JP2018112580A - Image forming apparatus - Google Patents

Abstract

An object of the present invention is to provide an image forming apparatus capable of suppressing layer disorder of a toner layer by using a toner having a large charge attenuation coefficient while also maintaining transferability of a toner image from an image carrier onto a recording medium. An image forming apparatus includes an image carrier and a developing device. The image carrier has a support and an amorphous silicon photosensitive layer formed on the surface of the support. The developing device includes a developer carrier which is disposed opposite to the image carrier and carries a magnetic one-component developer made of only magnetic toner, and a developer carrier which is disposed at a predetermined distance from the developer carrier and which carries the developer. It has a metal regulating member that regulates the layer thickness of the magnetic one-component developer supported on the body. The arithmetic mean roughness Ra of the surface of the photosensitive layer at the initial stage of use is within the range of 40 nm or more and 70 nm or less, and the charge attenuation coefficient of the magnetic toner is within the range of 0.008 or more and 0.05 or less. [Selection diagram] Figure 2

Description

  The present invention relates to an image forming apparatus including an image carrier on which a toner image is formed on a surface and a developing device that develops an electrostatic latent image on the image carrier.

  In an image forming apparatus using an electrophotographic system such as a copying machine, a printer, a facsimile, etc., a powder developer is mainly used, and an electrostatic latent image formed on an image carrier such as a photosensitive drum is used as a developer. A general process is to perform a fixing process after visualizing and transferring the toner image onto a recording medium.

  Developers are broadly divided into two-component developers consisting of toner and magnetic carrier, and one-component developers consisting only of magnetic toner, and are carried on a developing roller (developer carrier) by a magnetic regulating blade. The triboelectric charge of the developed developer is promoted. Further, the regulating blade serves as a regulating unit that regulates the layer thickness of the developer layer formed on the developing roller, and the gap (gap) between the regulating blade and the developing roller needs to be strictly adjusted. .

  In the magnetic one-component developing method using a one-component developer, the toner layer on the developing roller is disturbed due to overcharging in the regulating portion, and a problem that the half image becomes non-uniform is likely to occur. Therefore, by using a toner that easily loses charge, specifically, a toner having a large charge attenuation coefficient, it is possible to suppress overcharging when passing through the regulation blade and to suppress layer disturbance.

  For example, Patent Document 1 discloses a developing device in which a magnetic toner having a large charge attenuation coefficient is combined with a specular mag roller having an oxide film layer formed on the surface as a developing roller. In the configuration described in Patent Document 1, it is possible to suppress toner layer disturbance by using toner having a large charge attenuation coefficient. Further, by using a mirror surface mag roller, the toner layer is reduced in the transport amount, so that the charge of the toner is improved and the variation in the charge amount is reduced. As a result, toner scattering is suppressed and developability in a high humidity environment is improved.

Japanese Patent Laid-Open No. 2006-133644

  However, the specular mag roller contributes to the charging of the toner only to the toner existing in the lower layer portion (near the roller) of the toner layer in contact with the roller surface, and for the charging of the toner existing in the upper layer portion of the toner layer. Does not contribute. Therefore, particularly in a high temperature and high humidity environment, the charge amount of the toner decreases, so that it becomes difficult to transfer the toner image from the photosensitive drum onto the paper, and transfer defects tend to occur.

  SUMMARY OF THE INVENTION In view of the above problems, the present invention uses a toner having a large charge attenuation coefficient, and suppresses toner layer disturbance while maintaining the transferability of a toner image from an image carrier onto a recording medium. An object is to provide a forming apparatus.

  In order to achieve the above object, a first configuration of the present invention is an image forming apparatus including an image carrier and a developing device. The image carrier has a support and an amorphous silicon photosensitive layer formed on the surface of the support. The developing device is disposed opposite to the image carrier, and carries a developer carrier carrying a magnetic one-component developer composed of only magnetic toner, and is arranged at a predetermined interval with respect to the developer carrier, and the developer carrier. And a metal regulating member that regulates the layer thickness of the magnetic one-component developer carried on the body. The arithmetic average roughness Ra of the surface of the photosensitive layer in the initial use is in the range of 40 nm to 70 nm, and the charge attenuation coefficient of the magnetic toner is in the range of 0.008 to 0.05.

  The “arithmetic mean roughness Ra” in this specification is based on the surface roughness defined in 1994 edition of JISB0601.

  According to the first configuration of the present invention, by using a magnetic toner having a charge attenuation coefficient of 0.008 or more and 0.05 or less, the amount of charge injected from the developer carrier to the toner and the toner flows out to the image carrier. The balance with the charge amount is adjusted. As a result, it is possible to effectively suppress the occurrence of fog due to a decrease in toner charge amount and the occurrence of transfer failure due to toner overcharge. Further, when used together with an image carrier having an arithmetic surface roughness of the photosensitive layer of 40 nm or more and 70 nm or less, the contact area of the toner with respect to the surface of the photosensitive layer is reduced, and the adhesion force of the toner to the image carrier can be reduced. it can. As a result, transferability is improved even in a high-temperature and high-humidity environment, and the occurrence of transfer defects is suppressed.

1 is a side sectional view showing a schematic configuration of an image forming apparatus 100 according to an embodiment of the present invention. The elements on larger scale which show the structure of the image formation part P in FIG. Side surface sectional view of the developing device 8 mounted in the image forming apparatus 100 of the present embodiment. The top view of the developing device 8 mounted in the image forming apparatus 100 of this embodiment. Schematic showing a core-shell structure of toner used in the image forming apparatus 100 of the present embodiment.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a side sectional view showing an internal structure of an image forming apparatus 100 according to an embodiment of the present invention, and FIG. 2 is a partially enlarged view of an image forming portion P in FIG. In the image forming apparatus (in this case, a monochrome printer) 100, an image forming portion P that forms a monochrome image by each process of charging, exposure, development, and transfer is disposed. In the image forming section P, along the rotation direction of the photosensitive drum 1 (counterclockwise direction in FIG. 1), the charging device 4, the exposure unit (laser scanning unit, etc.) 7, the developing device 8, the transfer roller 14, and the cleaning A device 19 and a static elimination device 6 are provided.

  When an image forming operation is performed, the photosensitive drum 1 rotating in the counterclockwise direction is uniformly charged by the charging device 4, and electrostatically is applied on the photosensitive drum 1 by the laser beam from the exposure unit 7 based on the document image data. A latent image is formed, and a developer (toner) is attached to the electrostatic latent image by the developing device 8 to form a toner image.

  The toner is supplied to the developing device 8 from the toner container 9. Note that the image data is transmitted from a host device such as a personal computer (not shown). Further, a static elimination device 6 that removes residual charges on the surface of the photosensitive drum 1 is provided on the downstream side of the cleaning device 19 with respect to the rotation direction of the photosensitive drum 1.

  A sheet is conveyed from the sheet cassette 10 or the manual sheet feeder 11 via the sheet conveyance path 12 and the registration roller pair 13 toward the photosensitive drum 1 on which the toner image is formed as described above, and the transfer roller 14. The toner image formed on the surface of the photosensitive drum 1 is transferred onto the sheet by (image transfer unit). The sheet on which the toner image has been transferred is separated from the photosensitive drum 1 and conveyed to the fixing device 15 to fix the toner image. The sheet that has passed through the fixing device 15 is conveyed to the upper part of the apparatus through the sheet conveying path 16, and is discharged to the discharge tray 18 by the discharge roller pair 17 when an image is formed on only one side of the sheet (during single-sided printing).

  The photosensitive drum 1 includes a metal cylindrical element tube (support) 1a and a photosensitive layer 1b formed on the surface of the element tube 1a. Examples of the metal forming the raw tube 1a include aluminum, iron, titanium, and magnesium. As the photosensitive layer 1b, an organic photosensitive layer using an organic photoconductor, an inorganic photosensitive layer using an inorganic photoconductor, or the like can be used, but amorphous silicon formed by vapor deposition of silane gas or the like because of its high durability. A photosensitive layer is preferred. The characteristics of the photosensitive layer 1b of the photosensitive drum 1 will be described later.

  The charging device 4 includes a charging roller 41 that contacts the photosensitive drum 1 and applies a charging bias to the drum surface and a charging cleaning roller 42 for cleaning the charging roller 41 in the charging housing.

  The charging roller 41 is made of, for example, conductive rubber, and is disposed so as to contact the photosensitive drum 1. As shown in FIG. 2, when the photosensitive drum 1 rotates in the counterclockwise direction, the charging roller 41 that contacts the surface of the photosensitive drum 1 is rotated in the clockwise direction. At this time, the surface of the photosensitive drum 1 is uniformly charged by applying a predetermined voltage to the charging roller 41. Further, as the charging roller 41 rotates, the charging cleaning roller 42 that contacts the charging roller 41 is driven to rotate counterclockwise to remove the foreign matter attached to the surface of the charging roller 41.

  The cleaning device 19 includes a cleaning blade 51 and a collection spiral 52. The cleaning blade 51 is made of urethane rubber or the like. The tip of the cleaning blade 51 is in contact with the rotation direction of the photosensitive drum 1 (see the arrow in FIG. 2) in the counter direction. The collecting spiral 52 is disposed near the lower part of the housing and rotates to convey the collected toner in one of the longitudinal directions of the housing (the direction perpendicular to the paper surface of FIG. 2) to a waste toner container (not shown). And send it out.

  3 and 4 are a side sectional view and a plan view of the developing device 8 mounted on the image forming apparatus 100. FIG. FIG. 3 shows the developing device 8 as viewed from the back side of FIG. For the sake of convenience, FIG. 4 shows a state in which the top cover is removed and the inside of the developing device 8 can be seen. As shown in FIGS. 3 and 4, the developing device 8 includes a developing container 22 that contains a magnetic one-component developer (hereinafter simply referred to as a developer) made of only magnetic toner, and a first container that agitates and conveys the developer. A stirring screw 23 and a second stirring screw 24, a developing roller 25, and a regulating blade 29 are provided.

  The inside of the developing container 22 is divided into a first transfer chamber 22b and a second transfer chamber 22c by a partition wall 22a formed integrally with the developing container 22. The partition wall 22a extends in the longitudinal direction of the developing container 22 and partitions the first transfer chamber 22b and the second transfer chamber 22c in parallel. As shown in FIG. 3, the partition wall 22 a does not exist at both ends in the longitudinal direction of the developing container 22, and the right end in the longitudinal direction of the partition wall 22 a is connected to the first communication together with the side wall of the developing container 22. On the other hand, the left end portion in the longitudinal direction of the partition wall 22a forms a second communication portion 22f together with the side wall portion of the developing container 22. The first and second communication portions 22e and 22f are opened so that the developer can be transferred between the first transfer chamber 22b and the second transfer chamber 22c.

  A first stirring screw 23 is disposed in the first transfer chamber 22b, and a second stirring screw 24 is disposed in the second transfer chamber 22c. The first and second stirring screws 23 and 24 include spiral blades that are spirally formed in the axial direction. The first agitating screw 23 conveys the developer in the first conveying chamber 22b in the direction of arrow P while agitating the developer, and conveys it to the second conveying chamber 22c, and the second agitating screw 24 moves to the second conveying chamber 22c. The developer that has been conveyed is conveyed in the direction of arrow Q while being agitated and supplied to the developing roller 25. That is, a developer circulation path is formed in the developing container 22 by the first transfer chamber 22b, the first communication portion 22e, the second transfer chamber 22c, and the second communication portion 22f. The first stirring screw 23 and the second stirring screw 24 stir and mix the developer to frictionally charge the developer.

  The developing roller 25 is formed in a cylindrical shape with a nonmagnetic material such as aluminum and incorporates a magnetic pole member 26. Further, the developing roller 25 is rotatably supported in the developing container 22 at a position adjacent to the second stirring screw 24. Further, the developing roller 25 is exposed from the opening of the developing container 22 and is opposed to the photosensitive drum 1 that is an image carrier with a certain interval. Then, the toner is supplied to the photosensitive layer 1b of the photosensitive drum 1 by rotating according to the rotation of the photosensitive drum 1 (see FIG. 1). The detailed configuration of the developing roller 25 will be described later.

  A magnetic pole member 26 made of a permanent magnet having a plurality of magnetic poles is fixed inside the developing roller 25. A magnetic brush is formed by attaching (carrying) developer to the surface of the developing roller 25 by the magnetic force of the magnetic pole member 26. The developing roller 25 is rotatably supported by the developing container 22 in a state parallel to the first stirring screw 23 and the second stirring screw 24. The first stirring screw 23, the second stirring screw 24, and the developing roller 25 are rotationally driven by a motor (not shown). Further, magnetic seal members 27 for preventing leakage of the developer from the gap between the developing container 22 and the developing roller 25 are disposed at both ends of the developing roller 25.

  The regulating blade 29 is formed such that its longitudinal direction (direction perpendicular to the paper surface of FIG. 3) is larger than the maximum developing width of the developing roller 25, and is arranged at a predetermined interval from the developing roller 25. The amount of toner supplied to the photosensitive drum 1 is regulated. As the material of the regulating blade 29, magnetic SUS (stainless steel) or the like is used. Note that magnetism may be imparted by attaching a permanent magnet to the non-magnetic regulating blade 29.

  DS rollers 31 a and 31 b are rotatably inserted on the rotation shaft of the developing roller 25. The DS rollers 31 a and 31 b strictly regulate the distance between the developing roller 25 and the photosensitive drum 1 by contacting both end portions of the outer peripheral surface of the photosensitive drum 1. The DS rollers 31a and 31b have built-in bearings, and the drum surface can be prevented from being worn by being rotated by being driven by the photosensitive drum 1.

  The developer supplied from the second stirring screw 24 is carried on the surface of the developing roller 25 to form a magnetic brush. The magnetic brush is regulated to a constant layer thickness by the regulating blade 29 and is further conveyed toward the opposing area (developing area) between the developing roller 25 and the photosensitive drum 1 by the rotation of the developing roller 25. When a predetermined bias voltage is applied to the developing roller 25, a potential difference is generated between the developing roller 25 and the photosensitive drum 1, and the toner in the magnetic brush formed on the developing roller 25 is photosensitive in the developing region. The electrostatic latent image supplied to the photosensitive drum 1 and developed on the photosensitive drum 1 is developed into a toner image. Further, when the magnetic brush is separated from the photosensitive drum 1 as the developing roller 25 rotates, excess developer on the photosensitive drum 1 is collected by the magnetic brush by the alternating current component of the developing bias.

  When the toner in the developing container 22 is reduced by development, the toner (developer) stored in the toner container 9 (see FIG. 1) is first conveyed through the toner supply port 22d (see FIG. 4). Replenished to the upstream end of the chamber 22b.

(Characteristics of photosensitive layer of photosensitive drum 1)
Hereinafter, characteristics of the photosensitive layer 1b, which is a characteristic part of the photosensitive drum 1 of the present embodiment, will be described. The photosensitive drum 1 of the present embodiment has a surface roughness in which the arithmetic average roughness Ra of the surface of the photosensitive layer 1b in the initial stage of use is in the range of 40 [nm] to 70 [nm]. The surface state may be at least in the initial use of the photosensitive drum 1 (the state at the start of use, in other words, the state after factory shipment). In addition, the arithmetic average roughness Ra, the ten-point average roughness Rz described later, and the average interval Sm are measured by a surface roughness measuring method defined in 1994 edition of JIS B0601 using a stylus type two-dimensional roughness measuring instrument. Is done.

  When the arithmetic average roughness Ra of the surface of the photosensitive layer 1b in the initial stage of use is smaller than 40 [nm], the toner adhesion to the photosensitive layer increases when the chargeability of the toner decreases in a high-temperature and high-humidity environment. Density decreases due to defects. When the arithmetic average roughness Ra is larger than 70 [nm], the gap between the cleaning blade 51 and the surface of the photosensitive layer 1b becomes large. For this reason, slipping of the external additive and contamination of the charging roller 41 due to the slipping of the external additive start from a relatively early stage of durable printing, and image defects such as vertical stripes due to uneven charging on the surface of the photosensitive drum 1 occur. The arithmetic average roughness Ra of the surface of the photosensitive layer 1b in the initial use of the photosensitive drum 1 is preferably in the range of 40 [nm] or more and 70 [nm] or less, and 40 [nm] or more and 55 [nm] or less. It is more preferable that it is within the range.

  When the arithmetic average roughness Ra of the surface of the photosensitive layer 1b in the initial use of the photosensitive drum 1 is in the range of 40 [nm] to 70 [nm], the surface of the photosensitive layer 1b in the initial use of the photosensitive drum 1 The ten-point average roughness Rz is preferably in the range of 0.4 [μm] to 0.9 [μm].

  This is because, even if the arithmetic average roughness Ra is within the above range, if there are large irregularities, the cleaning blade 51 cannot follow the surface shape of the photosensitive drum 1 although it deforms to some extent, and the photosensitive drum 1 and the cleaning blade. This is a rule for preventing the gap between the gap 51 and the gap 51 from increasing. Note that when the gap between the photosensitive drum 1 and the cleaning blade 51 becomes large, slipping of an external additive or the like occurs.

  In other words, if a large convex portion exists on the surface of the photosensitive drum 1 and the tip of the convex portion comes into contact with the cleaning blade 51, the concave portion located between the large convex portions contacts the cleaning blade 51. This is because it does not make sense to define the magnitude of the arithmetic average roughness Ra. In other words, it is preferable that the surface of the photosensitive drum 1 has no irregularities and has minute irregularities, and this condition is defined by the ten-point average roughness Rz and the arithmetic average roughness Ra. . Note that the ten-point average roughness Rz defines that there are no sudden irregularities.

  The arithmetic average roughness Ra of the surface of the photosensitive layer 1b in the initial use of the photosensitive drum 1 is in the range of 40 [nm] or more and 70 [nm] or less, and the ten-point average roughness Rz is 0.4 [μm] or more and 0. When it is in the range of .9 [μm] or less, the average interval Sm of the unevenness is preferably 14 [μm] or less.

  This is due to the following reason. Even when the arithmetic average roughness Ra and the ten-point average roughness Rz are within the above ranges, when the large convex portion exists apart, the cleaning blade 51 contacts (supports) the large convex portion. Here, the average interval Sm of the unevenness is used for determining whether or not the large convex portion is separated.

  The cleaning blade 51 is elastically deformable, and is deformed so as to come into contact with the photosensitive drum 1 between large protrusions (portions). In particular, when the interval between the convex portions is wide, the contact area between the cleaning blade 51 and the photosensitive drum 1 increases. When the contact area increases, the driving torque of the photosensitive drum 1 increases due to friction with the cleaning blade 51 and the wear of the cleaning blade 51 becomes severe, eventually causing the sticking slip of the cleaning blade 51 and slipping of the external additive. Or the edge of the cleaning blade 51 is lost. Needless to say, if the edge of the cleaning blade 51 is lost, a good image cannot be obtained.

  Further, when the average interval Sm is increased, the protruding portion (mountain) is increased (the crest of the peak is wide), and when the top portion of the protruding portion is worn due to long-term use, a wide flat portion is generated at the top portion and contact with the cleaning blade 51 The area increases.

  The arithmetic average roughness Ra of the surface of the photosensitive layer 1b in the initial use of the photosensitive drum 1 is in the range of 40 [nm] to 70 [nm], and the ten-point average roughness Rz is 0.4 [μm] or more. When it is in the range of 0.9 [μm] or less, the skewness Rsk is preferably 0.3 or more.

Here, the skewness Rsk is one of the parameters representing the strength of the surface roughness, and represents the symmetry (degree of distortion of the irregularities) between the peak and valley when the average line is the center, and the following formula ( In the reference length made dimensionless by the cube of the root mean square height Rq as in 1), it is represented by the root mean square of Z (x).

  When Rsk is larger than 0, the unevenness is a shape that is biased downward with respect to the average line. On the other hand, when Rsk is smaller than 0, the unevenness has a shape biased upward with respect to the average line. In other words, it is considered that when the skewness Rsk of the photosensitive layer is larger than 0, the contact area is reduced because the point of contact with the cleaning blade 51 is more pointed. In the present embodiment, by satisfying Rsk ≧ 0.3, the contact area between the photosensitive drum 1 and the cleaning blade 51 is reduced, and friction is effectively reduced.

  The arithmetic average roughness Ra of the surface of the photosensitive layer 1b in the initial use of the photosensitive drum 1 is in the range of 40 [nm] to 70 [nm], and the ten-point average roughness Rz is 0.4 [μm] or more. When it is in the range of 0.9 [μm] or less, the ratio (Ra [nm] / Sm [μm]) of the arithmetic average roughness Ra [nm] to the average interval Sm [μm] of the unevenness is 3 or more. Is preferred.

  By forming irregularities with a surface roughness satisfying the above range irregularly on the surface of the photosensitive layer 1 b in the axial direction and the circumferential direction of the photosensitive drum 1, the friction between the photosensitive drum 1 and the cleaning blade 51. This can reduce the driving torque of the photosensitive drum 1 and the wear of the edge of the cleaning blade 51. In particular, by satisfying Ra [nm] / Sm [μm] ≧ 3, an uneven shape having a height (depth) of three times or more with respect to the average interval Sm is obtained, so that the photosensitive drum 1 and the cleaning blade 51 are provided. The contact area is reduced, and friction is effectively reduced.

  The irregularities on the surface of the photosensitive layer 1b of the photosensitive drum 1 are preferably present irregularly. Irregular means that the irregularity does not have a certain regularity when the irregularity is seen in any one direction within a certain plane. When there is no unevenness in a certain direction (there is no unevenness in design, but the case where there is actually a minute unevenness corresponds to an example where there is no unevenness) is irregular.

  In addition, the arithmetic average roughness Ra, the ten-point average roughness Rz, and the average interval Sm are preferably in the above ranges over the entire image forming area on the surface of the photosensitive drum 1.

(Characteristics of toner used in developing device 8)
Next, the developer used in the developing device 8 will be described in detail. The developer used in the developing device 8 is a magnetic toner as a magnetic one-component developer. FIG. 5 is a schematic view showing a core-shell structure of toner used in the image forming apparatus 100 of the present embodiment. The magnetic toner 90 has a core-shell structure including a toner core 92 and a toner shell 93 formed so as to cover the surface 92 a of the toner core 92. The toner core 92 is a classified product containing magnetic powder and produced by a pulverization method. The toner core 92 has an anionic property. The anionicity of the toner core 92 is confirmed by, for example, whether or not the toner core 92 exhibits negative chargeability of −10 μC / g or more in frictional charging using a standard carrier provided by the Imaging Society of Japan. Further, the anionicity of the toner core 92 under an aqueous medium is confirmed by whether or not the negative chargeability of −10 mV or more is shown in the zeta potential measurement.

  The toner shell 93 is made of a thermosetting resin such as a melamine resin or a urea resin, and is formed so as to cover the surface 92 a of the toner core 92. The toner shell 93 has a cationic property.

  As a method for forming the toner shell 93, an in situ polymerization method, a submerged curing coating method or a coacervation method is preferable, and an in situ polymerization method is more preferable from the viewpoint of reactivity. In the in situ polymerization method, the resin shell supplied from the aqueous medium reacts on the surface 2a of the toner core 92 to be converted into a resin, whereby the toner shell 93 is formed. The method for forming the toner shell 93 is not particularly limited as long as it is a method by which the magnetic toner 90 having a desired average particle size and particle size distribution can be obtained.

  As a resin raw material used for forming the toner shell 93, from the viewpoint of sufficiently suppressing the aggregation of the magnetic toner 90 and ensuring excellent film forming properties, urea-based, urethane-based, amide-based melamine-based, urea-resorcin-based, etc. From the viewpoints of low water absorption and storage stability, urea-based resin raw materials such as melamine-based or urea-resorcin-based are preferable. Since the melamine resin and the urea resin have low water absorption, binding between the toners is suppressed when the toner after shelling is dried, and changes in the average particle size and particle size distribution of the toner can be suppressed.

  Specifically, the toner shell 93 made of a melamine resin may be formed by condensation polymerization of methylol melamine which is a precursor (methylol product) generated by addition reaction of melamine and formaldehyde. Further, the toner shell 93 may be formed by condensation polymerization of methylolated urea which is a precursor (methylolated product) generated by addition reaction of urea and formaldehyde. The resin raw material used for forming the toner shell 93 is not particularly limited as long as it is used in the above method.

  The toner shell 93 is preferably formed in a solvent capable of dissolving methylolated products such as methylolmelamine and methylolated urea. As this solvent, for example, water, methanol or ethanol is preferably used.

  In forming the toner shell 93, it is preferable to contain a dispersant in the solvent. Accordingly, the toner core 92 can be highly dispersed in the solvent, and the surface 92a of the toner core 92 can be uniformly coated with the methylolated product.

  Examples of the dispersant include sodium polyacrylate, polyparavinylphenol, partially saponified polyvinyl acetate, isoprenesulfonic acid, polyether, isobutylene / maleic anhydride copolymer, sodium polyaspartate, starch, gum arabic, and polyvinylpyrrolidone. And at least one dispersant selected from the group consisting of sodium lignin sulfonate can be used. One type of dispersant selected from the above group may be used, or two or more types of dispersant selected from the above group may be used in combination. The concentration of the dispersant is not particularly limited, but is preferably 75 parts by mass or less with respect to 100 parts by mass of the toner core 92.

  The temperature at which the toner shell 93 is formed is not particularly limited, but is preferably 40 ° C. or higher and 80 ° C. or lower, and more preferably 55 ° C. or higher and 70 ° C. or lower. In this temperature range, the formation of the toner shell 93 on the surface 92a of the toner core 92 proceeds satisfactorily, whereby a dispersion liquid of the magnetic toner 90 formed into a shell is obtained. Thereafter, a washing step and a drying step are performed as necessary to obtain the shelled magnetic toner 90 mother particles.

  With the core-shell structure, a magnetic toner 90 having a charge attenuation coefficient adjusted within a range of 0.008 to 0.05 is obtained. The electric resistance value of the magnetic toner 90 is adjusted by the thickness of the toner shell 93 and external additives such as silica and titanium oxide added to the outside of the toner shell 93.

(Toner charge decay coefficient)
The magnetic toner 90 is adjusted so that the charge attenuation coefficient is in the range of 0.008 to 0.05. Hereinafter, measurement of the charge decay coefficient will be described. The charge decay coefficient represents the charge decay rate of the toner, and can be specifically measured using the following electrostatic diffusivity measuring device. First, as a measurement cell, a metal measurement cell in which a recess having an inner diameter of 10 mm and a depth of 1 mm is formed is used. Toner is put into this measurement cell and pushed in from above with a slide glass. Then, the overflowing toner is scraped off from the measurement cell by reciprocating the surface of the measurement cell with the slide glass that has been pushed in. At this time, the degree of pressing with the slide glass is adjusted so that the amount of toner filling the recesses is 0.04 g or more and 0.06 g or less.

Next, the measurement cell filled with the toner is allowed to stand for 12 hours in an environment at a temperature of 32.5 ° C. and a relative humidity of 80%. After that, the measurement cell is placed in an electrostatic diffusivity measurement device while being grounded, and corona discharge is performed. I do. Then, after 0.7 seconds have elapsed from the end of corona discharge, the surface potential of the toner is continuously measured. Based on the measurement result, a charge decay coefficient (charge decay rate) α is calculated from the following equation (1).
V = V ₀ exp (−α√t) (1)
In the above formula (1), V represents the surface potential (V), V ₀ represents the initial surface potential (V), α represents the charge decay coefficient (charge decay rate), and t represents the decay time. (Seconds). Specific examples of the electrostatic diffusivity measuring apparatus include NS-D100 type (manufactured by Nano Seeds Co., Ltd.).

  This charge attenuation occurs mainly in the area (development area) where the developing roller 25 and the photosensitive drum 1 are opposed to each other. If the potential difference between the developing bias applied to the developing roller 25 and the surface potential of the photosensitive drum 1 is large, the amount of charge injected from the developing roller 25 to the toner also increases, but at the same time flows out to the photosensitive drum 1 side. The (attenuation) charge amount also increases. The charge attenuation coefficient of the toner is related to the injection / attenuation ratio. The larger the value, the lower the ability to store charges in the toner, and the charge attenuation ratio increases. As a result, a phenomenon occurs in which the toner charge amount does not increase more than a certain level. Specifically, if the charge attenuation coefficient is too large, the level of the maximum charge amount itself becomes too low, and thus problems such as fogging occur. On the other hand, if the charge attenuation coefficient is small, it is difficult for the charge to escape and a transfer failure occurs due to overcharging of the toner.

  In view of this, in the image forming apparatus 100 of the present embodiment, development is performed by using toner having a charge attenuation coefficient of 0.008 or more and 0.05 or less, more preferably toner having a charge attenuation coefficient of 0.022 or more and 0.05 or less. The balance between the amount of charge injected into the toner from the roller 25 and the amount of charge flowing out to the photosensitive drum 1 side is adjusted. As a result, it is possible to effectively suppress the occurrence of fog due to a decrease in toner charge amount and the occurrence of transfer failure due to toner overcharge.

  In addition, when the charge attenuation coefficient of the toner is large, the charge amount of the toner is reduced in a high temperature and high humidity environment, and transfer failure from the photosensitive drum 1 to the paper may occur. In the present embodiment, the photosensitive layer 1b. In combination with the photosensitive drum 1 having an arithmetic surface roughness Ra of 40 nm to 70 nm, the contact area of the toner with respect to the surface of the photosensitive layer 1b is reduced, and the adhesion force of the toner to the photosensitive drum 1 can be reduced. it can. As a result, transferability is improved even in a high-temperature and high-humidity environment, and the occurrence of transfer defects is suppressed. Further, since the arithmetic surface roughness Ra of the photosensitive layer 1b is as extremely small as 40 nm or more and 70 nm or less, the cleaning failure due to the toner external additive slipping through the gap between the photosensitive layer 1b and the cleaning blade 51, and the charging roller 41 associated therewith. There is no pollution.

  In the case of the magnetic one-component development method, since there is no separation pole in the magnetic pole member 26 in the developing roller 25, the toner with charge attenuation or charge injection is not separated from the developing roller 25 and the charge amount is reduced. Overcharged toner continues to be present on the developing roller 25. Therefore, the present invention is particularly effective in the magnetic one-component development system.

  In the magnetic one-component development method, the method of regulating the thickness of the toner layer on the developing roller 25 uses a magnetic metal member as the regulating blade 29 as in the present embodiment, and faces the developing roller 25 in a non-contact manner. And a method of using a rubber member as the regulating blade 29 and bringing it into contact with the developing roller 25. When a configuration in which the magnetic metal regulating blade 29 is opposed to the developing roller 25 in a non-contact manner, charge can be injected from the regulating blade 29 to the toner. Therefore, a toner having a large charge attenuation coefficient as in this embodiment. It is effective when using.

  In addition, this invention is not limited to the said embodiment, A various change is possible in the range which does not deviate from the meaning of this invention. For example, in the above-described embodiment, a monochrome printer has been described as an example of the image forming apparatus 100. However, the image forming apparatus 100 can be applied to, for example, a tandem type or rotary type color printer. Further, the present invention can also be applied to an image forming apparatus such as a copying machine, a facsimile, or a multifunction machine having these functions. However, it is necessary to include the photosensitive drum 1 and the one-component developing type developing device 8. Further, it is preferable to have a cleaning blade 51 as a means for cleaning the photosensitive drum 1.

  The photosensitive drum 1 in the above embodiment uses the cylindrical element tube 1a as a support, but may use a support of another shape. Other shapes may be a plate shape or an endless belt shape. In the above-described embodiment, the photosensitive drum 1 uses amorphous silicon as the photosensitive layer 1b. However, for example, the photosensitive drum 1 may include a charge injection blocking layer that blocks injection of charges from the support. Hereinafter, the effects of the present invention will be described in more detail with reference to examples.

  The relationship between the surface roughness of the photosensitive layer 1b of the photosensitive drum 1, the image density, and the cleaning property was investigated. As a test method, the arithmetic average roughness Ra of the photosensitive layer 1b was changed, and 1000 test images with a printing rate of 5% including a solid (solid) image in a high temperature and high humidity environment (30 ° C., 80%) were continuously obtained. Printed. As for developability, an average value of density (image density; ID) of a solid image was calculated, and it was determined whether or not it was equal to or higher than a target value (1.0). With regard to the cleaning property, the image is visually observed for occurrence of vertical streaks due to poor cleaning, and when the vertical streaks are not recognized, ○, when the vertical streaks are slightly recognized, Δ, The case where it was recognized notably was set as x.

  The test conditions were a photosensitive drum 1 in which an amorphous silicon photosensitive layer was formed as a photosensitive layer 1b on the outer peripheral surface of an aluminum tube 1a, and Ra of the photosensitive layer 1b was 30 nm, 40 nm, 55 nm, 70 nm, and 80 nm. . As the toner, a positively chargeable toner having an average particle diameter of 6.8 μm and a charge attenuation coefficient of 0.05 was used. As the cleaning blade 51, a urethane rubber blade having a length (free length) from the base end portion to the tip end portion of 11.0 mm and a thickness of 2.0 mm is used, and the angle with respect to the outer peripheral surface of the photosensitive drum 1 is 24. °, the biting amount was set to 1.2 mm, and the linear pressure was set to 20.0 N / m. The results are shown in Table 1.

  As can be seen from Table 1, when the charge attenuation coefficient of the toner is 0.05, the density (ID) of the solid image falls below the target value when the Ra of the photosensitive layer 1b is less than 40 nm. This is because as the Ra of the photosensitive layer 1b decreases, the toner adhesion increases and the transferability from the photosensitive drum 1 to the paper decreases. On the other hand, when Ra of the photosensitive layer 1b was larger than 70 nm, vertical stripes due to poor cleaning occurred. This is because when the Ra of the photosensitive layer 1 b increases, the external additive slips through the gap between the cleaning blade 51 and the photosensitive layer 1 b, and the external additive adheres to the charging roller 41 and the surface of the photosensitive drum 1. This is because uneven charging occurs.

  The relationship between the toner charge attenuation coefficient, the image density, and the layer disturbance of the toner layer on the developing roller 25 was investigated. The test method is to change the charge attenuation coefficient of the toner and continuously print 1000 test images with a printing rate of 5% including solid (solid) images and half images in a high-temperature and high-humidity environment (30 ° C, 80%). did. As for developability, the average value of the density (image density; ID) of the solid image was calculated in the same manner as in Example 1, and it was determined whether it was equal to or higher than the target value (1.0). Concerning toner layer disturbance, visually observe whether density irregularity due to toner layer irregularity has occurred in the half image, and when density irregularity is not recognized, ○, when density irregularity is slightly observed △, and the case where density unevenness is remarkably recognized as x.

  The test conditions were the same photosensitive drum 1 as in Example 1 in which an amorphous silicon photosensitive layer was formed as the photosensitive layer 1b on the outer peripheral surface of the aluminum tube 1a, and Ra of the photosensitive layer 1b was 40 nm. Further, positively chargeable toners having an average particle diameter of 6.8 μm and charge attenuation coefficients of 0.002, 0.008, 0.022, 0.036, 0.05, and 0.064 were used. The cleaning blade 51 was the same as in Example 1. The results are shown in Table 2.

  As is clear from Table 2, when the Ra of the photosensitive layer 1b is 40 nm, the solid image density (ID) falls below the target value when the charge attenuation coefficient of the toner exceeds 0.05. This is because when the charge attenuation coefficient of the toner increases, the charge amount of the toner decreases in a high-temperature and high-humidity environment, and the transferability from the photosensitive drum 1 to the paper decreases. On the other hand, when the charge attenuation coefficient of the toner is smaller than 0.008, the toner layer on the developing roller 25 is disturbed. This is because, when the charge attenuation coefficient of the toner is small, the toner is overcharged when the magnetic brush carried on the developing roller 25 passes through the regulating blade 29 and adheres firmly to the developing roller 25, so that the toner layer This is because the layer thickness becomes non-uniform.

  From the results shown in Tables 1 and 2, by setting the Ra of the photosensitive layer 1b of the photosensitive drum 1 and the charge attenuation coefficient of the toner within a predetermined range, it is possible to reduce image density, cleaning failure, and toner layer disorder. It was confirmed that both the resulting image defects can be effectively suppressed. Table 3 summarizes the results of Tables 1 and 2 and other combinations of Ra and charge attenuation coefficient of the photosensitive layer 1b.

＊１；層乱れ
＊２；クリーニング不良

* 1; Layer disorder * 2; Poor cleaning

  As a result of a similar test for other combinations of Ra of the photosensitive layer 1b and the charge attenuation coefficient of the toner, the Ra of the photosensitive layer 1b is in the range of 40 nm to 70 nm and the charge attenuation coefficient of the toner is 0.008. When it is in the range of 0.05 or less (shaded area in Table 3), the image density does not decrease, and the image defect is in a range where there is no practical problem. Further, when the Ra of the photosensitive layer 1b is in the range of 40 nm to 55 nm and the charge attenuation coefficient of the toner is in the range of 0.022 to 0.05 (shaded area in Table 3), the image density is decreased. There was no occurrence of image defects.

  From the above, the photosensitive drum 1 in which Ra of the photosensitive layer 1b is 40 nm or more and 70 nm or less, preferably 40 nm or more and 55 nm or less, and the charge attenuation coefficient are 0.008 or more and 0.05 or less, preferably 0.022 or more and 0.05. By combining with the following toners, it is possible to improve the transferability of the toner from the photosensitive drum 1 to the paper even in a high-temperature and high-humidity environment and maintain the image density, and also due to poor cleaning or disturbance of the toner layer. It has been confirmed that defective images can be effectively suppressed.

  The present invention can be used in an image forming apparatus including a magnetic one-component developing system using magnetic toner. By utilizing the present invention, there is provided an image forming apparatus capable of suppressing a decrease in image density due to a transfer failure regardless of the use environment, and also suppressing an image defect due to a cleaning failure or a toner layer disorder on a developing roller. be able to.

1 Photosensitive drum (image carrier)
1a Element tube (support)
1b Photosensitive layer 8 Developing device 25 Developing roller (developer carrier)
29 Regulation blade (regulation member)
41 Charging roller (charging member)
51 Cleaning blade (cleaning member)
90 Magnetic toner 100 Image forming apparatus

Claims (5)

An image carrier having a support and an amorphous silicon photosensitive layer formed on the surface of the support;
A developer carrier that is disposed opposite to the image carrier and carries a magnetic one-component developer composed of only a magnetic toner; and a developer carrier that is disposed at a predetermined interval with respect to the developer carrier. A metal regulating member that regulates the layer thickness of the magnetic one-component developer carried on the developing device, and
In an image forming apparatus comprising:
The arithmetic average roughness Ra of the surface of the photosensitive layer in the initial use is in the range of 40 nm to 70 nm, and the charge attenuation coefficient of the magnetic toner is in the range of 0.008 to 0.05. Image forming apparatus.   The arithmetic average roughness Ra of the surface of the photosensitive layer in the initial use is in the range of 40 nm to 55 nm, and the charge attenuation coefficient of the magnetic toner is in the range of 0.022 to 0.05. The image forming apparatus according to claim 1.   3. The image formation according to claim 1, wherein the magnetic toner has an anionic core and a cationic shell formed so as to cover a surface of the core. apparatus.   4. The image forming apparatus according to claim 1, further comprising a cleaning member that is disposed in contact with the surface of the image carrier and that cleans the surface of the image carrier. 5.   The image forming apparatus according to claim 1, further comprising a charging member that is disposed in contact with or in proximity to the surface of the image carrier and charges the image carrier.

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