Cleaning member and image forming apparatus

A cleaning member includes a core and first and second foamed elastic layers wound around an outer peripheral surface of the core in a double-helical pattern. The compressive stress F1 of the first foamed elastic layer is greater than the compressive stress F2 of the second foamed elastic layer. The cleaning member cleans a member to be cleaned with the first and second foamed elastic layers in contact with a surface of the member to be cleaned.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based on and claims priority under 35 USC 119 from Japanese Patent Application No. 2018-073249 filed Apr. 5, 2018.

BACKGROUND

Technical Field

The present invention relates to a cleaning member and an image forming apparatus.

SUMMARY

According to an aspect of the invention, there is provided a cleaning member including a core and first and second foamed elastic layers wound around the outer peripheral surface of the core in a double-helical pattern. The compressive stress F1 of the first foamed elastic layer is greater than the compressive stress F2 of the second foamed elastic layer. The cleaning member cleans a member to be cleaned with the first and second foamed elastic layers in contact with a surface of the member to be cleaned.

DETAILED DESCRIPTION

Configuration of Image Forming Apparatus

FIG. 1illustrates an exemplary configuration of an image forming apparatus1according to an exemplary embodiment. The illustrated image forming apparatus1is a monochrome printer including an image forming unit10that forms an image corresponding to image data; a user interface (UI)4that receives an instruction from a user and displays, for example, a message for the user; a controller5that controls the operation of the entire image forming apparatus1; and an image processor6that is connected to external devices such as a personal computer (PC)2and an image reader3and processes image data received therefrom.

The image forming apparatus1further includes a recording medium feeding unit40that feeds recording media to the image forming unit10and a toner cartridge45that supplies toner to the image forming unit10.

FIG. 2illustrates an exemplary configuration of the image forming unit10according to an exemplary embodiment.

As shown inFIGS. 1 and 2, the image forming unit10includes a photoconductor drum12that is rotatably disposed, that allows an electrostatic latent image to be formed thereon, and that carries a toner image, the photoconductor drum12being an example of an object to be charged; a charging device100that charges a surface of the photoconductor drum12; an exposure device14that exposes, on the basis of image data, the photoconductor drum12charged by the charging device100; a developing device15that develops an electrostatic latent image formed on the photoconductor drum12; and a cleaner16that cleans the surface of the photoconductor drum12after transfer. The photoconductor drum12in the exemplary embodiment includes a rotating shaft (not shown) having an axis extending from the front (out of the page) to the rear (into the page) of the image forming apparatus1.

The image forming unit10further includes a transfer roller20that forms a transfer nip with the photoconductor drum12and transfers a toner image formed on the photoconductor drum12to a recording medium; and a fixing device30that fixes the transferred toner image to the recording medium.

The image forming unit10further includes a stripper17that strips, from the surface of the photoconductor drum12, the recording medium to which the toner image is transferred by the transfer roller20.

In the image forming unit10according to the exemplary embodiment, the photoconductor drum12, the charging device100, the developing device15, the cleaner16, and the stripper17are integrated into an image forming module11. The image forming module11is attachable to and detachable from the image forming apparatus1and is replaceable, for example, at the end of the life of the photoconductor drum12.

In this image forming apparatus1, the image forming unit10performs an image formation process on the basis of various control signals fed from the controller5. Specifically, under the control of the controller5, image data input from the PC2or the image reader3is processed by the image processor6and is fed to the image forming unit10. In the image forming unit10, while the photoconductor drum12is rotated in the direction of an arrow A, the photoconductor drum12is charged to a predetermined potential by the charging device100and is exposed by the exposure device14that radiates light on the basis of the image data transmitted from the image processor6. As a result of this, an electrostatic latent image corresponding to the image data is formed on the photoconductor drum12. The electrostatic latent image formed on the photoconductor drum12is then developed, for example, as a black (K) toner image by the developing device15to form a toner image corresponding to the image data on the photoconductor drum12.

The toner image formed on the photoconductor drum12is electrostatically transferred, by the transfer roller20, to a recording medium transported to the transfer nip.

Thereafter, the recording medium to which the toner image is transferred is stripped from the surface of the photoconductor drum12by the stripper17and is transported to the fixing device30. The toner image on the recording medium transported to the fixing device30is fixed to the recording medium with heat and pressure by the fixing device30. The recording medium on which a fixed image is formed is transported to a paper output stacker (not shown) of the image forming apparatus1.

The toner (residual toner) deposited on the surface of the photoconductor drum12after transfer is removed from the surface of the photoconductor drum12by the cleaner16after transfer is complete.

In this manner, the image formation process is repeated for the number of cycles corresponding to the number of prints.

Configuration of Charging Device

Next, a configuration of the charging device100according to an exemplary embodiment will be described.

As shown inFIG. 2, the charging device100includes a charging roller50that is rotatably supported and that charges the photoconductor drum12, the charging roller50being an example of a charging member or a member to be cleaned; and a cleaning roller60that is rotatably supported and that cleans a surface of the charging roller50, the cleaning roller60being an example of a cleaning member.

Here, as described above, the photoconductor drum12includes a rotating shaft having an axis extending from the front to the rear of the image forming apparatus1. The charging roller50and the cleaning roller60of the charging device100are disposed along the axial direction of the photoconductor drum12.

The charging roller50and the cleaning roller60are pressed against the photoconductor drum12by an elastic member (not shown). Thus, a charging layer54, which will be described later, of the charging roller50is in pressed contact with the surface of the photoconductor drum12. A foamed elastic layer70, which will be described later, of the cleaning roller60is in pressed contact with the charging layer54of the charging roller50.

In the exemplary embodiment, the charging roller50is driven by the rotation of the photoconductor drum12, which is driven by a driving unit (not shown), to rotate in the direction of an arrow B. Furthermore, the cleaning roller60is driven by the rotation of the charging roller50to rotate in the direction of an arrow C.

Configuration of Charging Roller

Next, the charging roller50will be described.

The charging roller50according to an exemplary embodiment includes a charging shift52that is disposed along the rotating shaft of the photoconductor drum12and that is rotatably supported by bearings (not shown); and the charging layer54that is disposed around the periphery of the charging shift52and that is in contact with the surface of the photoconductor drum12to charge the photoconductor drum12.

The charging shift52is formed of a conductive material such as a metal or an alloy. The charging shift52may be formed by treating the surface of a nonconductive material to be conductive, for example, by plating treatment.

The charging shift52has a cylindrical shape, and its opposite ends protrude from the opposite ends of the charging layer54. The opposite ends of the charging shift52protruding from the charging layer54are rotatably supported by bearings (not shown), and a voltage is applied to one of the ends through the bearing by a power supply unit (not shown).

For example, the charging layer54is formed of a conductive elastic layer disposed on the charging shift52and a surface layer disposed on the conductive elastic layer.

The conductive elastic layer of the charging layer54may be formed by adding a conductor to an elastic material. The conductive elastic layer may optionally contain any additives commonly added to rubber, such as softeners, plasticizers, curing agents, vulcanizing agents, vulcanization accelerators, age resistors, and fillers such as silica and calcium carbonate.

Examples of elastic materials that may be used to form the conductive elastic layer include rubber materials such as silicone rubber, ethylene-propylene rubber, epichlorohydrin-ethylene oxide copolymer rubber, epichlorohydrin-ethylene oxide-allyl glycidyl ether copolymer rubber, and acrylonitrile-butadiene copolymer rubber. These may be used alone or as a mixture of two or more.

Examples of conductors that may be used include electronic conductors and ionic conductors. Examples of electronic conductors include fine powders of carbon blacks such as Ketjen black and acetylene black; pyrolytic carbon and graphite; conductive metals and alloys such as aluminum, copper, nickel, and stainless steel; conductive metal oxides such as tin oxide, indium oxide, titanium oxide, tin oxide-antimony oxide solid solutions, and tin oxide-indium oxide solid solutions; and insulating materials surface-treated to be conductive. Examples of ionic conductors include perchlorates and chlorates of oniums such as tetraethylammonium and lauryltrimethylammonium; and perchlorates and chlorates of alkali metals and alkaline earth metals such as lithium and magnesium.

These conductors may be used alone or in a combination of two or more. The amount of conductor added is not particularly limited. In the case of an electronic conductor, the amount thereof may be in the range of from 1 part by mass to 60 parts by mass relative to 100 parts by mass of the elastic material. In the case of an ionic conductor, the amount thereof may be in the range of from 0.1 parts by mass to 5.0 parts by mass relative to 100 parts by mass of the elastic material.

The surface layer of the charging layer54is for preventing the charging layer54from being contaminated by foreign matter such as residual toner. The material of the surface layer may be, for example, a resin or rubber. Specific examples include polyesters, polyimides, nylon copolymers, silicone resins, acrylic resins, polyvinyl butyrals, ethylene tetrafluoroethylene copolymers, melamine resins, fluorocarbon rubbers, epoxy resins, polycarbonates, polyvinyl alcohols, celluloses, polyvinylidene chlorides, polyvinyl chlorides, polyethylenes, and ethylene-vinyl acetate copolymers.

A conductive material may be incorporated into the surface layer in order to adjust the resistance value thereof. Examples of conductive materials include carbon black, conductive metal oxides, and ionic conductors. The conductive material may be a powder having a particle size of 3 μm or less. A single conductive material may be used alone, or two or more conductive materials may be used in combination.

Furthermore, insulating particles such as alumina and silica may be incorporated into the surface layer.

Depending on, for example, the particle size, the content, and the dispersion state of the particles contained in the surface layer, irregularities are formed in the surface of the charging roller50, more particularly, the surface of the charging layer54of the charging roller50. When irregularities are formed in the surface of the charging roller50, the charging performance of the photoconductor drum12may be greater than when, for example, the surface of the charging roller50is smooth. In addition, filming, i.e., the phenomenon in which toner and external additives for toner adhering to the surface of the charging roller50are rubbed onto the surface of the photoconductor drum12and adhere to the surface in the form of a thin film may be suppressed. Furthermore, the friction between the charging roller50and the photoconductor drum12may be reduced, and the wear resistance between the charging roller50and the photoconductor drum12may be improved.

Here, an average spacing Sm of the irregularities in the surface of the charging roller50is a measure of the surface roughness of the charging layer54in accordance with JIS B 0601 (1994). The average spacing Sm of the irregularities in the exemplary embodiment is determined by sampling a segment from a roughness curve by a standard length in the direction of the mean line, calculating the sum of the lengths of portions of the mean line each extending between points corresponding to one peak and its neighboring valley within the sampled segment, and expressing the arithmetic mean spacing of the numerous irregularities in micrometers (μm).

In the exemplary embodiment, the average spacing Sm of the irregularities in the surface of the charging roller50is measured with a contact surface profilometer (SURFCOM 570, manufactured by Tokyo Seimitsu Co., Ltd.) in an environment at a temperature of 23° C. and a relative humidity of 55%. The measurement distance is 2.5 mm. A diamond-tipped stylus (5 μm in radius, 90° cone) is used. The average of three measurements taken at different sites is used as the average spacing Sm of the irregularities in the surface of the charging roller50.

In the exemplary embodiment, the average spacing Sm of the irregularities in the surface of the charging roller50is preferably in the range of from 50 μm to 300 μm, more preferably from 70 μm to 250 μm, for the reasons described above such as improving the charging performance on the photoconductor drum12, suppressing filming, and improving the wear resistance between the charging roller50and the photoconductor drum12.

Here, as described above, irregularities are formed in the surface of the charging roller50for reasons such as improving the charging performance on the photoconductor drum12, suppressing filming, and improving the wear resistance between the charging roller50and the photoconductor drum12. When the surface of the charging roller50having such irregularities is cleaned with a cleaning roller having a foamed elastic layer, foreign matter may remain on the surface (particularly in recesses) of the charging roller50depending on, for example, the configuration of the foamed elastic layer. Some of the scraped-off foreign matter may remain on the surface of the charging roller50, and foreign matter may be deposited on the irregularities in the surface of the charging roller50. An increased amount of deposition of foreign matter or in-plane variation due to local deposition of foreign matter on areas such as projections may vary the charging characteristics of the charging roller50.

To address these problems, the cleaning roller60according to the exemplary embodiment has the following configuration, so that an increase of foreign matter deposited on the surface of the charging roller50may be suppressed, while in-plane variation in the presence of foreign matter may be suppressed, and thus cleaning performance that is less likely to degrade and that is maintained over an extended period of time may be achieved.

Configuration of Cleaning Roller

Next, a configuration of the cleaning roller60according to an exemplary embodiment will be described.FIG. 3illustrates the configuration of the cleaning roller60according to the exemplary embodiment.FIG. 3shows the cleaning roller60as viewed from the direction perpendicular to the rotating shaft of the photoconductor drum12.FIG. 4is an enlarged view of the foamed elastic layer70, which will be described later, of the cleaning roller60according to the exemplary embodiment.FIG. 4corresponds to a side view of the foamed elastic layer70wound around a core62, which will be described later, in a helical pattern, as viewed from an axial direction Q described later.

The cleaning roller60includes the core62that is disposed along the rotating shaft of the photoconductor drum12and that is rotatably supported by bearings (not shown). The cleaning roller60also includes the foamed elastic layer70that includes first and second foamed elastic layers71and72disposed around the outer periphery of the core62in a double-helical pattern and that is in contact with the surface of the charging roller50(the charging layer54) to clean the surface of the charging roller50. As will be described in detail later, in the cleaning roller60according to the exemplary embodiment, the foamed elastic layer70(the first and second foamed elastic layers71and72) is bonded to the core62with an adhesive layer65(see, for example,FIGS. 6A and 6Bdescribed later) interposed therebetween.

The core62is formed of a material such as a metal, an alloy, or a resin. Examples of metals and alloys include metals such as iron (e.g., free-cutting steel), copper, brass, aluminum, and nickel and alloys such as stainless steel. Examples of resins include polyacetal resins. When the core62is formed of a metal or an alloy, the surface thereof may be subjected to surface treatment such as plating treatment. When the core62is formed of a nonconductive material such as a resin, the core62may be surface-treated to be conductive, for example, by plating treatment or may be used without such treatment.

The core62according to the exemplary embodiment has a cylindrical shape, and its opposite ends protrude from the opposite ends of the foamed elastic layer70and are rotatably supported by bearings (not shown). The core62may have an outer diameter of, for example, from 2 mm to 12 mm.

The foamed elastic layer70is a layer that is formed of what is called a foam having bubbles and that is formed of an elastic material that returns to its original shape when deformed by the application of an external force of 100 Pa. As shown inFIG. 4, the first and second foamed elastic layers71and72constituting the foamed elastic layer70each include a continuous skeletal portion70A and plural cells70B defined by the surrounding skeletal portion70A.

As described above, the first and second foamed elastic layers71and72of the foamed elastic layer70are wound around the outer periphery of the core62in a double-helical pattern.

In the foamed elastic layer70according to the exemplary embodiment, a compressive stress F1 of the first foamed elastic layer71is greater than a compressive stress F2 of the second foamed elastic layer72.

Here, in the cleaning roller60according to the exemplary embodiment, the first foamed elastic layer71, whose compressive stress F1 is greater than the compressive stress F2 of the second foamed elastic layer72, contributes to scraping off of foreign matter on the irregular surface (mainly in recesses) of the charging roller50. Specifically, since the compressive stress F1 of the first foamed elastic layer71is greater than the compressive stress F2 of the second foamed elastic layer72, the first foamed elastic layer71is provided with rigidity sufficient to scrape off foreign matter on the irregular surface of the charging roller50and hence contributes to scraping off of foreign matter.

On the other hand, in the cleaning roller60according to the exemplary embodiment, the second foamed elastic layer72, whose compressive stress F2 is less than the compressive stress F1 of the first foamed elastic layer71, functions to level, on the surface of the charging roller50, foreign matter remaining on the surface of the charging roller50and foreign matter scraped by the first foamed elastic layer71but remaining on the surface of the charging roller50. Specifically, since the compressive stress F2 of the second foamed elastic layer72is less than the compressive stress F1 of the first foamed elastic layer71, the second foamed elastic layer72tends to conform to the shapes of the irregularities in the surface of the charging roller50and foreign matter remaining on the surface of the charging roller50. This allows the second foamed elastic layer72to readily level foreign matter on the surface of the charging roller50, and thus the in-plane variation of foreign matter present on the surface of the charging roller50may be suppressed.

In the cleaning roller60according to the exemplary embodiment, since the first and second foamed elastic layers71and72are disposed in a double-helical pattern, the scraping off of foreign matter by the first foamed elastic layer71and the leveling of foreign matter by the second foamed elastic layer72are alternately and continuously performed on the surface of the charging roller50.

With this configuration, the charging device100according to the exemplary embodiment is less likely to experience, on the surface of the charging roller50, an increase of foreign matter and in-plane variation in the presence of foreign matter. As a result of this, the degradation in the cleaning performance of the charging roller50due to the cleaning roller60may be reduced, and the cleaning performance may be maintained over a long period of time.

Here, the compressive stress of the foamed elastic layer70(the first and second foamed elastic layers71and72) according to the exemplary embodiment is measured in the following manner in accordance with the method described in JIS K 7220 (2006). First, the foamed elastic body constituting the foamed elastic layer70is cut into 100 mm×100 mm to prepare a test specimen. The thickness of the test specimen is the thickness of the foamed elastic layer70(a thickness T1 of the first foamed elastic layer71and a thickness T2 of the second foamed elastic layer72). The cut-out foamed elastic body is then compressed in the thickness direction at a compression rate of 50 mm/min by using a precision force tester (manufactured by Aikoh Engineering Co., Ltd.) to measure its compressive stress at 40% deformation. The measurement of compressive stress at 40% deformation is performed in an environment at a temperature of 23° C. and a relative humidity of 55%.

In the same manner, three test specimens are measured for their compressive stress at 40% deformation, and their average values are used as the compressive stresses F1 and F2 of the foamed elastic layer70(the first and second foamed elastic layers71and72).

In the exemplary embodiment, the compressive stress F1 of the first foamed elastic layer71is preferably from 10 kPa to 20 kPa or from about 10 kPa to about 20 kPa, more preferably from 15 kPa to 18 kPa or from about 15 kPa to about 18 kPa, for ease of scraping off of foreign matter on the irregularities (mainly in recesses) in the surface of the charging roller50.

The compressive stress F2 of the second foamed elastic layer72is preferably from 7 kPa to 12 kPa or from about 7 kPa to about 12 kPa, more preferably from 8 kPa to 10 kPa or from about 8 kPa to about 10 kPa, for ease of leveling of foreign matter remaining on the surface of the charging roller50.

Furthermore, from the same viewpoints, F1/F2, which is the ratio of the compressive stress F1 of the first foamed elastic layer71to the compressive stress F2 of the second foamed elastic layer72, is preferably from 1 to 2 or from about 1 to about 2, more preferably from 1.5 to 1.9 or from about 1.5 to about 1.9.

To allow the first foamed elastic layer71to easily enter the irregularities in the surface of the charging roller50and easily exhibit the function of scraping off foreign matter on the surface (mainly in recesses) of the charging roller50, an average skeleton size D1 of the first foamed elastic layer71may be smaller than an average skeleton size D2 of the second foamed elastic layer72.

Furthermore, from the viewpoint described above, the average skeleton size D1 of the first foamed elastic layer71may be smaller than the average spacing Sm of the irregularities in the surface of the charging roller50. More specifically, the average skeleton size D1 of the first foamed elastic layer71is preferably from 0.3 times to 0.8 times, more preferably from 0.5 times to 0.7 times the average spacing Sm of the irregularities in the surface of the charging roller50.

Furthermore, to provide rigidity sufficient to scrape off foreign matter on the surface of the charging roller50, the average skeleton size D1 of the first foamed elastic layer71may be at least 0.3 times the average spacing Sm of the irregularities in the surface of the charging roller50. For the same reason, the average skeleton size D1 of the first foamed elastic layer71may be 30 μm or more.

To allow the second foamed elastic layer72to easily exhibit the function of leveling foreign matter remaining on the surface of the charging roller50, the average skeleton size D2 of the second foamed elastic layer72is preferably from 1.2 times to 3.2 times, more preferably from 1.5 times to 2.5 times, still more preferably from 1.5 times to 2.0 times the average spacing Sm of the irregularities in the surface of the charging roller50.

To provide conformability to the surface shape of the charging roller50, the average skeleton size D2 of the second foamed elastic layer72may be 3.2 times the average spacing Sm of the irregularities in the surface of the charging roller50. For the same reason, the average skeleton size D2 of the second foamed elastic layer72may be 600 μm or less.

Here, the average skeleton size D1 of the first foamed elastic layer71and the average skeleton size D2 of the second foamed elastic layer72each mean the average value of shortest distances between adjacent cells70B, that is, minimum thicknesses of skeletal portions70A that separate adjacent cells70B from each other.

The average skeleton size D1 or the average skeleton size D2 is measured as follows. First, regions near the surfaces of the first and second foamed elastic layers71and72disposed around the outer peripheral surface of the core62are observed from the side thereof under a VHX-900 microscope (manufactured by KEYENCE) at 100× magnification. Cells70B present in regions extending 2 mm from the surfaces of the first and second foamed elastic layers71and72are identified, and the shortest distance between adjacent cells70B (the minimum thickness of skeletal portions70A that separate adjacent cells70B from each other) is measured at ten points. The measured values are then averaged to determine the average skeleton size D1 of the first foamed elastic layer71and the average skeleton size D2 of the second foamed elastic layer72.

Next, the properties of the foamed elastic layer70(the first and second foamed elastic layers71and72), such as helix widths W1 and W2, helix angles θ1 and θ2, thicknesses T1 and T2, separation distance d between the first and second foamed elastic layers71and72, and helix pitch R of the foamed elastic layer70, will be described.

FIG. 5andFIGS. 6A and 6Billustrate configurations of the foamed elastic layer70(the first and second foamed elastic layers71and72) according to the exemplary embodiment.FIG. 5is an enlarged view of a segment V inFIG. 3, andFIGS. 6A and 6Bare enlarged views of sections of the cleaning roller60taken along the axial direction of the core62.FIG. 6Aillustrates an enlarged view of a section of the example of the cleaning roller60shown inFIGS. 3 to 5, andFIG. 6Billustrates an enlarged view of a section of another example of the cleaning roller60.

The properties of the foamed elastic layer70(the first and second foamed elastic layers71and72), such as the helix widths W1 and W2, the helix angles81and82, the thicknesses T1 and T2, the separation distance d between the first and second foamed elastic layers71and72, and the helix pitch R of the foamed elastic layer70, may each be determined depending on, for example, how easily the functions of the first and second foamed elastic layers71and72are exhibited, the function required depending on the surface shape of the charging roller50(the charging layer54), the peel resistance of the material constituting the foamed elastic layer70, and the ease of production.

Here, as shown inFIG. 5, the helix width W1 of the first foamed elastic layer71refers to the length of the first foamed elastic layer71in the axial direction (denoted by Q inFIG. 5) of the core62around which the first foamed elastic layer71is wound in a helical pattern. Likewise, the helix width W2 of the second foamed elastic layer72refers to the length of the second foamed elastic layer72in the axial direction Q of the core62around which the second foamed elastic layer72is wound in a helical pattern.

To allow the first and second foamed elastic layers71and72to easily exhibit their respective functions, the lower limits of the helix width W1 of the first foamed elastic layer71and the helix width W2 of the second foamed elastic layer72are each preferably 3 mm or more, more preferably 4 mm or more, still more preferably 5 mm or more. The upper limits of the helix width W1 of the first foamed elastic layer71and the helix width W2 of the second foamed elastic layer72are each preferably 10 mm or less, more preferably 7 mm or less, although depending on the helix angles θ1 and θ2, which will be described later.

The helix width W1 of the first foamed elastic layer71and the helix width W2 of the second foamed elastic layer72may be the same or different.

As shown inFIG. 5, the helix angle θ1 of the first foamed elastic layer71refers to the angle between the axial direction Q of the core62and the first foamed elastic layer71wound around the core62in a helical pattern. Likewise, the helix angle θ2 of the second foamed elastic layer72refers to the angle between the axial direction Q of the core62and the second foamed elastic layer72wound around the core62in a helical pattern.

For the first and second foamed elastic layers71and72to form a double helix, the difference between the helix angle θ1 of the first foamed elastic layer71and the helix angle θ2 of the second foamed elastic layer72is preferably 5° or less, more preferably 3° or less.

The helix angle θ1 of the first foamed elastic layer71and the helix angle θ2 of the second foamed elastic layer72are each preferably from 2° to 75°, more preferably from 4° to 75°, still more preferably from 8° to 45°.

As shown inFIGS. 6A and 6B, the thickness T1 of the first foamed elastic layer71and the thickness T2 of the second foamed elastic layer72refer to the thicknesses at the widthwise centers of the first foamed elastic layers71and the second foamed elastic layers72, respectively. The thickness T1 of the first foamed elastic layer71and the thickness T2 of the second foamed elastic layer72are measured by the following method. Specifically, the profile of the foamed elastic layer70(the thickness of the foamed elastic layer70) is measured with a laser measuring device (model LSM6200 Laser Scan Micrometer manufactured by Mitutoyo Corporation) by scanning the cleaning roller60in the axial direction Q (seeFIG. 5) of the cleaning roller60at a traverse speed of 1 mm/s with the peripheral direction of the cleaning roller60being fixed. The position in the peripheral direction is then shifted, and a measurement is made in the same manner (at a total of three positions at intervals of 120° in the peripheral direction). On the basis of this profile, the thicknesses at the widthwise centers of the first and second foamed elastic layers71and72are calculated.

The thickness T1 of the first foamed elastic layer71and the thickness T2 of the second foamed elastic layer72are each preferably from 1.0 mm to 4.0 mm, more preferably from 1.5 mm to 3.0 mm, still more preferably from 1.7 mm to 2.5 mm.

The thickness T1 of the first foamed elastic layer71and the thickness T2 of the second foamed elastic layer72may be the same or different. If the thickness T1 of the first foamed elastic layer71is different from the thickness T2 of the second foamed elastic layer72, the difference in thickness may be determined depending on, for example, the significance of the functions of the first and second foamed elastic layers71and72. Preferably, one thickness T1 or T2 is from more than 1 time to 1.2 times the other thickness T2 or T1.

The separation distance d between the first and second foamed elastic layers71and72refers to the distance (spacing), in the axial direction Q of the cleaning roller60, between the first and second foamed elastic layers71and72of the foamed elastic layer70wound around the core62in a double-helical pattern. In this example, the separation distance d between the first and second foamed elastic layers71and72is the distance between the right side of the first foamed elastic layer71and the left side of the second foamed elastic layer72, as shown inFIG. 5.

The separation distance d between the first and second foamed elastic layers71and72is preferably from 0 mm to 10 mm, more preferably from 0 mm to 5 mm. In other words, the separation distance d between the first and second foamed elastic layers71and72may be 0 in such a manner that the first and second foamed elastic layers71and72are wound such that the side (the right side inFIG. 5andFIG. 6B) of the first foamed elastic layer71and the side (the left side inFIG. 5andFIG. 6B) of the second foamed elastic layer72are in contact with each other along the axial direction Q, as shown inFIG. 6B.

The helix pitch R of the foamed elastic layer70refers to the distance, in the axial direction Q of the cleaning roller60, between a portion of the foamed elastic layer70wound around the core62in a double-helical pattern and an adjacent portion of the foamed elastic layer70. In this example, the helix pitch R of the foamed elastic layer70is the distance between the right edge of the foamed elastic layer70(the right side of the second foamed elastic layer72) and the left edge of the foamed elastic layer70(the left side of the first foamed elastic layer71), as shown inFIG. 5.

The helix pitch R of the foamed elastic layer70is preferably from 3 mm to 25 mm, more preferably from 15 mm to 22 mm.

The helix pitch R of the foamed elastic layer70may be larger than the separation distance d between the first and second foamed elastic layers71and72. In this case, if the foamed elastic layer70is brought into contact with the surface of the charging roller50while the cleaning roller60is rotated in the direction denoted by X inFIG. 3, for example, the time period from when the first foamed elastic layer71comes into contact with the surface of the charging roller50until the second foamed elastic layer72comes into contact with the surface of the charging roller50is shorter than the time period from when the second foamed elastic layer72comes into contact until the first foamed elastic layer71comes into contact.

Here, foreign matter adhering to the surface of the charging roller50is scraped off the surface of the charging roller50as a result of the contact of the first foamed elastic layer71. In this case, foreign matter remaining on the surface of the charging roller50without being scraped off by the first foamed elastic layer71has presumably become softer, by being rubbed by the first foamed elastic layer71, than before the contact of the first foamed elastic layer71. Therefore, it is presumed that if the time period from when foreign matter adhering to the surface of the charging roller50is scraped off by the first foamed elastic layer71until foreign matter remaining on the surface of the charging roller50is leveled by the second foamed elastic layer72is short, the foreign matter on the surface of the charging roller50may easily be leveled by the second foamed elastic layer72.

Therefore, the configuration in which the helix pitch R of the foamed elastic layer70is larger than the separation distance d between the first and second foamed elastic layers71and72may further suppress the in-plane variation of foreign matter present on the surface of the charging roller50.

To reduce the likelihood that a rotation error occurs when the cleaning roller60is rotated by the rotation of the charging roller50as in the exemplary embodiment, and to allow the first and second foamed elastic layers71and72to easily exhibit their respective functions, the numbers of turns of the first and second foamed elastic layers71and72around the core62are each preferably 1 or more, more preferably 1.3 or more, still more preferably 2 or more. When the cleaning roller60is rotated by the rotation of the charging roller50, there is no particular upper limit to the numbers of turns of the first and second foamed elastic layers71and72since the numbers of turns depend on the length of the core62.

When the cleaning roller60is rotated not by the rotation of the charging roller50but by itself, there is no particular upper limit to the numbers of turns of the first and second foamed elastic layers71and72around the core62.

Next, the adhesive layer65will be described. As described above, in the cleaning roller60, the foamed elastic layer70is bonded to the core62with the adhesive layer65interposed therebetween.

The adhesive layer65may be any layer capable of bonding the core62and the foamed elastic layer70together. For example, the adhesive layer65may be formed of a double-sided tape or any other adhesive.

Here, as shown inFIG. 6B, the cleaning roller60may be disposed around the core62with the separation distance d between the first and second foamed elastic layers71and72being 0, that is, with one side of the first foamed elastic layer71and the opposing side of the second foamed elastic layer72in contact with each other. When such a configuration is employed, the adhesive layer65may be formed of a single layer so as to simultaneously bond the first and second foamed elastic layers71and72, as shown inFIG. 6B, or the adhesive layer65may be separately provided for each of the first and second foamed elastic layers71and72.

Method for Producing Cleaning Roller

Next, an exemplary method for producing the cleaning roller60according to the exemplary embodiment will be described.FIGS. 7A to 7Cillustrate exemplary steps of the method for producing the cleaning roller60.

As shown inFIG. 7A, to obtain the first and second foamed elastic layers71and72, sheet-shaped foamed elastic members (e.g., foamed polyurethane sheets) each sliced to the desired thickness are first provided. These sheet-shaped foamed elastic members are cut to obtain strip-shaped foamed elastic members81and82each having the desired width and length.

The adhesive layers65formed of double-sided tapes and having adhesive surfaces of the same size as the strip-shaped foamed elastic members81and82are provided. The double-sided tapes, serving as the adhesive layers65, are then attached to the strip-shaped foamed elastic members81and82on their one surface.

The core62is also provided.

Next, as shown inFIG. 7B, the strip-shaped foamed elastic members81and82(the strips with the double-sided tapes) are placed such that the double-sided tapes constituting the adhesive layers65face upward. In this state, one end of the release paper of each of the double-sided tapes constituting the adhesive layers65is stripped. An end portion of the core62is then placed on the portions of the double-sided tapes (the adhesive layers65) from each of which the release paper has been stripped.

Subsequently, as shown inFIG. 7C, the release paper of each of the double-sided tapes constituting the adhesive layers65is stripped while the core62is rotated at the desired speed to wind the strip-shaped foamed elastic members81and82around the outer peripheral surface of the core62in a double-helical pattern. In this manner, the cleaning roller60including the first and second foamed elastic layers71and72disposed around the outer peripheral surface of the core62in a double-helical pattern is obtained.

Although the method illustrated inFIGS. 7A to 7Cinvolves simultaneously winding the strip-shaped foamed elastic members81and82around the core62, the method for producing the cleaning roller60is not limited thereto. It is also possible to wind the foamed elastic member81around the core62and then wind the foamed elastic member82around the core62or to wind the foamed elastic members81and82in the reverse order.

Here, the helix angle θ1 of the first foamed elastic layer71and the helix angle θ2 of the second foamed elastic layer72may be adjusted to the desired angles in the following manner. In winding the foamed elastic members81and82around the core62, the core62and the foamed elastic members81and82are positioned such that the longitudinal direction of the foamed elastic members81and82makes the desired angle with the axial direction of the core62.

If a tension is applied when the foamed elastic members81and82are wound around the core62, the tension may be high enough to leave no gap between the core62and the adhesive layers65(the double-sided tapes) bonded to the foamed elastic members81and82. Specifically, for example, the tension may be high enough to elongate the foamed elastic members81and82by 0% or more and 5% or less of their original length.

The foamed elastic members81and82tend to elongate as the foamed elastic members81and82are wound around the core62. This elongation differs in the thickness direction of the foamed elastic members81and82, with the outermost portion of the foamed elastic members81and82tending to elongate more. Accordingly, the elongation of the outermost portion of the foamed elastic members81and82after the winding of the foamed elastic members81and82around the core62may be about 5% of the original length of the outermost portion of the foamed elastic members81and82. An excessive elongation of the foamed elastic members81and82may decrease the elastic force of the first and second foamed elastic layers71and72.

The elongation of the foamed elastic members81and82is controlled by the radius of curvature of the foamed elastic members81and82wound around the core62and the thickness of the foamed elastic members81and82. The radius of curvature of the foamed elastic members81and82wound around the core62is controlled by the outer diameter of the core62and the angles (the helix angles θ1 and 02) at which the foamed elastic members81and82are wound around the core62.

For example, the radius of curvature of the foamed elastic members81and82wound around the core62is preferably from ((outer diameter of core62/2)+1 mm) to ((outer diameter of core62/2)+15 mm), more preferably from ((outer diameter of core62/2)+1.5 mm) to ((outer diameter of core62/2)+5.0 mm).

The longitudinal ends of the foamed elastic members81and82may be provided with regions where the foamed elastic members81and82are subjected to compression treatment in the thickness direction. Performing compression treatment on the foamed elastic members81and82may suppress peeling off of the foamed elastic members81and82after being bonded to the core62.

Specifically, the longitudinal ends of the foamed elastic members81and82before being bonded to the core62may be subjected to compression treatment (thermal compression treatment) in which heat and pressure are applied so that the percentage of compression in the thickness direction of the foamed elastic members81and82((thickness after compression/thickness before compression)×100) is from 10% to 70%. By this compression treatment, the longitudinal ends of the foamed elastic members81and82are plastically deformed into a flat shape.

While in the exemplary embodiment, the cleaning roller60, which is an example of a cleaning member, is in contact with the surface of the charging roller50, which is an example of a member to be cleaned, and is rotated by the rotation of the charging roller50, this configuration is a non-limiting example. As in the exemplary embodiment, the configuration in which the cleaning roller60is in constant contact with the surface of the charging roller50and is rotated by the rotation of the charging roller50may be employed. Alternatively, for example, a configuration in which the cleaning roller60comes into contact with the charging roller50only during cleaning of the charging roller50and is rotated by the rotation of the charging roller50, or a configuration in which the cleaning roller60comes into contact with the charging roller50only during cleaning of the charging roller50and is independently driven to rotate may be employed.

While in the exemplary embodiment, the cleaning roller60that cleans a surface of the charging roller50of the charging device100has been described as an example of a cleaning member, the cleaning member having the configuration described above may be a member that cleans a member to be cleaned other than the charging roller50. Also in this case, the cleaning member includes a foamed elastic layer70having first and second foamed elastic layers71and72, wherein the compressive stress F1 of the first foamed elastic layer71is greater than the compressive stress F2 of the second foamed elastic layer72.

Examples of members to be cleaned other than the charging roller50include transfer members, sheet transport belts, second transfer members (e.g., second transfer rollers) for intermediate transfer systems, and intermediate transfer bodies (e.g., intermediate transfer belts) for intermediate transfer systems. Furthermore, such a member to be cleaned and a cleaning member disposed in contact therewith may be combined into a unit for an image forming apparatus.

The image forming apparatus1according to the exemplary embodiment is not limited to the monochrome printer shown inFIG. 1and may be, for example, an image forming apparatus1having a known configuration, such as a tandem color printer. In the image forming apparatus1according to the exemplary embodiment, the internal devices and members need not be assembled into a cartridge but each may be directly disposed.

EXAMPLES

The present invention will hereinafter be described in more detail with reference to examples. It should be noted that exemplary embodiments of the present invention are not limited to the following examples.

Examples 1 to 14 and Comparative Examples 1 and 2

(1) Fabrication of Foamed Elastic Members

Fabrication of Foamed Elastic Member1

A melamine foam sheet (BASOTECT Type G) available from Inoac Corporation is used to obtain a sheet-shaped foamed elastic member1having a thickness of 2.4 mm.

Fabrication of Foamed Elastic Member2

A urethane sheet (EP-70) available from Inoac Corporation is used to obtain a sheet-shaped foamed elastic member2having a thickness of 2.4 mm.

Fabrication of Foamed Elastic Member3

A urethane sheet (ER-1) available from Inoac Corporation is used to obtain a sheet-shaped foamed elastic member3having a thickness of 2.4 mm.

Fabrication of Foamed Elastic Member4

A urethane sheet (MF-40) available from Inoac Corporation is used to obtain a sheet-shaped foamed elastic member4having a thickness of 2.4 mm.

Fabrication of Foamed Elastic Member5

A urethane sheet (MF-30) available from Inoac Corporation is used to obtain a sheet-shaped foamed elastic member5having a thickness of 2.4 mm.

Fabrication of Foamed Elastic Member6

A urethane sheet (MF-20) available from Inoac Corporation is used to obtain a sheet-shaped foamed elastic member6having a thickness of 2.4 mm.

Fabrication of Foamed Elastic Member7

A urethane sheet (MF-13) available from Inoac Corporation is used to obtain a sheet-shaped foamed elastic member7having a thickness of 2.4 mm.

Fabrication of Foamed Elastic Member8

A urethane sheet (MF-8) available from Inoac Corporation is used to obtain a sheet-shaped foamed elastic member8having a thickness of 2.4 mm.

Fabrication of Foamed Elastic Member9

A urethane sheet (MF-20) available from Inoac Corporation is used to obtain a sheet-shaped foamed elastic member9having a thickness of 2.3 mm.

(2) Fabrication of Cleaning Roller

Fabrication of Cleaning Roller1

The sheet-shaped foamed elastic members2and6are each cut into a strip having a width of 5 mm and a length of 360 mm.

To each cut-out strip, a double-sided tape having a thickness of 0.05 mm (No. 5605, available from Nitto Denko Corporation) is attached over the entire surface to be attached to a core to obtain two strips with the double-sided tapes.

The two resulting strips with the double-sided tapes are placed on a horizontal stage such that the release paper attached to each double-sided tape faces downward. Both of the two strips are then compressed from thereabove with stainless steel having its longitudinal ends heated so that the thickness of portions longitudinally extending 1 mm from the longitudinal ends of each strip is 15% of the thickness of the remaining portion.

The two strips with the double-sided tapes are then placed on a horizontal stage at a distance of 0 mm (i.e., in contact with each other) such that the release paper attached to each double-sided tape faces upward. The two strips with the double-sided tapes are then wound around a metal core (material, SUM24EZ; outer diameter, 5.0 mm; overall length, 338 mm) in a double-helical pattern at helix angles θ1 and θ2 of 25° while being tensioned so that the overall length of each strip increases by 0% to 5%.

By the foregoing process, a cleaning roller1including first and second foamed elastic layers disposed around the outer peripheral surface of a core in a double-helical pattern is obtained.

The compressive stresses F1 and F2 and their ratio F1/F2, the average skeleton sizes D1 and D2, the sheet widths W1 and W2, the helix angles θ1 and θ2, the separation distance d, and the thicknesses T1 and T2 of the cleaning roller1are shown in Table 1 below.

Fabrication of Cleaning Rollers2to11

Cleaning rollers2to11each including two foamed elastic layers disposed around the outer peripheral surface of a core in a double-helical pattern are obtained in the same manner as in Fabrication of Cleaning Roller1except that the foamed elastic members2and6cut into strips are replaced with foamed elastic members shown in Table 1 below.

The compressive stresses F1 and F2 and their ratio F1/F2, the average skeleton sizes D1 and D2, the sheet widths W1 and W2, the helix angles θ1 and θ2, the separation distance d, and the thicknesses T1 and T2 of the cleaning rollers2to11are shown in Table 1 below.

Fabrication of Cleaning Roller12

The sheet-shaped foamed elastic members2and6are each cut into a strip having a width of 4 mm and a length of 360 mm.

A cleaning roller12including first and second foamed elastic layers disposed around the outer peripheral surface of a core in a double-helical pattern is obtained in the same manner as in Fabrication of Cleaning Roller1except that these strips are used.

The compressive stresses F1 and F2 and their ratio F1/F2, the average skeleton sizes D1 and D2, the sheet widths W1 and W2, the helix angles θ1 and θ2, the separation distance d, and the thicknesses T1 and T2 of the cleaning roller12are shown in Table 1 below.

Fabrication of Cleaning Roller13

A cleaning roller13including first and second foamed elastic layers disposed around the outer peripheral surface of a core in a double-helical pattern is obtained in the same manner as the cleaning roller1except that the two strips with the double-sided tapes are wound around a core at helix angles θ1 and θ2 of 15°.

The compressive stresses F1 and F2 and their ratio F1/F2, the average skeleton sizes D1 and D2, the sheet widths W1 and W2, the helix angles θ1 and θ2, the separation distance d, and the thicknesses T1 and T2 of the cleaning roller13are shown in Table 1 below.

Fabrication of Cleaning Roller14

A cleaning roller14including first and second foamed elastic layers disposed around the outer peripheral surface of a core in a double-helical pattern is obtained in the same manner as the cleaning roller1except that the two strips with the double-sided tapes are wound around a core with the separation distance d therebetween set to 2 mm.

The compressive stresses F1 and F2 and their ratio F1/F2, the average skeleton sizes D1 and D2, the sheet widths W1 and W2, the helix angles θ1 and θ2, the separation distance d, and the thicknesses T1 and T2 of the cleaning roller14are shown in Table 1 below.

TABLE 1FoamedCompressiveCompressiveAverageSheetCleaningelasticstressstressskeletonwidthHelixSeparationThicknessrollerlayer No.[kPa]ratiosize [μm][mm]angle [°]distance d[mm]No.FirstSecondF1F2F1/F2D1D2W1W2θ1θ2[mm]T1T212612.712.61.016014055252502.42.424816.38.81.8510027055252502.42.431616.412.61.304014055252502.42.444616.312.61.2910014055252502.42.454416.316.31.0010010055252502.42.462812.78.81.446027055252502.42.473611.512.60.917014055252502.42.482512.712.61.016012055252502.42.496812.68.81.4314027055252502.42.4104716.312.61.2910024055252502.42.4112912.712.51.026014055252502.42.3122612.712.61.016014044252502.42.4132612.712.61.016014055151502.42.4142612.712.61.016014055252522.42.4
(3) Fabrication of Charging Rollers
Fabrication of Charging Roller1
Formation of Charging Layer

The following mixture for forming an elastic layer is kneaded in an open roll mill and is applied to the outer peripheral surface of a conductive charging shift formed of SUS416 stainless steel and having a diameter of 9 mm to form a cylindrical coating having a thickness of 1.5 mm. The coated core is placed in a cylindrical mold having an inner diameter of 12.0 mm, is vulcanized at 170° C. for 30 minutes, and is removed from the mold, following by surface polishing. In this manner, a cylindrical conductive elastic layer formed around the outer peripheral surface of the charging shift is obtained.

Mixture for Forming Elastic Layer

The following mixture for forming a surface layer is dispersed with a bead mill, and the resulting dispersion is diluted with methanol. The diluted dispersion is applied to the surface (outer peripheral surface) of the above conductive elastic layer by dip coating and then dried by heating at 140° C. for 15 minutes. In this manner, a charging roller1including the conductive elastic layer and a 4-μm-thick surface layer formed on the surface thereof is obtained.

The average spacing Sm of irregularities in the surface of the charging roller1is 90 μm.

Mixture for Forming Surface Layer

A charging roller2is obtained in the same manner as in Fabrication of Charging Roller1except that the following mixture for forming a surface layer is used to form a surface layer.

The average spacing Sm of irregularities in the surface of the charging roller2is 180 μm.

Mixture for Forming Surface Layer

Each combination of a cleaning roller and a charging roller shown in Table 2 below is attached to a drum cartridge for a DocuCentre-V C7775 color multifunction machine (manufactured by Fuji Xerox Co., Ltd.) and is evaluated for cleaning performance.

Evaluation of Cleaning Performance

A strip-like image pattern with a length in the output direction of 320 mm and a width of 30 mm is printed on sheets of A3 recording paper at an image density of 100% in an environment at 22° C. and 55% RH. The charging roller is inspected for deposits at the image pattern printing position each time 10,000 sheets are printed.

The inspection of deposits is performed by directly observing the surface of the charging roller under a confocal laser microscope (OLS1100, manufactured by Olympus Corporation), and the cleaning performance is evaluated.

Specifically, the inspection of deposits is performed on the surface layer of the charging roller at two points located 10 mm inward of the opposite axial ends and at three points dividing the distance between the two points into four segments of equal length. The number of rotations of the photoconductor drum at which G3 on the following criteria is reached is determined.

For each of the above five points on the surface layer of the charging roller, deposits are inspected at the center of the point and at two points located ±1 mm from the center, i.e., at a total of three points. The number of rotations of the photoconductor drum at which the maximum difference in deposit area between any three points among the five points reaches 40% or more is determined.

The cleaning performance is evaluated on the basis of the number of rotations of the photoconductor drum at which any of these two measures is reached. A larger number of photoconductors in the photoconductor drum indicates a better cleaning performance.

Criteria

G0: Deposits are found at a percentage of 10% or less per μm2on the surface of the charging roller.

G0.5: Deposits are found at a percentage of more than 10% and 20% or less per μm2on the surface of the charging roller.

G1: Deposits are found at a percentage of more than 20% and 30% or less per μm2on the surface of the charging roller.

G2: Deposits are found at a percentage of more than 30% and 50% or less per μm2on the surface of the charging roller.

G3: Deposits are found at a percentage of more than 50% per μm2on the surface of the charging roller.

The above results demonstrate that the cleaning performance is maintained over a longer period of time in Examples 1 to 14 than in Comparative Examples 1 and 2.