way, the electrostatic latent image on the photosensitive drum 1 is developed (reverse development method).

[0033] In this embodiment, negative toner is used as the developer, but positive toner may also be used. 3The toner used contained magnetic material. The movement of the toner inside the developing container, i.e., the toner fluidity, can be understood by a physical parameter called cohesion. Cohesion is an index that indicates how easily the toner clumps together; a high cohesion value indicates poor toner fluidity, and a low value indicates good fluidity.

[0034] (supply roller) The supply roller 43 has a conductive shaft and a sponge layer containing cross-linked urethane resin on the shaft. The supply roller 43 shown in FIG. 4(a) includes a conductive shaft 52 and a sponge layer 51 containing cross-linked urethane resin disposed on the outer periphery of the conductive shaft 52. The layer configuration of the supply roller 43 is not limited to one in which the sponge layer 51 is located on the outermost surface of the supply roller 43. Examples of the supply roller 43 include a supply roller 43 having an additional surface layer on the shaft 52 and the sponge layer 51 disposed on the outer periphery of the shaft 52, or a supply roller 43 having an additional elastic layer between the shaft 52 and the sponge layer 51. The sponge layer 51 may also be molded to contain a conductive agent. This can generate a potential difference by applying a voltage or the like to the development roller 41, thereby improving the performance required of the supply roller 43. The supply roller 43 may be configured to scrape residual toner from the development roller 41 and resupply the toner. The configuration of a supply roller according to one embodiment of the present invention is described in detail below.

[0035] <Shaft> The shaft 52 functions as a support member for the supply roller 43 and as an electrode. The shaft 52 is made of a conductive material such as a metal or alloy such as aluminum, copper alloy, or stainless steel; iron plated with chromium or nickel; or a conductive synthetic resin. The shaft 52 has a solid cylindrical or hollow cylindrical shape.

[0036] <Sponge layer> The sponge layer 51 (foam layer) contains a cross-linked urethane resin, which will be described later. The sponge layer 51 preferably has voids capable of storing toner particles within the layer so that it can uniformly supply toner particles to the surface of the developing roller 41 as the supply roller 43. Examples of the voids include numerous through-holes and non-through-holes. Another example of the voids is a porous layer with interconnected bubbles (open cells). When the voids are bubbles, the size of each bubble (cell) is expressed as the cell diameter. The sponge layer 51 containing the cross-linked urethane resin preferably has large open-cell voids. The characteristics of the sponge layer 51 with such voids, such as the average cell diameter, number of cells, air permeability, and overall layer density, are important. The physical properties of the sponge layer 51 are not particularly limited, but preferably have values ​​within the following ranges: Average surface cell diameter: 100 μm or more and 500 μm or less; Number of cells: 50 to 450 cells / inch; Airflow rate: 0.5L / min or more and 4.5L / min or less; Density: 0.05g / cm 3 More than 0.45g / cm 3 below The lower limit of the ventilation rate is the lowest value at which toner that has entered the cell can be easily expelled from the cell, and the upper limit is the maximum value at which appropriate toner can be supplied to the developing roller 41 and residual toner on the developing roller 41 can be properly scraped off.

[0037] The airflow rate can be measured using the following measurement method. As shown in FIG. 4(b), a measurement tool is prepared. The tool includes a pair of 1-cm-diameter through-holes 161a and 161b, symmetrically positioned about the center axis, on the sliding surface of a cylinder 162 having an inner diameter smaller than the outer diameter of the conductive layer, e.g., 1 mm smaller. The supply roller 43 is inserted into the measurement tool, and the conductive layer not covered by the cylinder 162 is sealed with a sealant. One through-hole 161b of the cylinder 162 is connected to a suction pump 166 equipped with a pressure gauge 164 and a flow meter 165. The other through-hole 161a of the cylinder 162 is placed under atmospheric pressure (101.3 kPa), and the suction pump 166 is driven to reduce the pressure to 125 Pa. The flow rate measured by the flow meter 165 at this time can be used as the airflow rate. This measurement can be performed not only at the center of the supply roller 43 in the longitudinal direction, but also over the entire longitudinal area.

[0038] The method for adjusting the air permeability is not particularly limited, and can be adjusted by a conventionally known method. For example, when adjusting the air permeability using a foamed elastic layer formed from a raw material composition containing polyol, polyisocyanate, blowing agent, catalyst, and foam stabilizer, a highly open cell structure can be obtained by adding a foam stabilizer that has a strong effect of opening up the cells (gas bubbles) formed in the surface layer. For example, commercially available products such as "L-3415" (trade name, manufactured by Momentive Performance Materials Japan, LLC) and "F-606" (trade name, manufactured by Shin-Etsu Chemical Co., Ltd.) are preferably used.

[0039] Of course, the breathability of the sponge layer can also be adjusted by components other than the foam stabilizer mentioned above. For example, the amount of foaming agent added and the type and amount of catalyst added can be used to adjust the breathability by controlling the foaming and curing reactions. To increase the breathability, the curing reaction can be suppressed and the foaming reaction promoted. In addition to adjusting the material components, the breathability can also be adjusted by a method in which a roller is rotated while applying a load stress to the sponge layer, or by a manufacturing method in which high-pressure air is blown onto the sponge layer to break the membrane that forms the cell skeleton near the surface, thereby forming interconnected cells with excellent breathability.

[0040] (Method of manufacturing the supply roller) The supply roller 43 of this embodiment is molded, for example, by the following manufacturing method. A roller molding die is prepared by holding an iron cylindrical member (16.5 mm inner diameter, 260 mm long) with a release agent applied to its inner surface and a stainless steel core (5 mm outer diameter, 270 mm long) between an upper bridge member and a lower bridge member. The lower bridge member has an injection hole for injecting the foaming material into the roller molding die. A blend of premixed polyol and polyisocyanate is placed in the tank of a casting machine and stirred and mixed in the casting machine. The polyurethane foam material that will form the inner layer of the foamed elastic layer is then placed in the foaming material receiving section. Using the same procedure, the polyurethane foam material that will form the surface layer of the foamed elastic layer is then placed in the foaming material receiving section, and two types of polyurethane foam material are separated into upper and lower sections within the foaming material receiving section. The polyurethane foam material for the surface layer is prepared to foam first, while the polyurethane foam material for the inner layer is prepared to foam subsequently. The foaming material receiving section is then attached to the lower bridge member, and the roller molding die is heated to promote foaming. The foam material is cured in the mold to produce a foam elastic roller.

[0041] (Poor solid tracking) As explained in FIG. 3, toner T is transported by agitation sheet 45b and guided through development opening 46c into development chamber 46a. The supply voltage applied by supply voltage application unit 49a causes toner T to be absorbed into supply roller 43 (in sponge layer 51 thereof). The amount of toner absorbed into supply roller 43 at this time is referred to as the "absorbed amount." If the absorbed amount is small, in a solid black image, the density meets the standard for one revolution of developing roller 41, but the density thereafter does not meet the standard and becomes lighter, resulting in an image defect known as poor solid tracking. Hereinafter, in a solid black image, one revolution of developing roller 41 (the leading edge of the image or recording material in the rotation direction) is referred to as the "white trailing edge." Furthermore, the area after the white trailing edge (the trailing edge of the image or recording material) is referred to as the "black trailing edge."

[0042] There is a sufficient amount of toner on one rotation of the developing roller 41, and sufficient density can be achieved only at the leading edge of the recording material P. However, after the first rotation of the developing roller 41, the density depends on the amount of toner supplied from the supply roller 43, so if the amount is small, sufficient density cannot be achieved.

[0043] The amount of toner content depends on the charging characteristics and fluidity of the toner during image formation. Therefore, there are two ways to increase the amount of toner content: either increasing the absolute value of the supply voltage even more than the absolute value of the development voltage, or improving the fluidity of the toner in the developing chamber 46a. The former, if performed continuously, can cause deterioration of the electrical conductivity of the supply roller 43 and reduce durability, so it is not a good solution. As for the latter, toner fluidity depends in part on the specific gravity and cohesion of the toner itself, but is also greatly influenced by the posture of the process cartridge 120 and the circulation within the developing chamber 46a, so it can be improved depending on the configuration.

[0044] The developing device 4 shown in FIG. 3 is in a position where the toner storage chamber 46b is disposed above the developing chamber 46a (a so-called gravity system). In the vertical direction Dr, the developing opening 46c is located below the agitation shaft 45a, and the center (rotation axis) of the supply roller 43 is located below the developing opening 46c. In this system, when the image forming apparatus 100 starts to operate, the toner T transferred to the developing chamber 46a by the agitation sheet 45b does not return to the toner storage chamber 46b, but remains in the direction of gravity (the vertical direction Dr), i.e., in the developing chamber 46a, even when the agitation sheet 45b stops operating. In this situation, if the agitation sheet 45b continues to rotate, the toner T in the developing chamber 46a is pushed in by its own weight, causing a clogging of the toner T and hindering toner circulation. At this time, the toner T collides with the wall of the developing device 4 and gathers, being pushed toward the center. Then, the toner T collected from both wall surfaces passes through the developing opening 46c, and a large powder pressure of the toner T is applied to the midpoint of the supply roller 43.

[0045] In this state, the supply roller 43 cannot adequately contain toner T, resulting in a low toner content. Furthermore, even after toner T is expelled onto the developing roller 41 due to the potential difference between the supply voltage and the developing voltage, the next toner T to be supplied is not properly supplied to the supply roller 43. This phenomenon occurs more easily after black printing than after white printing, and the amount of toner that is contained is more likely to be low. This causes poor solid image tracking. For this reason, in a solid black image where all the toner on the developing roller 41 needs to be expelled onto the photosensitive drum 1, the gravity-based developing device 4 exhibits particularly noticeable poor solid image tracking in the longitudinal center of the black image.

[0046] To solve this problem, other than adjusting the toner itself, one method for improving fluidity is to increase the amount of toner contained inside the supply roller 43 by increasing the amount of airflow through the supply roller 43. FIG. 5(a) is a graph showing the amount of airflow [L / min] through the supply roller 43 of this embodiment on the horizontal axis and the amount of toner contained in the black backing [g] on the vertical axis. As shown in the graph of FIG. 5(a), it can be seen that there is a correlation between the amount of airflow through the supply roller 43 for the black backing and the amount of toner contained. Specifically, the amount of toner contained increases as the amount of airflow increases. In this embodiment, poor solid printing performance occurs unless the amount of toner T contained in the supply roller 43 is 7g or more.

[0047] (Disadvantages of increasing ventilation and solutions) Next, we will discuss the issues associated with increasing the ventilation rate of the supply roller 43. Increasing the ventilation rate strengthens the foaming of the sponge, which tends to suppress the cross-linking structure of the sponge, making the supply roller 43 itself softer and more susceptible to deformation. If the process cartridge 120 is transported in a high-temperature, high-humidity environment or left standing for a long period of time with the ventilation rate increased, the supply roller 43 may be severely deformed permanently at the contact point between the supply roller 43 and the developing roller 41 due to the rigidity of the developing roller 41. A deformed supply roller 43 may cause image defects such as horizontal bands called supply roller sets in halftone images and solid black images. The contact pressure between the supply roller 43 and the developing roller 41 is stronger at the longitudinal ends where the fixed ends are located than at the longitudinal center, making the supply roller 43 particularly susceptible to deformation.

[0048] In FIG. 5(b), the horizontal axis shows the airflow rate [L / min] of the supply roller 43 of this embodiment, and the vertical axis shows the deformation [mm] of the supply roller 43 after being left in a harsh environment. Note that the harsh environment is the high-temperature, high-humidity environment described above. The graph in FIG. 5(b) shows the relationship between the airflow rate and deformation of the supply roller 43 after the supply roller 43 was left in a high-temperature, high-humidity environment with a temperature of 50°C and a humidity of 60% for three days. As shown in FIG. 5(b), the deformation rate increases as the airflow rate increases. In this embodiment, when the deformation rate exceeds 0.2 mm, horizontal bands become visible, causing image degradation (NG level).

[0049] Therefore, in this embodiment, both the poor solid image tracking problem, which can be solved by increasing the airflow rate, and the supply roller set problem, which occurs when the airflow rate is increased, are solved in the following way: that is, the poor solid image tracking problem is suppressed while the supply roller set problem is prevented. That is, in this embodiment, these image defects are solved by changing the airflow rate between the longitudinal ends and the central portion of the supply roller 43. As explained above, the poor solid image tracking problem occurs in the longitudinal central portion of the supply roller 43, while the supply roller set problem occurs at the ends. Therefore, by increasing the airflow rate in the longitudinal central portion of the supply roller 43 to a level where the poor solid image tracking problem does not occur, and by decreasing the airflow rate at both ends to a level where the supply roller set problem does not occur, both of these problems are solved.

[0050] (Method of changing the ventilation volume in the longitudinal direction) (Method 1) Two examples of methods for changing the air permeability between the center and both ends in the longitudinal direction of the supply roller 43 will be described below. The first is a pattern in which sponge layers 51 with different air permeabilities are joined as shown in FIG. 6. FIG. 6 shows method 1 for changing the air permeability in the longitudinal direction in this embodiment. As shown in FIG. 6(a), first, sponge rollers with two different air permeabilities, air permeability A and air permeability B, are made. Note that air permeability A is lower than air permeability B (A <B)。

[0051] As shown in Figure 6(b), in supply roller 43, a primer adhesive is applied to the rod-shaped core (shaft 52), and a sponge roller with high air permeability B and a sponge roller with low air permeability A are inserted. Hereinafter, the sponge roller with air permeability B will be referred to as sponge roller 51B, and the sponge roller with air permeability A will be referred to as sponge roller 51A. Sponge roller 51B is placed in the center in the longitudinal direction of the rod-shaped core, and sponge rollers 51A are placed at both ends of sponge roller 51B, i.e., at both ends in the longitudinal direction.

[0052] As shown in Fig. 6(c), sponge rollers 51A and 51B are closely spaced and bonded together in the longitudinal direction (the dashed line α portion). In this way, by using the method shown in Fig. 6, supply roller 43 with different ventilation amounts in the longitudinal direction can be produced.

[0053] (Method 2) The other method, Method 2, involves subjecting the completed sponge roller to a crushing process, gradually changing the airflow rate along its length. Figure 7 shows Method 2 for changing the airflow rate along its length. Figure 7 is a schematic diagram of the crushing section of the crushing device used in the crushing process. The crushing process is as follows: The sponge roller is sandwiched between two metal drums 1000 and 1001, and while pressure is applied to the foamed sponge layer, air is blown onto the sponge surface using an air nozzle 90. This breaks the surface cells of the sponge roller and opens the cells to the interior of the sponge. The crushing process is performed to stabilize the hardness and airflow rate of the supply roller 43, which are its performance characteristics. An air nozzle 90 with a diameter of 1 / 10 to 1 / 4 of the diameter of the supply roller 43 is positioned 5 to 30 mm from the surface of the supply roller 43. While the air nozzle 90 is moved in the axial direction Da of the supply roller 43, which is rotating at a speed of 1 rpm to 300 rpm, high-pressure air of 0.2 MPa to 1.0 MPa is sprayed from a direction approximately perpendicular to the surface of the supply roller 43.

[0054] At this time, the degree of cell interconnectivity in the longitudinal direction can be changed by varying the speed at which the air nozzle 90 is applied and the rotation speed of the supply roller 43 itself depending on the position in the longitudinal direction. For example, if the rotation speed of the supply roller 43 is increased to 300 rpm while keeping the longitudinal movement speed of the air nozzle 90 constant, the amount of air entering the supply roller 43 is reduced, making it difficult to increase the amount of ventilation. On the other hand, if the rotation speed of the supply roller 43 is decreased to 1 rpm, sufficient air enters the supply roller 43, making it easier to increase the amount of ventilation. Conversely, the amount of ventilation can also be controlled by keeping the rotation speed of the supply roller 43 at 100 rpm and slowing the longitudinal movement speed of the air nozzle 90 only at the center compared to the ends. During this crushing process, the amount of ventilation through the supply roller 43 can be continuously changed in the longitudinal direction.

[0055] (Area of ​​change in ventilation volume in the longitudinal direction) Consider the airflow rate of the supply roller 43 that will solve both the problems of poor solid tracking and supply roller set. To prevent poor solid tracking in this embodiment, the load inside the supply roller 43 must be 7.0 g or more, and the airflow rate at this time must be 2.5 L / min or more, as described in FIG. 5(a). To prevent supply roller set in this embodiment, the deformation must be 0.2 mm or less, and the airflow rate at this time must be 2.0 L / min or less, as described in FIG. 5(b).

[0056] The minimum airflow rate required for the supply roller 43 to suck in and expel toner is 0.5 L / min or more and less than 4.5 L / min. Therefore, the airflow rate in the center is preferably 2.5 L / min or more and less than 4.5 L / min to prevent poor solid printing performance, and the airflow rate at both ends is preferably 0.5 L / min or more and less than 2.0 L / min to prevent supply roller set. Furthermore, the ratio of the airflow rate in the center to the airflow rate at both ends is preferably 1.25 or more and less than 9.0. If the airflow rate in the center in the longitudinal direction is 4.5 L / min or more, supply roller set becomes an issue even in the center. Furthermore, if the airflow rate at the longitudinal ends is less than 0.5 L / min, the supply roller 43 will not be able to absorb enough toner, and the supply roller 43 will not function as intended.

[0057] The position for measuring the air permeability was the midpoint in the longitudinal direction in the center, and at both ends, it was measured at a position 1 / 10 of the way from both ends toward the midpoint in the longitudinal direction. The air permeability measured at each position should be within the above range.

[0058] <Toner edge scattering> By controlling the airflow rate in the longitudinal direction of the supply roller 43, it is possible to suppress both image defects, such as poor toner tracking that occurs significantly in the center of the image, and supply roller set defects that occur significantly at the edges. However, as the supply roller 43 continues to be used, toner circulation in the developing chamber 46a deteriorates, accelerating toner degradation, particularly in the image edge regions and in the range where the airflow rate of the supply roller 43 has been set low and supply roller set defects have been suppressed.

[0059] FIG. 8 is a schematic diagram illustrating the longitudinal end of the developing blade 42, illustrating toner edge scattering. In the end region where toner degradation has accelerated, toner is sandwiched in the toner regulating section at the contact point between the developing roller 41 and the developing blade 42. Due to friction with the developing roller 41 and heat, the toner melts and fuses to the surface of the developing blade 42. Here, the area on the surface of the developing blade 42 where toner fusion occurs is referred to as fused portion A. When toner fusion begins to occur on the surface of the developing blade 42, toner supplied from the supply roller 43 to the developing roller 41 gradually accumulates in fused portion A and fuses in the same manner, causing the fused toner to grow. When the height of the fused material at fused portion A reaches approximately 100 to 150 μm or more, a gap is formed between the developing blade 42 and the developing roller 41, and toner is blown out in the direction of arrow B (see also the dashed arrow B in FIG. 1). Furthermore, the formation of fused material on the developing blade 42 makes it impossible to form a uniform toner coat on the developing roller 41 in the longitudinal direction, resulting in uneven thickness of the toner coat on the developing roller 41. As a result, centrifugal force caused by the rotation of the developing roller 41 causes toner to peel off from the toner coat and scatter in areas on the developing roller 41 where the thickness has become thicker than the appropriate thickness. That is, toner leaks out from the gap between the developing roller 41 and the developing blade 42 and scatters, and toner peels off from the developing roller 41 and scatters due to the fused material on the developing blade 42. Note that although arrow B is shown in one direction in FIGS. 1 and 8, toner does not actually scatter in only one direction.

[0060] The toner blown out in the direction of arrow B scatters as the developing roller 41 rotates, so that each time an image forming operation is performed and recording material P is transported, toner scattering occurs on the developing blade 42 and near the end of the developing container. If the recording material P continues to be transported further, the toner scattering will progress inside the device main body 110, and there is a risk that the inside of the device main body 110 and the recording material P being transported will become soiled.

[0061] <Control flow for suppressing toner scattering> 9 shows a flowchart of the control for suppressing toner scattering in the first embodiment. Using this flowchart, the control for suppressing toner fusion to the surface of the developing blade 42 will be described. In step (hereinafter referred to as S) 101, the control unit 200 starts image formation upon receiving a print start signal. In addition to the print start signal, the control unit 200 also receives various information for printing, such as the number of prints.

[0062] In S102, the control unit 200 determines whether or not a continuous printing operation is being performed based on the information on the number of prints. If the control unit 200 determines in S102 that continuous printing is being performed, the process proceeds to S103. In S103, the control unit 200 executes a sheet interval sequence to discharge toner at the longitudinal end (development end) of the developing roller 41. Here, the sheet interval refers to the interval in continuous printing between the rear end of the recording material P (preceding sheet) (or toner image) on which an image is formed and the front end of the recording material P (subsequent sheet) (or toner image) on which an image is formed following the preceding sheet.

[0063] The control unit 200 irradiates the photosensitive drum 1 with laser light L from the exposure device 3 only in the areas corresponding to both ends of the developing roller 41 between sheets, and sets the potential on the photosensitive drum 1 to a dark potential (VL). The control unit 200 develops the areas on the photosensitive drum 1 irradiated with the laser light (VL areas) with toner supplied from the developing roller 41. This operation is called toner discharge at the development end. Even if toner discharge at the development end is performed, it is performed between sheets, so there is no or only a small effect on the image formed on the recording material P.

[0064] In S104, the control unit 200 determines whether the printing operation has ended, and if it determines that the predetermined printing operation has not ended, the process returns to S103, and toner is discharged from the development edge between sheets during continuous printing. If the control unit 200 determines in S104 that the printing operation has ended, the process proceeds to S105.

[0065] In S105, the control unit 200 executes a post-rotation sequence, discharges toner from the development edge in the same manner as in S103, and then terminates the process. If the control unit 200 determines in S102 that continuous printing is not being performed, it advances the process to S105. The post-rotation sequence refers to operations performed after the image forming operation is completed, such as stopping the application of high voltage, ending temperature control of the fixing device, and separating the development roller 41 from the photosensitive drum 1. Even if toner discharge from the development edge is performed, it is performed after the printing operation is completed, so there is little or no impact on the image formed on the recording material P. After toner discharge from the development edge is performed, the development roller 41 and the photosensitive drum 1 are separated. In the first embodiment, toner discharge from the development edge is performed in the paper interval sequence and the post-rotation sequence for each printing operation. Details and effects of this sequence will be described in the following examples.

[0066] <Evaluation experiment> The details of the experiment conducted to demonstrate the effect of Example 1 will be described. The supply roller 43 used in the example, which has different air permeability between the center and the ends, is shown in Table 1 below. This is attached to a cartridge as shown in Figure 3 to create a process cartridge 120. After that, a specific gravity of 1.45 g / cm 3 The toner was filled with 460 g, and durability evaluation of toner scattering was carried out in a low-temperature, low-humidity environment (temperature 15°C, humidity 10%). The process speed was set to 280 mm / sec, and recording material P on which a horizontal line image with a print rate of 2% was formed was continuously conveyed, and the evaluation was carried out until 30,000 sheets were printed.

[0067] After every 10,000 sheets, the stains on the edge of the printing material P and the process cartridge 120 were removed, and the state of toner scattering inside the developing device 4 and the apparatus main body 110 was checked and evaluated. The edge of the printing material P is the edge in the direction perpendicular to the conveying direction (also the main scanning direction), which corresponds to the edge in the longitudinal direction of the developing roller 41.

[0068] During the sheet interval sequence and post-rotation sequence, the area and width of the toner developed on the photosensitive drum 1 were determined to be the area at both ends of the supply roller 43 where the airflow rate was 1.8 L / min. The width refers to the length of the supply roller 43 in the longitudinal direction. A solid black image was developed on the photosensitive drum 1, covering one revolution of the developing roller 41, with a width of 30 mm from both ends of the supply roller 43. The photosensitive drum 1 was also exposed to the edge mask area of ​​the exposure device 3, i.e., the area that can be exposed in the main scanning direction, and the toner was developed. During normal image formation, the edge mask area of ​​the exposure device 3 is specified from the perspective of the laser light writing position in the main scanning direction and the stability of the light amount. However, the sheet interval sequence and post-rotation sequence are performed during non-image formation, when no image is formed on the recording material P. Therefore, the purpose of the sequence is to develop and discharge toner to the edge areas of the developing chamber 46a, given the condition that printing is performed during non-image formation. Therefore, considerations that are required during normal image formation do not need to be taken into account during non-image formation.

[0069] [Table 1] Table 1 shows the central air permeability [L / min] (3.5) and end air permeability [L / min] (1.8) of the supply roller 43 in this example.

[0070] Toner scattering was evaluated by ranking the toner into A to C based on whether it scattered into the process cartridge 120 and the developing container, whether it contaminated the inside of the image forming apparatus 100 body, and whether it stained the evaluation paper that was passed through. A: Not visible to the naked eye, no toner scattering B: Slight visible to the naked eye, slight scattering of toner onto the process cartridge and developing container C: Visible toner contamination inside the image forming device and toner stains on the evaluation paper

[0071] The image quality for each example after printing is summarized in Table 2 below. As a comparative example, a process cartridge and developing device were created under the same conditions, and an evaluation experiment was conducted under the same conditions with a configuration that did not perform the toner scattering suppression process (toner discharge from the development end) (hereinafter referred to as the toner development sequence) as shown in Figure 9.

[0072] [Table 2]

[0073] Regarding the results in Table 2, in the case of the comparative example, there was no toner scattering up to 10,000 sheets, and the test was classified as Level A. However, at 20,000 sheets, toner scattering into the developing container was confirmed, and the test was classified as Level B. At 30,000 sheets, toner contamination inside the image forming device and toner stains on the evaluation paper were confirmed, and the test was classified as Level C.

[0074] On the other hand, in Example 1, the toner development sequence was performed in the end region of the supply roller 43 for each paper passing operation, so toner scattering was suppressed for all numbers of sheets, resulting in Level A. This is the effect of forcibly developing (discharging) deteriorated toner in the end region of the developing chamber 46a by performing the toner development sequence for each image forming operation. By appropriately developing the deteriorated toner on the photosensitive drum 1, toner is suppressed from fusing to the surface of the developing blade 42.

[0075] In the first embodiment, the developing device 4 and the photosensitive drum 1 are in contact only during image formation driven by a motor, and toner is developed on the photosensitive drum 1. However, this is not limited to this. It is also effective in a configuration in which the developing device 4 and the photosensitive drum 1 are in constant contact. In particular, in a configuration in which the developing device 4 is in constant contact with the photosensitive drum 1, the contact-separation operation that occurs for each print job in the developing device-separation configuration does not occur. As a result, the toner in the developing chamber 46a is not loosened by the contact-separation operation or vibration of the developer container, which leads to uneven distribution and poor circulation of toner between the developing chamber 46a and the toner storage chamber 46b, and toner deterioration tends to be accelerated. The first embodiment is also effective in a configuration other than the developing device-separation configuration.

[0076] As described above, according to the first embodiment, it is possible to suppress toner fusion to the developing blade and toner scattering into the main body of the image forming apparatus. [Example]

[0077] In Example 1, toner was continuously supplied (developed) to the longitudinal end regions during the sheet interval sequence and post-rotation sequence in a print job. This resulted in toner that would otherwise accumulate and fuse at the fused portion A between the developing blade 42 and the developing roller 41 being expelled onto the photosensitive drum 1, thereby preventing toner from fusing to the developing blade 42. Supplying toner during the sheet interval and post-rotation sequence for each job may increase the amount of toner that does not contribute to image formation. Therefore, in Example 2, the toner development sequence is executed at a timing corresponding to the number of rotations of the developing roller 41 and the number of prints, thereby preventing an increase in the amount of toner that does not contribute to image formation.

[0078] <Control of Example 2> FIG. 10 shows a flowchart of the control for suppressing toner scattering in the second embodiment. This flowchart will be used to explain the control for suppressing toner fusion to the surface of the developing blade 42. Explanations that overlap with those in the first embodiment will be omitted. In the following explanation, the toner development sequence in the second embodiment will also be referred to as a periodic sequence. It is also assumed that the control unit 200 has a counter and manages the number of prints by using the counter.

[0079] In S201, the control unit 200 receives a print start signal and starts image formation. In S202, the control unit 200 references a counter and determines whether the total number of prints after the previous periodic sequence is equal to or greater than X. Here, X as the predetermined number is a threshold value for determining whether or not to execute a periodic sequence, and will be described later. If the control unit 200 determines in S202 that the number of prints is equal to or greater than X, it proceeds to S203.

[0080] In S203, the control unit 200 executes a periodic sequence to discharge toner from the longitudinal ends (development ends). Note that the periodic sequence of Example 2 is performed in the longitudinal end regions of the supply roller 43 executed in Example 1, where the airflow rate is 1.8 L / min, and a solid black image is developed on the photosensitive drum 1 for three revolutions of the development roller 41 in a width of 30 mm from both ends of the supply roller 43.

[0081] In S204, the control unit 200 initializes a counter that counts the number of prints to 0 so that the counter can be used to determine whether or not to execute the next periodic sequence. The counter value is realized by writing information to the RAM 203 of the image forming apparatus 100 or the nonvolatile memory 127 attached to the process cartridge 120 and the developing device 4.

[0082] In S205, the control unit 200 determines whether the printing operation has ended, and if it determines that the printing operation has ended, it ends the print job in S206 and ends the process. If the control unit 200 determines in S205 that the printing operation has not ended, it returns the process to S202 and continues the image forming operation. If the control unit 200 determines in S202 that the number of prints since the previous regular sequence is less than X, it advances the process to S205. In this case, the regular sequence is not executed.

[0083] <Evaluation experiment> Details and effects will be described in the following examples. The contents of the experiments conducted to demonstrate the effects of Example 2 will be explained. The conditions, criteria, comparative examples, etc. of the evaluation experiments overlap with those of Example 1, so explanations will be omitted.

[0084] In Example 2, evaluation experiments were conducted after setting several conditions for the threshold value of X sheets used in the determination in S202 of Fig. 10. Example 2-1 was an example in which the threshold value for conveying A4 portrait was X=50 sheets, and Example 2-2 was an example in which X=100 sheets. Table 3 below summarizes the image levels for each example after printing.

[0085] [Table 3] Table 3 shows the evaluation results for print counts of 10,000 sheets (second column), 20,000 sheets (third column), and 30,000 sheets (fourth column).

[0086] The results of Table 3 will now be explained. The comparative example is not explained here because the conditions and evaluation results were the same as those of Example 1. In Example 2-1, when the threshold value X was 50 sheets, the regular sequence was performed frequently and toner discharge control was implemented, so toner scattering was suppressed even when up to 30,000 sheets were printed. In Example 2-2, when the threshold value X was 100 sheets, toner scattering did not occur up to 20,000 sheets, and even when up to 30,000 sheets were printed, Level B required for the image forming apparatus 100 was satisfied. Therefore, under the conditions of Example 2, it is desirable to set the threshold value X to 100 sheets or less (X≦100). Furthermore, because the inter-sheet / post-rotation sequence is not performed for each print job, an increase in the amount of toner used that does not contribute to image formation can be suppressed.

[0087] In the second embodiment, the toner development sequence is periodically executed according to the number of printed sheets in portrait orientation on A4 paper, but the conditions for executing the toner development sequence are not limited to this. For example, the number of rotations of the development roller 41 may be managed by RAM 203 or the like in the image forming apparatus 100, and a threshold value (predetermined number of rotations) for that number of rotations may be set to periodically execute the development sequence. This is because it is known that the toner is rubbed against the rotating members when the development device 4 including the development roller 41 and the supply roller 43 is driven, accelerating toner deterioration.

[0088] As described above, according to the second embodiment, it is possible to suppress toner fusion to the developing blade and toner scattering into the main body of the image forming apparatus. [Example]

[0089] In the second embodiment, the toner development sequence is periodically executed in accordance with the number of prints and the number of rotations of the developing roller 41, thereby suppressing not only the phenomenon of toner scattering but also the increase in the amount of toner that does not contribute to image formation. Here, when the toner development sequence is periodically executed in accordance with the number of prints and the number of rotations of the developing roller 41, an interrupt is inserted once during image formation, stopping the image formation operation and executing the toner development sequence. For example, in a job with a large number of continuous prints, the number of times the periodic sequence is executed increases, which may increase the waiting time for printing. Therefore, in the third embodiment, the toner development sequence is periodically executed in accordance with the printing coverage rate, thereby suppressing the increase in waiting time.

[0090] <Control of Example 3> Fig. 11 shows a flowchart for suppressing toner scattering in the third embodiment. This flowchart will be used to explain the control for suppressing toner fusion to the surface of the developing blade 42. Explanations will be omitted if they overlap with those in the first and second embodiments. Furthermore, the processes of S301 and S303 to S306 in Fig. 11 are the same as the processes of S201 and S202 to S205 in Fig. 10, and therefore explanations will be omitted.

[0091] In S302, the control unit 200 determines whether the average print rate stored in the RAM 203 and / or nonvolatile memory 207 is Y% or less. Here, Y% is a threshold value for determining whether to execute a periodic sequence, and is, for example, 4%. If the control unit 200 determines in S302 that the average print rate is greater than Y% in terms of A4 paper, it advances the process to S307 without executing the periodic sequence. If the control unit 200 determines in S302 that the average print rate is Y% or less, it advances the process to S303, and executes the periodic sequence according to the number of prints from S303 onwards. In S306, the control unit 200 rewrites (stores) the information in the RAM 203 and / or nonvolatile memory 207 with information at the end of the print operation, ends the print job, and ends the process. Note that if the answer is No in S303, the control unit 200 advances to S307, and if the answer is No in S306, it returns to S302.

[0092] The control unit 200 measures the emission count of the laser light from the exposure device 3 and can detect the amount of toner used in printing (hereinafter referred to as toner consumption) based on the measured emission count. For example, the control unit 200 (CPU 201) can use a system for detecting toner consumption by counting the number of dots. The control unit 200 counts the number of dots in an image formed on the photosensitive drum 1 (hereinafter referred to as the number of image dots) and estimates the amount of toner consumed Xg in the developer container. The control unit 200 estimates the amount of toner consumed Xg used in printing by converting the number of image dots into a value corresponding to the amount of toner. To do this, the control unit 200 needs to know the amount of toner consumed per dot in advance. In the third embodiment, the amount of toner consumed Xo per dot, obtained in advance through an experiment or the like, is stored in the non-volatile memory 207 of the process cartridge 120. The amount of toner consumed Xo per dot is, for example, 10 ng (Xo = 10 ng).

[0093] <Evaluation experiment> Details and effects will be described in the following examples. The contents of the experiments conducted to demonstrate the effects of Example 3 will be explained. The conditions, criteria, comparative examples, etc. of the evaluation experiments overlap with those of Examples 1 and 2, so explanations will be omitted.

[0094] In Example 3, evaluation experiments were conducted under several conditions for the average print rate shown in S302 of Fig. 11. When printing in A4 paper equivalent values, Example 3-1 was set with an average print rate of 2%, Example 3-2 was set with an average print rate of 5%, and Example 3-3 was set with an average print rate of 10%.

[0095] Table 4 below summarizes the image levels for each example after printing. [Table 4] Table 4 shows the evaluation results for print counts of 10,000 sheets (second column), 20,000 sheets (third column), and 30,000 sheets (fourth column).

[0096] Regarding the results in Table 4, in Example 3-1, the average print rate was 2%, which was below the threshold Y% (=4%) as the predetermined print rate, and the threshold for implementing the periodic sequence was also set to the same value (X=50 sheets) as in Example 2-1. As a result, the frequency of the periodic toner development sequence was high, and toner discharge control was implemented, thereby successfully suppressing toner scattering. In Example 3-2, the average print rate was 5%, which, based on the judgment in S302 of the flowchart in FIG. 11, was greater than the threshold Y%, and this was the condition under which the periodic toner development sequence was not implemented. Toner scattering reached Level B when printing 20,000 and 30,000 sheets, meeting the level required for the image forming apparatus 100.

[0097] In Example 3-3, the average print rate was 10% and the periodic sequence was not executed, but it was confirmed that the print quality was level A up to 20,000 sheets. When the average print rate was 10%, the time to replenish the toner was reached at 25,000 sheets, so the evaluation was terminated. However, at 25,000 sheets, the print quality was level B, satisfying the level required for the image forming apparatus 100.

[0098] Therefore, under the conditions of Example 3, it is desirable to set the print rate threshold for the periodic toner development sequence to 4%. Also, because the periodic toner development sequence is not performed according to the print job count, it was confirmed that, for example, for users who often print with an average print rate of 5% or more, it is possible to suppress an increase in standby time.

[0099] In Example 3, a periodic toner development sequence was performed according to the average print rate (A4 portrait equivalent). The threshold Y% in S302 of FIG. 11 can be set as follows: The higher the average print rate, the greater the amount of toner consumed per A4 sheet of paper, and the greater the toner consumption, the shorter the time until the end of the life of the developing device 4. It is known that toner degradation is accelerated by the operation of the developing device 4, including the developing roller 41 and the supply roller 43. Because toner is consumed before toner degradation accelerates, the higher the average print rate, the less likely it is that toner will fuse to the surface of the developing blade 42 and cause toner scattering. Based on this, experiments and the like are conducted in advance, and the threshold Y% is set to, for example, 4%.

[0100] As described above, according to the third embodiment, it is possible to suppress toner fusion to the developing blade and toner scattering into the main body of the image forming apparatus. [Example]

[0101] In the third embodiment, by periodically executing the toner development sequence according to the average printing rate of the image, it was possible to reduce not only the phenomenon of toner scattering but also interruptions during continuous printing and reduce the user's waiting time. Here, when the toner development sequence is executed for paper (hereinafter referred to as small size paper (second size recording material)) that is narrower than A4 paper (first size recording material) as the specified recording material, the difference in the development area in the longitudinal direction of the small size paper and the development area of ​​A4 paper makes it impossible to respond to the level of accelerated toner deterioration, and toner scattering may occur.

[0102] In particular, in jobs involving a large number of continuous prints of small-size paper, toner in the longitudinal edge regions is not consumed during image formation, but instead is repeatedly rubbed against the developing roller 41, accelerating toner degradation more than in a normal printing mode. This is because, when printing on small-size paper, the longitudinal area of ​​the paper being conveyed is shorter than that of A4 paper, resulting in a greater thermal impact from the fixing device 10 and a severe temperature rise in the image forming apparatus 100. To address this, the control unit 200 controls conveyance so as to lengthen the paper gap and reduce throughput even during the image formation sequence. As a result, images are not formed, particularly at the longitudinal edge regions, and the developing device 4 continues to rotate without toner being consumed, accelerating toner degradation. Therefore, in the fourth embodiment, the conditions of the toner development sequence are changed depending on the size of the recording material P to be printed and the print mode. The print mode includes a normal paper feed mode as a first mode in which the recording material P is conveyed at a normal conveyance speed (first speed) and a small-size paper feed mode as a second mode in which the recording material P is conveyed at a reduced throughput (second speed) as described above. This makes it possible to prevent toner scattering even when printing on small size paper.

[0103] <Control of Example 4> Fig. 12 shows a flowchart for suppressing toner scattering in the fourth embodiment. This flowchart will be used to explain the control for suppressing toner fusion to the surface of the developing blade 42. Explanations will be omitted if they overlap with those of the first to third embodiments. Furthermore, S401 and S405 in Fig. 12 are the same as the processes of S201 and S205 in Fig. 10, and S406 is the same as the process of S307 in Fig. 11, so explanations will be omitted.

[0104] In S402, the control unit 200 determines whether the size of the recording material P on which the image is formed is A4 paper. If the control unit 200 determines in S402 that the size of the recording material P on which the image is formed is A4 paper, it determines that the normal paper passing mode is in effect and proceeds to S407. In S407, the control unit 200 performs the toner development sequence described in, for example, embodiment 1 (FIG. 8), embodiment 2 (FIG. 9), or embodiment 3 (FIG. 10), and ends the process.

[0105] If the control unit 200 determines in S402 that the size of the recording material P on which the image is formed is shorter in the longitudinal direction than A4 paper (small size paper), the process proceeds to S403. In S403, the control unit 200 determines that the mode is small size paper passing mode, and executes a small size toner development sequence, discharging toner in the non-image printing area. The small size toner development sequence will be described later. In S404, the control unit 200 counts the number of times the small size toner development sequence has been executed, and stores the count in the RAM 203 and / or non-volatile memory 127. Note that if the answer is No in S405, the process returns to S402.

[0106] The small size toner development sequence in S403 is a sequence in which a solid black image for two revolutions of the developing roller 41 is developed on the photosensitive drum 1 in the non-image printing area of ​​the recording material P to be printed during the paper interval sequence and post-rotation sequence. For example, if the size of the recording material P to be printed is A5 paper portrait, the non-image printing area is set to a width of 50 mm (>30 mm) from both ends of the supply roller 43. This is because, in addition to the amount of ventilation in the end areas of the supply roller 43, executing the small size paper passing mode creates areas where toner is not consumed, which accelerates toner degradation.

[0107] <Evaluation experiment> Details and effects will be described in the following examples. The contents of the experiments conducted to demonstrate the effects of Example 4 will be explained. The conditions, criteria, comparative examples, etc. of the evaluation experiments overlap with those of Examples 1 to 3, so explanations will be omitted.

[0108] In Example 4, an evaluation experiment was conducted under several conditions in the small-size paper feed mode of S403 in FIG. 12. Durability evaluation of toner scattering was conducted in a low-temperature, low-humidity environment (temperature 15°C, humidity 10%). Using A5 paper, the process speed was set to 280 mm / sec, and images with horizontal lines at a 2% coverage were continuously printed on the A5 paper. Evaluation was conducted until 15,000 sheets had been passed through. In addition, every 5,000 sheets, the contamination of the edge of the A5 paper in the direction perpendicular to the paper feed direction (the longitudinal direction of the developing blade 42, etc.) was evaluated. The process cartridge 120 was also removed, and the state of toner scattering within the developing device 4 and the image forming apparatus 100 main body was checked and evaluated.

[0109] In Example 4, a solid black image for two revolutions of the developing roller 41 was developed on the photosensitive drum 1 during the inter-paper sequence and post-rotation sequence in a 50 mm wide region from both longitudinal ends of the supply roller 43. As Comparative Example 1, a mode in which the toner development sequence was not performed was performed, and as Comparative Example 2, a similar evaluation was performed in the same mode as the toner development sequence performed with A4 paper.

[0110] Table 5 below summarizes the image levels for each example after printing. [Table 5] Table 5 shows the evaluation results for print counts of 5,000 sheets (second column), 10,000 sheets (third column), and 15,000 sheets (fourth column).

[0111] Regarding the results in Table 5, Comparative Example 1 was rated Level B at 5,000 sheets because the regular toner development sequence was not performed. However, after 10,000 sheets, toner scattering and contamination inside the image forming apparatus 100 were confirmed, resulting in a rating of Level C. In Comparative Example 2, the regular toner development sequence was performed, but the toner development area at both longitudinal ends was narrow (30 mm wide). Therefore, toner scattering was confirmed after 10,000 sheets, resulting in a rating of Level C. In Example 4, the toner development area was extended (50 mm wide) in accordance with the size of the recording material P to be printed, thereby successfully suppressing toner scattering. Therefore, under the conditions of Example 4, it is desirable to set the printing area in the longitudinal direction of the regular toner development sequence to be extended in accordance with the size of the recording material P to be printed.

[0112] The image forming apparatus 100 of the fourth embodiment is an apparatus capable of passing recording materials P with a paper width up to A4 / LTR paper, and has been described using the corresponding process cartridge 120 and developing device 4 as an example, but this is not limiting. For example, if the image forming apparatus, process cartridge, and developing device are capable of passing recording materials P with a paper width up to A3 paper, it is desirable that the width of the image area implemented by the supply roller 43 and toner development sequence be changed accordingly.

[0113] As described above, according to the fourth embodiment, it is possible to suppress toner fusion to the developing blade and toner scattering into the main body of the image forming apparatus.

[0114] <Other embodiments> In the above-described embodiment, in the toner development sequence, development with toner is performed at both ends in the longitudinal direction, but development may also be performed in other regions, for example, the entire region in the longitudinal direction.

[0115] In the above-described embodiment, development is performed to increase the fluidity of the toner at the end portions, but this is not limiting. Toner may be expelled from the end portions in the longitudinal direction or other regions, including the entire region, by means other than the developing means.

[0116] The present invention can also be realized by supplying a program that realizes one or more of the functions of the above-described embodiments to a system or device via a network or a storage medium, and having one or more processors in the computer of the system or device read and execute the program. It can also be realized by a circuit (e.g., ASIC) that realizes one or more of the functions.

[0117] The disclosure of this embodiment includes the following configuration. (Configuration 1) An image forming apparatus for forming an image on a recording material, an image carrier that carries an electrostatic latent image; a developer carrier that carries a developer and develops the electrostatic latent image with the developer to form a developer image; a supply roller that contacts the developer carrier and supplies the developer to the developer carrier; a regulating member that regulates the developer carried on the developer carrier; a storage chamber for holding the developer; a developing chamber having the developer carrier, the supply roller, and the regulating member; a developing opening separating the developing chamber from the containing chamber; a stirring shaft provided in the accommodation chamber; an agitating member that rotates around the agitating shaft in the containing chamber to agitate the developer; Equipped with the developing opening is located above the rotation axis of the supply roller, the stirring shaft is installed above the developing opening, the absolute value of the air permeability at the center of the supply roller in the longitudinal direction is greater than the absolute value of the air permeability at both end portions; An image forming apparatus comprising: a control unit that controls the developer carried on the developer carrier to eject toner onto end regions in the longitudinal direction of the image carrier. (Configuration 2) 2. The image forming apparatus according to claim 1, wherein the control means controls the image carrier so that toner is discharged only to the edge region of the image carrier. (Configuration 3) The image forming apparatus according to configuration 1 or 2, characterized in that the control means performs the control at the timing between the rear end of a predetermined recording material and the front end of a recording material conveyed following the predetermined recording material when continuous image formation is performed, and / or at the timing after image formation is completed. (Configuration 4) 4. The image forming apparatus according to any one of configurations 1 to 3, wherein the image carrier and the developer carrier are in contact with each other even when no image formation is being performed. (Configuration 5) The image forming apparatus according to any one of configurations 1 to 4, wherein the control means performs the control each time the number of sheets on which images have been formed on recording materials since the previous control has been performed reaches a predetermined number, or each time the number of rotations of the developer carrier reaches a predetermined number of rotations. (Configuration 6) 6. The image forming apparatus according to any one of configurations 1 to 5, wherein the control means performs the control based on a printing rate when forming an image on a recording material. (Configuration 7) The image forming apparatus according to configuration 6, wherein the control means does not perform the control when the printing rate exceeds a predetermined printing rate, and performs the control when the printing rate is equal to or less than the predetermined printing rate. (Configuration 8) 8. The image forming apparatus according to any one of configurations 1 to 7, wherein the end region has an airflow rate of 0.5 L / min or more and less than 2.0 L / min. (Configuration 9) The image forming apparatus according to any one of configurations 1 to 8, wherein the control unit is capable of forming images on recording materials of a plurality of sizes having different longitudinal dimensions, and changes the length of the end region depending on the size of the recording material. (Configuration 10) the plurality of sizes include a recording material having a first size in the longitudinal direction and a recording material having a second size in the longitudinal direction that is shorter than the first size, The image forming apparatus according to configuration 9, wherein the control means makes the length of the edge region when forming an image on the recording material of the second size longer than the length of the edge region when forming an image on the recording material of the first size. (Configuration 11) The image forming apparatus described in configuration 10 is characterized in that the control means is capable of controlling conveyance in a first mode in which the recording material of the first size is conveyed at a first speed, or a second mode in which the recording material of the second size is conveyed at a second speed slower than the first speed, and the length of the edge region when image formation is performed in the second mode is made longer than the length of the edge region when image formation is performed in the first mode. (Configuration 12) 12. The image forming apparatus of any one of Configurations 1 to 11, wherein the airflow rate is 2.5 L / min or more and less than 4.5 L / min at the center of the supply roller, and 0.5 L / min or more and less than 2.0 L / min at both ends of the supply roller, and the ratio of the airflow rate at the center to the airflow rate at both ends is 1.25 or more and less than 9.0. [Explanation of symbols]

[0118] 1 Photosensitive drum 41 Developing roller 42 Developing blade 43 Supply roller 45 Stirring section 200 control section

Claims

1. An image forming apparatus for forming an image on a recording material, an image carrier that carries an electrostatic latent image; a developer carrier that carries a developer and develops the electrostatic latent image with the developer to form a developer image; a supply roller that contacts the developer carrier and supplies the developer to the developer carrier; a regulating member that regulates the developer carried on the developer carrier; a storage chamber for holding the developer; a developing chamber having the developer carrier, the supply roller, and the regulating member; a developing opening separating the developing chamber from the containing chamber; a stirring shaft provided in the accommodation chamber; an agitating member that rotates around the agitating shaft in the containing chamber to agitate the developer; Equipped with the developing opening is located above the rotation axis of the supply roller, the stirring shaft is installed above the developing opening, the absolute value of the air permeability at the center of the supply roller in the longitudinal direction is greater than the absolute value of the air permeability at both end portions; An image forming apparatus comprising: a control unit that controls the developer carried on the developer carrier to eject toner onto end regions in the longitudinal direction of the image carrier.

2. 2. The image forming apparatus according to claim 1, wherein the control means controls the toner to be discharged only onto the edge areas of the image carrier.

3. The image forming apparatus according to claim 1, characterized in that the control means performs the control at the timing between the rear end of a predetermined recording material when continuous image formation is performed and the front end of a recording material transported following the predetermined recording material, and / or at the timing after image formation is completed.

4. 2. The image forming apparatus according to claim 1, wherein the image carrier and the developer carrier are in contact with each other even when no image is being formed.

5. The image forming apparatus according to claim 1, characterized in that the control means performs the control each time the number of sheets on which images have been formed on recording materials since the previous control reaches a predetermined number, or each time the rotation speed of the developer carrier reaches a predetermined rotation speed.

6. 2. The image forming apparatus according to claim 1, wherein the control means performs the control based on a printing rate when forming an image on a recording material.

7. 7. The image forming apparatus according to claim 6, wherein the control means does not perform the control when the printing rate exceeds a predetermined printing rate, and performs the control when the printing rate is equal to or less than the predetermined printing rate.

8. 2. The image forming apparatus according to claim 1, wherein the end region is a region where the ventilation rate is equal to or greater than 0.5 L / min and less than 2.0 L / min.

9. 2. The image forming apparatus according to claim 1, wherein the control means is capable of forming images on a plurality of sizes of recording material having different longitudinal sizes, and changes the length of the end region depending on the size of the recording material.

10. the plurality of sizes include a recording material having a first size in the longitudinal direction and a recording material having a second size in the longitudinal direction that is shorter than the first size, 10. The image forming apparatus according to claim 9, wherein the control means makes the length of the edge region when forming an image on the second size recording material longer than the length of the edge region when forming an image on the first size recording material.

11. The image forming apparatus of claim 10, wherein the control means is capable of controlling transport in a first mode in which the recording material of the first size is transported at a first speed, or a second mode in which the recording material of the second size is transported at a second speed slower than the first speed, and the length of the end region when forming an image in the second mode is made longer than the length of the end region when forming an image in the first mode.

12. 12. The image forming apparatus according to claim 1, wherein the airflow rate is 2.5 L / min or more and less than 4.5 L / min at the center of the supply roller, and 0.5 L / min or more and less than 2.0 L / min at both ends of the supply roller, and the ratio of the airflow rate at the center to the airflow rate at both ends is 1.25 or more and less than 9.0.

Images