JP7375529B2 - Charging device, image forming unit, and image forming device - Google Patents

Description

The present invention relates to a charging device, an image forming unit, and an image forming apparatus, and is suitable for application to, for example, an image forming apparatus using an electrophotographic method and having an image forming unit equipped with a charging device.

In image forming devices that use electrophotography, such as printers, copiers, facsimile machines, and multifunction devices, an electrostatic latent image is formed on the surface of the photosensitive drum by exposing the uniformly charged surface of the photosensitive drum to light using an exposure device. By developing this electrostatic latent image with toner, a toner image is formed on the surface of the photosensitive drum, and this toner image is transferred to a recording medium.

In this type of image forming apparatus, a contact charging type is often used as a charging member to uniformly charge the surface of the photosensitive drum, in which a charging roller contacts the surface of the photosensitive drum to charge the surface of the photosensitive drum. (For example, see Patent Document 1).

Japanese Patent Application Publication No. 2015-090409

However, in the contact charging method, unevenness in the charging potential tends to occur in the axial direction of the charging roller due to the roughness of the surface of the charging roller, and this is a factor that tends to cause unevenness in the charging potential on the surface of the photosensitive drum. It became. In other words, with the conventional technology, uneven charging potential tends to occur on the surface of the photosensitive drum, and as a result, so-called fog, in which toner is deposited on the non-printing area of the paper (the area that should be a white background), tends to occur. had.

The present invention has been made in consideration of the above points, and aims to propose a charging device, an image forming unit, and an image forming apparatus that can suppress fog.

The present invention includes a charging member that charges the surface of an image carrier carrying an electrostatic latent image on its surface while rotating in contact with the surface of the image carrier. regulation) is 2.30 or more and 5.02 or less, and the length in the axial direction of the charging member at the contact portion between the surface of the charging member and the surface of the image carrier is the evaluation length L, and the Assuming that a certain length cut out from the evaluation length L is a reference length l, the average interval Sm of unevenness in the axial direction of the charging member on the surface of the charging member within the reference length l (JIS B 0601 -1994) is 0.17 mm or more and the reference length l or less.

By doing so, variations in the distance between the surface of the charging member and the surface of the image carrier are reduced, and unevenness in charging potential is less likely to occur on the surface of the image carrier.

The present invention can realize a charging device, an image forming unit, and an image forming apparatus that can suppress fog.

FIG. 3 is a side sectional view showing a printing mechanism of the image forming apparatus. FIG. 3 is an enlarged view showing the configuration of a charging section. FIG. 2 is a block diagram showing a control mechanism of the image forming apparatus. It is a graph schematically showing the definition of kurtosis Sku. FIG. 3 is a diagram schematically showing definitions of an evaluation length L, a reference length l, and an average interval Sm of unevenness. FIG. 3 is a diagram schematically showing the definition of the root mean square slope Sdq. 2 is a table showing the kurtosis Sku, average unevenness interval Sm, root mean square slope Sdq, fog evaluation value ΔE, and evaluation results measured for Samples 1 to 11. FIG. 3 is a diagram showing a predetermined area on the surface of a photosensitive drum and a mending tape attached to the predetermined area. FIG. 3 is a diagram showing a reference tape to which no toner is attached and a blank sheet to which a mending tape to which toner is attached is pasted. It is a graph showing a good range of kurtosis Sku and average interval Sm of unevenness. FIG. 7 is a diagram showing the relationship between the surface shape of the charging roller, the sharpness Sku, and the average spacing Sm of unevenness. FIG. 7 is a diagram showing the surface shape of the charging roller when the average interval Sm of the unevenness is set as the reference length l.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, modes for carrying out the invention (hereinafter referred to as embodiments) will be described in detail using the drawings.

[1. Printing mechanism of image forming device]
FIG. 1 shows a printing mechanism of an image forming apparatus 1. As shown in FIG. Note that FIG. 1 is a side sectional view showing the printing mechanism of the image forming apparatus 1. As shown in FIG. An image forming apparatus 1 shown in FIG. 1 is a printer that forms a color image on a medium P such as paper or film using an electrophotographic method. Note that here, the right side of the figure is the front side of the image forming apparatus 1, and the left side of the figure is the rear side, and the direction from the front side of the image forming apparatus 1 to the rear side is the rear direction, and the direction from the rear side to the front side is the front direction. , the direction from the bottom to the top of the image forming apparatus 1 is upward; the direction from the top to the bottom is downward; the direction from the front to the back of the image forming apparatus 1 in the figure is right; The direction from the side to the front side is defined as the left direction.

This image forming apparatus 1 is provided with a conveyance path R serving as a path for a medium P inside, and further includes a medium supply section 2, a conveyance section 3, an image forming section 4, and a transfer path along this conveyance path R. A fixing section 5 and a fixing section 6 are provided.

The medium supply unit 2 is located at the most upstream side in the conveyance direction of the medium P (hereinafter referred to as the medium conveyance direction) indicated by an arrow Ar1 in the figure, and is connected to a cassette (paper feed tray) 21 and a hopping roller (feed paper roller) 22. The cassette 21 is a member that stores the media P in a stacked state, and is detachably attached to the lower part of the image forming apparatus 1, for example. The hopping roller 22 is a member that separates the media P stored in the cassette 21 one by one from the top and feeds them out to the conveyance path R.

The conveyance section 3 is located downstream of the medium supply section 2 in the medium conveyance direction, and includes a conveyance roller pair 31 (31A, 31B) composed of two conveyance rollers arranged opposite to each other across the conveyance path R. are doing. Specifically, the conveyance unit 3 includes a pair of conveyance rollers 31A located on the upstream side in the medium conveyance direction (that is, the side close to the medium supply unit 2), and a pair of conveyance rollers 31A located on the downstream side in the medium conveyance direction (that is, the side far from the medium supply unit 2). ) and a pair of transport rollers 31B located at The pair of conveyance rollers 31 (31A, 31B) conveys the medium P fed out to the conveyance path R by the medium supply unit 2 by sandwiching it between the two conveyance rollers, and also corrects the skew of the medium P. It is a member.

The image forming unit 4 and the transfer unit 5 are located downstream of the transport unit 3 in the medium transport direction, and face each other with the image forming unit 4 on the upper side and the transfer unit 5 on the lower side with the transport path R in between. It is located. Note that the image forming section 4 and the transfer section 5 are specific examples of the image forming unit according to the present invention.

The image forming section 4 includes a plurality of developing sections 41 (41K, 41C, 41M, 41Y). Specifically, the image forming section 4 includes four developing sections 41K, 41C, 41M, and 41Y arranged in order from the upstream side in the medium conveyance direction.

The developing units 41K, 41C, 41M, and 41Y are devices that form toner images (developer images) on the medium P using toners (developer) of different colors. Specifically, the developing section 41K uses black toner to produce a black toner image, the developing section 41C uses cyan toner to produce a cyan toner image, and the developing section 41Y uses yellow toner to produce a yellow toner image. , the developing section 41M forms magenta toner images on the medium P using magenta toner.

The developing units 41K, 41C, 41M, and 41Y have the same configuration except that they use different toners, and each includes a photosensitive drum 42, a charging unit 43, an exposure device 44, a developing roller 45, and a toner supply unit 46. and a cleaning blade 47. The developing units 41K, 41C, 41M, and 41Y each expose the surface of the photosensitive drum 42, which has been uniformly charged by the charging unit 43, with light from the exposure device 44, thereby creating an electrostatic charge on the surface of the photosensitive drum 42. A toner image is formed on the surface of the photosensitive drum 42 by forming a latent image and attaching toner supplied from the toner supply section 46 to the electrostatic latent image via the developing roller 45. The toner image thus formed on the surface of the photosensitive drum 42 is transferred onto the medium P by a transfer section 5, which will be described later. Further, the developing units 41K, 41C, 41M, and 41Y each remove toner remaining on the surface of the photosensitive drum 42 without being transferred to the medium P by scraping it off with a cleaning blade 47. The details of the configuration of the developing sections 41K, 41C, 41M, and 41Y will be described later.

On the other hand, the transfer section 5 includes a conveyance belt 51, a drive roller 52, a driven roller 53, a transfer roller 54, and a cleaning blade 55. The conveyance belt 51 is an annular member provided below the image forming section 4, and includes a drive roller 52 located upstream (front side) of the transfer section 5 in the medium conveyance direction, and a drive roller 52 located downstream of the transfer section 5 in the medium conveyance direction. It is stretched by a driven roller 53 located on the rear side. The conveyor belt 51 has an upper straight portion 51U extending from the upstream side to the downstream side in the medium conveyance direction of the image forming section 4 along the conveyance path R, and a lower straight portion 51L parallel to the upper straight portion 51U. have. The conveyor belt 51 moves the medium P conveyed by the conveyance unit 3 by the drive roller 52 so that the upper straight portion 51U moves in the same direction as the medium conveyance direction indicated by the arrow Ar1 in the figure. It is conveyed so as to pass under the developing sections 41K, 41C, 41M, and 41Y in order.

The drive roller 52 is a roller that causes the conveyor belt 51 to travel by being rotated by the power of a drive motor (not shown). The driven roller 53 is a roller that rotates as the conveyor belt 51 runs.

A total of four transfer rollers 54 are provided, one for each photosensitive drum 42 of the developing sections 41K, 41C, 41M, and 41Y. Each transfer roller 54 is disposed below each photosensitive drum 42 to face each other, with the upper straight portion 51U of the conveyor belt 51 interposed therebetween. Each transfer roller 54 charges the medium P to a polarity opposite to that of the toner when the medium P conveyed by the conveyance belt 51 passes between each transfer roller 54 and each photosensitive drum 42. This is a member that transfers the toner image formed on each photosensitive drum 42 onto the medium P. The cleaning blade 55 is a member that removes toner adhering to the lower straight portion 51L of the conveyor belt 51 by scraping it off.

The fixing section 6 is located downstream of the image forming section 4 and the transfer section 5 in the medium conveyance direction. The fixing unit 6 is a device that fixes the toner image transferred to the medium P by the transfer unit 5 onto the medium P by applying heat and pressure. The fixing unit 6 includes a heating roller 61 disposed on the upper side with the conveyance path R interposed therebetween, and a pressure roller 62 disposed on the lower side. The heating roller 61 has a heater inside, and is a member that heats the toner image transferred to the medium P when the medium P passes between the heating roller 61 and the pressure roller 62. The pressure roller 62 is biased toward the heating roller 61, and when the medium P passes between the heating roller 61 and the pressure roller 62, the toner image transferred to the medium P is This is a member that applies pressure. The printing mechanism of the image forming apparatus 1 is as described above.

Note that a manual feed tray (not shown) is attached to the front side of the image forming apparatus 1, and the medium P set on this manual feed tray is transferred from the manual feed tray to the inside of the image forming apparatus 1 (specifically, between the conveyance rollers of the conveyance unit 3). 31B). By doing so, the image forming apparatus 1 can print using the medium P set in the manual feed tray.

Here, the printing operation during color printing by the image forming apparatus 1 will be briefly described. The image forming apparatus 1 feeds out the media P stored in the cassette 21 of the media supply section 2 one by one onto the conveyance path R using the hopping roller 22 . The medium P fed out to the conveyance path R is conveyed to the transfer section 5 by the conveyance section 3, and sequentially passes through the developing sections 41K, 41C, 41M, and 41Y of the image forming section 4 by the conveyance belt 51 of the transfer section 5. It is transported like this. Here, the developing units 41K, 41C, 41M, and 41Y form toner images of each color on the respective photosensitive drums 42. The toner images of each color thus formed on each photosensitive drum 42 are transferred onto the medium P by each transfer roller 54 of the transfer section 5, thereby forming a color toner image on the medium P.

The medium P on which the color toner image is formed is conveyed to the fixing section 6 by a conveyor belt 51. The fixing unit 6 fixes the color toner image onto the medium P. As a result, a color image is printed on the medium P. Thereafter, the medium P is discharged onto a stacker (not shown) provided outside the image forming apparatus 1. The operation of the image forming apparatus 1 during color printing is as described above.

[2. Configuration of developing section]
Next, details of the configuration of the developing sections 41K, 41C, 41M, and 41Y will be described. As described above, the developing sections 41K, 41C, 41M, and 41Y have the same configuration except that they use different toners, so only the details of the configuration of the developing section 41K will be described here.

As shown in FIG. 1, the developing section 41K includes a photosensitive drum 42, a charging section 43, an exposure device 44, a developing roller 45, a toner supply section 46, and a cleaning blade 47.

The photosensitive drum 42 is a member that carries an electrostatic latent image on its surface, and is configured to rotate at a predetermined circumferential speed. Note that the photosensitive drum 42 is a specific example of an image carrier according to the present invention. The photosensitive drum 42 is constructed using a photosensitive member (for example, an organic photosensitive member). Specifically, the photosensitive drum 42 includes a conductive support and a photoconductive layer covering the outer periphery (surface) of the conductive support. The conductive support is made of, for example, a metal pipe made of aluminum or stainless steel. The photoconductive layer has, for example, a structure in which a charge generation layer and a charge transport layer are laminated in this order.

The charge generation layer mainly contains a charge generation substance and a binder resin. Various organic pigments and organic dyes can be used as the charge generating substance. Among them, metal-free phthalocyanines, copper indium chloride, gallium chloride, tin, oxytitanium, zinc, vanadium and other metals or their oxides, chloride-coordinated phthalocyanines, or azos such as monoazo, hisazo, trisazo or polyazo. Pigments and the like are preferred. The charge generating layer is made of fine particles of these charge generating substances, such as polyester resin, polyvinyl acetate, polyacrylic ester, polymethacrylic ester, polyester, polycarbonate, polyvinyl acetoacetal, polyvinyl propional, polyvinyl butyral, phenoxy resin, epoxy resin, etc. It is used as a dispersion layer bound with various binder resins such as resin, urethane resin, cellulose ester, or cellulose ether.

The charge transport layer mainly contains a charge transport substance and a binder resin. Examples of the charge transport substance include heterocyclic compounds such as carbazole, indole, imidazole, oxazole, pyrazole, oxadiazole, pyrazoline, and thiadiazole, aniline derivatives, hydrazone compounds, aromatic amine derivatives, stilbene derivatives, or compounds thereof. Electron-donating substances such as polymers having groups in their main chains or side chains are used. Binder resins in the charge transport layer include polycarbonate, polymethyl methacrylate, polystyrene, vinyl polymers such as polyvinyl chloride, polyester, polyester carbonate, polysulfone, polyimide, phenoxy, epoxy, silicone resins, or polymers or partial polymers thereof. Examples include crosslinked cured products, and polycarbonate is particularly preferred. Furthermore, the binder resin may contain various additives such as an antioxidant and a sensitizer, if necessary.

The charging unit 43 is a device that charges the surface of the photosensitive drum 42, and as shown in an enlarged view in FIG. It has a cleaning roller 43B arranged so as to slide thereon. Note that the charging section 43 is a specific example of a charging device according to the present invention, and the charging roller 43A is a specific example of a charging member according to the present invention.

The charging roller 43A is a roller that charges the surface of the photosensitive drum 42 by applying a voltage from the charging roller power source 43V, and is in contact with the surface of the photosensitive drum 42 so as to be driven by the photosensitive drum 42. Rotate. Note that since the charging roller 43A is arranged parallel to the photosensitive drum 42, the axial direction of the charging roller 43A and the axial direction of the photosensitive drum 42 can be considered to be the same direction. This charging roller 43A has a core metal 43A1 made of a conductive material and an elastic layer 43A2 having conductivity formed on the outer peripheral surface of the core metal 43A1. For the core metal 43A1, a metal shaft body made of electroless nickel plated SUM, SUS, or the like is often used. The elastic layer 43A2 is often made of rubber, thermoplastic elastomer, resin, or the like so that it can be nipped with the photosensitive drum 42 in order to obtain proper discharge with the photosensitive drum 42. Further, the elastic layer 43A2 is not limited to a single layer, and may have a multilayer structure of two or more layers as necessary.

Examples of the material constituting the elastic layer 43A2 of the charging roller 43A include epichlorohydrin rubber (CO, ECO, GECO), ethylene propylene rubber (EPM, EPDM), acrylonitrile-butadiene rubber (NBR), hydrogenated acrylonitrile-butadiene rubber ( H-NBR), styrene-butadiene rubber (SBR), butadiene rubber (BR), isoprene rubber (IR), chloroprene rubber (CR), urethane rubber, silicone rubber, etc., or a mixture of two or more thereof. A rubber composition having the rubber composition as a main component can be used. In particular, a rubber mainly composed of epichlorohydrin rubber (ECO) or a rubber mainly composed of a mixture of epichlorohydrin rubber (ECO) and acrylonitrile-butadiene rubber (NBR) may be used as the elastic layer 43A2. many. Incidentally, in this embodiment, a rubber whose main component is epichlorohydrin rubber (ECO) is used as the elastic layer 43A2.

Regarding the conductive properties of the elastic layer 43A2, in general, if the resistance (electrical resistance) is too large, image defects will occur due to charging unevenness or poor charging on the surface of the photosensitive drum 42, and if the resistance (electrical resistance) is too small, the photosensitive A leak occurs due to a scratch on the surface of the drum 42, resulting in a defective image. Therefore, an appropriate resistance region exists in the conductive properties of the elastic layer 43A2. In order to obtain an appropriate resistance range, the elastic layer 43A2 is given a predetermined conductivity using an ion conductive material, an ion conductive agent, carbon black, metal oxide, or the like. Note that the elastic layer 43A2 can be made of an electronically conductive or ionically conductive material, but partial resistance unevenness may easily affect the charging unevenness of the photosensitive drum 42, so in order to suppress resistance unevenness, , ionically conductive materials are often used.

Specifically, this elastic layer 43A2 is preferably a resistance layer having a volume resistivity of 10 ⁶ to 10 ⁹ Ω. Note that the resistance value of the charging roller 43A (that is, the volume resistance value of the elastic layer 43A2) varies depending on the temperature, humidity, and measurement voltage in the case of ionic conductivity. Measured under environmental conditions.

Further, this elastic layer 43A2 needs to form a minute gap between the surface of the charging roller 43A and the surface of the photosensitive drum 42 to secure an area that contributes to discharge based on Paschen's law. . For this reason, the hardness of the elastic layer 43A2 is adjusted so that an appropriate nip can be obtained between the elastic layer 43A2 and the surface of the photosensitive drum 42. The hardness of the elastic layer 43A2 is measured by peak measurement using, for example, a micro rubber hardness meter (MD-1capa type A) manufactured by Kobunshi Keiki Co., Ltd. Specifically, the charging roller 43A is placed on the sample stage, the indenter is applied, and the measured value displayed on the micro rubber hardness meter is read as an integer value. At this time, it is preferable that the measured value read (that is, the hardness of the elastic layer 43A2) is in the range of 35 degrees to 80 degrees. On the other hand, the range of hardness of the elastic layer 43A2 includes the purpose of absorbing cylindrical runout and shape variations of the charging roller 43A and the photosensitive drum 42, so that if an appropriate nip with respect to the photosensitive drum 42 is obtained, , there is no need to be particular about this range (that is, 35 degrees to 80 degrees). Incidentally, in this embodiment, the actual measurement value of the elastic layer 43A2 falls within the range of 45 degrees to 57 degrees.

Further, predetermined polishing marks and surface roughness are formed on the surface of the elastic layer 43A2 (that is, the shape of the surface facing the surface of the photosensitive drum 42) by cutting, polishing, or molding. Furthermore, the surface of this elastic layer 43A2 can be subjected to surface treatment or coating.

Specifically, the surface of the elastic layer 43A2 may be subjected to surface treatment such as ultraviolet irradiation or electron beam irradiation. Regarding coating, there are methods such as dipping, spraying, and coating. Examples of the material to be applied (ie, coating agent) include isocyanate compounds and polyols. The isocyanate compounds and polyols mentioned here include, for example, toluene diisocyanate (TDI), methylene diisocyanate (MDI), xylylene diisocyanate (XDI), naphthalene diisocyanate (NDI), hexamethylene diisocyanate (HDI), and isophorone diisocyanate (IPDI). Further examples include polyester polyols, polycarbonate polyols, silicone diols, acrylic fluoropolymers, acrylic silicone polymers, fluoropolymers, and multiples and modified products thereof. Incidentally, a conductive agent such as carbon black or an ion conductive agent is added to the coating agent, if necessary. Particles can also be mixed into the coating agent. Examples of the particles to be mixed include one or a combination of two or more of acrylic resin, urethane resin, fluororesin, polyamide resin, polycarbonate resin, polyester resin, isocyanate resin, and the like.

The cleaning roller 43B is a roller that removes foreign matter adhering to the surface of the charging roller 43A, contacts the surface of the charging roller 43A under pressure, and rotates following the charging roller 43A. This cleaning roller 43B has a core body 43B1 and an elastic layer 43B2 formed on the outer peripheral surface of the core body 43B1. For the core body 43B1, for example, SUM plated with electroless nickel, a metal shaft body such as SUS, or a resin such as polyacetal (POM) can be used. The elastic layer 43B2 may have a single layer or a laminated structure of two or more layers. Further, the elastic layer 43B2 may be configured to include a foam, or may be configured to include two layers, a solid layer and a foam layer. Further, the elastic layer 43B2 may cover the entire surface of the core body 43B1 (excluding both ends in the axial direction), or may be arranged in a spiral shape on the surface of the core body 43B1. It's okay. In short, it is sufficient that the elastic layer 43B2 is configured to clean the surface of the charging roller 43A.

The material constituting the elastic layer 43B2 includes, for example, foamable resin such as polyurethane, polyethylene, polyamide, or polypropylene, silicone rubber, fluororubber, urethane rubber, ethylene propylene rubber (EPM, EPDM), acrylonitrile-butadiene, etc. One or two types of rubber (NBR), hydrogenated acrylonitrile-butadiene rubber (H-NBR), styrene-butadiene rubber (SBR), butadiene rubber (BR), isoprene rubber (IR), chloroprene rubber (CR), etc. A mixture of the above can be used. In addition, auxiliary agents such as a foaming aid, a foam stabilizer, a catalyst, a curing agent, a plasticizer, and a vulcanization accelerator may be added to these materials as necessary.

Note that from the viewpoint of ease of removing foreign matter from the surface of the charging roller 43A, a material having bubbles (so-called foam) is preferable as the material constituting the elastic layer 43B2. In particular, in order to prevent scratches on the surface of the charging roller 43A due to friction, and to prevent tearing or damage over a long period of time, a polyurethane foam that is resistant to tearing and tension is used as the elastic layer 43B2. It is preferable to use More specifically, the density (defined in JIS K7222) is 20 to 80 kg/m ³ , the hardness (defined in JIS K6400-2, D method) is 100 to 410 N, and the tensile strength (defined in JIS K6400-5) is A polyurethane foam having a pressure of 60 to 300 kPa and an elongation (defined in JIS K6400-5) of 100 to 220% is preferred. The configuration of the charging section 43 is as described above.

Returning to FIG. 1, the exposure device 44 is a device that forms an electrostatic latent image on the surface (surface layer portion) of the photosensitive drum 42 by irradiating and exposing the surface of the photosensitive drum 42 with light (irradiation light). . This exposure device 44 is supported by, for example, a housing (not shown) of the image forming apparatus 1. The exposure device 44 includes, for example, a plurality of light sources that emit irradiation light and a lens array that forms an image of the irradiation light on the surface of the photosensitive drum 42 . Note that, as a light source of the exposure device 44, for example, a light emitting diode (LED), a laser element, or the like is used.

The developing roller 45 is a member that carries toner on the surface for developing the electrostatic latent image formed on the surface of the photosensitive drum 42, and is arranged so as to be in contact with the surface of the photosensitive drum 42, and for example, is arranged around a predetermined circumference. The photosensitive drum 42 rotates at a speed opposite to that of the photosensitive drum 42. The developing roller 45 has, for example, a metal shaft and a semiconductive urethane rubber layer covering the outer periphery (surface) of the metal shaft. Toner contained in a toner supply section 46 is supplied to the developing roller 45 by a supply roller (not shown) or the like.

The toner supply unit 46 has a container containing toner. In other words, black toner is stored in the toner supply section 46 of the developing section 41K. Similarly, the toner supply section 46 of the development section 41C stores cyan toner, the toner supply section 46 of the development section 41M stores magenta toner, and the toner supply section 46 of the development section 41Y stores yellow toner. is accommodated.

The toners of each color each contain a predetermined coloring agent, release agent, charge control agent, treatment agent, etc., and are manufactured by appropriately mixing these components or subjecting them to surface treatment. . Among these components, the colorant, mold release agent, and charge control agent each function as internal additives. In addition to the internal additives, the toner also contains external additives such as silica and titanium oxide, and a binder resin such as polyester resin.

The cleaning blade 47 is a member that scrapes and removes toner remaining on the surface of the photosensitive drum 42 without being transferred to the medium P, and is disposed such that one end thereof is in contact with the surface of the photosensitive drum 42. This cleaning blade 47 is made of, for example, a flexible rubber material or plastic material. The configuration of the developing section 41K is as described above. The configurations of the developing units 41C, 41M, and 41Y are also the same as that of the developing unit 41K, except that the toner stored in the toner supply unit 46 is different.

[3. Control mechanism of image forming device]
Next, the control mechanism of the image forming apparatus 1 will be explained using FIG. 3. Note that FIG. 3 is a block diagram showing the control mechanism of the image forming apparatus 1 and the objects to be controlled. As shown in FIG. 3, the image forming apparatus 1 includes, as a control mechanism, a control section 70, a reception memory 71, an image data editing memory 72, an operation section 73, a sensor group 74, and a power supply circuit 80. have.

The control unit 70 includes an interface (hereinafter referred to as I/F) control unit 75, a main control unit 76, an exposure device control unit 44S, a fixing control unit 6S, a transport motor control unit 3S, and a drive control unit 4S. have.

The I/F control unit 75 receives print data and control commands sent from an external device (not shown) such as a personal computer, and transmits information indicating the device status of the image forming apparatus 1 to the external device. The main control unit 76 includes a microprocessor, ROM, RAM, input/output ports, and the like, and controls the operation of the image forming apparatus 1 by, for example, executing a predetermined program. Specifically, the main control unit 76 receives print data and control commands received by the I/F control unit 75 from the I/F control unit 75, and controls the exposure device control unit 44S, fixing control unit 6S, and conveyance motor control unit. 3S and the drive control unit 4S to perform printing operations.

The reception memory 71 temporarily stores print data received by the I/F control unit 75. The image data editing memory 72 stores image data obtained by editing the print data stored in the receiving memory 71. The operation unit 73 includes, for example, a display unit (LED lamp, etc.) for displaying the device status of the image forming apparatus 1, and an input unit (buttons, touch panel, etc.) for the user to give instructions to the image forming apparatus 1. . The sensor group 74 includes various sensors that monitor the operating state of the image forming apparatus 1. Specifically, the sensor group 74 includes a position detection sensor for the medium P, a temperature/humidity sensor, a print density sensor, a remaining toner amount detection sensor, and the like.

The exposure device control section 44S sends the image data stored in the image data editing memory 72 to the exposure device 44, and also controls the driving of the exposure device 44. The fixing control unit 6S controls the voltage applied to the fixing unit 6 when fixing the toner image transferred to the medium P to the medium P. The conveyance motor control section 3S controls the operation of the conveyance section 3 when the conveyance section 3 (conveyance roller pair 31A, 31B) conveys the medium P. The drive control unit 4S controls the operation of the drive motor 48 for driving the photosensitive drum 42.

The power supply circuit 80 includes a charging roller power supply 43V, a developing roller power supply 45V, a toner supply section power supply 46V, and a transfer roller power supply 54V. These charging roller power source 43V, developing roller power source 45V, toner supply section power source 46V, and transfer roller power source 54V respectively supply voltages based on instructions from the main control section 76 to the charging roller 43A, the developing roller 45, and the toner supply section. 46 and transfer roller 54.

The surface of the photosensitive drum 42 is charged by applying a voltage to the charging roller 43A from the charging roller power source 43V. Further, by applying a voltage to the developing roller 45 from the developing roller power source 45V, the toner carried by the developing roller 45 adheres to the electrostatic latent image formed on the surface of the photosensitive drum 42 and is developed. Further, by applying a voltage to, for example, a supply roller (not shown) of the toner supply section 46 by the toner supply section power supply 46V, toner is supplied from the toner supply section 46 to the developing roller 45 via the supply roller. Further, by applying voltage to the transfer roller 54 from the transfer roller power source 54V, the toner image formed on the surface of the photosensitive drum 42 can be transferred to the medium P. The control mechanism of the image forming apparatus 1 is as described above. Note that the image forming apparatus 1 may further include a control mechanism other than the control mechanism shown in FIG.

[4. Charging roller surface roughness]
Next, the surface roughness of the charging roller 43A will be explained. In this embodiment, we focus on the sharpness Sku, which is a parameter related to the surface roughness of the charging roller 43A, and the average spacing Sm of unevenness, and how the occurrence of fog changes by changing these values. We verified whether

In the verification, 11 types of charging rollers 43A shown below as samples 1 to 11 were created, and fog on the medium P was evaluated by mounting each of these in the image forming apparatus 1 and performing printing. The charging rollers 43A of Samples 1 to 11 are each made so that the surface roughness of the elastic layer 43A2 is different. Samples 1 to 5 are non-polished products in which particles form the surface roughness of the elastic layer 43A2 and the surface is not polished. Samples 6 and 7 are non-polished products in which particles are not included in the elastic layer 43A2 and the surface is not polished. Samples 8 to 10 are unpolished products that do not contain particles in the elastic layer 43A2, and are polished products that have a polished surface. Sample 11, like Samples 1 to 5, has elastic layers made of particles. This is a non-polished product in which the surface roughness of the layer 43A2 is formed and the surface is not polished.

Here, for Samples 1 to 5 and 11, the average particle diameter of the particles contained in the elastic layer 43A2 was set to φ20 μm, and the surface roughness was adjusted by adjusting the particle content. The components of the particles included in the elastic layer 43A2 include acrylic particles, urethane particles, polyamide resin particles, silicone resin particles, fluororesin particles, styrene resin particles, phenol resin particles, polyester resin particles, olefin resin particles, epoxy resin particles, Nylon resin particles, carbon, graphite, balloon carbide, silica, alumina, titanium oxide, zinc oxide, magnesium oxide, zirconium oxide, calcium sulfate, calcium carbonate, magnesium carbonate, calcium silicate, aluminum nitride, boric acid nitride, talc, carrion Examples include clay, diatomaceous earth, glass beads, and hollow glass spheres.

Furthermore, for Samples 8 to 10, the surface of the elastic layer 43A2 was polished with a polishing machine to match a predetermined dimension (thickness), and then dry polishing was performed with a grindstone to adjust the surface roughness. Specifically, in the dry polishing, for example, with the charging roller 43A rotated, a rotating polishing wheel is brought into contact with the surface of the elastic layer 43A2, and the polishing wheel is moved in the axial direction of the charging roller 43A. Do it as you like. In samples 8 to 10, the surface roughness of the elastic layer 43A2 was adjusted by changing the rotation speed of the polishing wheel, for example, 1000 rpm for sample 8, 2000 rpm for sample 9, 3000 rpm for sample 10, etc.

Regarding Samples 6 and 7, the surface roughness of the elastic layer 43A2 differs due to the difference in the method of forming the elastic layer 43A2 (cutting, molding, surface treatment, coating, etc.).

Samples 1 to 11 are thus prepared with different surface roughnesses. In fact, for these samples 1 to 11, a hybrid laser confocal microscope was used to measure the kurtosis Sku, the average spacing Sm of the unevenness, and the root mean square slope Sdq of the unevenness, which are indicators of surface roughness. . Specifically, the surface sharpness Sku, the average interval Sm of unevenness, and the root mean square slope Sdq are measured at three locations at both ends and the center in the axial direction of the charging roller 43A, and the average value of the three locations is determined. were taken as the respective measured values of kurtosis Sku, average spacing Sm of unevenness, and root mean square slope Sdq. Note that the measurement conditions of the hybrid laser confocal microscope at this time were: magnification: 20 times, resolution: 0.18 μm, gain: 334, and channel: Blue.

Here, the definitions of the kurtosis Sku, the average interval Sm of unevenness, and the root mean square slope Sdq will be briefly explained. The kurtosis Sku is a parameter defined by ISO 25178, and represents the sharpness of the height distribution of the unevenness formed on the surface. As shown in the graphs of FIGS. 4(A) to (C), when the kurtosis Sku=3, the height distribution of the unevenness becomes a normal distribution, and when the kurtosis Sku>3, the average There are more irregularities with heights near the average value (in other words, the heights of the irregularities become uniform around the average value), and when the kurtosis is Sku < 3, the irregularities with heights around the average value become more common. This means that the height of the unevenness becomes smaller (that is, the height of the unevenness becomes more variable). In other words, it can be said that the sharpness Sku indicates the degree of variation in the height of the unevenness.

The average spacing Sm of unevenness is a parameter defined in JIS B 0601-1994, and as shown in FIG. The average value of the length Xsi (i=1 to m) corresponding to the valley (concave) is expressed in millimeters (mm). Here, the reference length l is defined in JIS B 0601, and is one-fifth of the evaluation length L as a standard, as shown in FIG. 5(B). Further, here, the length in the axial direction of the contact portion of the surface of the charging roller 43A (that is, the surface of the elastic layer 43A2) with the surface of the photosensitive drum 42 (that is, the nip portion of the charging roller 43A) is defined as the evaluation length L. . Specifically, the length of the nip portion of the charging roller 43A is 224.15 mm, which corresponds to the A4 size medium P, and the reference length l is 44.83 mm, which is 224.15/5. There is. In this way, the average interval Sm of the unevenness indicates the average interval of the unevenness in the axial direction at the nip portion of the charging roller 43A. The larger Sm is, the larger the interval between the unevenness in the axial direction in the nip portion of the charging roller 43A is, which means that the number of unevenness existing in the axial direction is smaller. Note that the reference length l may be a certain length cut out from the evaluation length L, but here, it is set to one-fifth of the evaluation length L as a standard length.

The root mean square slope Sdq is a parameter defined by ISO 25178, and represents the severity of surface undulations. As shown in FIG. 6(A), this root mean square slope Sdq is 0 when the surface is completely flat, and as shown in FIG. 6(B), when the surface is sloped (that is, uneven ) becomes larger. FIG. 6(B) shows a plane having a tilt component of 45°, and in this case, the root mean square tilt Sdq is 1. In other words, the larger the root mean square slope Sdq, the more rugged the surface is (that is, the surface has sharper unevenness).

Here, the table of FIG. 7 shows the values of the kurtosis Sku, the average spacing Sm of concavities and convexities, and the root mean square slope Sdq actually measured for Samples 1 to 11. As shown in this table, Samples 1 to 11 (indicated by numbers in circles in the table) have different kurtosis Sku, average unevenness spacing Sm, and root mean square slope Sdq, and have different surface roughness. There is.

Next, a description will be given of a fog evaluation method performed by mounting each of the above-mentioned samples 1 to 11 on the image forming apparatus 1. In this embodiment, ΔE, which indicates color difference, is used as the fog evaluation value. ΔE is defined by CIE, and specifically, ΔE is defined by two colors (L ₁ ^* , a ₁ ^* , b ₁ ^* ) and (L ₂ ^* , a ₂ ^* ) in the L ^* a ^* b ^* color space. , b ₂ ^* ), it is expressed by the following formula.

(Formula)...ΔE=√(L ₂ ^* - L ₁ ^* ) ² + (a ₂ ^* - a ₁ ^* ) ² + (b ₂ ^* - b ₁ ) ²

Note that the L ^* a ^* b ^* color space is one of the complementary color spaces, has a dimension L meaning lightness, and complementary color dimensions a and b, and is based on a nonlinear compression of the coordinates of the XYZ space.

In this embodiment, the charging rollers 43A of Samples 1 to 11 were each mounted on the image forming apparatus 1, and the ΔE was measured. Here, a method for measuring ΔE will be explained. In this embodiment, the charging roller 43A of one of the developing sections 41K, 41C, 41M, and 41Y (for example, the developing section 41M) is replaced with the charging roller 43A of samples 1 to 11 in order to measure ΔE. did.

At this time, in the image forming apparatus 1, the correction values of various voltages are set to ±0, and the white paper (excellent white paper) is slightly thicker than the plain paper set in the manual feed tray in an environment of 20 degrees Celsius and 80% humidity. ) on the medium P.

Specifically, first, the medium P is set in the manual feed tray under non-exposure conditions (that is, blank printing), and the medium P is fed into the image forming apparatus 1 from the manual feed tray. Here, just before the medium P reaches the transfer roller 54 located below the developing section 41M, the conveyance of the medium P is stopped, and a mending tape is pasted on a predetermined area of the surface of the photosensitive drum 42 of the developing section 41M. then peel it off.

At this time, as shown in FIG. 8A, the area where the mending tape is pasted is a distance D1 from the lower end of the photosensitive drum 42 to the upstream side in the rotational direction of the photosensitive drum 42 (direction indicated by arrow Ar2 in the figure). The range extends to a distant point. Further, the distance D1 at this time is, for example, 16.9 mm. In other words, the area on the surface of the photosensitive drum 42 to which the mending tape is attached is the part that comes into contact with the printing surface of the medium P while the medium P is conveyed approximately the distance D1 after reaching the transfer roller 54. I can say that.

Further, FIG. 8(B) shows the mending tape Mt used at this time. The mending tape Mt is in the form of a band, and the length D2 in the transverse direction (width) is 18.0 mm, which is longer than D1, and the length D3 in the longitudinal direction is approximately the same as the length in the axial direction of the photosensitive drum 42. It has become.

Incidentally, since the printing at this time is performed under non-exposure conditions, toner should not adhere to a predetermined area on the surface of the photosensitive drum 42, but due to uneven charging occurring on the surface of the photosensitive drum 42, toner adheres. Therefore, when the mending tape Mt is attached to a predetermined area on the surface of the photosensitive drum 42 and then peeled off, the toner adhering to the predetermined area on the surface of the photosensitive drum 42 is transferred to the mending tape Mt. It can be said that the larger the amount of toner transferred to the mending tape Mt, the more likely fog will occur on the medium P.

In this embodiment, the color of the mending tape Mt to which no toner has adhered (that is, it is not attached to the photosensitive drum 42) and the color of the mending tape Mt to which toner transferred from the surface of the photosensitive drum 42 has adhered are shown. By measuring the difference in color, ΔE, which is an evaluation value of fog, was measured.

That is, as shown in FIG. 9, first, a mending tape (hereinafter referred to as reference tape) MtN to which no toner is attached is pasted onto a predetermined blank paper (excellent white) Wp. Furthermore, a mending tape Mt to which toner is attached, which has been peeled off from the surface of the photosensitive drum 42, is attached to this blank paper Wp. Then, the color of the reference tape MtN to which no toner is attached is set as the first color, and the color of the mending tape Mt to which toner is attached (the color of the hatched area) is set as the second color. These color differences, ΔE, were measured using a spectral colorimeter (CM-2600d) manufactured by Konica Minolta. At this time, ΔE is measured for the color of the reference tape MtN and each of the colors Pt1 to Pt5 at five locations on the mending tape Mt to which toner is attached, and finally the average value of the five ΔEs is calculated. Calculate and use this as the measured value of ΔE.

In this embodiment, such ΔE measurement is performed for each of samples 1 to 11. The ΔE values measured in this manner for each of Samples 1 to 11 are shown in the table of FIG. As mentioned above, this ΔE represents the color difference between the color of the reference tape MtN and the color of the mending tape Mt to which toner is attached, so the larger this ΔE is, the more toner is attached to the mending tape Mt. This means that there is a large amount of toner. A large amount of toner adhering to the mending tape Mt means that a large amount of toner is transferred from the photosensitive drum 42 to the non-printing area of the medium P, and fog is likely to occur.

In fact, when we visually checked whether fog had occurred on the medium P, we found that if ΔE was less than 1.8, we could not recognize the occurrence of fog, and if ΔE was 1.8 or more, I was able to recognize the occurrence of fog. Therefore, in the table of FIG. 7, samples 4 to 7 with a ΔE of less than 1.8 are evaluated as ○ as being able to suppress the occurrence of fog, and samples with a ΔE of 1.8 or more are evaluated as ○. For Samples 1 to 3 and Samples 8 to 11, the evaluation results were given as × because the occurrence of fog could not be suppressed.

In this embodiment, based on the evaluation results of Samples 1 to 11 shown in the table of FIG. 7, a good range of the sharpness Sku regarding the surface roughness of the charging roller 43A and the average spacing Sm of the unevenness is defined. Here, using a graph shown in FIG. 10 in which the vertical axis is the kurtosis degree Sku and the horizontal axis is the average spacing Sm of the asperities, a description will be given of the good range of the kurtosis degree Sku and the average spacing Sm of the asperities.

Incidentally, on this graph, Samples 1 to 11 are plotted based on their respective kurtosis degrees Sku and average spacing Sm of concavities and convexities. Also, among samples 1 to 11, for those with an evaluation result of ○, a mark is placed next to the number in the box, and for those whose evaluation result is ×, an x mark is placed next to the number in the box.

From this graph, it can be seen that for samples 4 to 7 with evaluation results of 0, the minimum value of the kurtosis Sku is 2.30 and the maximum value is 5.02. From this, the favorable range of the kurtosis Sku was determined to be 2.30 or more and 5.02 or less.

Here, FIG. 11 shows the relationship between the surface shape of the charging roller 43A (that is, the surface shape of the elastic layer 43A2), the sharpness Sku, and the average interval Sm of unevenness. This FIG. 11 is divided into four parts: upper left, lower left, upper right, and lower right. The upper left part shows the surface shape of the charging roller 43A when the sharpness Sku is large and the average interval Sm of unevenness is small. , the lower left part shows the surface shape of the charging roller 43A when the kurtosis Sku is small and the average spacing Sm of the asperities is also small, and the upper right part shows the surface shape of the charging roller 43A when the kurtosis Sku is large and the average spacing Sm of the asperities is also large. The lower right portion of the surface shape of the charging roller 43A shows the surface shape of the charging roller 43A when the sharpness Sku is large and the average interval Sm of the unevenness is also large. Note that the surface shape of the charging roller 43A shown in FIG. 11 is deformed. Further, among the four portions shown in FIG. 11, the surface shape of the charging roller 43A when the sharpness Sku and the average spacing Sm of the unevenness are within the good range is the upper right portion.

For example, as shown in the upper right part of FIG. 11, as the sharpness Sku of the surface of the charging roller 43A increases, the heights of the convex portions formed on the surface of the charging roller 43A become uniform, so that the heights of the convex portions and the photosensitive drum 42 become more uniform. It is thought that the variation in the distance to the surface becomes smaller, and as a result, uneven charging on the surface of the photosensitive drum 42 is suppressed and fog is suppressed. From this, it is considered that the minimum value of the kurtosis Sku is preferably 3 or more, at which the height distribution of the unevenness becomes a normal distribution, but fog was suppressed even with a value of 2.30. This is considered to be because the average interval Sm of .

Furthermore, from the graph of FIG. 10, it can be seen that for samples 4 to 7 with evaluation results of 0, the minimum value of the average spacing Sm of the unevenness is 0.17 mm, and the maximum value is 0.41 mm. Here, the good range of the average spacing Sm of the unevenness is not 0.17 mm or more and 0.41 mm or less, but 0.17 mm or more and the reference length l (l = 44.83 mm) or less.

Here, using FIGS. 11 and 12, the reason why the maximum value of the good range of the average spacing Sm of the unevenness is set as the reference length l will be explained. FIG. 12 shows the surface shape of the charging roller 43A (that is, the surface shape of the elastic layer 43A2) when the average interval Sm of the unevenness is the reference length l. The surface shape of the charging roller 43A shown in FIG. 12 is also deformed.

For example, as shown in the upper right portion of FIG. 11, the larger the average interval Sm between the unevenness on the surface of the charging roller 43A, the larger the flat portion located between the protrusions on the surface of the charging roller 43A. As a result, the probability that discharge will occur between the flat portion of the charging roller 43A and the photosensitive drum 42 increases, so it is thought that uneven charging on the surface of the photosensitive drum 42 is suppressed and fog is suppressed. Therefore, it is preferable that the average interval Sm between the concave and convex portions is large, but in order to form a minute gap between the surface of the charging roller 43A and the surface of the photosensitive drum 42, as shown in FIG. One convex portion is required at each end of the reference length l. Therefore, in this embodiment, the maximum value of the good range of the average spacing Sm of the unevenness is set as the reference length l.

Here, let us also consider the case where the kurtosis degree Sku and the average spacing Sm of unevenness are outside the good range. Specifically, if we consider the case where the kurtosis Sku is larger than 5.02 and the case where the average spacing Sm of unevenness is smaller than 0.17, in these cases, as can be seen from the table in FIG. Then, the root mean square slope Sdq increases, and the surface of the charging roller 43A becomes more rugged (the surface becomes sharper). When the surface of the charging roller 43A becomes more uneven, the distance between the surface of the charging roller 43A and the surface of the photosensitive drum 42 increases, so uneven charging on the surface of the photosensitive drum 42 cannot be suppressed, and fogging cannot be suppressed. It is thought that it will not be possible.

From the above, in this embodiment, the good range of the kurtosis Sku on the surface of the charging roller 43A is defined as 2.30 or more and 5.02 or less, and the good range of the average spacing Sm of the unevenness is set as 0.17 mm. In the above, it was specified that the length was equal to or less than the reference length l (l = 44.83 mm). By doing this, in this embodiment, variations in the distance between the surface of the charging roller 43A and the surface of the photosensitive drum 42 are reduced, and as a result, uneven charging on the surface of the photosensitive drum 42 is suppressed, and fogging is suppressed. be able to.

[5. Summary and effects]
As described so far, in this embodiment, the favorable range of the kurtosis Sku on the surface of the charging roller 43A, which rotates and contacts the surface of the photosensitive drum 42 to charge the surface, is set to 2.30 or more, 5. 0.02 or less, and the good range of the average spacing Sm of unevenness in the axial direction of the charging roller 43A on the surface of the charging roller 43A was defined as 0.17 mm or more and the reference length l or less.

By doing so, in this embodiment, variations in the distance between the surface of the charging roller 43A and the surface of the photosensitive drum 42 are reduced, and unevenness in charging potential is less likely to occur on the surface of the photosensitive drum 42. Thus, according to the present embodiment, fog on the medium P can be suppressed, and the print quality by the image forming apparatus 1 can be improved.

[6. Other embodiments]
[6-1. Other embodiment 1]
In the above-described embodiment, if the fog evaluation value ΔE is less than 1.80, the fog on the medium P cannot be visually recognized. Based on the range of kurtosis Sku of 6 and the range of average spacing Sm of unevenness, the good range of kurtosis Sku is 2.30 or more and 5.02 or less, and the good range of average spacing Sm of unevenness is 0.17 mm. Above, the standard length was defined as 1 mm or less. Here, for example, when printing is performed with the image forming apparatus 1 using a higher quality medium P (for example, glossy paper) on which toner is easily applied, fog on the medium P is detected even if ΔE is less than 1.80. It has been found that fog on the medium P cannot be visually recognized if ΔE is less than 0.70.

Therefore, when it is assumed that printing will be performed on such a medium P, the range of kurtosis Sku of samples 6 and 7 in which ΔE is less than 0.70 among samples 4 to 7 and the average spacing Sm of unevenness should be determined. Based on the range, the good range of the kurtosis Sku may be defined as 2.30 or more and 3.61 or less, and the good range of the average spacing Sm of unevenness may be defined as 0.25 mm or more and 0.35 mm or less.

In other words, when only printing on plain paper such as general copy paper is considered, the favorable range of the kurtosis Sku on the surface of the charging roller 43A is 2.30 or more and 5.02 or less, and the average pitch of the unevenness. The good range of Sm may be defined as 0.17 mm or more and the reference length lmm or less. If printing on higher quality glossy paper is also considered, the good range of sharpness Sku should be 2.30 or more. 3.61 or less, and the good range of the average spacing Sm of unevenness may be defined as 0.25 mm or more and 0.35 mm or less. In other words, the good range of kurtosis Sku on the surface of the charging roller 43A is set to 2.30 or more and 5.02 or less, more preferably 2.30 or more and 3.61 or less, and the average unevenness is The favorable range of the distance Sm may be set to 0.17 mm or more and the reference length lmm or less, more preferably 0.25 mm or more and 0.35 mm or less.

[6-2. Other Embodiment 2]
Further, in the embodiment described above, a good range of kurtosis Sku and a good range of average interval Sm of unevenness on the surface of the charging roller 43A are defined, but in addition to this, a good range of root mean square slope Sdq is defined. may also be specified. Specifically, as shown in the table of FIG. 7, for samples 4 to 7 with evaluation results of 0, the maximum value of the root mean square slope Sdq is 8.15. Further, as the root mean square slope Sdq is smaller, the undulations on the surface of the charging roller 43A become gentler, and the variation in the distance between the surface of the charging roller 43A and the surface of the photosensitive drum 42 becomes smaller. Based on these facts, the good range of the root mean square slope Sdq may be defined as 8.15 or less.

[6-3. Other Embodiment 3]
Furthermore, in the embodiment described above, the length in the axial direction of the surface of the charging roller 43A that contacts the surface of the photosensitive drum 42 (that is, the nip portion of the charging roller 43A) is defined as the evaluation length L. With L being 224.15 mm and one-fifth of the evaluation length L being the reference length l, this reference length l was 44.83 mm. However, the present invention is not limited to this, and if the image forming apparatus 1 is compatible with, for example, an A3 size medium P, and the length of the nip portion of the charging roller 43A in the axial direction is different from that in the embodiment described above, charging The numerical values of the evaluation length L and the reference length l may be changed according to the axial length of the nip portion of the roller 43A. In this case, the maximum value of the good range of the average spacing Sm of the unevenness also changes from 44.83 mm.

[6-4. Other embodiment 4]
Furthermore, in the embodiments described above, the present invention is applied to the charging unit 43, which is a specific example of a charging device including a charging member (charging roller 43A) for charging the surface of the image carrier while rotating while contacting the surface of the image carrier. Applied. The present invention is not limited to this, and may be applied to a charging device having a different configuration from the charging section 43 as long as it includes a charging member having the same surface shape as the charging roller 43A. For example, the present invention may be applied to a charging device including a charging member made of a belt instead of a roller. Further, in the embodiment described above, the present invention is applied to the image forming section 4 and the transfer section 5, which are specific examples of an image forming unit including a charging device. The present invention is not limited to this, and may be applied to an image forming unit having a configuration different from that of the image forming section 4 and the transfer section 5 as long as it includes a charging device. For example, an image forming unit that can handle a single color or five or more colors, or a so-called secondary transfer method in which a toner image formed on a photosensitive drum is primarily transferred to an intermediate transfer belt, and then secondarily transferred from the intermediate transfer belt to a medium. It may also be applied to the forming unit.

[6-5. Other Embodiment 5]
Further, in the embodiment described above, the present invention is applied to the image forming apparatus 1 which is an electrophotographic color printer. The present invention is not limited to this, and may be applied to an image forming apparatus having a configuration different from the image forming apparatus 1 as long as it includes an image forming unit having a charging device. For example, it may be applied to an image forming apparatus that is a monochrome printer or an image forming apparatus that has an intermediate transfer belt, and is not limited to printers, but also applicable to image forming apparatuses such as copying machines, facsimile machines, and multifunction devices. You may.

[6-6. Other embodiment 6]
Furthermore, the present invention is not limited to the embodiments described above. That is, the scope of the present invention extends to embodiments in which a part or all of the above-described embodiments are arbitrarily combined, and embodiments in which a part is extracted.

The present invention can be widely used in image forming apparatuses such as printers using electrophotography.

1... Image forming device, 4... Image forming section, 5... Transfer section, 41K, 41C, 41M, 41Y... Developing section, 42... Photosensitive drum, 43... Charging section, 44... Exposure device, 45...Developing roller, 46...Toner supply unit, 47...Cleaning blade, 43A1...Core metal, 43A2...Elastic layer, Sku...Kurarity, Sm...Average interval of unevenness, Sdq...Root mean square Square root slope, ΔE...Fog evaluation value, Mt...Mending tape, MtN...Reference tape, P...Medium.

Claims (7)

comprising a charging member that charges the surface while rotating in contact with the surface of an image carrier carrying an electrostatic latent image on the surface;
The surface of the charging member has a sharpness Sku (defined in ISO 25178) of 2.30 or more and 5.02 or less, and the charging member has a contact portion between the surface of the charging member and the surface of the image carrier. The electrification on the surface of the charging member within the reference length l, where the length in the axial direction of the member is an evaluation length L, and a constant length cut out from the evaluation length L is a reference length l. A charging device characterized in that an average interval Sm (defined in JIS B 0601-1994) of unevenness in the axial direction of the member is 0.17 mm or more and the reference length l or less. The charging device according to claim 1, wherein the reference length l is 44.83 mm, and the evaluation length L is five times the reference length l. A claim characterized in that, on the surface of the charging member, the sharpness Sku is 2.30 or more and 3.61 or less, and the average interval Sm of the unevenness is 0.25 mm or more and 0.35 mm or less. 1. The charging device according to 1. The charging device according to claim 1 or 2, wherein the root mean square slope Sdq (defined in ISO 25178) on the surface of the charging member is 8.15 or less. The charging device according to any one of claims 1 to 4, wherein the charging member is a charging roller. An image forming unit comprising the charging device according to claim 1. An image forming apparatus comprising the image forming unit according to claim 6.

Images