JP4656228B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an electrophotographic image forming apparatus and a charging roller cleaning roller used in the image forming apparatus.

  An electrophotographic image forming apparatus includes an electrostatic latent image carrier that carries an electrostatic latent image. When forming an image, the outer peripheral surface of the electrostatic latent image carrier is first uniformly charged to a predetermined potential by a charging device, and then an electrostatic latent image is formed on the electrostatic latent image carrier by exposure by an exposure device. Is done. The electrostatic latent image formed on the electrostatic latent image carrier is visualized with toner supplied from the developing device, whereby a toner image is formed on the electrostatic latent image carrier. The toner image formed on the electrostatic latent image carrier is transferred to a recording sheet such as paper directly or via an intermediate transfer member. The recording sheet to which the toner image has been transferred is heated and pressurized by a fixing device, whereby the toner image is fixed on the recording sheet.

  A charging roller, which is a type of charging device, is disposed in contact with the outer peripheral surface of the electrostatic latent image carrier, and the outer peripheral surface of the electrostatic latent image carrier is predetermined by applying a charging voltage to the charging roller. Charged to potential. The charging roller includes a cored bar and a conductive elastic layer that covers the outer periphery of the cored bar. As the conductive elastic layer, solid rubber or resin foam is used, and conductivity is imparted by adding carbon black or metal powder.

  A toner external additive on the electrostatic latent image carrier or a foreign matter such as toner may adhere to the outer peripheral surface of the charging roller, and this causes a problem that image quality deteriorates when charging failure occurs. is there.

  In order to solve such a problem, a technique has been proposed in which a cleaning roller for removing foreign matter attached to the outer peripheral surface of the charging roller is disposed in contact with the outer peripheral surface of the charging roller.

  Patent Documents 1 to 3 disclose a technique using a charging roller cleaning roller.

  The technique of Patent Document 1 is characterized in that the surface of the charging roller cleaning roller is formed of a polyurethane foam layer, and the number of cells in the polyurethane foam layer is increased. According to the technique of Patent Document 1, it is possible to increase the frequency with which the cell wall surface of the polyurethane foam layer contacts the charging roller, thereby improving the scraping property of the foreign matter.

  The technologies of Patent Document 2 and Patent Document 3 are characterized in that the surface of the cleaning roller for the charging roller is formed of an open cell melamine resin layer, and the density of the melamine resin layer is reduced. According to the techniques of Patent Document 2 and Patent Document 3, the melamine resin layer has excellent flexibility, and the scraped foreign matter easily enters the inside of the melamine resin layer. Foreign matter is difficult to accumulate in the cell. Therefore, the charging roller is hardly damaged by the cleaning roller or the foreign matter on the surface of the cleaning roller.

JP 2006-330613 A JP 2004-361916 A JP 2005-227411 A

  However, in the cleaning roller according to the technique of Patent Document 1, since each cell of the polyurethane foam layer is very small, foreign substances such as external additives are easily filled in the cells on the surface. For this reason, the wall surface of the cell of the polyurethane foam layer becomes difficult to contact the outer peripheral surface of the charging roller, and the scraping property of the foreign matter is not necessarily improved sufficiently. Further, when the polyurethane foam layer has a closed cell structure, the external additive tends to aggregate inside the surface cell or adhere to the cell wall surface. The outer peripheral surface is easily damaged.

  In addition, the cleaning roller according to the technique of Patent Document 2 and Patent Document 3 is large in each cell of the melamine resin layer, so the frequency of the wall surface of the cell of the melamine resin layer contacting the outer peripheral surface of the charging roller is low, The scraping ability of foreign matter is deteriorated. Furthermore, since the melamine-based resin layer has an open cell structure, foreign matter scraped off by the wall surface of the cell on the surface tends to escape from the melamine-based resin layer via another cell. In addition, since foreign substances are likely to enter the inside of the melamine-based resin layer, the foreign substances accumulated inside the melamine-based resin layer aggregate due to long-term use, thereby reducing the recovery performance of the foreign substances.

  Therefore, the present invention efficiently recovers foreign matters such as toner external additives attached to the outer peripheral surface while preventing damage to the outer peripheral surface of the charging roller, and improves its recovery performance over a long period of time. It is an object to provide a charging roller cleaning roller that can be maintained and an image forming apparatus including the same.

In order to solve the above problems, an image forming apparatus according to the present invention provides:
An electrostatic latent image carrier carrying an electrostatic latent image;
A charging roller disposed in contact with the outer peripheral surface of the electrostatic latent image carrier and charging the outer peripheral surface of the electrostatic latent image carrier;
An image forming apparatus comprising: a charging roller cleaning roller disposed in contact with the outer peripheral surface of the charging roller to remove foreign matter attached to the outer peripheral surface of the charging roller;
The charging roller cleaning roller includes a cored bar and a polyurethane foam layer covering an outer peripheral surface of the cored bar,
The polyurethane foam layer has 40 to 80 cells per inch,
The outer peripheral surface of the cleaning roller was observed with a scanning electron microscope at a magnification of 100 times, the opening area S1 and the entire area S were calculated for the wall surface of the observed cell, and the aperture ratio = (S1 / S × 100). The opening ratio of the wall surface of the cell of the polyurethane foam layer determined by (1) is 3% to 50%,
A precharging member for making the charging polarity of the deposit on the outer peripheral surface of the charging roller uniform is provided upstream of the charging roller cleaning roller in the rotation direction of the charging roller.

  According to the present invention, since the number of cells of the polyurethane foam layer of the cleaning roller for the charging roller is 40 pieces / inch or more, a large amount of foreign substances such as an external additive of the toner in the nip portion between the charging roller and the cleaning roller. The cell can be contacted. In addition, the number of cells of the polyurethane foam layer is 80 / inch or less, and each cell has a certain size, so that it is difficult for the cells to be clogged with foreign substances. Furthermore, the opening ratio of the cell wall surface of the polyurethane foam layer is set to 3% or more and 50% or less, whereby the structure of the polyurethane foam layer becomes an open cell structure close to the closed cell structure. Therefore, more foreign substances can be taken in than the general closed-cell structure polyurethane foam layer, and in comparison with a general open-cell structure, the aggregation of foreign substances hardly occurs. Therefore, the foreign matter adhering to the outer peripheral surface of the charging roller can be efficiently recovered, and the recovery performance can be satisfactorily maintained over a long period of time.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of the invention will be described with reference to the accompanying drawings. In the following description, terms indicating a specific direction (for example, “up”, “down”, “left”, “right”, and other terms including them, “clockwise direction”, “counterclockwise” ”) Is used to facilitate understanding of the invention with reference to the drawings, and the present invention should not be construed as being limited by the meaning of these terms.

[1. Image forming apparatus]
FIG. 1 shows a portion related to image formation of an electrophotographic image forming apparatus according to the present invention. The image forming apparatus may be any of a copier, a printer, a facsimile machine, and a multi-function machine having a combination of these functions. The image forming apparatus 1 includes a photoreceptor 12 that is an electrostatic latent image carrier. In the embodiment, the photoconductor 12 is formed of a cylindrical body, but the present invention is not limited to such a form, and an endless belt type photoconductor can be used instead. The photoreceptor 12 is drivingly connected to a motor (not shown), and is rotated in the direction of arrow 14 based on the driving of the motor. Around the photoconductor 12, a charging station 16, an exposure station 18, a developing station 20, a transfer station 22, and a cleaning station 24 are arranged along the rotation direction of the photoconductor 12.

  The charging station 16 includes a charging roller 26 as a charging device that charges the photosensitive layer, which is the outer peripheral surface of the photosensitive member 12, to a predetermined potential. The configuration of the charging roller 26 will be described later. In the exposure station 18, the image light 30 emitted from the exposure device 28 disposed in the vicinity of the photosensitive member 12 or away from the photosensitive member 12 travels toward the outer peripheral surface of the charged photosensitive member 12. A passage 32 is provided. On the outer peripheral surface of the photoconductor 12 that has passed through the exposure station 18, an electrostatic latent image is formed that includes a portion where the image light is projected and the potential is attenuated and a portion where the charged potential is substantially maintained. In the embodiment, the portion where the potential is attenuated is the electrostatic latent image portion, and the portion where the charged potential is substantially maintained is the electrostatic latent image non-image portion. The developing station 20 includes a developing device 34 that visualizes the electrostatic latent image using a powder developer. The developing device 34 includes a developing roller 40 that is disposed to face the outer peripheral surface of the photoconductor 12 and a housing 42 that stores the developer. For example, a one-component developer is used as the developer. As the toner constituting the developer, it is preferable to use a toner having a small particle diameter, which can improve the image quality. Specifically, the average particle diameter of the toner is preferably 4.5 μm or more and 7.0 μm or less. In addition, the average particle diameter as used in this specification shall point out the volume average particle diameter obtained by the measurement using the flow type particle image analyzer FPIA-2100 made by Sysmex Corporation. Here, the volume average particle diameter means a particle diameter obtained by the following method. First, a projected area is calculated for each particle, and assuming a sphere having the same projected area as the calculated projected particle area, the diameter and volume of the sphere are set as the particle diameter and the volume of the particle, respectively. After obtaining the particle diameter and volume for a predetermined number of particles by this method, it represents a volume-based distribution with the particle diameter as the horizontal axis and the integrated value of the volume as the vertical axis. The particle size at 50% is defined as the volume average particle size. The transfer station 22 includes a transfer device 36 that transfers a visible image formed on the outer peripheral surface of the photoreceptor 12 to a sheet 38 such as paper or film. In the embodiment, the transfer device 36 is represented as a cylindrical roller, but other types of transfer devices (for example, wire discharge transfer devices) can also be used. The cleaning station 24 includes a cleaning device 40 that collects untransferred toner remaining on the outer peripheral surface of the photoconductor 12 without being transferred to the sheet 38 at the transfer station 22 from the outer peripheral surface of the photoconductor 12. In the embodiment, the cleaning device 40 is shown as a plate-like blade, but other types of cleaning devices (for example, a rotary type or a fixed type brush type cleaning device) can be used instead.

  When the image forming apparatus 1 having such a configuration forms an image, the photoconductor 12 rotates clockwise based on the driving of a motor (not shown). At this time, the outer peripheral portion of the photoreceptor passing through the charging station 16 is charged to a predetermined potential by the charging roller 26. The charged outer periphery of the photoconductor is exposed to image light 30 at an exposure station 18 to form an electrostatic latent image. The electrostatic latent image is conveyed to the developing station 20 along with the rotation of the photosensitive member 12, where it is visualized as a developer image by the developing device 34. The visualized developer image is conveyed to the transfer station 22 along with the rotation of the photosensitive member 12, and is transferred to the sheet 38 by the transfer device 36 there. The sheet 38 to which the developer image has been transferred is conveyed to a fixing station (not shown), where the developer image is fixed to the sheet 38. The outer peripheral portion of the photosensitive member that has passed through the transfer station 22 is conveyed to the cleaning station 24 where the developer remaining on the outer peripheral surface of the photosensitive member 12 without being transferred to the sheet 38 is recovered.

[2. (Charging roller)
The charging roller 26 includes a metal core 50 and a conductive elastic layer 52 that covers the outer periphery of the metal core 50. As the material of the conductive elastic layer 52, for example, solid rubber or resin foam is used, and conductivity is imparted by adding conductive particles such as carbon black or metal powder. The charging roller 26 is disposed in parallel with the photoreceptor 12 and rotatable. The charging roller 26 is drivingly connected to a motor (not shown) and is rotated counterclockwise in the figure by driving the motor. As a result, the photosensitive member 12 and the charging roller 26 rotate in the direction of movement in the same direction (so-called with direction) at the contact portion. A power supply 68 for applying a charging voltage is connected to the charging roller 26. When the charging voltage is applied to the charging roller 26 by turning on the power supply 68, the outer peripheral surface of the photoreceptor 12 is predetermined. Is charged to a potential of

  On the outer peripheral surface of the charging roller 26, a foreign additive such as toner external toner or toner on the photosensitive member 12 may adhere to the contact portion with the photosensitive member 12. Thus, in order to remove the foreign matter adhering to the outer peripheral surface of the charging roller 26, the first cleaning roller 54 and the second cleaning roller 60 as the charging roller cleaning roller come into contact with the outer peripheral surface of the charging roller 26. Are arranged.

[3. (Charging roller cleaning roller)
The first cleaning roller 54 includes a metal core 56 and a polyurethane foam layer 58 that covers the outer periphery of the metal core 56. The specific configuration of the polyurethane foam layer 58 will be described in detail later. The first cleaning roller 54 is disposed in parallel to the charging roller 26 and rotatable. The first cleaning roller 54 is drivingly connected to a motor (not shown), and rotates in the clockwise direction in the drawing based on the driving of the motor. As a result, the charging roller 26 and the cleaning roller 54 rotate in the direction of movement in the same direction at the contact portion (nip portion) 66 (so-called with direction). As shown in FIG. 2, the foreign matter on the charging roller 26 is scraped off by the cleaning roller 54 at the nip portion 66.

The peripheral speed of the cleaning roller 54 is determined according to the peripheral speed of the charging roller 26. Specifically, the ratio R (V _B / V _A ) of the peripheral speed V _B of the cleaning roller 54 to the peripheral speed V _A of the charging roller 26 is set to be 0.5 or more and 3 or less, for example. If the peripheral speed ratio R (V _B / V _A ) is set to be smaller than 0.5, a sufficient scraping force for the foreign matter on the charging roller 26 by the cleaning roller 54 cannot be secured. On the other hand, if the peripheral speed ratio R (V _B / V _A ) is set to be larger than 3, an excessive load is applied to the polyurethane foam layer 58 of the cleaning roller 54. Note that the cleaning roller 54 may be driven by the charging roller 26 without driving the motor to the cleaning roller 54. In that case, the peripheral speed ratio R (V _B / V _A ) is 1.0.

  The cleaning roller 54 is arranged so that the contact pressure to the charging roller 26 is 5N or more and 30N or less. If the contact pressure to the charging roller 26 is smaller than 5N, the cleaning roller 54 cannot sufficiently secure the foreign matter scraping force on the charging roller 26. On the other hand, if the contact force to the charging roller 26 is greater than 30N, an excessive load is applied to the charging roller 26.

  The cleaning roller 54 is preferably arranged so that the contact nip width between the cleaning roller 54 and the charging roller 26 is 3 mm or more and 8 mm or less in the circumferential direction. By setting the contact nip width to 3 mm or more, the scraping force of the foreign matter on the charging roller 26 by the cleaning roller 54 can be sufficiently secured, and by setting the contact nip width to 8 mm or less, the load on the charging roller 26 is suppressed. it can.

  The amount of the polyurethane foam layer 58 biting into the charging roller 26 is preferably 5% to 40% of the thickness of the polyurethane foam layer 58. By setting the biting amount to 5% or more, it is possible to sufficiently secure the scraping force of the foreign matter on the charging roller 26 by the cleaning roller 54. By setting the biting amount to 40% or less, the polyurethane foam layer 58 of the cleaning roller 54 It is possible to suppress the load applied to.

  A scraping member 70 is disposed in contact with the outer peripheral surface of the cleaning roller 54. At the contact portion between the cleaning roller 54 and the scraping member 70, a part of the foreign matter contained in the polyurethane foam layer 58 of the cleaning roller 54 is scraped off by the scraping member 70. Thereby, it is possible to prevent excessive foreign matter from accumulating inside the polyurethane foam layer 58 and to suppress aggregation of foreign matters inside the polyurethane foam layer 58. However, in the present invention, the scraping member is not necessarily provided. A specific example of the configuration of the scraping member will be described later.

  A power supply for applying a predetermined voltage to the cleaning roller 54 is formed between the cleaning roller 54 and the charging roller 26 to form an electric field that electrostatically moves foreign matter on the charging roller 26 to the cleaning roller 54. May be connected.

  Similar to the first cleaning roller 54, the second cleaning roller 60 includes a metal core 62 and a polyurethane foam layer 64 that covers the outer periphery of the metal core 62. The polyurethane foam layer 64 has the same configuration as the polyurethane foam layer 58 of the first cleaning roller 54. Similar to the first cleaning roller 54, the second cleaning roller 60 is arranged in parallel to the charging roller 26 and rotatable in the so-called with direction with respect to the charging roller 26. In the embodiment, the second cleaning roller is disposed downstream of the first cleaning roller 54 in the rotation direction of the charging roller 26, but is disposed upstream of the first cleaning roller 54. May be. Further, similarly to the first cleaning roller 54, a scraping member for scraping off foreign matters contained in the polyurethane foam layer 64 may be disposed in contact with the outer peripheral surface of the second cleaning roller 60. Good. Further, instead of the second cleaning roller 60, another type of cleaning member (fixed or rotating cleaning brush or the like) may be used. However, in the present invention, it is not always necessary to provide a plurality of cleaning members for the charging roller, and only the first cleaning roller 54 may be provided.

[4. (Polyurethane foam layer of cleaning roller)
As shown in FIG. 3, the polyurethane foam layer 58 has a large number of cells (bubbles) 80. A cell 80 having an opening 82 on the wall surface is connected to another cell 80 through the opening 82. When the ratio of the area S ₁ of the opening 82 to the area S of the entire wall surface of the cell 80 (S ₁ / S × 100) is defined as the opening ratio, the opening ratio of the cell wall surface of the polyurethane foam layer 58 is 3% or more and 50%. It is as follows. The opening ratio is higher than the opening ratio (about 1%) of a polyurethane foam having a general closed cell structure manufactured by a known mechanical floss method or the like, and is generally manufactured by a known chemical foaming method or the like. It is lower than the open area ratio (about 60%) of polyurethane foam having an open cell structure. That is, the polyurethane foam layer 58 has an open cell structure close to a closed cell structure. Therefore, more foreign substances can be taken in than the general closed-cell structure polyurethane foam layer, and in comparison with a general open-cell structure, the aggregation of foreign substances hardly occurs. Therefore, it is possible to sufficiently secure the foreign substance recovery performance and maintain the recovery performance well over a long period of time.

  In addition, the polyurethane foam layer 58 has 40 to 80 cells per inch. This number of cells is smaller than the number of cells of a general closed-cell structure polyurethane foam (about 100 cells / inch) and larger than the number of cells of a general open-cell structure polyurethane foam (about 25 cells / inch). . That is, the polyurethane foam layer 58 can bring a larger number of cells into contact with foreign matter at a nip portion 66 between the cleaning roller 54 and the charging roller 26 than a polyurethane foam having a general open cell structure. Moreover, since each cell of the polyurethane foam layer 58 is larger than a polyurethane foam having a general closed-cell structure, it is difficult for foreign matter to be clogged in each cell.

  The polyurethane foam layer 58 has a hardness as low as that of a general open cell structure. In the present specification, the hardness of the polyurethane foam layer 58 is determined so that the polyurethane foam layer 58 is pressed to a depth corresponding to 30% of the surface side of the thickness (until the thickness of the polyurethane foam layer 58 becomes 70% of the original). It is represented by the magnitude of the load per unit length that the pressing surface receives when it is pushed into the contacting surface. Specifically, the hardness of the polyurethane foam layer 58 is preferably 2 gf / mm or more and 6 gf / mm or less. This hardness is smaller than the hardness when the polyurethane foam layer has a general closed cell structure (about 8.5 gf / mm), and the hardness when the polyurethane foam layer has a general open cell structure (0.8 gf). / Mm). By setting the hardness of the polyurethane foam layer 58 to 2 gf / m or more, it is possible to sufficiently ensure the scraping power of the foreign matter by the polyurethane foam layer 58, so that the foreign matter on the charging roller 26 is separated from the charging roller 26 and the polyurethane foam layer. It is possible to prevent slipping through the nip portion 66 with 58. By setting the hardness of the polyurethane foam layer 58 to 8 gf / m or less, the polyurethane foam layer 58 can be prevented from pressing the outer peripheral surface of the charging roller 26 with an excessive force. Therefore, it is possible to prevent foreign matter on the charging roller 26 from being crushed by the polyurethane foam layer 58 and causing filming on the outer peripheral surface of the charging roller 26.

  Furthermore, the average value of the cell diameter of the polyurethane foam layer 58 is preferably 100 μm or more and 500 μm or less. The average value of the cell diameter is smaller than the cell diameter (about 700 μm) of a general open-cell structure polyurethane foam layer, and larger than the cell diameter (about 80 μm) of a general closed-cell structure polyurethane foam layer. . That is, since the polyurethane foam layer 58 has finer cells than a polyurethane foam layer having a general open cell structure, the polyurethane foam layer 58 is frequently in contact with foreign matter on the charging roller 26 and can more reliably scrape foreign matter. .

Furthermore, the polyurethane foam layer 58 has a lower density than a polyurethane foam layer having a general closed cell structure. Specifically, the density of the polyurethane foam layer 58 is preferably 0.03 g / cm ³ or more and 0.2 g / cm ³ or less. Thereby, the flexibility of the polyurethane foam layer 58 can be sufficiently secured, and the charging roller 26 can be prevented from being pressed by the polyurethane foam layer 58 with an excessive force.

When a predetermined electric field is formed between the charging roller 26 and the cleaning roller 54, the polyurethane foam layer 58 is provided with conductivity. In this case, the volume resistivity of the polyurethane foam layer 58 is preferably 10 ³ Ωcm or more and 10 ⁷ Ωcm or less. Thereby, the polyurethane foam layer 58 has appropriate electrical conductivity, and an appropriate electric field can be formed between the charging roller 26 and the cleaning roller 54.

[5. (Polyurethane foam production method)
With respect to the polyurethane foam layer 58 having the above configuration, a method for producing a polyurethane foam as a material thereof will be described.

  The polyurethane foam used in the present invention is produced by a method combining a known mechanical flossing method and a known chemical foaming method.

  The mechanical flossing method and the chemical foaming method are common in that foaming is performed by mixing a polyol and an isocyanate. However, in the mechanical froth method, a foaming agent is not used as a raw material, and physical foaming is performed by mixing a gas for forming bubbles such as an inert gas, whereas in a chemical foaming method, a raw material is used. The difference is that a foaming agent is used and chemical foaming is performed by a chemical reaction between the isocyanate and the foaming agent. When the mechanical floss method is employed, a polyurethane foam having a homogeneous closed cell structure can be produced, but it is difficult to produce a polyurethane foam having an open cell structure having a low density. On the other hand, when the chemical foaming method is employed, a low-density open-cell structure polyurethane foam can be easily produced, but it is difficult to produce a homogeneous closed-cell structure polyurethane foam.

  In contrast to these conventional manufacturing methods, the polyurethane foam manufacturing method used in the present invention is used in the chemical foaming method in addition to the polyol, isocyanate and gas for forming bubbles used in the mechanical floss method. A foaming agent is used as a raw material, which combines physical foaming due to the incorporation of gas for forming bubbles and chemical foaming associated with the chemical reaction of the isocyanate and the foaming agent. Therefore, homogeneous cells formed by physical foaming are joined together by chemical foaming, and a homogeneous and low density polyurethane foam, that is, a polyurethane foam having an open cell structure close to a closed cell structure can be produced. Hereinafter, a specific manufacturing method will be described.

  The polyurethane foam used in the present invention is produced from the beginning through a raw material adjustment step, a mixing step, and a heating step.

  In the raw material adjusting step, each raw material used for manufacturing the polyurethane foam is adjusted. As raw materials, secondary materials such as polyol, isocyanate, gas for forming bubbles such as inert gas, foaming agent, and catalyst are used.

  As a polyol, the well-known polyol which has an active hydrogen group is used individually or in combination of 2 or more types, for example. Specifically, examples of the polyol used include polyether polyol, polyester polyol, polycarbonate polyol, and polydiene-based polyol. As the isocyanate, for example, a well-known aromatic system such as toluene diphenyl diisocyanate (TDI), TDI prepolymer, methylene diphenyl diisocyanate (MDI), crude MDI, polymeric MDI, uretdione-modified MDI, or carbodiimide-modified MDI, aliphatic or aliphatic Various polyisocyanates such as ring systems are used. For example, nitrogen is used as the gas for forming bubbles. As the foaming agent, a raw material that generates a gas by a chemical reaction with isocyanate is used, and specifically, water or the like is used. The blowing agent is mixed with the polyol in advance before the mixing step. As the catalyst, for example, an amine catalyst and an organic acid salt catalyst are used. Amine-based catalysts are mainly used to promote rapid chemical foaming, and organic acid salt-based catalysts are mainly used to cure the polyurethane foam backbone. As the organic acid salt catalyst, it is preferable to use a heat-sensitive catalyst that exhibits a catalytic effect by required heating. Thereby, the hardening of the skeleton of the polyurethane foam can be delayed more than the chemical foaming carried by the amine-based catalyst, and chemical foaming can surely occur.

  Factors that determine the hardness of the polyurethane foam include, for example, the type of polyol and the isocyanate index. In the present specification, the isocyanate index refers to a percentage of the ratio N / M of the number of moles of isocyanate groups in isocyanate to the total number of moles M of hydroxyl groups of the blowing agent and hydroxyl groups of the polyol. In order to form the polyurethane foam to have the above-mentioned desired hardness, for example, a polyether polyol or a polyester polyol having a molecular weight of 1000 to 6000 and a functional group number of 2 to 5 is preferably used as the polyol. It is preferable to adjust the isocyanate index to 90 to 110.

  When water is used as a foaming agent, when each raw material is mixed, carbon dioxide is generated by a chemical reaction between water and isocyanate, thereby forming bubbles (cells). In order to form a low-density polyurethane foam having fine cells, carbon dioxide generated by a chemical reaction between water and isocyanate is placed inside the bubbles (cells) physically generated by the gas for forming bubbles. Need to get in. In order to achieve this object, it is preferable to adjust the mixing amount of water to 0.3 to 1.5 parts by mass with respect to 100 parts by mass of the polyol.

  In the mixing step, a polyol, an isocyanate, a gas for forming bubbles, a catalyst, and the like mixed with a foaming agent such as water are mixed. As a result, first, physical foaming occurs, and homogeneous bubbles (cells) having a bubble-forming gas as a nucleus are formed. Then, a gas such as carbon dioxide is generated by causing a chemical reaction between the blowing agent contained in the polyol and the isocyanate, and this gas enters the cell formed by physical foaming, and the cell diameter as a whole. Increases and the cells are connected. Thereby, a cell having a large diameter is formed while being homogeneous.

  In the heating step, the mixed raw material is heated to accelerate the resinification reaction and cure the polyurethane foam skeleton. The heating temperature and heating time in the heating step are appropriately determined according to the raw material of the polyurethane foam in accordance with a known mechanical flossing method.

  According to the manufacturing method demonstrated above, the polyurethane foam with a high opening rate of a cell wall surface is formed compared with the polyurethane foam manufactured by the mechanical floss method. For this reason, when the polyurethane foam is impregnated with a solution containing a conductive substance or the like, the solution easily penetrates into the polyurethane foam, so that a function such as conductivity can be easily imparted.

  The polyurethane foam manufactured in this way is processed into a desired shape and fixed to a cored bar, whereby the cleaning roller 54 is manufactured.

  Then, the method to provide electroconductivity to a polyurethane foam is demonstrated. As a method for imparting conductivity to the polyurethane foam, for example, a foam molding method using a raw material mixed with a conductive material such as carbon black, polypyrrole or an ionic conductive material, or a conductive material as described above is used. Examples include a method in which a polyurethane foam is impregnated with a solution to be contained and then the polyurethane foam is heated and dried.

  More preferably, a method of impregnating polyurethane foam into a solution containing carbon black is employed. According to this method, even after the conductivity is imparted, the properties of the polyurethane foam are not impaired, and it is possible to avoid as much as possible that the electrical resistance value and hardness of the polyurethane foam vary depending on the environment. The above carbon black refers to carbon black in a broad sense. Examples of carbon black that can be used include carbon black in a narrow sense such as furnace black, thermal black, channel black, acetylene black, ketjen black, and color black, and graphite. In addition, a polymer material obtained by polymerizing vinyl monomers in a branched manner on the surface of carbon black or graphite in a narrow sense can be used as the carbon black in a broad sense.

  A specific method for imparting conductivity to the polyurethane foam by impregnation will be described.

  First, carbon black is mixed with water or an organic solvent together with a binder to prepare an impregnating liquid having a predetermined viscosity. The binder is used to adhere and fix carbon black in the polyurethane foam. As the binder, a material having elasticity even after being fixed to the polyurethane foam is suitably used. Specifically, for example, rubber latex or the like is used. The viscosity of the impregnating liquid is not particularly limited, but is preferably about 8 to 15 cps under a temperature condition of 25 degrees from the viewpoint of allowing the impregnating liquid to easily penetrate into the polyurethane foam. The viscosity of the impregnating liquid can be adjusted, for example, by adjusting the blending ratio of water or an organic solvent and carbon black, or by adding a surfactant.

  When the polyurethane foam is impregnated with the impregnation liquid, the impregnation liquid penetrates from the surface of the polyurethane foam to the inside. Examples of the impregnation method include a method of applying an impregnation liquid on the surface of the polyurethane foam, a method of immersing the polyurethane foam in the impregnation liquid, and the like. It is preferable that the impregnating liquid penetrates from the surface of the polyurethane foam into a thickness portion of about 0.02 mm to 0.1 mm. Adjustment of the degree of impregnation with the impregnating liquid is performed by adjusting the conditions for squeezing the impregnating liquid from the impregnating liquid container, the polyurethane foam cell size, the impregnating liquid concentration, or the viscosity of the impregnating liquid. By doing.

By using the above impregnation liquid preparation method and impregnation method, it is possible to impart appropriate conductivity to the polyurethane foam layer 58 while suppressing an increase in the hardness of the polyurethane foam layer 58. The volume resistivity of the polyurethane foam layer 58 is preferably 10 ³ Ωcm or more and 10 ⁷ Ωcm or less. Further, from the viewpoint of reducing the influence on the hardness of the polyurethane foam layer 58, the volume resistivity of the polyurethane foam layer 58 is more preferably 10 ⁴ Ωcm or more and 10 ⁷ Ωcm or less, and more preferably 10 ⁵ Ωcm or more and 10 ⁷ Ωcm or less. Even more preferably.

  After the above impregnation is completed, the polyurethane foam is dried by heating. As a result, the water or organic solvent in the impregnating liquid that has penetrated into the polyurethane foam evaporates and the binder in the impregnating liquid is cured. When the binder is cured, the conductive material contained in the impregnating solution together with the binder is fixed to the cell wall surface of the polyurethane foam, thereby imparting conductivity to the polyurethane foam. The polyurethane foam is dried by heating, for example, at a temperature of 120 ° C. or more and 130 ° C. or less for a time of 20 minutes or more and 30 minutes or less. The conditions for the heat drying are the material and size of the polyurethane foam before drying, In addition, it is appropriately determined depending on the type of binder in the impregnating liquid.

  When conductivity is imparted to the polyurethane foam layer 58 of the cleaning roller 54, a predetermined electric field is formed between the charging roller 26 and the cleaning roller 54. Electrical action can also be used.

  More specifically, when most of the deposits (for example, toner or external additives) on the outer peripheral surface of the charging roller 26 are positively charged, the charging roller 26 and the cleaning roller 54 For example, a DC electric field (for example, a potential difference of 100 volts or more and 1000 volts or less) in which a negative current (for example, −30 μA or more and −10 μA or less) flows from the cleaning roller 54 to the charging roller 26 is formed. In this case, the positively charged deposit on the charging roller 26 is easily transferred to the cleaning roller 54 by the action of an electric field, and the outer peripheral surface of the charging roller 26 can be efficiently cleaned. However, the configuration of the electric field formed between the charging roller 26 and the cleaning roller 54 is not particularly limited. For example, by forming an AC electric field, not only the deposit charged to the positive polarity but also the negative polarity. It is also possible to make it possible to efficiently collect deposits that are electrically charged.

[6. Scraping member)
Next, the configuration of the scraping member that scrapes off the foreign matter in the polyurethane foam layer 58 of the cleaning roller 54 will be specifically described. The shape of the scraping member is not particularly limited, and for example, a blade-like, rod-like, or roller-like scraping member is used.

  In the embodiment shown in FIG. 1, a blade-shaped scraping member 70 is used. Thus, when using the blade-shaped scraping member 70, the material of the scraping member 70 is not specifically limited, For example, rubbers, such as urethane rubber, or metals, such as stainless steel or iron, are used. Even when a bar-shaped scraping member is used, the material of the scraping member is not particularly limited, and for example, rubber or metal can be used.

  In the embodiment shown in FIG. 4, a roller-shaped scraping member 72 is used. For example, iron is used as the material of the scraping member 72, but the material is not necessarily limited thereto. As a material other than iron used for the roller-shaped scraping member 72, for example, a metal such as aluminum, stainless steel, or an alloy, or a rubber such as urethane, EPDM, or NBR is used. Further, a roller having a plurality of layers such as a roller in which the surface of a metal roller or a rubber roller is covered with a coat layer may be used as the scraping member 72. Furthermore, a roller having a brush-like surface layer can also be used as the scraping member 72.

  The scraping member 72 is disposed parallel to the cleaning roller 54 and rotatably. The scraping member 72 is drivingly connected to a motor (not shown), and is rotated counterclockwise in the drawing by driving the motor. As a result, the cleaning roller 54 and the scraping member 72 rotate in the same direction (so-called with direction) at their contact portions.

  A scraper 74 made of metal, for example, is disposed in contact with the outer peripheral surface of the scraping member 72. Thereby, the foreign matter on the scraping member 72 scraped off from the cleaning roller 54 is scraped off by the scraper 74. Therefore, the scraping performance of the scraping member 72 can be satisfactorily maintained over a long period of time, and accordingly, the cleaning performance of the cleaning roller 54 can be maintained.

  In the embodiment shown in FIG. 4, not only an electric field (for example, a potential difference of 200 volts) is formed between the charging roller 26 and the cleaning roller 54, but also a predetermined electric field is generated between the cleaning roller 54 and the scraping member 72. It is preferable to configure so as to form a potential difference (for example, a potential difference of 100 volts). Thereby, the scraping performance of the scraping member 72 can be enhanced.

[7. (Pre-charging member)
As shown in FIG. 5, a pre-charging member 76 for making the charging polarity of the deposit on the outer peripheral surface of the charging roller 26 uniform may be provided upstream of the cleaning roller 54 in the rotation direction of the charging roller 26. In this case, by applying a predetermined positive or negative voltage to the pre-charging member 76, the charge polarity of the deposit on the charging roller 26 is made positive or negative, thereby cleaning the deposit. It becomes easy to collect by the roller 54.

In the embodiment shown in FIG. 5, the precharging member 76 has a base material 77 and brush fibers 78 attached to the base material 77. For the base material 77, a conductive material is used. Specific materials used for the substrate 77 include, for example, conductive nylon resin, polyester resin, acrylic resin, or vinylon resin. The brush fiber 78 is implanted in the base material 77. As the material of the brush fiber 78, for example, nylon resin such as nylon 66 or nylon 6, polyester resin, fluorine resin, acrylic resin, or vinylon resin is used. In addition, a conductive material such as carbon black is added to the material of the brush fiber 78, thereby imparting conductivity to the brush fiber 78. The single yarn diameter (thickness) of the brush fiber 78 is preferably 10 μm or more and 50 μm or less, and more preferably 20 μm or more and 30 μm or less. The density of the brush fibers 78 is preferably 50 kF / inch ² or more and 400 kF / inch ² or less, more preferably 200 kF / inch ² or more and 300 kF / inch ² or less. The pile length (projection length from the base material 77) of the brush fiber 78 is preferably 0.5 mm or more and 10 mm or less, and more preferably 3 mm or more and 8 mm or less. The volume resistivity of the brush fiber 78 is preferably 10 ⁵ Ωcm or more and 10 ¹⁴ Ωcm or less, more preferably 10 ⁶ Ωcm or more and 10 ⁸ Ωcm or less.

When a negative voltage is applied to the charging roller 26, the negatively charged toner among the toners on the photoconductor 12 is difficult to adhere to the charging roller 26, so that most of the toner attached to the charging roller 26 has a positive polarity. Charged. However, on the outer peripheral surface of the charging roller 26, not only the positively charged deposits but also the deposits having a charge amount of zero or substantially zero and the negatively charged deposits are present. Therefore, it is preferable to apply a positive voltage to the pre-charging member 76, whereby the charge polarity of the deposit on the charging roller 26 can be made positive. The deposit on the charging roller 26 whose charging polarity is made positive by the pre-charging member 76 is efficiently recovered by the cleaning roller 54 to which a negative voltage is applied. In this case, if the volume resistivity of the brush fiber 78 is 10 ⁶ Ωcm or more and 10 ⁸ Ωcm or less, the bias current applied to the pre-charging member 76 is preferably 10 μA or more and 100 μA or less, and 40 μA or more and ⁸⁰ μA or less. It is desirable that

However, a negative voltage may be applied to the pre-charging member 76. In this case, the charge polarity of the deposit on the charging roller 26 can be made negative. The deposit on the charging roller 26 whose charging polarity is made negative by the pre-charging member 76 is efficiently collected by the cleaning roller 54 to which a positive voltage is applied. In this case, if the volume resistivity of the brush fiber 78 is 10 ⁶ Ωcm or more and 10 ⁸ Ωcm or less, the bias current applied to the pre-charging member 76 is preferably −100 μA or more and −10 μA or less, and −80 μA. It is desirable that it is -40 μA or less.

In a more specific embodiment in which the pre-charging member 76 is provided, it is made of conductive nylon resin, the single yarn diameter (thickness) is 20 μm, the density is 240 kF / inch ² , and the pile length (projection length from the base material 77) B) is used, and a brush fiber 78 having a volume resistivity of 10 ⁸ Ωcm is used. A plurality of brush fibers 78 are planted in the base material 77 in a dense state. The overall density of the brush fibers 78 is a square bar shape that extends in the length direction of the charging roller 26 and has a width of 10 mm. In this embodiment, a DC electric field (a potential difference of 2500 volts) is formed between the precharging member 76 and the charging roller 26 so that a current of +60 μA flows from the precharging member 76 toward the charging roller 26. . As a result, the deposit on the charging roller 26 is uniformly charged positively before being collected by the cleaning roller 54. Further, in this embodiment, between the scraping member 72 and the cleaning roller 54, and between the cleaning roller 54 and the charging roller 26, the scraping member 72 passes through the cleaning roller 54 to the charging roller 26 to −30 μA. A DC electric field (potential difference of 100 volts) is formed so that a current of −10 μA or less flows. As a result, the adhering matter whose charging polarity is made positive by the pre-charging member 76 as described above is satisfactorily removed from the charging roller 26 by the cleaning roller 54 and the scraping member 72.

  When the precharge member 76 is provided as described above, the bias applied to the precharge member 76 may be controlled so as to discharge foreign matters such as toner staying in the precharge member 76. For example, in a configuration in which a positive bias is applied to the pre-charging member 76 during cleaning of the charging roller 26, most of the foreign matter staying inside the pre-charging member 76 is negatively charged or has a charged amount. Zero or nearly zero. Therefore, the foreign matter staying in the pre-charging member 76 is controlled on the charging roller 26 by controlling the bias to be applied to the pre-charging member 76 at an appropriate timing and having a polarity opposite to that in the normal state, that is, a negative polarity bias. Can be exhaled. After the discharge of the foreign matter is completed, the precharge member 76 may be controlled to apply a normal polarity, that is, a positive polarity bias again. When the toner is conveyed again to the portion opposite to the pre-charging member 76 along with the rotation of the roller 26, it is positively charged by the pre-charging member 76 and is collected from the charging roller 26 by the cleaning roller 54 to which a negative-polarity bias is applied. .

  The configuration of the pre-charging member does not necessarily have a brush shape as described above as long as it has a desired charging function. For example, a blade-shaped precharging member may be used, and in this case, for example, a material similar to the brush fiber 78 described above or a metal such as stainless steel or aluminum is used as the material of the precharging member. A rotary pre-charging member can also be used. In this case, for example, a rotating member having an outer peripheral surface formed in a brush shape or a rotating member made of a foam is preferably used.

  While the present invention has been described with reference to the above-described embodiments, the present invention is not limited to the above-described embodiments. For example, in the present invention, the method for producing the polyurethane foam layer is not necessarily limited to the above-described embodiment, and does not prevent the polyurethane foam layer from being produced by another method.

  A test was conducted to confirm suitable physical properties of the polyurethane foam layer of the charging roller cleaning roller. Specifically, as the physical properties of the polyurethane foam layer, suitable values of the number of cells, the cell wall opening ratio, hardness, average cell diameter and density were confirmed.

  As the image forming apparatus, an image forming apparatus of Magiccolor 5570 manufactured by Konica Minolta Co., Ltd. was used, and an appropriately modified charging roller cleaning roller was mounted on the image forming apparatus. Note that the second cleaning roller 60 and the scraping member 70 according to the above-described embodiment were not mounted.

  As the polyurethane foam layer of the charging roller cleaning roller, one made of any one of the materials 1 to 14 shown in Table 1 was used. These materials 1 to 14 were produced by the method described in the above embodiment, using polyol, isocyanate, amine-based catalyst, organic acid salt-based catalyst, water (foaming agent) and foam stabilizer as raw materials. Specifically, polyether polyol (trade name Actol ED-37B (number average molecular weight 3000); manufactured by Mitsui Takeda Chemical Co., Ltd.) was used as the polyol. As the isocyanate, methylene diphenyl diisocyanate (MDI) (trade name Millionate MTL-S; manufactured by Nippon Polyurethane) was used. As an amine-based catalyst, Kaolyzer No. 23NP was used. EP73660A manufactured by PANTECHNOLOGY was used as the organic acid salt catalyst. As the foam stabilizer, linear dimethylpolysiloxane (trade name: Niaxsilicone L5614; manufactured by GE Silicones) was used. The amount of each raw material used is as shown in Table 1.

A method for measuring physical properties of materials 1 to 14 will be described. Regarding the number of cells, the surface of the cleaning roller (3 locations in the axial direction × 8 locations in the circumferential direction) was observed with a scanning electron microscope (SEM), and the number of cells per inch was measured at each observed location, and the average value thereof was measured. Was calculated. Regarding the aperture ratio of the cell wall, it was observed at a magnification of 100 to the outer peripheral surface by scanning electron microscopy (SEM) of the cleaning roller, the wall surfaces of the cells of the observed surface and the area S ₁ of the openings to calculate the total area S The aperture ratio (S ₁ / S × 100) was determined. Regarding the hardness, an aluminum disk having a diameter of 55 mm was pushed into the polyurethane foam layer, and the repulsive force in the indentation axial direction per unit length when the thickness of the polyurethane foam layer reached 70% was measured. This measured value (gf / mm) was taken as hardness. The average cell diameter is measured with a scanning electron microscope (SEM) on the surface of the supply roller (3 in the axial direction × 8 in the circumferential direction), and the diameter of 10 cells (240 in total) is measured at each observation location. It calculated from those measured values. Regarding the density, the weight of the polyurethane foam layer was obtained by subtracting the weight of the core metal from the weight of the cleaning roller, the volume of the polyurethane foam layer was obtained based on the dimensions, and the density was calculated from the weight and the volume.

One experimental example (Experimental Example 1 to Experimental Example 14) was set for each polyurethane foam material to be used. In all the experimental examples, the contact pressure of the charging roller to the photoconductor is set to 50 g / cm, and the charging voltage applied to the charging roller is a DC voltage (−600 V) and an AC voltage (peak-to-peak voltage: 2000V, frequency: 150 Hz) was set to a superimposed voltage. In all the experimental examples, the rotation direction of the cleaning roller was set to a so-called with direction with respect to the charging roller. For each experiment, the contact pressure of the cleaning roller to the charging roller, the ratio of the circumferential velocity V _B of the cleaning roller to the circumferential speed V _A of the charging roller R (V B _{/ V A),} the contact nip between the charging roller and the cleaning roller The width, the amount of cleaning roller biting into the charging roller, and the average particle size of the toner were set as shown in Table 2. The peripheral speed V _A of the charging roller was set to 180 m / s, the same speed as that of the photosensitive member, and the peripheral speed ratio R (V _B / V _A ) was adjusted by changing the peripheral speed of the cleaning roller.

  For each experimental example, 100,000 solid images were continuously printed using the above-described image forming apparatus in an environment with an ambient temperature of 23 ° C. and a relative humidity of 53%, and evaluation on removal of foreign matters on the charging roller after the continuous printing was completed. And the evaluation about the image quality was performed. The evaluation regarding the removal of the foreign matter on the charging roller was performed comprehensively based on the evaluation regarding the removal of the toner and the evaluation regarding the removal of the external additive. To evaluate the toner removal, a transparent adhesive tape (manufactured by 3M, Scotch Mending Tape) was applied to the outer peripheral surface of the charging roller, and then the adhesive tape was peeled off, whereby the amount of toner adhered to the adhesive tape. Was observed visually. The evaluation regarding toner removal was expressed as “A” when the toner did not adhere to the adhesive tape and the adhesive tape remained transparent, and “B” when the toner partially adhered to the adhesive tape. In this case, a toner attached to the entire surface of the adhesive tape is represented by “C” (see Table 2). The evaluation regarding the removal of the external additive was performed by observing the outer peripheral surface of the charging roller by observing the amount of the external additive (white) adhering to the outer peripheral surface (black) of the charging roller. The evaluation regarding the removal of the external additive is expressed as “A” when no external additive is adhered to the outer peripheral surface of the charging roller or when the external additive is partially adhered. The thinly covered with the additive is represented by “B”, and the entire outer peripheral surface of the charging roller is thickly covered with the external additive is represented by “C” (see Table 2). Comprehensive evaluation regarding the removal of the foreign matter on the charging roller is expressed by “A” when both the evaluation regarding the removal of toner and the evaluation regarding the removal of the external additive are “A”, one is “A”, The case of “B” is represented by “B”, the case where one is “A” and the other is “C” is represented by “C”, and the case where both are not “A” is represented by “D” (Table 2). reference). Evaluation regarding image quality is expressed as “A” in the case where image disturbance due to charging failure during continuous printing of solid images did not occur even when printing 50,000 sheets, and when it occurred before printing 50,000 sheets Is represented by “B”, is represented by “C” when it occurs before printing 10,000 sheets, and is represented by “D” when it occurs from the initial continuous printing to 5,000 sheets printing (see Table 2). . In the above evaluation, “A” and “B” are used as acceptance criteria.

  The test results shown in Table 2 will be examined.

  As for Experimental Examples 1 to 10 using the materials 1 to 10, the evaluation regarding the removal of foreign matters and the evaluation of the image quality both satisfy the acceptance criteria. On the other hand, in all of Experimental Examples 11 to 14 using the materials 11 to 14, the evaluation regarding the removal of the foreign matter and the evaluation of the image quality were bad.

  The reason why the evaluation in Experimental Example 11 is poor is that the number of cells (35 / inch) of the material 11 is smaller than the number of cells (40 to 85 / inch) of the other materials, so that the polyurethane foam layer in contact with the charging roller This is probably because the number of cells is small and the foreign matter on the charging roller cannot be sufficiently scraped off by the cleaning roller. From this, it was found that the number of cells of the polyurethane foam layer is preferably 40 / inch or more.

  The reason why the evaluation in Experimental Example 12 is bad is that the number of cells of the material 12 (85 cells / inch) is larger than the number of cells of other materials (35-80 cells / inch). This is considered to be because the foreign matter is filled up with foreign matter, and the foreign matter aggregates in the cells on the surface of the cleaning roller, and the force with which the cleaning roller scrapes off the foreign matter is reduced. From this, it was found that the number of cells of the polyurethane foam layer is preferably 80 / inch or less. Therefore, the number of cells in the polyurethane foam layer is preferably 40 cells / inch or more and 80 cells / inch or less.

  The reason why the evaluation in Experimental Example 13 is bad is that the aperture ratio (2%) of the cell wall surface of the material 13 is lower than the aperture ratio (3-55%) of the cell wall surface of the other material, and the material 13 is almost completely independent. This is thought to be due to the bubble structure. Specifically, when the polyurethane foam layer has a closed cell structure, the foreign matter scraped off by the cleaning roller does not easily enter the inside of the polyurethane foam layer and agglomerates in the cells near the surface of the polyurethane foam layer. It is easy to stick to the wall. When agglomerates or sticking substances of foreign matter are generated on the surface of the cleaning roller, the agglomerates or sticking substances come into contact with the outer peripheral surface of the charging roller, thereby damaging the outer peripheral surface of the charging roller. Is thought to worsen. From this, it was found that the opening ratio of the cell wall surface of the polyurethane foam layer is preferably 3% or more.

  The reason why the evaluation in Experimental Example 14 is bad is that the opening ratio (55%) of the cell wall surface of the material 14 is higher than the opening ratio (2 to 50%) of the cell wall surface of the other material. This is probably because foreign matter is gradually accumulated in the cleaning roller, and the cleaning roller foreign matter scraping force gradually decreases. From this, it was found that the opening ratio of the cell wall surface of the polyurethane foam layer is preferably 50% or less. Therefore, the opening ratio of the cell wall surface of the polyurethane foam layer is preferably 3% or more and 50% or less.

  Further, in Experimental Example 1 to Experimental Example 10 in which both the evaluation regarding the removal of foreign matter and the evaluation regarding the image quality satisfy the acceptance criteria, the hardness of the material is 2 to 6 gf / mm. From this, it was confirmed that if the hardness of the polyurethane foam layer is 2 gf / mm or more and 6 gf / mm or less, sufficient cleaning performance can be secured by satisfying other conditions.

  Furthermore, in Experimental Example 1 to Experimental Example 10 in which both the evaluation regarding the removal of foreign matter and the evaluation regarding the image quality satisfy the acceptance criteria, the average cell diameter is 100 to 500 μm. From this, it was confirmed that if the average cell diameter of the polyurethane foam layer is 100 μm or more and 500 μm or less, sufficient cleaning performance can be secured by satisfying other conditions.

In addition, the density of the polyurethane foam layer is 0.03 to 0.2 g / cm ³ in Experimental Example 1 to Experimental Example 10 in which both the evaluation regarding the removal of foreign matter and the evaluation regarding the image quality satisfy the acceptance criteria. From this, it was confirmed that if the density of the polyurethane foam layer is 0.03 g / cm ³ or more and 0.2 g / cm ³ or less, sufficient cleaning performance can be secured by satisfying other conditions.

1 is a diagram illustrating a schematic configuration of an image forming apparatus according to the present invention. FIG. 4 is an enlarged cross-sectional view illustrating a contact portion between a charging roller and a cleaning roller. It is a figure which shows the cell structure of a polyurethane foam layer. It is a figure which shows embodiment which uses a roller-shaped scraping member. It is a figure which shows embodiment using a pre-charging member.

Explanation of symbols

1: Image forming device, 12: Photoconductor, 16: Charging station, 18: Exposure station, 20: Development station, 22: Transfer station, 24: Cleaning station, 26: Charging roller, 28: Exposure device, 30: Image light 32: passage, 34: developing device, 36: transfer device, 38: sheet, 40: cleaning device, 42: housing, 44: developing roller, 50: cored bar, 52: conductive elastic layer, 54: first Cleaning roller, 56: core metal, 58: polyurethane foam layer, 60: second cleaning roller, 62: core metal, 64: polyurethane foam layer, 66: contact portion (nip portion) between charging roller and cleaning roller, 68: Power supply, 70, 72: Scraping member, 76: Pre-charging member, 80: Cell of polyurethane foam layer, 82 The opening of the cell wall.

Claims (12)

An electrostatic latent image carrier carrying an electrostatic latent image;
A charging roller disposed in contact with the outer peripheral surface of the electrostatic latent image carrier and charging the outer peripheral surface of the electrostatic latent image carrier;
An image forming apparatus comprising: a charging roller cleaning roller disposed in contact with the outer peripheral surface of the charging roller to remove foreign matter attached to the outer peripheral surface of the charging roller;
The charging roller cleaning roller includes a cored bar and a polyurethane foam layer covering an outer peripheral surface of the cored bar,
The polyurethane foam layer has 40 to 80 cells per inch,
The outer peripheral surface of the cleaning roller was observed with a scanning electron microscope at a magnification of 100 times, the opening area S1 and the entire area S were calculated for the wall surface of the observed cell, and the aperture ratio = (S1 / S × 100). The opening ratio of the wall surface of the cell of the polyurethane foam layer determined by (1) is 3% to 50%,
An image characterized in that a pre-charging member for making the charged polarity of the deposit on the outer peripheral surface of the charging roller uniform is provided upstream of the charging roller cleaning roller in the rotation direction of the charging roller. Forming equipment. 2. The image forming apparatus according to claim 1 , wherein a contact pressure of the charging roller cleaning roller to the charging roller is 5 N / m or more and 30 N / m or less. The amount of penetration of the polyurethane foam layer into the charging roller is 5% to 40% of the thickness of the polyurethane foam layer,
3. The image forming apparatus according to claim 1 , wherein a contact nip width between the charging roller cleaning roller and the charging roller in a circumferential direction of the charging roller cleaning roller is 3 mm or more and 8 mm or less. Scraping member for scraping the foreign matters contained in the interior of the polyurethane foam layer, in any one of claims 1 to 3, characterized in that it is arranged in contact with the outer peripheral surface of the charging roller cleaning roller The image forming apparatus described. The image forming apparatus according to claim 1, wherein a cleaning member different from the charging roller cleaning roller is disposed in contact with the outer peripheral surface of the charging roller. 6. The image forming apparatus according to claim 1, wherein the charging roller and the cleaning roller for the charging roller rotate in a direction in which the charging roller and the charging roller move in the same direction. Including toner used to visualize the electrostatic latent image,
The image forming apparatus according to claim 1, wherein the toner has an average particle size of 4.5 μm or more and 7.0 μm or less. An aluminum disk having a diameter of 55 mm was pushed into the polyurethane foam layer, and the repulsive force in the indentation axial direction per unit length measured when the thickness of the polyurethane foam layer reached 70% was 2 gf / The image forming apparatus according to claim 1, wherein the image forming apparatus has a thickness of not less than mm and not more than 6 gf / mm . The image forming apparatus according to claim 1, wherein an average value of the cell diameters is 100 μm or more and 500 μm or less . The image forming apparatus according to claim 1, wherein the density of the polyurethane foam layer is 0.03 g / cm ³ or more and 0.2 g / cm ³ or less . The image forming apparatus according to claim 1, wherein the polyurethane foam layer has a volume resistivity of 10 ³ Ωcm or more and 10 ⁷ Ωcm or less . The polyurethane foam layer is manufactured by mixing a polyol, an isocyanate, a gas for forming bubbles, and a foaming agent that generates a gas by a chemical reaction with the isocyanate . The image forming apparatus according to any one of the above.

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