Image forming apparatus

Abstract

To suppress the occurrence of cleaning failure and toner fusion caused by the influence of predetermined toner formed when an image is not formed.SOLUTION: When the predetermined toner formed during the non-image formation passes through the transfer portion, the predetermined bias which is less than the discharge start voltage and which has the same polarity as the toner is applied to the transfer member.SELECTED DRAWING: Figure 6

Description

[Technical Field]

[0001] The present invention relates to a cleaning device that uses a blade to clean toner remaining on an image carrier, and an image forming apparatus that is equipped with a cleaning device that uses a fur brush to clean toner remaining on an intermediate transfer belt onto which toner is transferred from the image carrier. [Background technology]

[0002] In conventional electrophotography, the surface of a photosensitive drum (image carrier) is charged and exposed to light, creating a latent image, which is then developed with colored toner to form a visible image. The toner image is then transferred to transfer paper or the like and fixed using a heated roller or the like to form an image. After the transfer process, untransferred toner, external additives, and discharge products remain on the photosensitive drum surface, requiring their removal by cleaning prior to the next image formation process. Various cleaning methods for removing residual toner, such as those using fur brushes, magnetic brushes, or elastic cleaning blades, have been used. Among these, a method that uses a cleaning blade to scrape off the toner by rubbing it against the image carrier is commonly used due to its simplicity and low cost. Furthermore, with the recent trend toward higher speeds and higher image quality in image forming devices, the toner used has become lower in melting point and more spherical, making it difficult to ensure cleaning performance using a cleaning blade alone. Therefore, in addition to a configuration that cleans residual toner from the photosensitive drum with a cleaning blade, a cleaning auxiliary device may be provided to assist in removing residual toner from the image carrier. (See, for example, Patent Document 1.) For example, a fur brush capable of applying a bias is placed in front of the cleaning blade and comes into contact with the image carrier, and the fur brush removes residual toner before it reaches the cleaning blade. Pre-cleaning can be performed with the fur brush, which reduces the load on the cleaning blade. In addition, the amount of toner approaching the contact point (heat source) between the cleaning blade and the drum can be reduced, which prevents toner from fusing.

[0003] There are also image forming devices using an intermediate transfer method, in which a toner image formed on a photosensitive drum is first transferred to an intermediate transfer belt, and then the toner image transferred to the intermediate transfer belt is transferred to a recording material. If the intermediate transfer belt is provided with an elastic layer to improve transferability, cleaning with a cleaning blade may cause the blade to curl up. Therefore, fur brushes are sometimes used as a means for cleaning residual toner remaining on the intermediate transfer belt, and cleaning voltages of different polarities are applied to the fur brushes to perform electrostatic cleaning. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2009-300860 Summary of the Invention [Problem to be solved by the invention]

[0005] As described above, when a cleaning blade and an auxiliary cleaning means (electrostatic fur brush) are used as cleaning means for the photosensitive drum, and an electrostatic fur brush is used as cleaning means for the intermediate transfer belt, the following problems arise.

[0006] That is, when no image is being formed, control toner for adjusting image quality or refresh toner for suppressing developer degradation may be formed (these toners may be referred to as control toners hereinafter). Since control toners that do not directly contribute to image formation are sent directly to the cleaning unit without being transferred to the recording material, a large amount of toner is sent to the cleaning unit at once. In particular, when electrostatic cleaning is used for the intermediate transfer belt, if a large amount of control toner is transferred to the intermediate transfer belt, cleaning defects may occur.

[0007] Therefore, in order to prevent such adjustment toner from being electrostatically transferred to the intermediate transfer belt, a bias opposite to the normal transfer bias is applied, and the adjustment toner is passed through the primary transfer unit without being transferred to the intermediate transfer belt, and is then recovered by a cleaning unit for the photosensitive drum.

[0008] However, in this case, when the adjustment toner passes through the primary transfer unit, it is discharged by the voltage applied to the primary transfer unit, changing the charge amount of the adjustment toner. This increases the adhesion of the adjustment toner to the photosensitive drum, which can make it difficult to clean it sufficiently with the auxiliary cleaning unit. In particular, refresh toner used to prevent developer degradation is typically formed as a solid image, resulting in a large toner load per unit area. As a result, adjustment toner that cannot be cleaned by the auxiliary cleaning unit (electrostatic fur brush) is sent to the cleaning blade unit downstream, potentially destroying the external additive layer accumulated on the tip of the cleaning blade.

[0009] The external additive layer deposited on the tip of the cleaning blade usually acts as a blocking layer, preventing toner from being sent to the friction area (heat source) where the blade and the photosensitive drum rub against each other. This prevents toner from fusing by keeping it away from the heat source. However, as mentioned above, the external additive layer may be destroyed by the adjustment toner that was not cleaned, resulting in toner fusing.

[0010] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide an image forming apparatus that can suppress toner fusion on an image carrier with a simple configuration while reducing the load of cleaning the intermediate transfer belt. [Means for solving the problem]

[0011] The image forming apparatus of the present invention for solving the above-mentioned problems includes an image carrier, a developing device to which a developing bias is applied and which develops a latent image formed on the image carrier with toner, an intermediate transfer belt to which the toner formed on the image carrier is transferred, a transfer member which transfers the toner image formed on the image carrier to the intermediate transfer belt at a transfer section, a first application section which applies a transfer bias to the transfer member, a cleaning blade which comes into contact with the image carrier to clean toner remaining on the image carrier, a fur brush which is provided upstream of the cleaning blade in the rotation direction of the image carrier and which comes into contact with the image carrier to clean toner remaining on the image carrier, and a second application section which applies a cleaning bias to the fur brush. In an image forming apparatus having a second application unit and a control unit capable of performing a toner consumption operation to transfer a predetermined toner from the developing device to the image carrier, the control unit is configured to, when performing the toner consumption operation, control the first application unit so that a predetermined bias is applied to the transfer member when the predetermined toner passes through the transfer unit, the predetermined bias having the same polarity as the charging polarity of the toner, the difference between which and the DC voltage of the developing bias is less than a discharge start voltage, and the absolute value of which is greater than the absolute value of the DC voltage of the developing bias, and to control the second application unit so that a cleaning bias of the opposite polarity to the toner is applied when the predetermined toner passes through the fur brush.

[0012] Another configuration of the present invention includes an image carrier, a developing device to which a developing bias is applied and which develops a latent image formed on the image carrier with toner, an intermediate transfer belt to which the toner formed on the image carrier is transferred, a transfer member which transfers the toner image formed on the image carrier to the intermediate transfer belt in a transfer section, and a first applying section which applies a transfer bias to the transfer member, a cleaning blade that comes into contact with the image carrier to clean toner remaining on the image carrier; a fur brush that is provided upstream of the cleaning blade in the rotation direction of the image carrier and that comes into contact with the image carrier to clean toner remaining on the image carrier; and a second application unit that is capable of applying a cleaning bias to the fur brush. In an image forming apparatus having a control unit capable of performing a toner consumption operation to transfer a predetermined toner from the developing device to the image carrier, the control unit is configured to, when performing the toner consumption operation, control the first application unit so that a predetermined bias is applied to the transfer member when the predetermined toner passes through the transfer unit, the predetermined bias having the same polarity as the charging polarity of the toner, and the difference between the DC voltage of the developing bias is less than a discharge start voltage, and the difference is 10% or less of the absolute value of the DC voltage of the developing bias, and to control the second application unit so that a cleaning bias of the opposite polarity to the toner is applied when the predetermined toner passes through the fur brush. [Effects of the Invention]

[0013] According to the present invention, it is possible to provide an image forming apparatus that can suppress toner fusion on an image carrier with a simple configuration while reducing the load of cleaning the intermediate transfer belt. [Brief explanation of the drawings]

[0014] [Figure 1] 1 is an explanatory diagram of a configuration of an image forming apparatus; [Figure 2] Belt cleaning device schematic diagram [Figure 3] Schematic diagram of the secondary transfer belt cleaning device [Figure 4] Detailed cross-sectional view of cleaning means [Figure 5] Schematic functional block diagram of an image forming apparatus [Figure 6] An explanatory diagram of the voltage applied to the primary transfer body [Figure 7] Graph for explaining discharge start voltage in Example 1 [Figure 8] Flowchart in Example 1 [Figure 9] Results of Example 1 and Comparative Example [Figure 10] Flowchart in Example 2 [Figure 11] Results of Example 2 and Comparative Example DETAILED DESCRIPTION OF THE INVENTION

[0015] The following examples are described with reference to the drawings. The dimensions, materials, shapes, and relative positions of the components described in the examples are not intended to limit the scope of the present invention unless otherwise specified.

[0016] <Image forming device> 1 is a schematic diagram of the image forming apparatus in this embodiment, which is a tandem-type, intermediate transfer, four-color full-color printer using an electrophotographic process.

[0017] The image forming apparatus has a CPU (control means) that controls the image forming apparatus. Connected to this CPU are a RAM (storage means) used as working memory, a ROM that stores programs executed by the CPU and various data, and a video controller that processes input image formation information. The video controller, which processes the image information, forms an image based on image information input from a personal computer (PC), image reader, etc. A toner image corresponding to the image information input to the control means is formed on a recording material P and printed out.

[0018] The image forming apparatus is provided with an image forming unit inside the apparatus body for forming a toner image on a recording material (hereinafter referred to as paper) P. The image forming unit has an imaging unit 3Y that forms a yellow toner image, an imaging unit 3M that forms a magenta toner image, an imaging unit 3C that forms a cyan toner image, and an imaging unit 3K that forms a black toner image.

[0019] <Imaging unit> The imaging units are all similar electrophotographic process mechanisms, with the only difference being the color of the developer (toner) used, and each includes a photosensitive drum 4, a charging device 5, an exposure device 6, a developing device 7, and a drum cleaning device 9.

[0020] The electrophotographic process and image forming operation of the imaging unit having the above configuration are well known, and therefore will not be described here. The symbols Y, M, C, and K representing the toner colors yellow, magenta, cyan, and black will be omitted where appropriate.

[0021] In the image forming apparatus of this embodiment, the exposure device 6 is a laser scanner, and the developing device 7 is a reversal developing device that uses a developer in which negatively charged toner (negative toner) is mixed with a magnetic carrier. The drum cleaning device 9 is a device that uses a cleaning blade and a fur brush. A predetermined positive polarity primary transfer bias is applied to the primary transfer roller 8 from a power supply unit that serves as an application unit.

[0022] <Charging means> The charging means 5 in the present invention is a contact-type charging roller, and may be charged by utilizing the discharge phenomenon that occurs in the minute gap between the charging means 5 and the photosensitive drum 4. In this case, a charging bias voltage under predetermined conditions is applied to the core of the charging means 5. In this embodiment, the applied DC bias was set to -500 V, and the AC bias was set to a peak-to-peak bias that was at least twice the discharge start voltage in that environment, and the photosensitive drum 1 was uniformly charged to approximately -500 V.

[0023] A corona charging type charging means may also be used. In this case, a discharge electrode and a grid electrode are used. A voltage is applied to the discharge electrode, and the photosensitive drum 4 is uniformly charged using the discharge phenomenon. For example, -1000 μA is applied to the discharge electrode and -600 V is applied to the grid electrode, and the image forming portion of the rotating photosensitive drum 4 is uniformly charged to approximately -500 V. The charging potential is negative, and the photosensitive drum is charged to the negative side. The charging potential is adjusted in accordance with the development bias value depending on the environment and the state of the image forming device.

[0024] <Exposure means> The exposure means 6 is equipped with a semiconductor laser that performs image exposure based on image information on the photosensitive drum 4, the surface of which has been uniformly charged by the charging means 5. The exposure potential of the laser light is -200 V. Although an example using a semiconductor laser will be described in the present invention, other means such as an LED may also be used. A potential measuring means (not shown) is provided to measure the potential of the photosensitive drum 1 after exposure, so that it can be confirmed whether the charging potential and exposure potential are actually at the specified potential.

[0025] <Developing method> The developing means 7 includes a developing container containing a two-component developer, a mixture of non-magnetic toner and magnetic carrier, and a developing sleeve rotatably mounted at the opening of the developing container. In the present invention, the axial length of the developing sleeve is 325 mm. The developing sleeve magnetically holds the developer in the developing container using a magnet fixedly disposed inside and transports it to the developing section, which is the gap between the developing sleeve and the photosensitive drum 4. A voltage power supply is connected to the developing sleeve, which applies a developing bias consisting of a DC voltage (-400 V) superimposed on an AC voltage (Vpp of 1600 V). This developing bias causes the toner to adhere to the latent image, thereby performing development. The setting value of the developing bias is an example and is set to a value adjusted appropriately according to the charging potential (dark area potential) and exposure potential (light area potential) of the photosensitive drum.

[0026] <Primary transfer means> In each imaging unit, the toner images of each color are sequentially superimposed in a predetermined manner and primarily transferred from the photosensitive drum 4, which rotates at a predetermined peripheral speed in the direction of arrow B, to the intermediate transfer belt (intermediate transfer body) of the intermediate transfer belt unit, which rotates at a predetermined peripheral speed in the direction of arrow A. As a result, a four-color superimposed color toner image of Y+M+C+K is formed on the intermediate transfer belt (hereinafter referred to as the intermediate transfer belt).

[0027] The intermediate transfer belt 2 is stretched around a tension roller 32, a drive roller 31, and a secondary transfer opposing roller 33. The intermediate transfer belt 2 rotates when the drive roller 31 is driven by a drive motor.

[0028] The intermediate transfer body 2 is an endless belt-like structure with a three-layer structure consisting of a resin layer, an elastic layer, and a surface layer from the back side. The resin layer is made of a resin material such as polyimide or polycarbonate, and has a thickness of 70 to 100 μm. The elastic layer is made of an elastic material such as urethane rubber or chloroprene rubber, and has a thickness of 200 to 250 μm.

[0029] Furthermore, the surface layer material is required to reduce the adhesion of toner to the surface of the intermediate transfer body 2 and improve secondary transfer performance. For example, a material that reduces surface energy and enhances lubricity can be dispersed in a single resin material such as polyurethane, polyester, or epoxy resin. Alternatively, two or more elastic materials (elastic rubber, elastomer), such as butyl rubber, can be dispersed in a material that reduces surface energy and enhances lubricity. Examples of materials that reduce surface energy and enhance lubricity include one or more types of powder or particles, such as fluororesin, or particles with different particle sizes. The thickness of the surface layer is preferably 5 to 10 μm. In this embodiment, the intermediate transfer body 8 is added with a conductive agent, such as carbon black, to adjust the resistance, resulting in a volume resistivity of 1E+8 to 1E+14 Ω·cm.

[0030] The primary transfer body 8, which serves as the transfer member, is a roller made of hydrin rubber molded onto a metal shaft with adjusted electrical resistance. The primary transfer body 8 is positioned about 2 mm downstream from the photosensitive drum 4 and is pressed toward the photosensitive drum 4 with a specified pressure. During transfer, a transfer bias is applied to transfer the toner image from the photosensitive drum 4 to the intermediate transfer body 2. At this time, there may be a small amount of carrier in addition to toner present on the photosensitive drum 4. As mentioned above, by providing an elastic layer on the intermediate transfer body 2, damage to the photosensitive drum 4 at the primary transfer section is reduced even if a hard object such as carrier is sandwiched between the primary transfer body 8.

[0031] <Toner> The toner is configured to be negatively charged by friction with the magnetic carrier. In this invention, the carrier contains ferrite and has an average particle size of approximately 40 μm. The toner is obtained by kneading a polyester-based resin binder with pigment and wax components, then pulverizing and classifying the mixture. Several types of external additives are attached to the toner surface for purposes such as charge control, fluidity, and transferability improvement. The external additives include silica, titanium oxide, and inorganic fine particles with a primary particle average diameter of 30 to 300 nm, cubic and / or rectangular parallelepiped particle shape, and perovskite crystals. In this example, strontium titanate fine powder was externally added as the inorganic fine particles with perovskite crystals. It is preferable to add 0.05 to 2.00 parts by weight per 100 parts by weight of the final toner particles before external addition; in this example, 0.5 parts by weight of strontium titanate fine powder was externally added. The strontium titanate used as inorganic fine particles is preferably particles that have not been subjected to a sintering process.

[0032] This strontium titanate fine powder has a cubic particle shape and / or a rectangular parallelepiped particle shape, and when supplied to a cleaning blade portion of the photosensitive drum (described later), it serves to polish the surface of the photosensitive drum 4. The material of the inorganic fine particles may be barium titanate fine powder, calcium titanate fine powder, or the like, in addition to strontium titanate.

[0033] The inorganic fine powder of perovskite crystal used in the present invention has an average primary particle size of 30 to 300 nm, preferably 40 to 300 nm, and more preferably 40 to 250 nm. If the average particle size is less than 30 nm, the abrasive effect of the particles in the cleaner part of the photosensitive drum is insufficient, while if it exceeds 300 nm, the abrasive effect is too strong and scratches occur on the surface of the photosensitive drum, which is unsuitable.

[0034] Furthermore, the perovskite-type crystalline inorganic fine powder is not necessarily present on the surface of the toner particles as primary particles, and may exist as aggregates. Even in such cases, good results can be obtained as long as the content of aggregates having a particle size of 600 nm or more is 1% by number or less. If the content of particles and aggregates having a particle size of 600 nm or more exceeds 1% by number, scratches will occur on the surface of the photosensitive drum, even if the primary particle size is less than 300 nm, making it unsuitable.

[0035] <Photoconductor> In the present invention, the photoreceptor drum 4 is a negatively charged organic photoreceptor (OPC) with an axial length of 360 mm and an outer diameter of 84 mm. The photoreceptor drum 4 has a photoconductive layer formed on a conductive substrate, the photoconductive layer being primarily composed of an organic photoconductor. An OPC generally comprises a conductive metal substrate, on which a charge generation layer, a charge transport layer, and a surface protection layer made of organic materials are laminated. For example, each layer was constructed using materials described in JP-A-2005-43806. In this embodiment, the outermost layer of the photoreceptor drum 4 was hardened using, for example, an electron beam irradiation device (EC150 / 45 / 40mA, manufactured by Iwasaki Electric Co., Ltd.).

[0036] The elastic deformation rate of the surface of the electron beam-cured photosensitive drum 4 is preferably 48% or more and 65% or less. The universal hardness value (HU) of the surface of the electrophotographic photosensitive member is preferably 150 N / mm2 or more and 220 N / mm2 or less.

[0037] The photosensitive drum 4 is rotated in the direction of the arrow by a driving device (not shown) at a process speed (peripheral speed) of normally 400 mm / s.

[0038] The universal hardness (HU) and elastic deformation rate of the surface of the electrophotographic photoreceptor were measured using a Fischerscope H100V microhardness tester (manufactured by Fischer) under a temperature of 23°C and a humidity of 50%RH. The Fischerscope H100V is a device that measures continuous hardness by contacting an indenter with the object to be measured (the peripheral surface of the electrophotographic photoreceptor), continuously applying a load to the indenter, and directly reading the indentation depth under the load. A Vickers square pyramidal diamond indenter with a facing angle of 136° was used as the indenter. The indenter was pressed against the peripheral surface of the electrophotographic photoreceptor. The final load applied to the indenter (final load) was 6 mN, and the time (holding time) for maintaining the final load of 6 mN on the indenter was 0.1 seconds. 273 measurement points were used.

[0039] FIG. 3 shows a schematic output chart of a Fischerscope H100V (manufactured by Fischer). FIG. 4 shows an example of an output chart of a Fischerscope H100V (manufactured by Fischer) when the electrophotographic photoreceptor of the present invention is used as the measurement target. In FIGS. 3 and 4, the vertical axis represents the load F (mN) applied to the indenter, and the horizontal axis represents the indenter's indentation depth h (μm). FIG. 3 shows the results when the load applied to the indenter was gradually increased until it reached its maximum (A→B), and then gradually decreased (B→C). FIG. 4 shows the results when the load applied to the indenter was gradually increased until it finally reached 6 mN, and then gradually decreased.

[0040] Here, the universal hardness value (HU) can be calculated from the indentation depth of the indenter when a final load of 6 mN is applied to the indenter using the following formula: In the formula, HU means universal hardness (HU), Ff means the final load, Sf means the surface area of ​​the indented part of the indenter when the final load is applied, and hf means the indentation depth of the indenter when the final load is applied. HU=Ff(N) / Sf(mm^2) (Equation 1)

[0041] The elastic deformation rate can be determined from the amount of work (energy) performed by the indenter on the measurement target (the peripheral surface of the electrophotographic photosensitive member), i.e., the change in energy due to an increase or decrease in the load of the indenter on the measurement target (the peripheral surface of the electrophotographic photosensitive member). Specifically, the elastic deformation rate is the value (We / Wt) obtained by dividing the elastic deformation work We by the total work Wt. The total work Wt is the area of ​​the region surrounded by ABDA in Figure 3, and the elastic deformation work We is the area of ​​the region surrounded by CBDC.

[0042] <Belt cleaning device 120> 3, the belt cleaning device 120 has a device housing 12 arranged near the intermediate transfer belt 2. Inside this device housing 12, electrostatic fur brushes 122 and 123, aluminum metal rollers 124 and 125, and cleaning blades 126 and 127 are provided.

[0043] The fur brush is made of carbon-dispersed nylon, acrylic, or polyester fibers with a thread resistance of 3E+5 to 1E+13 (Ω / cm) and a fiber thickness of 2 to 15 denier, planted on a metal roller at a planting density of 50,000 to 500,000 fibers per inch^2. In this embodiment, a brush with a length of 333 mm in the main scanning direction was used, but this is not limited to this.

[0044] The electrostatic fur brushes 122 and 123 are disposed in sliding contact with the intermediate transfer belt 2, maintaining a penetration depth of approximately 1.0 to 2.0 mm, and are configured to rotate in the direction of the arrows at 20 to 80% of the conveyance speed of the intermediate transfer belt 2, driven by a drive motor (not shown). The metal rollers 124 and 125 are disposed in contact with the electrostatic fur brushes 122 and 123, maintaining a penetration depth of 1.5 to 2.5 mm, and are configured to rotate in the direction of the arrows at the same speed as the electrostatic fur brushes 122 and 123. The cleaning blades 126 and 127 that abut against the metal rollers 124 and 125 are made of plate-shaped rubber such as urethane. The cleaning blades 126 and 127 are 1.6 to 2.2 mm thick. The IRHD hardness of the cleaning blades 126 and 127 is 70 to 78° (23°C, 50% RH). The cleaning blades 126 and 127 are disposed so as to maintain an intrusion amount of 0.5 to 2.0 mm into the metal roller.

[0045] A negative voltage of −75 μA, controlled by a constant current, is applied from a DC power supply to the metal roller 124, a cleaning member located upstream in the rotational direction of the intermediate transfer belt 2 (−75 μA in this embodiment, but not limited to this). Meanwhile, a positive voltage of +75 μA, controlled by a constant current, is applied from a DC power supply to the metal roller 125, a cleaning member located downstream in the rotational direction of the intermediate transfer belt 6 (+75 μA in this embodiment, but not limited to this). A cleaning electric field suitable for the cleaning toner is formed between the fur brushes, and residual toner on the intermediate transfer belt 6 is attracted to and removed by the fur brushes 122 and 123. The attracted and removed toner is further transferred from the fur brushes 122 and 123 to the metal rollers 124 and 125 by the electric field, and then scraped off by the cleaning blades 126 and 127. That is, the electrostatic fur brush 122 is a first cleaning brush to which a first cleaning voltage (positive polarity) is applied, electrostatically cleaning residual toner from the intermediate transfer belt 2. The electrostatic fur brush 123 is a second cleaning brush to which a second cleaning voltage (negative polarity) is applied, and which electrostatically cleans the toner remaining on the intermediate transfer belt 2.

[0046] <Secondary transfer belt cleaning means> 3, the secondary transfer belt cleaning device 50 has a device housing 50 arranged near the secondary transfer belt 99. Inside this device housing 50, electrostatic fur brushes 501 and 502, aluminum metal rollers 503 and 504, and cleaning blades 505 and 506 are provided. The components used are the same as those of the belt cleaning device 120, and the voltage applied is the same as that of the belt cleaning device 120.

[0047] <Cleaning Method> FIG. 4 is a detailed cross-sectional view of the cleaning device. The cleaning device includes a housing 300 and a fur brush 304 (a toner scraping device and an image carrier polishing device). The fur brush 304 is disposed with a penetration depth of 0.7 mm relative to the photosensitive drum 4. It rotates in the same direction as the rotation of the photosensitive drum 4 while in contact with the surface of the photosensitive drum 4, at a speed faster than the peripheral speed of the photosensitive drum. In this embodiment, the fur brush 304 rotates at 110% of the rotational speed. A cleaning blade 301 that contacts the surface of the photosensitive drum 4 is disposed downstream in the direction of rotation of the photosensitive drum 4 from the contact point between the fur brush 304 and the photosensitive drum 4. A collection roller 302 is disposed downstream in the direction of rotation of the fur brush 304 from the contact point between the fur brush 304 and the photosensitive drum 4, in contact with the fur brush 304, and rotates in the same direction as the rotation of the fur brush 304. The peripheral speed of the collection roller 302 is faster than that of the fur brush, and in this embodiment, it is 105% of the rotational speed of the fur brush. Furthermore, a plate-shaped scraper member 303 is disposed on the collection roller 302 downstream in the rotation direction of the collection roller 302 from the contact point of the fur brush 304. The plate-shaped scraper member 303 is disposed so that its leading edge abuts against the collection roller 302 with a predetermined pressure.

[0048] The collection roller 302 is connected to a potential switching means 307 as a bias application device, which allows a bias to be applied to the collection roller 302. The potential switching means 307 is connected to a control means for controlling the timing of potential application and the applied potential. During cleaning, a positive cleaning bias, which is opposite in polarity to the toner, is applied to the collection roller 302 by the potential switching means 307. The fur brush is made of a conductive material such as conductive fiber. When the fur brush 304 comes into contact with the collection roller 302 to which the cleaning bias is applied, the potential of the fur brush 304 is set to a potential slightly smaller (in absolute value) than the cleaning bias. Since the fur brush 304 also has a positive potential, opposite in polarity to the toner, the toner on the surface of the photosensitive drum 4 is not only mechanically captured by the rubbing fur brush 304 but also electrostatically captured, thereby further improving cleaning efficiency. The application of the cleaning bias to the collection roller 302 is initiated in synchronization with the timing at which the charging means 5 starts driving after the photosensitive drum 4 starts rotating. The conveying means 306 is disposed below the scraper member 303 in the direction of gravity.

[0049] <Cleaning blade> The cleaning blade 301 used in the present invention is made of urethane rubber, has an axial length of 340 mm, and is in contact with the photosensitive drum 4 at a predetermined contact pressure. The required physical properties of the cleaning blade 301 are as follows: hardness (IRHD) of 65° or more and 85° or less, a coefficient of rebound resilience at 25°C of 15 to 60%, an elongation at break in a tensile test of 300% or less, and a Young's modulus of 50 to 200 kg / cm2. The 100% modulus is preferably in the range of 4.0 MPa to 9.0 MPa. More preferably, the hardness (IRHD) is 70° or more and 80° or less, an elongation at break in a tensile test of 250% or less, and a coefficient of rebound resilience at 25°C of 15% to 35%. Regarding the method for measuring each required physical property, the hardness (IRHD) was measured on the prepared cleaning blade using a Wallace hardness tester in accordance with JIS K 6253. The 100% modulus was measured using a tensile tester (Unitron TS-3013) manufactured by Ueshima Seisakusho Co., Ltd. on the produced cleaning blade 301, in accordance with JIS K 6251. The elongation at break in the tensile test was measured using a tensile tester (Unitron TS-3013) manufactured by Ueshima Seisakusho Co., Ltd. on the produced cleaning blade, in accordance with JIS K 6251. Next, the rebound resilience was measured using a Lübke-type rebound resilience tester manufactured by Ueshima Seisakusho Co., Ltd. on the produced cleaning blade 301, in accordance with JIS K 6255, in an environment of 25°C.

[0050] <Fur Brush> The fur brush 304, located upstream of the cleaning blade 301 in the direction of rotation of the photosensitive drum 4, will now be described. The fur brush 304, an auxiliary cleaning member, assists in removing residual toner from the photosensitive drum 4 before it reaches the cleaning blade. The rotating member, the fur brush 304, has fibers attached to its shaft. It is manufactured by wrapping a fabric material with fibers attached around a 12 mm diameter metal shaft. The fibers of the fur brush 304 are made of bundles of 6-denier acrylic monofilaments, attached to a substrate at a bristle density of 70 kF / inch² (fiber density per monofilament). The overall outer diameter of the fur brush is 21.4 mm, and the length of the brush fibers, calculated by subtracting 12.1 mm, the diameter of the core, from this outer diameter, is 4.5 mm. The fur brush 304 uses conductive fibers, with the resistance of the fibers adjusted by dispersing a certain amount of conductive particles, such as carbon, in the fibers. In this embodiment, the required physical properties of the fur brush 304 are a tensile strength of 50 to 80 cn / dtex and an electrical resistance of 10 to 12 LOGΩ in an environment of a temperature of 23° C. and a humidity of 50%.

[0051] <Recovery roller> The recovery roller 302 was made of a solid stainless steel material with an outer diameter of 13 mm, and a voltage of +400 V was applied to it.

[0052] <Scraper> The scraper member 303 may be made of a nylon sheet material or a polyurethane rubber blade, but in this embodiment, the same material as the cleaning blade 301 described above is used.

[0053] <Image formation operation> 5 is a schematic functional block diagram of the image forming apparatus 200. A CPU 301 as a control unit has a function of generating various command signals and executing arithmetic processing to operate various sensors, motors, and the like of the image forming apparatus 200 in accordance with the electrophotographic process.

[0054] The image forming device 200 comprehensively controls each part of the image forming device 200 and executes the image forming operation based on instructions from the operation unit, image data from the image reading unit, or image formation signals (image data, control commands) from an external device.

[0055] The image forming operation refers to the steps of forming an electrostatic image of the image to be formed and output on the recording material P, forming a toner image, performing primary and secondary transfer of the toner image, and fixing the toner image formed on the recording material P. The CPU 301 also has a built-in memory for storing data. The image data generation unit 302 has the function of converting various image data into laser control signals and sending control signals to the laser driving units 303a to 303d. The image data generation unit 302 also has the function of generating toner patterns for toner concentration detection. The laser driving units 303a to 303d drive the laser elements of the laser scanners 3a to 3d based on the signals sent from the image data generation unit 302, and control the laser illumination and light intensity. The density detection sensor driving circuit 305 has the function of controlling the ON / OFF and driving current of the LEDs inside the density detection sensor 70 according to command signals from the CPU 301. The density detection sensor detection circuit 306 amplifies the light-receiving voltage signal from the density detection sensor 70 and sends it to the CPU 301. The motor control unit 91 is electrically connected to each drive motor (not shown) and has the function of controlling the drive timing and drive speed. The voltage control unit 92 has the function of controlling the output of biases required for the image formation process, such as a charging bias, a developing bias, and a transfer bias. The CPU 301 is also electrically connected to the paper feed cassette 60, the I / F unit 85, and the timer 90, and is further connected to the operation unit U through the I / F unit 85. The CPU 301 can form images using the recording material S stored in the paper feed cassette 60. The operation unit U accepts user operations and is configured, for example, with an LCD touch panel. The operation unit U may also be an external terminal, such as a personal computer, connected to the image forming apparatus.

[0056] The CPU 301 is also electrically connected to the controller 87 and the image processing unit 84. Image information 88 is sent to the CPU 301 through the controller 87. The CPU 301 can form an image by processing the received image information 88 in the image processing unit 84.

[0057] <Fusion-suppressing toner zone> In this embodiment, a control is performed to periodically supply a fusion-suppressing toner band to the cleaning portion of the photoconductor to suppress toner fusion. Specifically, the fusion-suppressing toner band is supplied between sheets (between images) every predetermined number of sheets.

[0058] The fusion-inhibiting toner band is a half-tone image formed across substantially the entire longitudinal length of the image area. The fusion-inhibiting toner band passes through the fur brush 304 before being supplied to the cleaning blade 301. A cleaning bias of opposite polarity to that of the toner is applied to the fur brush 304, so most of the toner is electrostatically cleaned. On the other hand, external additives supplied with the toner have smaller particle sizes than the toner, and therefore have high adhesive strength and cannot be collected by an electric field strong enough to collect the toner. Therefore, they are supplied to the cleaning blade 301 without being collected by the fur brush 304. The external additives are then blocked by the cleaning blade 301, forming an external additive layer between the cleaning blade 301 and the photosensitive drum 4. By forming this external additive layer, even if residual toner is sent to the cleaning blade 301, the toner can be blocked from moving toward the sliding portion (heat source) between the photosensitive drum 4 and the cleaning blade 301. This effectively suppresses toner fusion caused by frictional heat between the cleaning blade 301 and the photosensitive drum. [Example]

[0059] The toner consumption control in this embodiment will be described.

[0060] <Toner consumption control> Here, toner consumption control in this embodiment will be described. The image forming apparatus of this embodiment is configured to periodically execute control to transfer toner (predetermined toner) from the developing device 7 to the photosensitive drum 4 when no image is being formed. Specifically, as will be described later, the above control is executed based on the image printing rate (image information). This makes it possible to prevent external additives from being embedded in the toner and causing deterioration when many images with low printing rates are output. The toner consumption control determines the amount of toner to be consumed according to the usage state of the developing device 7, and consumes the toner by developing the toner on the photosensitive drum 4.

[0061] In this embodiment, the toner amount on the photosensitive drum 4 is 0.5 mg / cm^2, the toner consumption length is the entire exposure width in the main scanning direction and 600 mm in the sub-scanning direction, and the toner consumption amount is adjusted by the control frequency.

[0062] The control frequency is determined by the usage state of the developing device 7. The usage state of the developing device 7 here refers to the image printing rate and the number of printed pages. In this embodiment, toner consumption control is executed by interrupting the paper feed when printing of 100 or more A4-sized pages with an image printing rate of 4% or less is performed in succession. Although this embodiment is implemented as described above, toner consumption control is not limited to this method and value as long as it can consume toner from the developing device 7. The toner consumed by toner consumption control is collected from the intermediate transfer belt 2 by the secondary transfer belt cleaning device 50.

[0063] <Various voltage settings for toner consumption control> The voltage settings for toner consumption control will be described using Figure 6. When the above-described toner consumption control is implemented, the voltages applied to the charging means 5, developing means 7, and recovery roller 302 are the same as those during image formation. The voltage applied to the primary transfer body 8 is of the opposite polarity (negative in this embodiment) to that used in normal image formation. In other words, when the above-described toner consumption control is implemented, the CPU 301 controls the voltage applied by the power supply unit to the primary transfer body 8 so that a bias (predetermined bias) of the same polarity as the normal charging polarity of the toner is applied.

[0064] In this embodiment, the voltage value applied to the primary transfer body 8 was set to be equivalent to the image area potential (drum potential of the image area after development) in the toner image forming section of the photosensitive drum 4. During image formation, toner is developed in the latent image area (image exposed area) on the photosensitive drum 4 up to the potential applied to the developing means 7, so the potential in the toner image forming section is the value of the voltage applied to the developing means 7. In this embodiment, a voltage of -400 V (DC voltage of the developing bias) was applied to the primary transfer body 8. It is desirable that the voltage value applied to the primary transfer body 8 be equivalent to the potential in the toner image forming section, but it may be applied to the negative side of the DC voltage applied to the developing means as long as it is less than the discharge start voltage.

[0065] Furthermore, the voltage applied to the developing means from the positive side may be applied from the developing potential to the positive side as long as it is a value that does not substantially transfer toner to the transfer cleaning device. In this embodiment, the voltage may be applied from the developing potential to the positive side as long as it is 10% or less of the development contrast, which is the difference between the latent image potential and the voltage applied to the developing means. Alternatively, the voltage may be applied from the developing potential to the positive side as long as it is 10% or less of the DC potential of the developing bias. This prevents toner from being substantially transferred to the transfer cleaning device. In this embodiment, the voltage value applied to the primary transfer body 8 should be a voltage that is higher on the negative side than the latent image potential of 100V by 90% or more of the development contrast of 300V (-270V).

[0066] As described above, in this embodiment, the above-described toner consumption control (toner refresh operation in the developing device) can be executed when no image is being formed. That is, control can be executed to transfer a predetermined toner from the developing means (developing device) 7 to the photosensitive drum 4. When executing the above control, CPU 301 controls the power supply unit so that the predetermined bias is applied to primary transfer body 8 before the leading edge of the predetermined toner (refresh toner image) transferred from the developing means 7 passes through the primary transfer unit. CPU 301 also controls the power supply unit so that this predetermined bias is applied until the trailing edge of the predetermined toner passes through the primary transfer unit.

[0067] <Discharge start voltage> Here, the discharge inception voltage will be explained using FIG. 7. While the method for determining the discharge inception voltage will be explained using an example, other known methods for determining the discharge current amount and discharge inception voltage value may be used. In this example, the discharge inception voltage was determined as follows. Specifically, a constant voltage was applied to the primary transfer roller 8, and the applied current was detected using an ammeter. The current-voltage characteristic was obtained based on the detected current value. The point at which the slope of the obtained characteristic changes is the discharge inception voltage. In this example, an approximation curve (1) was drawn using the measurement points of −200 V, −400 V, and −600 V, and an approximation curve (2) was drawn using the measurement points of −800 V, −1000 V, and −1200 V. The discharge inception voltage was calculated from the intersection of the lines (1) and (2). In this example, the calculated value was −640 V.

[0068] If a voltage higher than this discharge start voltage is applied to the negative side, the discharge will impart a charge to the toner developed using toner consumption control, causing the toner charge to increase. The charged toner cannot then be adequately cleaned by the fur brush 304, and a large amount of toner is supplied to the external additive layer accumulated on the tip of the cleaning blade, destroying the external additive layer. As a result, the toner approaches the heat source caused by friction between the cleaning blade and the drum, causing the toner to fuse to the drum surface and resulting in blank images.

[0069] <Transfer cleaning> Here, we will explain the phenomenon that occurs when a development potential is applied to the primary transfer means in a positive direction during toner consumption control. As mentioned above, the voltage applied to the primary transfer body 8 is set to a voltage that is higher than the discharge start voltage but is higher on the positive side by 10% or more of the contrast, which is the difference between the latent image potential and the development potential, relative to the DC voltage of the development bias. In this case, toner is transferred to the intermediate transfer belt by the primary transfer means and supplied to the secondary transfer belt cleaning device 50. The secondary transfer belt cleaning device 50 is designed to clean residual toner normally. Therefore, if a large amount of toner is supplied, as in toner consumption control, cleaning failure occurs, and unnecessary toner may adhere to the paper during the next image formation, resulting in a dirty image.

[0070] Therefore, it is necessary to limit the voltage applied to the primary transfer means to a certain value or less during toner consumption control.

[0071] In this embodiment, the toner consumed by the toner consumption control is cleaned by the secondary transfer cleaning means, but it may also be cleaned by the transfer cleaning means.

[0072] <Implementation flow> The flow of operations in the first embodiment will be described with reference to FIG.

[0073] After a job is started (S1), image formation begins (S2). Next, it is determined whether the image coverage rate is below a threshold (S3). If it is above the threshold (N in S3), it is determined whether the job has ended (S7), and if it has not ended, it returns to image formation (S2). If it is below the threshold (Y in S3), the number of printed pages is counted (S5) and it is determined whether it is above the threshold (S5). If it is not above the threshold (N in S5), it returns to image formation (S2). If it is above the threshold (Y in S5), toner consumption control is executed (S6) and it is determined whether the job has ended (S7). If the job has not ended, it returns to image formation (S2), and if it has ended (Y in S7), it ends the job.

[0074] <Comparative Example> FIG. 9 shows the results of this example and the comparative example.

[0075] In Comparative Example 1, the voltage applied to the primary transfer member 8 for toner consumption control was -2000 V, which is greater than the discharge start voltage. In Comparative Example 2, the voltage was set to +100 V, at which the toner consumption control transfers to the intermediate transfer belt. Using an image forming apparatus, 1000k A3-size, full-page white images were continuously output on both sides to verify whether toner contamination occurred on the backside of the images after printing. Finally, a full-page solid image was printed to verify whether white spots due to fusion occurred. A solid image is an image with a 100% image coverage and a toner coverage of 0.5 mg / cm^2. In this example, neither image contamination nor white spots due to fusion occurred. However, in Comparative Example 1, white spots due to fusion occurred, and in Comparative Example 2, toner contamination occurred on the backside of the images after printing.

[0076] As described above, it is possible to suppress the occurrence of blank images due to fusion. [Example]

[0077] In Example 1, the voltage applied to the primary transfer body 8 is set to a constant value, but the value of the voltage applied to the developing means 7 during image formation operation may be detected and the voltage applied to the primary transfer body 8 may be changed.

[0078] <Setting and controlling the voltage applied to the primary transfer body> This will be explained using Figure 10. After a job is started (S1), image formation begins (S2). Next, it is determined whether the image coverage rate is below a threshold (S3). If it is above the threshold (N in S3), it is determined whether the job has ended (S7). If it has not ended, the process returns to image formation (S2). If it is below the threshold (Y in S3), the number of printed sheets is counted (S5) and determined whether it is above the threshold (S5). If it is not above the threshold (N in S5), the process returns to image formation (S2). If it is above the threshold (Y in S5), the voltage applied to the developing means is detected (S6). After detection, the voltage applied to the primary transfer body 8 is changed to be equivalent to the detected voltage (S7). Next, toner consumption control is executed (S8), and it is determined whether the job has ended (S9). If the job has not ended, it returns to image formation (S2); if it has ended (Y in S9), the process ends.

[0079] By implementing this control, even if the voltage applied to the developing means is changed while the paper is passing, the primary transfer applied voltage can be set appropriately, and white dot images due to fusion can be suppressed.

[0080] <Comparative Example> FIG. 11 shows the results of this example and the comparative example.

[0081] In Comparative Example 3, the voltage applied to the primary transfer of the toner consumption control was set to -400 V, which was below the discharge start voltage and at a level where the toner in the toner consumption control would not be transferred to the intermediate transfer belt. Using an image forming apparatus, 2000k full-page white images on A3 size paper were continuously output on both sides, more than in Example 1, and the voltage applied to the developing unit was changed every 100 sheets to maintain a constant image density. We checked whether toner contamination occurred on the backside of the images that had been fed through the paper, and finally printed a full-page image to check whether whiteout images due to fusion occurred. In this Example, neither image contamination nor whiteout images due to fusion occurred, but in Comparative Example 3, whiteout images due to fusion occurred.

[0082] <Other> In this embodiment, an example of performing a toner consumption operation as a developer refreshing operation in a developing device has been described, but this is not limited to this. For example, this can also be applied when a patch image (corresponding to the specified toner in this embodiment) passes through a transfer section during an adjustment operation in which a patch image for image adjustment is formed to adjust image formation conditions. This can also be applied during a toner supply operation in which a toner band (corresponding to the specified toner in this embodiment) is supplied as a lubricant to a cleaning blade of a photosensitive drum.

[0083] In addition, in this embodiment, when the toner fusion suppression toner band passes through the primary transfer section, a bias similar to that used in the toner consumption operation (a bias of the same polarity as the toner and less than the discharge start voltage) may be applied to the primary transfer body 8.

[0084] That is, when the toner fusion suppressing toner band passes through the primary transfer unit, the CPU 301 may control the voltage applied by the power supply unit to the primary transfer body 8 so that a bias of the same polarity as the normal charging polarity of the toner is applied at a bias less than the discharge start voltage. Also, if the bias is less than the discharge start voltage, the DC voltage applied to the developing means may be applied to the negative side. However, the toner fusion prevention toner band is formed so that the amount of toner carried per unit area is smaller than that of the predetermined toner image formed during the toner consumption operation (developer refreshing operation) described above, and therefore the voltage may be equal to or higher than the discharge start voltage when the toner fusion prevention toner band passes through the primary transfer portion. [Explanation of symbols]

[0085] 2 Intermediate transfer body 3 Imaging unit 4 Photosensitive drum 5. Charging means 6 Exposure means 7. Developing Methods 8 Primary transfer means 9 Cleaning Device 301 Cleaning Blade 302 Bias Roller 303 Bias Roller Blade 304 Fur Brush Roller 306 Conveying screw 307 Bias application device 308 Pre-cleaning static elimination device

Claims

1. an image carrier; a developing device to which a developing bias is applied and which develops the latent image formed on the image carrier with toner; an intermediate transfer belt onto which the toner formed on the image carrier is transferred; a transfer member that transfers the toner image formed on the image carrier to the intermediate transfer belt at a transfer section; a first applying unit that applies a transfer bias to the transfer member; a cleaning blade that comes into contact with the image carrier to clean the toner remaining on the image carrier; a fur brush that is provided upstream of the cleaning blade in the rotation direction of the image carrier and that is capable of contacting the image carrier to clean toner remaining on the image carrier; a second applying unit capable of applying a cleaning bias to the fur brush; a control unit capable of executing a toner consumption operation for transferring a predetermined toner from the developing device to the image carrier, an image forming apparatus configured to control the control unit to control the first application unit so that, when performing the toner consumption operation, a predetermined bias is applied to the transfer member when the specified toner passes through the transfer unit, the predetermined bias having the same polarity as the charging polarity of the toner, the difference between which and the DC voltage of the developing bias is less than a discharge start voltage, and the absolute value of which is greater than the absolute value of the DC voltage of the developing bias; and to control the second application unit so that a cleaning bias of the opposite polarity to the toner is applied when the specified toner passes through the fur brush.

2. 2. The image forming apparatus according to claim 1, wherein the absolute value of the predetermined bias is smaller than the absolute value of the dark potential of the image carrier.

3. 2. The image forming apparatus according to claim 1, wherein the predetermined bias is applied from at least before the leading edge of the predetermined toner passes through the transfer section until after the trailing edge of the predetermined toner passes through the transfer section.

4. a first cleaning brush that is rotatably provided, to which a first cleaning bias is applied, and that comes into contact with the intermediate transfer belt to clean toner remaining on the intermediate transfer belt; 2. The image forming apparatus according to claim 1, further comprising: a second cleaning brush that is rotatably provided, to which a second cleaning bias is applied, and that contacts the intermediate transfer belt to clean toner remaining on the intermediate transfer belt.

5. 2. The image forming apparatus according to claim 1, wherein the control unit executes the toner consumption operation based on image information.

6. an image carrier; a developing device to which a developing bias is applied and which develops the latent image formed on the image carrier with toner; an intermediate transfer belt onto which the toner formed on the image carrier is transferred; a transfer member that transfers the toner image formed on the image carrier to the intermediate transfer belt in a transfer section; a first application section that applies a transfer bias to the transfer member; a cleaning blade that comes into contact with the image carrier to clean the toner remaining on the image carrier; a fur brush that is provided upstream of the cleaning blade in the rotation direction of the image carrier and that is capable of contacting the image carrier to clean toner remaining on the image carrier; a second applying unit capable of applying a cleaning bias to the fur brush; a control unit capable of executing a toner consumption operation for transferring a predetermined toner from the developing device to the image carrier, The control unit is configured to control the first application unit so that, when performing the toner consumption operation, a predetermined bias is applied to the transfer member when the specified toner passes through the transfer unit, the predetermined bias having the same polarity as the charging polarity of the toner, and whose difference from the DC voltage of the developing bias is less than a discharge start voltage, and the difference is 10% or less of the absolute value of the DC voltage of the developing bias, and to control the second application unit so that a cleaning bias of the opposite polarity to the toner is applied when the specified toner passes through the fur brush.

7. 7. The image forming apparatus according to claim 6, wherein the absolute value of the predetermined bias is smaller than the absolute value of the DC voltage of the developing bias.

8. 7. The image forming apparatus according to claim 6, wherein the predetermined bias is applied from at least before the leading edge of the predetermined toner passes through the transfer section until after the trailing edge of the predetermined toner passes through the transfer section.

9. a first cleaning brush that is rotatably provided, to which a first cleaning bias is applied, and that cleans toner remaining on the intermediate transfer belt; 7. The image forming apparatus according to claim 6, further comprising: a second cleaning brush that is rotatably provided, to which a second cleaning bias is applied, and that cleans toner remaining on the intermediate transfer belt.

10. 7. The image forming apparatus according to claim 6, wherein the control unit executes the toner consumption operation based on image information.

Images