Sleeve, developer carrier, and developing device

Abstract

A rotatable sleeve (28) comprises a developer carrying and conveying unit (28S) that carries and conveys, to a developing position, a developer containing a toner and a carrier, the developer carrying and conveying unit (28S) having a groove section (51) that is a section in which grooves are formed and a non-groove section (52) that is a section in which grooves are not formed. When the depth of the grooves is D, the radius of the carrier is r, and the width of the grooves in the rotation direction of the sleeve is W, D > r and W > 2r are satisfied, and the arithmetic mean height Sa of the surface of the non-groove section (52) is 0.001 μm to 0.070 μm.

Description

Sleeve, Developer Carrier, and Developing Device

[0001] The present disclosure relates to a sleeve, a developer carrier, and a developing device that develops an electrostatic latent image formed on an image carrier such as a photosensitive drum with toner.

[0002] As a method for developing an electrostatic latent image formed on an image carrier using toner, a method using a two-component developer containing toner and a carrier is known. In the case of the two-component development method, immediately after toner is replenished, the toner is sufficiently stirred with the carrier by a stirring member, and then carried on a developer carrier such as a developing sleeve. For this reason, the developer carrier normally carries a carrier that carries toner, rather than carrying toner alone.

[0003] However, when a regulating member regulates the layer thickness of the developer carried on the developer carrier, or when the developer is carried on the surface of the developer carrier and conveyed, toner may separate from the carrier and adhere alone to the developer carrier. If toner adheres alone to the developer carrier, the surface potential of the developer carrier at the facing portion where the developer carrier faces the image carrier locally changes depending on the charge amount of the adhered toner, and this may cause variation in the amount of toner developed onto the image carrier and the density after fixing (hereinafter, this may also be simply referred to as density unevenness).

[0004] As a countermeasure against such adhesion of toner to the developer carrier, Patent Document 1 proposes a configuration in which toner adhered to the developer carrier is recovered by a member such as a scraper. Further, Patent Document 2 proposes a configuration that suppresses accumulation of toner on the developer carrier by coating the surface of the developer carrier with titanium nitride.

[0005] Japanese Patent Application Laid-Open No. 9-251237, Japanese Patent Application Laid-Open No. 2013-064856

[0006] However, in the case of the configuration in which toner adhered to the developer carrier is recovered by a member such as a scraper as in Patent Document 1, the configuration of the device becomes complicated, and the cost of the device increases. Also, in the case of the configuration in which the surface of the developer carrier is coated with titanium nitride as in Patent Document 2, the cost of the device increases.

[0007] One aspect of this disclosure is to provide a configuration that can suppress toner adhesion to the developer carrier at low cost.

[0008] One aspect of the present disclosure is a rotatable sleeve comprising a developer carrying and transporting unit for carrying and transporting a developer containing toner and a carrier to a developing position, the developer carrying and transporting unit having a grooved portion which is a portion in which grooves are formed and a non-grooved portion which is a portion in which grooves are not formed, wherein when the depth of the groove is D, the radius of the carrier is r, and the width of the groove in the rotational direction of the sleeve is W, D > r and W > 2r are satisfied, and the arithmetic mean height Sa of the surface of the non-grooved portion is 0.001 μm or more and 0.070 μm or less.

[0009] Another aspect of the present disclosure is a developer carrier comprising a rotatable sleeve and a magnet disposed inside the sleeve, wherein the sleeve comprises a developer carrier transport section for transporting a developer containing toner and carrier to a developing position, the transport section having a grooved section which is a portion in which grooves are formed and a non-grooved section which is a portion in which grooves are not formed, wherein when the depth of the grooves is D, the radius of the carrier is r, and the width of the grooves in the rotational direction of the sleeve is W, D > r and W > 2r are satisfied, and the arithmetic mean height Sa of the surface of the non-grooved section is 0.001 μm or more and 0.070 μm or less.

[0010] Another aspect of the present disclosure is a developing apparatus comprising a developing container for containing a developer containing toner and a carrier, a rotatable sleeve and a magnet disposed inside the sleeve, wherein the sleeve comprises a developer carrying section for carrying and transporting the developer to a developing position, the carrying section having a grooved section which is a portion in which a groove is formed and a non-grooved section which is a portion in which the groove is not formed, and where D is the depth of the groove, r is the radius of the carrier and W is the width of the groove in the rotational direction of the sleeve, D > r and W > 2r, and the arithmetic mean height Sa of the surface of the non-grooved section is 0.001 μm or more and 0.070 μm or less.

[0011] According to this disclosure, the adhesion of toner to the developer carrier can be suppressed at low cost.

[0012] Other features and advantages of this disclosure will become apparent from the following description with reference to the accompanying drawings. In the accompanying drawings, the same or similar components are given the same reference numeral.

[0013] A schematic cross-sectional view of the image forming apparatus according to the first embodiment. A schematic cross-sectional view of the developing apparatus according to the first embodiment. A schematic longitudinal cross-sectional view of the developing apparatus according to the first embodiment. A perspective view of the developing sleeve according to the first embodiment. A schematic diagram illustrating the shape of the grooves formed in the developing sleeve according to the first embodiment. A schematic diagram illustrating another first example of the shape of the grooves formed in the developing sleeve according to the first embodiment. A schematic diagram illustrating another second example of the shape of the grooves formed in the developing sleeve according to the first embodiment. A schematic diagram illustrating the shape of the grooves formed in the developing sleeve. A schematic diagram illustrating the shape of the grooves formed in the developing sleeve. A schematic diagram illustrating the shape of the grooves formed in the developing sleeve. A schematic diagram illustrating the shape of the grooves formed in the developing sleeve. A schematic diagram illustrating the transport state of the developer on the surface of the developing sleeve. A schematic diagram showing a magnified view of the area around the grooves to illustrate the transport state of the developer on the surface of the developing sleeve. A graph showing the relationship between temperature and toner viscosity. A schematic diagram illustrating sleeve ghosting. A schematic diagram showing a state where image unevenness occurs due to sleeve ghosting. A schematic diagram illustrating density measurement due to sleeve ghosting. A schematic diagram illustrating a model of particle adhesion to an uneven surface. A graph showing the relationship between the van der Waals forces acting between the plane L, the convex portion G and the particle P and the height h. A graph showing the relationship between the van der Waals forces acting between the surface and the particle P and the arithmetic mean height Sa of the uneven surface. A graph showing the non-electrostatic adhesion force of Example 1 and Comparative Example 1. A graph showing the relationship between the arithmetic mean height Sa and the average density difference in each example and comparative example. A schematic cross-sectional view of the developing apparatus according to the second embodiment. A schematic cross-sectional view showing the relationship between the apex position of the transport guide and the nearest position of the regulating blade to the developing sleeve in the developing apparatus according to the second embodiment. A graph showing the relationship between the arithmetic mean height Sa and the silica coverage rate in each example and comparative example. A graph showing the relationship between the arithmetic mean height Sa and the average density difference in each example and comparative example.

[0014] <First Embodiment> The first embodiment will be described using Figures 1 to 18. First, the schematic configuration of the image forming apparatus 100 of this embodiment will be described using Figure 1. In this embodiment, as an example of the image forming apparatus 100, a case in which a tandem-type full-color printer is used will be described.

[0015] [Image Forming Apparatus] The image forming apparatus 100 of this embodiment is a full-color image forming apparatus 100 employing an electrophotographic method, and is equipped with four image forming units Pa, Pb, Pc, and Pd. The configuration of each image forming unit is substantially the same except for the difference in development color. Therefore, unless otherwise specified, the image forming unit Pa will be described as a representative, and for the other image forming units, the subscripts b, c, and d will be added to indicate that they are the configurations of that image forming unit, and detailed descriptions will be omitted.

[0016] The image forming unit Pa includes a photosensitive drum 1a as an image carrier that holds a toner image. The photosensitive drum 1a is an example of a photoreceptor for electrophotography and is formed in a cylindrical shape. Such a photosensitive drum 1a rotates in the direction of the arrow in Figure 1 (counterclockwise). Around the photosensitive drum 1a are arranged a charger 2a as a charging unit, a laser beam scanner 3a as a latent image forming unit, a developing device 4a, a primary transfer roller 6a, a cleaning device 19a, and the like.

[0017] Next, the overall image forming sequence of the image forming apparatus 100 with the above configuration will be described. First, the surface of the photosensitive drum 1a is uniformly charged to a predetermined charging potential by the charger 2a. The photosensitive drum 1a, which has been charged by the charger 2a, is then scanned and exposed by a laser beam scanner 3a, which is an example of an exposure apparatus, using laser light modulated by an image signal.

[0018] The laser beam scanner 3a incorporates a semiconductor laser, which is controlled based on input image data to emit laser light. For example, it is controlled to emit laser light in response to a document image information signal (image data) input from a document reading device having a photoelectric conversion element such as a CCD, or in response to an image information signal input from an external terminal. As a result, the surface potential of the photosensitive drum 1a, which is charged by the charger 2a, changes in the image area, and an electrostatic latent image is formed on the photosensitive drum 1a.

[0019] The electrostatic latent image formed on the photosensitive drum 1a is inverted and developed by the developing device 4a using toner to form a visible image, i.e., a toner image. In this embodiment, the developing device 4a uses a two-component development method that uses a developer containing toner and a carrier as the developer. That is, each developing device 4a, 4b, 4c, and 4d contains a two-component developer containing toner of each color. Specifically, developing device 4a contains yellow (Y) toner, developing device 4b contains magenta (M) toner, developing device 4c contains cyan (C) toner, and developing device 4d contains black (K) toner. Therefore, by performing the above process for each image forming unit Pa, Pb, Pc, and Pd, toner images of four colors, yellow, magenta, cyan, and black, are formed on the photosensitive drums 1a, 1b, 1c, and 1d, respectively.

[0020] Furthermore, an intermediate transfer belt 5, which is an intermediate transfer body, is positioned below each image forming section Pa, Pb, Pc, and Pd. The intermediate transfer belt 5 is suspended by rollers 61, 62, and 63 and is movable in the direction of the arrow. The toner images on each photosensitive drum 1a to 1d are sequentially transferred to the intermediate transfer belt 5 by primary transfer rollers 6a to 6d, which are primary transfer members. As a result, the toner images of four colors, yellow, magenta, cyan, and black, are superimposed on the intermediate transfer belt 5 to form a full-color image. In addition, any toner that remains on the photosensitive drum 1a without being transferred to the intermediate transfer belt 5 is collected by a cleaning device 19a.

[0021] The full-color image on the intermediate transfer belt 5 is removed from the feed cassette 12 and transferred to a recording material S (such as a sheet of paper or an OHP sheet) via the feed roller 13 and feed guide 11 by the action of the secondary transfer roller 10. Toner that remains on the surface of the intermediate transfer belt 5 without being transferred to the recording material S is collected by the intermediate transfer belt cleaning device 18. Meanwhile, the recording material S on which the toner image has been transferred is sent to the fuser 16, where the image is fixed and then discharged into the discharge tray 17.

[0022] [Two-component developer] The developer used in this embodiment is a two-component developer consisting of a non-magnetic toner and a magnetic carrier. As described below, by adding 8 parts by mass of non-magnetic toner to 92 parts by mass of magnetic carrier and mixing them, a negatively charged toner can be obtained. Each of these will be explained in detail below.

[0023] [Toner] The toner of this embodiment consists of a binder resin, a release agent, a colorant, and inorganic fine particles. As the binder resin, a combination of crystalline resin and amorphous resin is used, and polyester resin is used. Polyester resin can be suitably used because it is easy to design a product that balances both fixing properties and electrostatic properties.

[0024] In the amorphous polyester, a peak molecular weight of 3500 to 20000 is preferable from the viewpoint of low-temperature fixability and abrasion resistance. In this embodiment, a material with a molecular weight of 5000 was used. Furthermore, the acid value of the amorphous polyester is preferably 5 mg KOH / g or more and 30 mg KOH / g or less from the viewpoint of static charge retention in high-temperature and high-humidity environments. In this embodiment, a material with an acid value of 5 mg KOH / g was used. In addition, the hydroxyl value of the amorphous polyester is preferably 20 mg KOH / g or more and 70 mg KOH / g or less from the viewpoint of low-temperature fixability and static charge retention. In this embodiment, a material with an acid value of 40 mg KOH / g was used.

[0025] From the viewpoint of suppressing blooming, the weight-average molecular weight of the crystalline polyester is preferably between 15,000 and 50,000. In this embodiment, a crystalline polyester with a weight-average molecular weight of 25,000 was used. From the viewpoint of crystallization, the sum of the acid value and hydroxyl value of crystalline polyester C is preferably between 0.1 mg KOH / g and 5.0 mg KOH / g. In this embodiment, a crystalline polyester with a sum of 2 mg KOH / g was used. The content of amorphous polyester in the binder resin is preferably between 80.0% by mass and 97.0% by mass. In this embodiment, it was set to 90% by mass.

[0026] As a release agent, hydrocarbon waxes such as paraffin wax and Fischer-Tropsch wax are preferably used. The content is preferably 2 parts by mass or more and 10 parts by mass or less per 100 parts by mass of binder resin. In this embodiment, it was 5 parts by mass. The melting point is preferably 60°C or higher and 120°C or lower, and in this embodiment, one with a melting point of 76°C was used.

[0027] Examples of colorants include those formulated to produce black using carbon black as a black colorant, a yellow colorant, a magenta colorant, and a cyan colorant. Pigments may be used alone as colorants, or dyes and pigments may be used in combination. The colorant content is preferably 0.1 parts by mass or more and 30.0 parts by mass or less per 100 parts by mass of the binder resin. In this embodiment, 7 parts by mass of carbon black were added.

[0028] Inorganic fine particles are used as external additives to adhere to the toner surface and adjust its fluidity and chargeability. Examples of inorganic fine particles include silica fine particles, titanium oxide fine particles, alumina fine particles, or composite oxide fine particles thereof. Among inorganic fine particles, silica fine particles and titanium oxide fine particles are preferred for improving fluidity and uniformizing charge. From the viewpoint of improving adhesion to toner matrix particles, it is preferable that the inorganic fine particles are hydrophobized with a hydrophobic agent such as a silane compound, silicone oil, or a mixture thereof. The content of the external additive is preferably 0.3 parts by mass or more and 10.0 parts by mass or less per 100 parts by mass of toner matrix particles. In this embodiment, 1.0 part by mass of silica fine particles with an average primary particle size of 10 nm, 2.0 parts by mass of silica fine particles with an average primary particle size of 100 nm, and 0.7 parts by mass of titanium oxide fine particles with an average primary particle size of 45 nm are added.

[0029] The method for producing toner particles is not particularly limited, and known methods such as grinding, suspension polymerization, dissolution-suspension, emulsification-aggregation, and dispersion polymerization can be used. In this embodiment, toner was produced by grinding. The volume-average particle size (D4) of the toner is preferably 5 μm or more and 10 μm or less. In this embodiment, a particle size of 5.8 μm was used and measured using a "CDA-1000X" (aperture diameter: 100 μm, manufactured by Sysmex Corporation).

[0030] [Magnetic Carrier] In this embodiment, the magnetic carrier (hereinafter sometimes simply referred to as "carrier") is a magnetic carrier particle having a magnetic core particle and a coating resin layer covering the surface of the magnetic core particle. As the magnetic core particle of the magnetic carrier according to this embodiment, conventional magnetic particles such as ferrite and magnetite can be used. In addition, magnetic core particles in which resin is filled into ferrite or magnetite particles having voids can be used. Among these, magnetic cores in which resin is filled into magnetic particles having voids are preferred from the viewpoint of being able to reduce the magnetization amount of the magnetic carrier. Furthermore, by changing the composition ratio of the metal oxide raw materials, ferrite with a desired magnetization amount can be obtained.

[0031] The magnetic core particles preferably have a volume-average particle size (D50) of 20 μm or more and 80 μm or less, which allows for uniform coating of the coating resin, prevents magnetic carrier adhesion, and provides an appropriate density of magnetic particles for obtaining high-quality images.

[0032] The coating resin layer may contain inorganic fine particles with a number-average particle size of 50 nm or more and 200 nm or less. By forming minute irregularities on the carrier surface, it is expected that the adhesion force with the toner will be reduced. Examples of inorganic fine particles include silica fine particles, titanium oxide fine particles, alumina fine particles, or composite oxide fine particles thereof. A carrier with a volume-average particle size (D50) of 40 μm was used and measured using "Microtrac MT3300EX" (manufactured by Nikkiso Co., Ltd.). Using the toner and carrier described above, 8 parts by mass of toner was added to 92 parts by mass of magnetic carrier and mixed to obtain a two-component developer.

[0033] [Developing Apparatus] Next, the developing apparatus 4a will be described with reference to Figures 2 and 3. The other developing apparatuses 4b to 4d have the same configuration as developing apparatus 4a, so their description will be omitted. Developing apparatus 4a has a developing container 22 for containing a two-component developer, a developing sleeve 28 as a developer carrier, and first and second transport screws 25 and 26 as transport members. Furthermore, in this embodiment, developing apparatus 4a has a vertical stirring type configuration in which the inside of the developing container 22 is divided vertically into a developing chamber 23 as a first chamber and a stirring chamber 24 as a second chamber by a partition wall 27 whose approximate central part extends along the rotation axis direction of the developing sleeve 28. The developer is contained in the developing chamber 23 and the stirring chamber 24.

[0034] A developer supply unit 31 is located above the developing container 22. The developer supply unit 31 contains replenishment developer, and by rotating the developer supply screw 32, the replenishment developer is supplied to the developing container 22 via the supply path 30. In addition, a developer discharge port 40 is formed in the side wall of the developing container 22, and any excess developer in the developing container 22 is discharged from the discharge port 40, transported by the discharge screw 41, and collected in a recovery container (not shown).

[0035] The developing chamber 23 and the agitation chamber 24 are equipped with first and second transport screws 25 and 26, respectively. The first transport screw 25 is positioned at the bottom of the upper developing chamber 23, almost parallel to the rotation axis of the developing sleeve 28, and rotates clockwise in Figure 2, transporting the developer in the developing chamber 23 while agitating it in one direction along the rotation axis. The second transport screw 26 is positioned at the bottom of the lower agitation chamber 24, almost parallel to the first transport screw 25, and rotates counterclockwise in Figure 2, opposite to the first transport screw 25. The second transport screw 26 transports the developer in the agitation chamber 24 while agitating it along the rotation axis in the opposite direction to the first transport screw 25.

[0036] In this way, the developer is circulated between the developing chamber 23 and the stirring chamber 24 through the openings (i.e., communication sections) 11 and 12 at both ends of the partition wall 27 by the rotation of the first and second transport screws 25 and 26.

[0037] An opening is formed in the developing container 22 at a position corresponding to the developing area facing the photosensitive drum 1a, and a developing sleeve 28 is rotatably disposed in this opening so as to be partially exposed to the photosensitive drum 1a side. The developing sleeve 28 carries and transports the developer contained in the developing container 22 and supplies the developer to the developing position on the photosensitive drum 1a.

[0038] Inside the developing sleeve 28, a magnetic roller 28m is positioned in a non-rotating manner as a magnet for supporting the developer on the surface of the developing sleeve 28. Upstream in the rotational direction of the developing sleeve 28 from the position where the developing sleeve 28 faces the photosensitive drum 1a, a regulating blade 29 is positioned opposite the outer circumferential surface of the developing sleeve 28 as a regulating member for regulating the thickness of the developer layer supported on the developing sleeve 28. In this embodiment, the regulating blade 29 is installed above the developing sleeve 28 with a predetermined gap between it and the outer circumferential surface of the developing sleeve 28.

[0039] The magnetic roller 28m has a developing pole S2 that faces the developing area and supports the developer onto the developing sleeve 28 during development, and magnetic poles S1, N1, N2, and N3 that support and transport the developer, and is fixed inside the developing sleeve 28 in a non-rotating state. In particular, magnetic pole S1 as the first magnetic pole is a regulating pole that faces the regulating blade 29 via the developing sleeve 28. Furthermore, on the upstream side of the regulating pole S1 with respect to the rotation direction of the developing sleeve 28, magnetic poles N3 and N1, which are of the same pole, are arranged next to each other. Magnetic poles N3 and N1 are installed on the inside of the developing container 22 compared to the other magnetic poles, and a repulsive magnetic field is formed between these magnetic poles N3 and N1, which peels the developer off the developing sleeve 28, and the peeled developer is collected in the stirring chamber 24.

[0040] The regulating blade 29 is composed of a non-magnetic member made of a metal such as an aluminum alloy, extending along the rotation axis of the developing sleeve 28, and is positioned upstream of the position facing the photosensitive drum 1a in the rotational direction of the developing sleeve 28, as described above. Both the toner and carrier of the developer pass between the tip of the regulating blade 29 and the developing sleeve 28 and are sent to the developing unit.

[0041] The amount of developer transported to the developing unit is adjusted by adjusting the gap between the regulating blade 29 and the surface of the developing sleeve 28, thereby adjusting the amount of developer carried on the developing sleeve 28. In this embodiment, the regulating blade 29 adjusts the amount of developer coating per unit area on the developing sleeve 28 to, for example, 30 mg / cm². ２ It is regulated accordingly. Furthermore, it is preferable to set the gap between the regulating blade 29 and the developing sleeve 28 to 300 to 700 μm. In this embodiment, it was set to 400 μm.

[0042] [Configuration of Developing Area] The developing sleeve 28 is disposed opposite to the photosensitive drum 1a with a predetermined gap (SD gap) therebetween to form a developing area, and rotates in the direction of the arrow shown in the figure (counterclockwise direction) during development. The developing sleeve 28 carries a two-component developer whose layer thickness is regulated by a regulating blade 29, and conveys the two-component developer to the developing area opposite to the photosensitive drum 1a, thereby supplying the developer to an electrostatic latent image formed on the photosensitive drum 1a. A developing bias voltage obtained by superimposing an alternating voltage on a negative direct current voltage Vdc is applied to the developing sleeve 28. Due to a potential difference between the developing sleeve 28 and the photosensitive drum 1a, toner flies from the developer carried on a surface of the developing sleeve 28 in the developing area to the electrostatic latent image on the photosensitive drum 1a, and the electrostatic latent image is developed with the toner.

[0043] In the present embodiment, the charge amount of the charger 2 and the light amount of the laser beam scanner 3 are set such that a white background portion on the photosensitive drum 1a is -800V and a solid image portion corresponding to a maximum image signal value is -440V. The direct current voltage Vdc applied to the developing sleeve 28 was -640V, and an alternating voltage with a frequency of 12kHz was intermittently applied for two cycles at an amplitude of 1400V. The alternating current waveform is a rectangular wave, and the voltage between alternating current waveforms (hereinafter referred to as blank time) is only Vdc. In the present embodiment, the blank time is set to 0.3 ms.

[0044] Further, the outer diameter of the developing sleeve 28 is 20 mm, the outer diameter of the photosensitive drum 1a is 30 mm, and the SD gap is 300 µm. A driving device such as a motor (not shown) rotates the photosensitive drum 1a at a surface speed of 435 mm / s, and rotates the developing sleeve 28 at a surface speed of 740 mm / s, which is approximately 1.7 times the surface speed of the photosensitive drum 1a. Here, the surface speed of 435 mm / s of the photosensitive drum 1a is substantially equal to the surface speed of the intermediate transfer belt 5 and the conveying speed of the recording material S, and is referred to as an image forming speed. The above values of the developing bias waveform, the dimensions of the developing sleeve 28 and the photosensitive drum 1a, and the rotation speed are merely examples of the embodiment, and are not limited thereto.

[0045] With the above settings, the toner contained in the developer carried on the surface of the developing sleeve 28 is stripped from the carrier by the alternating voltage in the development area. Due to the negative DC voltage Vdc, the toner has relatively positive polarity with respect to the white background area on the photosensitive drum 1a, and relatively negative polarity with respect to the solid image area on the photosensitive drum 1a. The toner flies onto the photosensitive drum 1a for the solid image area, and flies onto the developing sleeve 28 for the white background area. Here, the potential difference between the drum potential of the white background area and the developing DC voltage Vdc is a potential difference necessary to prevent toner adhesion to the white background area on the photosensitive drum 1a when a developing bias voltage obtained by superimposing an AC voltage on a DC voltage is used, and is preferably 100 V or more. In the present embodiment, this potential difference is set to 160 V.

[0046] [Configuration of Developing Sleeve] Next, the configuration of the developing sleeve 28 will be described in further detail. The developing sleeve 28 is made of a non-magnetic material formed of an aluminum alloy, and a roughening process for improving developer conveyability is formed on the surface thereof. That is, in the present embodiment, the developing sleeve 28 is made of an aluminum alloy. Examples of the roughening process include blasting, in which fine hard particles are projected onto the surface of the developing sleeve 28 (see, for example, Japanese Examined Patent Publication No. 1-5711 and Japanese Examined Patent Publication No. 1-32506), and knurling, in which irregularities are formed on the surface by cutting or rolling (see, for example, Japanese Unexamined Patent Publication No. 54-79043). Along with the longer service life of developing devices, knurling, which provides excellent wear resistance, has become mainstream.

[0047] In the present embodiment, as shown in FIG. 4, the developing sleeve 28 is made of an aluminum alloy (for example, A6063 (JIS H4100, JIS H4000)), and a plurality of grooves 51 for conveying the developer are formed in parallel on the surface thereof. The plurality of grooves 51 are formed, for example, by flat knurling. FIG. 4 is a perspective view of the developing sleeve 28 of the present embodiment, and FIG. 5 is an enlarged schematic view of a part of the surface of the developing sleeve 28 in a cross-section obtained by cutting the developing sleeve 28 of the present embodiment in a direction orthogonal to the rotational axis direction.

[0048] As shown in Figure 4, in this embodiment, 72 grooves 51 are formed parallel to the rotational axis direction of the developing sleeve 28, extending around the entire circumference of the region 28S (developer carrying and transport section that carries and transports the developer containing toner and carrier to the developing position), which is the surface that carries and transports the developer 10 mm inward from both ends of the developing sleeve 28. That is, the region 28S (developer carrying and transport section) on the surface of the developing sleeve 28 has a grooved portion where grooves 51 are formed and a non-grooved portion where grooves 51 are not formed. No grooves 51 are formed in the regions (gold ring portions) 50a and 50b extending 10 mm from both ends of the developing sleeve 28 in the direction of the rotational axis. That is, the multiple grooves 51 are formed in the circumferential direction of the developing sleeve 28, in the region 28S of the outer circumferential surface of the developing sleeve 28, on the side of the region 50a at one end and on the side of the region 50b at the other end with respect to the rotational axis direction. In regions 50a and 50b, the gap between the opening of the developing container 22 and the developing sleeve 28 is sealed. The sealing method may be to bring a sealing member into contact with regions 50a and 50b, or a sheet-shaped magnet may be installed to seal it magnetically.

[0049] As shown in Figure 5, in this embodiment, the multiple grooves 51 are symmetrical V-shaped grooves with a depth D = 60 [μm] and a width W = 156 [μm] in the direction of rotation of the developing sleeve 28. 72 grooves are formed on the developing sleeve 28 parallel to the rotation axis, with a spacing of approximately I = 717 [μm] between them. The angle θ of the V-shape of the grooves 51 is approximately 40 [°]. The cross-sectional shape of the grooves 51 is not limited to a V-shape, as long as the developer catches on and is transported in that part. For example, it may have a cross-sectional shape with a substantially flat bottom surface and a pair of side walls, as in the groove 51a of another first example shown in Figure 6, or it may have a U-shaped cross-sectional shape with a curved bottom surface, as in the groove 51b of another second example shown in Figure 7. Furthermore, the multiple grooves 51 formed on the surface region 28S (developer-carrying and transporting section) of the developing sleeve 28 may have a so-called twill pattern with two different angles that intersect each other in the direction of the rotation axis. However, regardless of the shape, the carrier must be shaped so that at least one carrier fits into the groove 51 so that the carrier catches in the groove 51. For this reason, it is preferable that the depth D of the groove 51 > the radius r of the carrier and the width W of the groove 51 > the diameter 2r of the carrier.

[0050] Here, we will explain in detail the shape of the groove 51 formed in the developing sleeve 28. In order for the developer, that is, the magnetic carrier which is responsible for transporting the developer, to catch in the groove 51, it is best to make the width W of the groove 51 wider than the diameter 2r of the magnetic carrier, as shown in Figure 8A. This is because, as shown in Figure 8B, if the width W of the groove 51 is narrower than the diameter 2r of the magnetic carrier, the magnetic carrier will not fit into the groove 51 regardless of the depth of the groove 51, and the magnetic carrier will not catch in the groove 51.

[0051] Furthermore, as shown in Figure 9A, it is preferable that the depth D of the groove 51 be at least greater than the radius r of the magnetic carrier. This is because, as shown in Figure 9B, if the depth D of the groove 51 is shallower than the radius r of the magnetic carrier, the magnetic carrier does not grip the groove 51 well, resulting in a weak grip and making the magnetic carrier more prone to slipping.

[0052] Furthermore, it is preferable that the width W of the groove 51 is smaller than the width of 10 magnetic carriers (20r). This is because if the width W of the groove 51 is larger than the width of 10 magnetic carriers (20r), the magnetic carriers may not easily catch on the groove 51, and the effect of the groove 51 in transporting magnetic carriers may not be fully obtained. Therefore, it is desirable that the following equations 1 and 2 be satisfied: 20r > W > 2r ... (1) D > r ... (2)

[0053] Furthermore, while sufficient grip can be obtained if the depth D of the groove 51 is greater than the radius r of the magnetic carrier, setting it to be deeper than the diameter 2r of the magnetic carrier will ensure that the entire magnetic carrier is gripped, preventing it from slipping out of the groove 51. Therefore, it is preferable to set D > 2r.

[0054] Furthermore, the arithmetic mean height Sa (hereinafter sometimes referred to as surface roughness Sa) of the surface of the protrusions 52 (non-grooved portions, which are the portions between the multiple grooves 51 in the circumferential direction of the developing sleeve 28) on the outer surface of the developing sleeve 28 is set to 0.001 μm or more and 0.070 μm or less. In this embodiment, the surface roughness Sa of the protrusions 52 is processed to be 0.048 μm. The surface roughness Sa of the protrusions 52 is not limited to the above value as long as it is between 0.001 μm and 0.070 μm for reasons described later. Normally, surface processing of metals includes cutting, plastic processing such as rolling, grinding, polishing such as barrel polishing and buffing, and lapping, but the processing method is not limited as long as the surface roughness of the protrusions 52 formed between the grooves 51 of the developing sleeve 28 can be within the above range, and in this embodiment, burnishing, a type of rolling, is used.

[0055] Furthermore, when calculating the arithmetic mean height Sa of the surface of the protrusions 52 (non-grooved portions, which are parts where grooves 51 are not formed) formed between the grooves 51 of the developing sleeve 28, it is preferable to exclude scratches and grooves with a depth of 5 μm or more, regardless of the purpose for which their shape was created.

[0056] Here, Sa is calculated using the following formula based on ISO 25178, where A is the measurement surface in question, and x and y are mutually orthogonal axes on that measurement surface.

[0057] Furthermore, while there are two methods for measurement, the contact method, which involves moving a stylus along the surface, and the non-contact method, which uses light or a laser, in this embodiment, Sa was measured using a microscope with a confocal optical system (VK-X100 KEYENCE) under the following conditions: • Objective lens: 50x • Measurement mode: Surface shape • Measurement size (number of pixels): High resolution (2048 x 1536) • Measurement quality: High precision • Pitch: 0.01 μm • S-filter (low-pass filter): None • L-filter (high-pass filter): 0.025 mm • Measurement range: 300 μm x 220 μm

[0058] In this embodiment, six locations were measured in total: three locations in the rotational axis direction of the developing sleeve 28, and three locations on the back side of these three locations, using the method described above. The three locations in the rotational axis direction are: a point 10 mm in the direction of region 50b from the boundary between region 50a and region 28S (developer-carrying and transporting section) where the groove 51 is formed; the center point in the rotational axis direction of region 28S (developer-carrying and transporting section) where the groove 51 is formed; and a point 10 mm in the direction of region 50a from the boundary between region 50b and region 28S (developer-carrying and transporting section) where the groove 51 is formed. In addition, two locations were measured in the circumferential direction of the developing sleeve 28 for each of the three locations in the rotational axis direction mentioned above. Specifically, these were points rotated 180° in the circumferential direction of the developing sleeve 28 relative to the three locations in the rotational axis direction mentioned above, i.e., a total of six points on the back side were measured. The average of these values ​​is then used as the surface roughness Sa of the protrusion 52.

[0059] If the maximum and minimum values ​​of these measured values ​​are between 0.001 μm and 0.070 μm, then the surface roughness (arithmetic mean height Sa) of the protrusions 52 (non-grooved portions, which are areas where grooves 51 are not formed) formed between the grooves 51 of the developing sleeve 28 is between 0.001 μm and 0.070 μm.

[0060] Figure 10 is a schematic diagram showing the developer transport on the developing sleeve 28 in this embodiment. The dashed lines in Figure 10 represent the developer distribution on the developing sleeve 28, and the circles represent the developer carriers. However, not all carriers are shown in Figure 10. The developer is mainly constrained in the grooves 51, forming spikes by the magnetic rollers 28m enclosed in the developing sleeve 28. The developer between the grooves 51 (developer on the protrusions 52) is subjected to force by the magnetic spikes constrained in the groove 51 on the upstream side in the transport direction, and is transported by being pushed out by the magnetic spikes.

[0061] Furthermore, as shown in Figure 11, both the developer constrained in the groove 51 and the developer on the protrusion 52 pushed out by the magnetic treadmill change shape to follow the magnetic field lines formed by the magnetic roller 28m, and are transported while exchanging the upper end A and lower end B of the magnetic treadmill. At this time, the toner supported on the carrier comes into direct contact with the surface of the developing sleeve 28, and if the adhesive force between the developing sleeve 28 and the toner is greater than the adhesive force between the carrier and the toner, the toner that should originally be supported on the carrier will adhere directly to the developing sleeve 28. The force acting on the toner changes in a complex way depending on the direction and location of the applied force, as well as the shape of the toner, making it difficult to generalize, but generally, the smaller the adhesive force between the carrier and the toner, and the greater the adhesive force between the developing sleeve 28 and the toner, the more likely the toner is to detach from the carrier and adhere to the developing sleeve 28 on its own. This tendency becomes more pronounced when using low-melting-point toner that enables low-temperature fixing, due to the softness of the toner itself. As described above, as the developing sleeve 28 rotates, toner that adheres to the developing sleeve 28 (hereinafter also referred to as sleeve-adhered toner) is formed on the surface of the developing sleeve 28.

[0062] In this embodiment, the toner is made of crystalline polyester to achieve sharp melt properties, aiming to maintain toner hardness at room temperature while enabling low-temperature fixing.

[0063] Here, the relationship between temperature and toner viscosity will be explained using the graph in Figure 12. In Figure 12, the solid line shows the viscosity characteristics of the toner used in this embodiment. On the other hand, the dotted line in Figure 12 shows the viscosity characteristics of a toner that does not use crystalline polyester. It can be seen that the viscosity change from the room temperature range (30 to 50°C) to the fixing range (viscosity around 1.0E+05Pa·S) is steeper for the toner of this embodiment that uses crystalline polyester. The temperature at which the viscosity becomes 1.0E+05Pa·S is 90°C for the toner used in this embodiment and 108°C for the toner that does not use crystalline polyester. For this reason, it can be said that the toner used in this embodiment is a toner that can be fixed at a lower temperature of approximately 18°C. On the other hand, regarding the viscosity of the toner used in this embodiment at room temperature, since it is a toner aimed at sharp melting properties, the difference from the toner that does not use crystalline polyester is small, but in reality, the viscosity at room temperature is slightly lower compared to the one that does not contain crystalline polyester. As a result, the toner used in this embodiment becomes softer at room temperature compared to toners that do not contain crystalline polyester, making it more likely to adhere to the developing sleeve 28. This phenomenon tends to be more pronounced when using low-melting-point toners that enable low-temperature fixing and aim to maximize the effect of low-temperature fixing.

[0064] [Sleeve Ghosting] As described above, when toner becomes detached and adheres to the developing sleeve 28 on its own, the amount of toner adhering to the developing sleeve fluctuates according to the potential difference (Vdr - Vdc, hereafter referred to as the contrast potential difference) between the potential Vdr on the photosensitive drum 1a and the potential Vdc on the developing sleeve 28 when the sleeve-adhered toner reaches the developing area. This fluctuation can cause image unevenness to become a problem.

[0065] This image unevenness generally occurs through the following process. First, as described above, sleeve-adhered toner is formed on the surface of the developing sleeve 28 as the developing sleeve 28 rotates. Next, when the sleeve-adhered toner reaches the developing region as the developing sleeve 28 rotates, the sleeve-adhered toner is subjected to an electrostatic force due to the contrast potential difference in the developing region, and the amount of sleeve-adhered toner after passing through the developing region differs from the amount of sleeve-adhered toner before passing through the developing region. Normally, the potential Vdc is always a constant value, but the potential Vdr is formed by the electrostatic latent image, so the above contrast potential difference differs depending on the position in the longitudinal direction (rotation axis direction) and the circumferential direction of the photosensitive drum 1a.

[0066] In such cases, even if the toner attached to the sleeve before passing through the development area is uniform along the rotation axis direction of the development sleeve 28 (hereinafter sometimes simply referred to as the rotation axis direction), the toner attached to the sleeve after passing through the development area will have a difference corresponding to the difference in the rotation axis direction of the contrast potential difference in the development area. In this embodiment, since it is a negative polarity two-component development method, the contrast potential difference is positive in the image area where the toner flies to the photosensitive drum 1a, and conversely, the contrast potential difference is negative in the white area where the toner returns to the development sleeve 28. The toner in the development area receives a force directed toward the photosensitive drum 1a when the contrast potential difference is positive, and a force directed toward the development sleeve 28 when the contrast potential difference is negative.

[0067] Therefore, if there is a difference in contrast potential difference in the direction of the rotation axis, the amount of toner attached to the sleeve corresponding to the negative contrast potential difference will be greater than the amount of toner attached to the sleeve corresponding to the positive contrast potential difference. Strictly speaking, since the development bias voltage is a DC voltage superimposed with an AC voltage, the AC component causes both the toner on the development sleeve 28 and the toner carried on the carrier to reciprocate. According to the inventors' studies, it has been found that the difference in the direction of the rotation axis of the toner attached to the sleeve is generally determined by the above-mentioned development contrast potential difference. That is, according to the inventors' studies, the above-mentioned difference in the direction of the rotation axis generated by passing through the development area, that is, the difference in the amount of toner attached to the sleeve in the direction of the rotation axis after passing through the development area when the amount of toner attached to the sleeve before passing through the development area was uniform in the direction of the rotation axis, is generally determined by the amount of toner attached to the sleeve before passing through the development area and the difference in the direction of the contrast potential difference in the development area. It has been found that the larger the amount of toner attached to the sleeve before passing through the development area, and the larger the absolute value of the difference in the direction of the rotation axis of the contrast potential difference, the larger the difference tends to be.

[0068] Therefore, by passing through the development area, the amount of toner attached to the development sleeve 28 fluctuates by an amount corresponding to the contrast potential difference with the amount of toner attached to the sleeve at any point on the sleeve, resulting in unevenness in the amount of toner attached to the sleeve corresponding to the electrostatic latent image. In other words, since the amount of toner attached to the sleeve before passing through the development area is itself formed by the contrast potential difference in the previous image formation, unevenness in the amount of toner attached to the sleeve ultimately occurs in the development area corresponding to the electrostatic latent image.

[0069] Subsequently, the toner attached to the sleeve is transported along the developing sleeve 28 with the developer supported on its surface as the developing sleeve 28 rotates, and reaches the developing region again after passing through the repulsive magnetic field formed inside the developing container 22 and the layer thickness regulation by the regulating blade 29. At this time, the unevenness in the amount of toner attached to the sleeve is uniformized by the transport motion of the magnetic fins described above, the retention motion of the developer in the repulsive magnetic field, and the friction of the regulating blade 29 against the surface of the developing sleeve 28. When it reaches the developing region again, if the unevenness in the amount of toner attached to the sleeve that was formed in the previous developing region has not been sufficiently eliminated by the uniformization effect accompanying the rotational motion of the developing sleeve 28 described above, the potential of the surface of the developing sleeve 28 changes according to the amount of charge of the toner attached to the sleeve.

[0070] In this embodiment, since it is a negative polarity two-component development method, if the amount of toner adhering to the sleeve is large, the surface of the development sleeve 28 becomes more negatively polarized, behaving as if the potential Vdc has increased in the negative direction. This effectively increases the contrast potential difference of the image area. The larger the contrast potential difference of the image area, the greater the amount of toner developed on the photosensitive drum 1a, so the amount of toner developed on the photosensitive drum 1a deviates from the originally intended amount of toner development depending on the amount of toner adhering to the sleeve.

[0071] Here, we consider an image pattern 200 in which, as shown in Figure 13A, a solid image patch 201 corresponding to the maximum image signal value is placed next to the white area in the direction of the rotation axis, and furthermore, a uniform halftone image 202 is placed at a position where the developing sleeve 28 has rotated once in the sub-scanning direction from the position of these solid image patches 201. Figure 13A and Figures 13B and 13C, which will be described later, are schematic diagrams showing the toner image formed on the photosensitive drum 1a. As described above, the difference in the amount of toner attached to the sleeve in the direction of the rotation axis after passing through the developing area tends to be larger the more toner attached to the sleeve before passing through the developing area, and the larger the absolute value of the difference in contrast potential difference in the direction of the rotation axis. For this reason, in the image pattern 200 shown in Figure 13A, unevenness in the amount of toner attached to the sleeve is likely to occur, and this is likely to manifest as density unevenness. Figure 13B shows a state in which significant unevenness in the amount of toner developed on the photosensitive drum 1a occurs in accordance with the difference in the amount of toner attached to the sleeve in the direction of the rotation axis, and density unevenness corresponding to the image of the previous rotation of the developing sleeve 28 appears as an image pattern 203.

[0072] This phenomenon is a hierarchical phenomenon of the image pattern, in that an image corresponding to the phase of the previous rotation of the developing sleeve 28 appears, and its main cause is the toner adhering to the sleeve due to the adhesion force between the developing sleeve 28 and the toner. For this reason, the unevenness in the amount of toner developed caused by the above phenomenon (image pattern 203 in Figure 13B) will henceforth be simply called sleeve ghosting. As explained above, sleeve ghosting occurs due to the interplay of the amount of toner adhering to the sleeve, the contrast potential difference in the development area, and the uniformizing effect of the amount of toner adhering to the sleeve as the developing sleeve 28 rotates.

[0073] [Relationship between surface roughness Sa and toner adhesion] As described above, the protrusions 52 of the developing sleeve 28 in this embodiment are processed to have a surface roughness (arithmetic mean roughness) Sa of 0.048 μm. By setting the surface roughness Sa of the developing sleeve 28 to this value, the adhesion between the developing sleeve 28 and the toner can be reduced compared to the surface roughness Sa in other cases, thereby suppressing the occurrence of sleeve ghosting.

[0074] Here, we will explain the adhesion force between the developing sleeve 28 and the toner. The adhesion force between two substances can generally be explained by a superposition of "electrostatic force," "liquid bridging force," and "van der Waals force." Of these, it is generally known that the van der Waals force is the force that is most sensitive to surface roughness. The van der Waals force acting between an uneven surface and a particle can generally be understood as follows. That is, as shown in Figure 14, we consider the van der Waals force acting between a surface having periodically occurring convex portions G of height h relative to a plane L, and a particle p approximated as a perfect sphere that is in contact with the convex portions G. In this case, as shown in Figure 15, the larger the height h, the more dominant the van der Waals force with the convex portions G (solid line g) becomes compared to the plane L, and conversely, if the height h is small, the more dominant the van der Waals force with the plane L (dashed line l) becomes compared to the convex portions G. The van der Waals force between the uneven surface and the particle p can be described by the superposition of the convex portion G and the plane L. As shown in Figure 16, the van der Waals force is convex downwards with respect to the surface roughness Sa, and has a minimum value at a certain value.

[0075] According to the inventors' studies, the van der Waals force between toner particles with a particle size (volume average particle size) of approximately 4 μm to 10 μm, which are used in dry two-component toners, and the surface of the aluminum alloy developing sleeve 28, is found to have a minimum value at a surface roughness Sa of approximately 0.010 μm. Furthermore, it was found that if the surface roughness Sa of the developing sleeve 28 is in the range of 0.001 μm to 0.070 μm, which includes this value, it is effective against sleeve ghosting.

[0076] Furthermore, the adhesive force acting between the surface irregularities of the developing sleeve 28 and the toner particles is a three-dimensional phenomenon acting between the three-dimensional irregularities on the curved surface of the developing sleeve 28 and the opposing curved surface of the toner particles. Therefore, from the viewpoint of reducing the adhesive force acting between them, the conventional specification of line roughness Ra (JIS B 0671-1 / ISO 13565-1) is insufficient. In fact, the inventors' investigations have confirmed that for Ra in a certain direction locally (for example, in the direction of the rotation axis) that is within the above range, measurement using the above measurement method results in deviation from the above range of Sa.

[0077] Let me explain this in detail. Table 1 shows the measured surface roughness Sa and linear roughness Ra of surfaces with various roughness levels. Surface roughness Sa captures a wider area of ​​the surface than linear roughness Ra, whereas linear roughness Ra only measures a portion of surface roughness Sa. Therefore, as can be seen from Table 1, it can be concluded that surface roughness Sa and linear roughness Ra are not correlated.

[0078] [Effects of this embodiment] Figure 17 shows the experimental results of investigating the non-electrostatic adhesion force between the developing sleeve 28 and toner in two cases: Example 1, which satisfies this embodiment, where the surface roughness Sa of the protrusion 52 is 0.048 μm, and Comparative Example 1, where the surface roughness Sa of the protrusion is 0.183 μm. In this experiment, the non-electrostatic adhesion force was measured as follows: (1) A developing device equipped with the developing sleeve to be used in the experiment is installed in an image forming apparatus, and one image of only the white area is printed. (2) The developing device equipped with the developing sleeve to be used in the experiment is removed from the image forming apparatus, and the two-component developer is peeled off from the surface of the developing sleeve, so that the sleeve-adhered toner is uniformly formed on the surface of the developing sleeve. A convenient method can be selected for peeling off the electrostatic developer from the developing sleeve, but in this experiment, the developer supported on the surface was peeled off by rotating only the developing sleeve. (3) With the developing sleeve fixed so as not to rotate, a flat plate made of aluminum alloy (hereinafter referred to as the aluminum plate) is brought close to the developing sleeve with a gap of 100 μm. (4) The aluminum plate is grounded, and a DC voltage is applied to the developing sleeve for a predetermined time. In this experiment, it was set to 5 seconds. The electrostatic force acting between the developing sleeve and the aluminum plate causes the toner adhering to the developing sleeve to fly towards the aluminum plate. (5) After the predetermined time has elapsed and the flying has stopped, the amount of toner adhering to the aluminum plate (hereafter, the amount of toner that has flown) is measured. The measurement method may be to transfer the toner to paper using transparent release tape and measure the density of the transferred area, or to count the number of toner particles using a microscope. (6) The same experiment is performed by varying the level of the applied DC voltage. In this experiment, six levels of experimentation were performed in 200V increments from 0V to 1200V. (7) The force F acting on the toner adhering to the sleeve is calculated from the applied DC voltage and the separately measured charge amount of the toner, and the relationship between the force F and the amount of toner that has flown is plotted. (8) The average value is calculated from the relationship between the force F and the amount of toner that has flown. While any appropriate calculation method can be selected, in this experiment, a cumulative Gaussian distribution was used for approximation, and the average value Fav was calculated. (9) The non-electrostatic adhesion force is calculated from the calculated average value Fav and the charge amount of the toner.In this experiment, the electrostatic term was calculated using a central charge model that replaces the toner charge amount with its central charge, and then calculated by subtracting the electrostatic term from Fave.

[0079] Figure 17 shows the results of calculating the non-electrostatic adhesion force using the method described above. It can be seen that the adhesion force of Example 1 is approximately half that of Comparative Example 1.

[0080] Figure 18 plots the density differences caused by sleeve ghosting when the image pattern 200 shown in Figure 13A is output for Example 1, Comparative Example 1, Comparative Example 2, and other Examples 1a, 1b, and 1c, which have different surface roughness Sa than Example 1 but satisfy the conditions of this embodiment, with the surface roughness Sa of the protrusions of each developing sleeve 28 on the horizontal axis. As shown in Figure 13C, the density difference is the density difference between points A1, A2, and A3 where the image pattern 203, which is sleeve ghosting, can occur, and points B1, B2, and B3 which are shifted in the direction of the rotation axis from the region where the image pattern 203 can occur. That is, it is the average value obtained by measuring the density difference ΔD1 between point A1 and point B1, the density difference ΔD2 between point A2 and point B2, and the density difference ΔD3 between point A3 and point B3. This is called ΔDave.

[0081] As shown in Figure 18, when the surface roughness Sa is 0.070 μm or less, the allowable level of concentration difference, ΔDave < 0.02, is achieved. Here, the surface roughness Sa of each example and comparative example is as follows: Comparative Example 1: 0.183 μm Comparative Example 2: 0.080 μm Example 1: 0.048 μm Another Example 1a: 0.063 μm Another Example 1b: 0.055 μm Another Example 1c: 0.042 μm

[0082] As described above, by setting the surface roughness Sa of the protrusions 52 of the developing sleeve 28 to 0.001 μm or more and 0.070 μm or less, the adhesion of toner to the developing sleeve 28 can be suppressed, thereby suppressing the occurrence of sleeve ghosting. Furthermore, in this embodiment, the occurrence of sleeve ghosting is suppressed by setting the surface roughness Sa of the protrusions 52 of the developing sleeve 28 within the above range, without newly providing other components such as a scraper or coating the surface of the developing sleeve with titanium oxide. Therefore, an increase in the cost of the device can also be suppressed. In other words, the adhesion of toner to the developing sleeve 28 can be suppressed at low cost, and the occurrence of sleeve ghosting can be suppressed. In particular, according to this embodiment, even when a low-melting-point toner using crystalline polyester as the binder resin for the toner is used, it is possible to suppress sleeve ghosting with a simple and inexpensive configuration.

[0083] Furthermore, the surface roughness Sa of the protrusion 52 is preferably 0.065 μm or less, more preferably 0.060 μm or less, and even more preferably 0.055 μm or less, as shown in Figure 18. However, if the surface roughness Sa of the protrusion 52 is reduced, the processing time and other costs will increase. Therefore, from the viewpoint of cost, the surface roughness Sa of the protrusion 52 is preferably 0.003 μm or more, more preferably 0.005 μm or more, and even more preferably 0.007 μm or more.

[0084] <Second Embodiment> The second embodiment will be described with reference to Figures 19 to 22. This embodiment differs from the configuration of the first embodiment described above in the configuration of the partition wall 27A of the developing apparatus 4A and the configuration of the magnet roller 28mA. The other configurations and operations are the same as those of the first embodiment described above, so the same reference numerals are used for similar configurations, and their description and illustration are omitted or simplified. The following description will focus on the differences from the first embodiment.

[0085] As described above, sleeve ghosting occurs due to the interplay of the amount of toner attached to the sleeve, the contrast potential difference in the development area, and the uniformization effect of the amount of toner attached to the sleeve as the development sleeve 28 rotates. The uniformization effect of the amount of toner attached to the sleeve as the development sleeve 28 rotates is mainly achieved by friction between the regulating blade 29 and the surface of the development sleeve 28, and is more pronounced the greater the friction force. On the other hand, the greater the friction force, the more the toner deteriorates as the external additive covering the toner surface becomes embedded or detached. When toner deterioration occurs as described above, the amount of charge and fluidity that were originally expected from the toner decrease, resulting in a decrease in image quality. From this perspective, sleeve ghosting and toner deterioration are in a trade-off relationship.

[0086] Furthermore, it has been found that when the aforementioned low-melting-point toner is used as a toner for energy saving, various problems caused by toner degradation, along with sleeve ghosting, become apparent. In view of the above, this embodiment describes an example in which the disclosure is applied to a low-load developing apparatus 4A configuration that reduces the load on the toner. With this configuration, toner degradation is suppressed, and sleeve ghosting, which tends to occur as a result, is improved by setting the surface roughness Sa of the protrusion 52 of the developing sleeve 28 to 0.001 μm or more and 0.070 μm or less, thereby achieving both suppression of toner degradation and suppression of sleeve ghosting.

[0087] [Configuration for Low Load on Toner] Figure 19 is a cross-sectional view of the developing apparatus 4A of this embodiment. The magnetic roller 28mA as a magnet in this embodiment consists of a developing pole N2 that faces the developing area and supports the developer on the developing sleeve 28 during development, magnetic poles S1 and S2 that support and transport the developer, a magnetic pole N1 for determining the amount of cutting by the regulating blade 29, and a magnetic pole N3 that forms a repulsive magnetic field with the above N1 pole to peel off the developer in the stirring chamber 24. That is, the magnetic roller 28mA of this embodiment has a magnetic pole N1 as a first magnetic pole that faces the regulating blade 29 via the developing sleeve 28, and a magnetic pole N3 as a second magnetic pole that is adjacent to magnetic pole N1 on the upstream side of magnetic pole N1 with respect to the rotation direction of the developing sleeve 28 and has the same pole as magnetic pole N1. Then, a repulsive magnetic field is formed between magnetic poles N3 and N1, so that the developer is peeled off from the developing sleeve 28.

[0088] In this embodiment, the magnetic pole N3 is positioned upstream of the magnetic pole N1, which is the magnetic pole facing the regulating blade 29, in the rotational direction of the developing sleeve 28, in order to form a repulsive magnetic field with the magnetic pole N1. This configuration reduces the magnetic force near the regulating blade 29, which is subjected to high stress in the developing container 22A, thereby reducing toner degradation.

[0089] Furthermore, in this embodiment, the partition wall 27A separating the first developing chamber 23 and the second stirring chamber 24 has a shape that extends to the vicinity of the regulating blade 29 and has a transport guide 55 as a guide part that guides the developer contained in the developing chamber 23 from above in the direction of gravity to the developing sleeve 28. The transport guide 55 is provided facing the upstream side of the developing sleeve 28 in the direction of rotation relative to the regulating blade 29. That is, the transport guide 55 faces the outer circumferential surface of the developing sleeve 28 upstream of the developing sleeve 28 in the direction of rotation relative to the regulating blade 29 and guides the developer downward in the direction of gravity from the developing chamber 23 toward the developing sleeve 28.

[0090] The surface of the transport guide 55 facing the regulating blade 29 (guide surface) also serves as a guide to properly supply developer from the gap between the regulating blade 29 and the transport guide 55 when driven by the first transport screw 25. Furthermore, by being positioned opposite the circumferential direction of the developing sleeve 28, the transport guide 55 functions as a regulating part that regulates the starting position of developer supply from the developing chamber 23 to the developing sleeve 28. The angle of the guide surface of the transport guide 55 is set in the direction normal to the surface of the developing sleeve 28. In addition, the nearest contact distance of the transport guide 55 to the surface of the developing sleeve 28 is set to 1 mm.

[0091] Furthermore, the closest contact position P1 with respect to the transport guide 55 on the outer surface of the developing sleeve 28 is set to a position of 130° in the circumferential direction, with the position where a horizontal line passing through the rotation center of the developing sleeve 28 intersects the outer surface of the developing sleeve 28 on the photosensitive drum 1a side being defined as 0°, and a clockwise angle being positive. In addition, the closest contact position of the partition wall 27 with respect to the developing sleeve 28, and the position P3 furthest upstream in the rotational direction of the developing sleeve 28, is set to a position of 180° in the circumferential direction of the developing sleeve 28.

[0092] In this embodiment, as shown in Figure 20, the apex P4 of the transport guide 55 in the direction of gravity is set to the position where the regulating blade 29 is closest to the developing sleeve 28, and in this embodiment, to be at an elevation angle of 30° with respect to the horizontal line passing through the lowest point P5. That is, the apex P4 of the transport guide 55 is located above the lowest point (closest contact position) P5 of the regulating blade 29 and the developing sleeve 28 in the direction of gravity. The reason for this is to store an amount of developer in the region between the transport guide 55 and the regulating blade 29 that is sufficient to stably coat the outer surface of the developing sleeve 28, even in a low-load configuration like this embodiment. The length L55 of the guide surface of the transport guide 55 is 11 mm.

[0093] Furthermore, in this embodiment, the transport guide 55 is integrally constructed with the partition wall 27 and is made of the same material as the developing container 22A. In addition, when the nearest contact position (developer supply start position) on the outer circumferential surface of the developing sleeve 28 with respect to the transport guide 55 is P1, and the nearest contact position on the outer circumferential surface of the developing sleeve 28 with respect to the regulating blade 29 is P2, the length R of the outer circumferential surface of the developing sleeve 28 from P1 to P2 in the rotational direction of the developing sleeve 28 is 2 mm or more. It is also preferable that the length R be 10 mm or less. That is, the desirable range for the distance from the regulating blade 29 to the transport guide 55 (the circumferential length R of the developing sleeve 28) is 2 mm or more and 10 mm or less. In this embodiment, the length R is set to approximately 5 mm.

[0094] This is because if the length R from the regulating blade 29 to the transport guide 55 is less than 2 mm, the transport path through which the developer is transported becomes narrower, and there is a risk of the developer clogging between the regulating blade 29 and the transport guide 55. On the other hand, if the length R is too long, that is, if the distance between the regulating blade 29 and the transport guide 55 is too wide, the contact distance between the developing sleeve 28 and the developer increases, which means that the time during which the developer is rubbed against the developing sleeve 28 by magnetic force increases, and there is a concern that the developer may deteriorate, which is undesirable. In this embodiment, by adopting the above-described configuration, it is possible to stably regulate the thickness of the developer layer on the developing sleeve 28 while reducing the stress applied to the toner near the regulating blade 29.

[0095] [Effects of this embodiment] Figure 21 shows the toner degradation of each of the following: Example 2, which satisfies the configuration of this embodiment and in which the surface roughness Sa of the protrusion 52 of the developing sleeve 28 is 0.048 μm; Comparative Examples 1 and 2 used in the first embodiment; and Comparative Examples 3, 4, 5, and 6, by measuring the silica coating rate of the toner. Comparative Examples 3, 4, and 5 are other Examples 1a, 1b, and 1c used in the first embodiment, and Comparative Example 6 is Example 1. In this verification, the silica coating rate of the toner contained in the developer after printing 30,000 images with an image print density of 1% in an environment of 30°C and 80% humidity was measured by ESCA (X-ray photoelectron spectroscopy). The measurement method and analysis method of ESCA are as follows.

[0096] [Method for Measuring Coverage by ESCA] When silica nanoparticles are used as inorganic nanoparticles, the coverage of the inorganic nanoparticles is calculated from the amount of silicon atoms (hereinafter also referred to as Si amount) derived from silica present on the surface of the toner particles, which is measured by ESCA (X-ray photoelectron spectroscopy). ESCA is an analytical method that detects atoms in a region of a few nanometers or less in the depth direction of the sample surface. Therefore, it is possible to detect atoms on the surface of the toner. A 60 mm diameter platen (equipped with a screw hole of approximately 1 mm in diameter for fixing the sample) attached to the device was used as the sample holder. Since the screw hole of the platen is through, the hole was sealed with resin or the like to create a recess for powder measurement with a depth of about 0.5 mm. The sample to be measured was packed into this recess with a spatula or the like and leveled off to prepare the sample.

[0097] The ESCA equipment and measurement conditions are as follows: Equipment used: PHI5000VersaProbeII (manufactured by ULVAC-PHI, Inc.) Analysis method: Narrow analysis X-ray source: Al-Kα X-ray conditions: 100 μm, 25 W, 15 kV Photoelectron acquisition angle: 45° Pass Energy: 58.70 eV Measurement range: 300 μm × 200 μm

[0098] [Method for Analyzing Coverage by ESCA] The analysis method first corrects the peak originating from the C-C bond of the carbon 1s orbital to 285 eV. Then, using the peak area originating from the silicon 2p orbital, where the peak top is detected between 100 eV and 105 eV, the amount of Si originating from silica relative to the total amount of constituent elements is calculated using a relative sensitivity factor provided by ULVAC-PHI, Inc. Next, the silica applied to the toner is measured using the same method as above, and the amount of Si originating from silica relative to the total amount of constituent elements is calculated. The ratio of the amount of Si measured in the toner to the amount of Si measured in the external additive is defined as the silica coverage in this disclosure.

[0099] Figure 21 shows that the silica coating rate in Example 2 is about 5% higher than that of Comparative Examples 1 to 6, which do not have a transport guide 55, indicating that the reduction in the toner's external additive is mitigated.

[0100] Furthermore, Figure 22 plots the density differences caused by sleeve ghosting when the image pattern 200 shown in Figure 13A was output for each of Example 2 and Comparative Examples 1 to 6, with the surface roughness Sa of the protrusions of each developing sleeve 28 on the horizontal axis. For the density difference, ΔDave, as explained in the first embodiment, was used.

[0101] As shown in Figure 22, the ΔDave in Example 2, which includes the transport guide 55, is larger than that in Comparative Examples 3 to 6, which do not include the transport guide 55. However, in Example 2, the ΔDave is improved by reducing the surface roughness Sa of the protrusion 52 of the developing sleeve 28 compared to Comparative Examples 1 and 2. Therefore, in the case of Example 2, it can be confirmed from Figures 21 and 22 that both toner degradation suppression and sleeve ghost suppression are achieved. That is, according to this embodiment, as with the first embodiment, the adhesion of toner to the developing sleeve 28 can be suppressed, and thus the occurrence of sleeve ghost can be suppressed. In addition, toner degradation can also be suppressed.

[0102] <Other Embodiments> The image forming apparatus 100 is not limited to a full-color printer; it may also be a monochrome or monocolor printer. Furthermore, the image forming apparatus 100 may be a printer, various printing machines, copiers, fax machines, or multifunction devices having multiple of these functions.

[0103] Furthermore, in the embodiments described above, drum-shaped organic photoreceptors, specifically photosensitive drums 1a to 1d, were used as the image carrier. However, inorganic photoreceptors such as amorphous silicon photoreceptors can also be used. It is also possible to use a belt-shaped photoreceptor. The charging method, transfer method, cleaning method, and fixing method are not limited to those described above.

[0104] Furthermore, while the first and second embodiments described above described the application of the present disclosure to developing apparatuses 4 and 4A in which the developing chamber 23 and agitation chamber 24 are arranged vertically, the developing apparatus is not limited to these. For example, the present disclosure can also be applied to developing apparatuses in which the developing chamber and agitation chamber are arranged horizontally, as has been done conventionally, or to other forms of developing apparatuses.

[0105] This disclosure is suitable for a developing apparatus that develops an electrostatic latent image formed on an image carrier such as a sleeve, a developer carrier, and a photosensitive drum using toner.

[0106] The present invention is not limited to the embodiments described above, and various modifications and variations are possible without departing from the spirit and scope of the invention. Accordingly, the following claims are attached to make the scope of the invention public.

[0107] This application claims priority based on Japanese Patent Application No. 2025-041795, filed on 14 March 2025, and Japanese Patent Application No. 2026-035637, filed on 5 March 2026, and all of the contents of those applications are incorporated herein by reference.

[0108] 4a, 4b, 4c, 4d, 4A... Developing device 22, 22A... Developing container 28... Developing sleeve (developer carrier) 28m, 28mA... Magnetic roller (magnet) 28S... Area (developer carrier transport section) 51... Groove (grooved section) 52... Protrusion (non-grooved section)

Claims

1. A rotatable sleeve comprising a developer carrying and transport section for carrying and transporting a developer containing toner and carrier to a developing position, the developer carrying and transport section having a grooved section which is a portion in which grooves are formed and a non-grooved section which is a portion in which grooves are not formed, wherein when the depth of the groove is D, the radius of the carrier is r, and the width of the groove in the rotational direction of the sleeve is W, D > r and W > 2r are satisfied, and the arithmetic mean height Sa of the surface of the non-grooved section is 0.001 μm or more and 0.070 μm or less.

2. The sleeve according to claim 1, wherein the arithmetic mean height Sa of the surface of the non-grooved portion is 0.065 μm or less.

3. The sleeve according to claim 1, wherein the arithmetic mean height Sa of the surface of the non-grooved portion is 0.060 μm or less.

4. The sleeve according to any one of claims 1 to 3, wherein the arithmetic mean height Sa of the surface of the non-grooved portion is 0.003 μm or more.

5. The sleeve according to any one of claims 1 to 3, wherein the arithmetic mean height Sa of the surface of the non-grooved portion is 0.005 μm or more.

6. The sleeve according to any one of claims 1 to 5, further satisfying 20r > W.

7. The sleeve according to claim 6, further satisfying D > 2r.

8. The sleeve according to claim 1, further satisfying D > 2r.

9. A developer carrier comprising: a rotatable sleeve; and a magnet disposed inside the sleeve, wherein the sleeve comprises a developer carrier and transport section for carrying and transporting a developer containing toner and carrier to a developing position, the transport section having a grooved section which is a portion in which a groove is formed; and a non-grooved section which is a portion in which the groove is not formed, wherein when the depth of the groove is D, the radius of the carrier is r, and the width of the groove in the rotational direction of the sleeve is W, D > r and W > 2r are satisfied, and the arithmetic mean height Sa of the surface of the non-grooved section is 0.001 μm or more and 0.070 μm or less.

10. The developer carrier according to claim 9, wherein the arithmetic mean height Sa of the surface of the non-grooved portion is 0.065 μm or less.

11. The developer carrier according to claim 9, wherein the arithmetic mean height Sa of the surface of the non-grooved portion is 0.060 μm or less.

12. The developer carrier according to any one of claims 9 to 11, wherein the arithmetic mean height Sa of the surface of the non-grooved portion is 0.003 μm or more.

13. The developer carrier according to any one of claims 9 to 11, wherein the arithmetic mean height Sa of the surface of the non-grooved portion is 0.005 μm or more.

14. A developer carrier according to any one of claims 9 to 13, further satisfying 20r > W.

15. The developer carrier according to claim 14, further satisfying D > 2r.

16. The developer carrier according to claim 9, further satisfying D > 2r.

17. A developing apparatus comprising: a developing container for containing a developer containing toner and a carrier; a developer carrier having a rotatable sleeve and a magnet disposed inside the sleeve, wherein the sleeve comprises a developer carrier and transport section for carrying and transporting the developer to a developing position, the carrier having a grooved section which is a portion in which a groove is formed and a non-grooved section which is a portion in which the groove is not formed, and where D is the depth of the groove, r is the radius of the carrier, and W is the width of the groove in the rotational direction of the sleeve, D > r and W > 2r, and the arithmetic mean height Sa of the surface of the non-grooved section is 0.001 μm or more and 0.070 μm or less.

18. The developing apparatus according to claim 17, wherein the arithmetic mean height Sa of the surface of the non-grooved portion is 0.065 μm or less.

19. The developing apparatus according to claim 17, wherein the arithmetic mean height Sa of the surface of the non-grooved portion is 0.060 μm or less.

20. The developing apparatus according to any one of claims 17 to 19, wherein the arithmetic mean height Sa of the surface of the non-grooved portion is 0.003 μm or more.

21. The developing apparatus according to any one of claims 17 to 19, wherein the arithmetic mean height Sa of the surface of the non-grooved portion is 0.005 μm or more.

22. A developing apparatus according to any one of claims 17 to 21, further satisfying 20r > W.

23. The developing apparatus according to claim 22, further satisfying D > 2r.

24. The developing apparatus according to claim 17, further satisfying D > 2r.

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