Sleeve, developer carrier, and developing apparatus

Abstract

This provides a configuration that can suppress toner adhesion to the developing sleeve at a low cost. [Solution] A rotatable sleeve (28) comprising a developer carrying and transporting unit (28S) for carrying and transporting a developer containing toner and carrier to a developing position, the developer carrying and transporting unit (28S) having a grooved portion (51) where grooves are formed and a non-grooved portion (52) where 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 (28) is W, D > R and W > 2R are satisfied, and the non-grooved portion (52) has a chromium layer (54) on the outer surface of the sleeve (28), and the thickness of the chromium layer (54) is 1 μm or more and 5 μm or less.

Description

Technical Field

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

Background Art

[0002] As a developing method for developing an electrostatic latent image formed on an image bearing member with toner, a method using a two-component developer containing toner and a carrier is known. In the case of the two-component developing method, the toner is sufficiently agitated with the carrier by an agitating member immediately after being replenished, and then carried on a developer bearing member such as a developing sleeve. For this reason, normally, the developer bearing member does not carry the toner alone, but carries the carrier that holds the toner.

[0003] However, when the layer thickness of the developer carried on the developer bearing member is regulated by a regulating member, or when the developer is carried and conveyed on the surface of the developer bearing member, the toner may separate from the carrier and adhere alone to the developer bearing member. If the toner adheres alone to the developer bearing member, the surface potential of the developer bearing member locally changes at the opposing portion where the developer bearing member faces the image bearing member, according to the charge amount of the adhered toner, and accordingly, there is a risk that the amount of toner developed onto the image bearing member and the density after fixing may fluctuate (hereinafter, this may be simply referred to as density unevenness).

[0004] As a countermeasure against such adhesion of toner to the developer bearing member, Patent Documents 1 to 3 propose configurations in which the toner adhered to the developer bearing member is collected by a member such as a scraper or a toner collection roll. Further, Patent Document 4 proposes a configuration that suppresses the accumulation of toner on the developer bearing member by coating the surface of the developer bearing member with titanium nitride.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

[0006] However, in configurations such as those described in Patent Documents 1 to 3, where toner adhering to the developer carrier is recovered using components such as a scraper or toner recovery roll, the device configuration becomes complex and the cost of the device increases. Also, in configurations such as those described in Patent Document 4, where the surface of the developer carrier is coated with titanium nitride, the cost of the device increases. [Means for solving the problem]

[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 a groove is formed and a non-grooved portion 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 non-grooved portion has a chromium layer on the outer surface of the sleeve, the thickness of the chromium layer is 1 μm or more and 5 μm or less.

[0009] Another aspect of the present disclosure is a rotatable sleeve comprising a developer carrying and transport section for carrying and transporting a developer containing toner and a carrier to a developing position, the developer carrying and 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 each of the grooved section and the non-grooved section is provided with a chromium layer on the outer surface of the sleeve.

[0010] 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 and transport section for carrying and transporting a developer containing toner and carrier to a developing position, the developer carrier and 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 non-grooved section has a chromium layer on the outer surface of the sleeve, the thickness of the chromium layer is 1 μm or more and 5 μm or less.

[0011] 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 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 each of the grooved section and the non-grooved section is provided with a chromium layer on the outer surface of the sleeve.

[0012] 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 sleeve comprising 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, the non-grooved section is provided with a chromium layer on the outer surface of the sleeve, and the thickness of the chromium layer is 1 μm or more and 5 μm or less.

[0013] 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 each of the grooved section and the non-grooved section is provided with a chromium layer on the outer surface of the sleeve. [Effects of the Invention]

[0014] According to this disclosure, the adhesion of toner to the developer carrier can be suppressed at low cost. [Brief explanation of the drawing]

[0015] [Figure 1] A schematic cross-sectional view of the image forming apparatus according to the first embodiment. [Figure 2] A schematic cross-sectional view of the developing apparatus according to the first embodiment. [Figure 3] A schematic longitudinal cross-sectional view of the developing apparatus according to the first embodiment. [Figure 4] A perspective view of the developing sleeve according to the first embodiment. [Figure 5] A schematic diagram illustrating the shape of a groove formed in the developing sleeve according to the first embodiment. [Figure 6] A schematic diagram illustrating a first alternative example of the shape of a groove formed in the developing sleeve according to the first embodiment. [Figure 7] A schematic diagram illustrating a second alternative example of the shape of a groove formed in the developing sleeve according to the first embodiment. [Figure 8] (a) and (b) are schematic diagrams illustrating the shape of a groove formed in a developing sleeve. [Figure 9] (a) and (b) are schematic diagrams illustrating the shape of a groove formed in a developing sleeve. [Figure 10] A schematic diagram for illustrating the conveyance state of developer on the surface of the developing sleeve. [Figure 11] A schematic diagram showing an enlarged view around the groove for illustrating the conveyance state of developer on the surface of the developing sleeve. [Figure 12] A graph showing the relationship between temperature and toner viscosity. [Figure 13] (a) A schematic diagram for explaining sleeve ghost, (b) a schematic diagram showing a state where image unevenness caused by sleeve ghost occurs, (c) a schematic diagram for explaining density measurement attributed to sleeve ghost. [Figure 14] A cross-sectional view schematically showing an enlarged part of the surface of the developing sleeve according to the first embodiment. [Figure 15] A cross-sectional view schematically showing an enlarged part of the surface of the developing sleeve according to the second embodiment. [Figure 16] A cross-sectional view schematically showing an enlarged part of the surface of the developing sleeve according to the third embodiment. [Mode for Carrying Out the Invention]

[0016] <First Embodiment> The first embodiment will be described with reference to Figures 1 to 14. First, the schematic configuration of the image forming apparatus 100 of this embodiment will be described with reference to Figure 1. In this embodiment, as an example of the image forming apparatus 100, a case using a tandem-type full-color printer will be described. Note that the image forming apparatus 100 is not limited to a tandem type in which a plurality of image forming units are arranged side by side, but may also be a rotary type arranged in a cylindrical shape. Furthermore, it is not limited to an intermediate transfer method in which the toner image is first transferred to an intermediate transfer body and then secondarily transferred to the recording material S, but may also be a direct transfer method in which the toner image is transferred directly from the photoreceptor to the recording material. Moreover, it is not limited to full color, but may also be monochrome or monocolor, and can be implemented in various applications such as printers, various printing machines, copiers, fax machines, and multifunction devices. The recording material S is, for example, a sheet, and may include, in addition to plain paper, special papers such as coated paper, recording materials of special shapes such as envelopes and index paper, and plastic film or cloth for overhead projectors.

[0017] [Image forming apparatus] The image forming apparatus 100 of this embodiment is a full-color image forming apparatus employing an electrophotographic method and comprises four image forming units Pa, Pb, Pc, and Pd. The configuration of each image forming unit is substantially the same except for the development color. Therefore, unless otherwise specified, the image forming unit Pa will be described as a representative unit, and for the other image forming units, the subscripts b, c, and d will be added to indicate that they are the respective image forming units, and detailed descriptions will be omitted.

[0018] The image forming unit Pa includes a photosensitive drum 1a as an image carrier that holds the 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 an exposure device, a developing device 4a, a primary transfer roller 6a, a cleaning device 19a, and the like.

[0019] 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.

[0020] 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. Note that the light source of the exposure device is not limited to a laser; LEDs or OLEDs may be used, and two-dimensional or three-dimensional array light sources may be used, not limited to scanning types.

[0021] 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.

[0022] 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 from 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 act as 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 the cleaning device 19a.

[0023] 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 remaining on the surface of the intermediate transfer belt 5 that is not 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 discharged into the discharge tray 17.

[0024] [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.

[0025] [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.

[0026] Amorphous polyester is preferably a peak molecular weight of 3500 to 20000 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.

[0027] 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 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.

[0028] 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. The melting point is preferably 60°C or higher and 120°C or lower, and in this embodiment, a wax with a melting point of 76°C was used.

[0029] Examples of colorants include those formulated to produce black using carbon black as a black colorant, yellow colorant, magenta colorant, and 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.

[0030] The toner resin used in this embodiment is prepared by the method described above, and the toner base resin has a softening point temperature Tm of 105°C. The softening point temperature Tm is measured using a constant-load extrusion type capillary rheometer, the "Flow Characteristics Evaluation Device Flow Tester CFT-500D" (manufactured by Shimadzu Corporation), in accordance with the manual included with the device.

[0031] 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 uniform 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.

[0032] 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).

[0033] [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 ferrite or magnetite particles having voids are filled with resin can be used. Among these, magnetic cores in which magnetic particles having voids are filled with resin 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.

[0034] 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.

[0035] 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.). In this embodiment, two types of carrier coating resin layers were used: one without inorganic fine particles (used in Comparative Examples 1 and 2 and the Example described later) and one containing silica fine particles of approximately 70 μm as inorganic fine particles (used in Comparative Example 3 and the Example described later). 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.

[0036] [Developing equipment] 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.

[0037] 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).

[0038] 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 in the opposite direction to the first transport screw 25, along the rotation axis.

[0039] 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.

[0040] 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. The developing sleeve 28 is made of a non-magnetic material consisting of an aluminum alloy.

[0041] 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.

[0042] 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.

[0043] The regulating blade 29 is composed of a non-magnetic material made of a plate-shaped 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.

[0044] The amount of developer transported to the developing section 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 by the magnetic force of the magnetic roller 28m. 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 The regulating blade 29 and the developing sleeve 28 have a gap of 200 to 1000 μm, preferably 300 to 700 μm. In this embodiment, it is set to 400 μm.

[0045] [Developing sleeve configuration] Next, the structure of the developing sleeve 28 will be explained in more detail. The developing sleeve 28 is made of a non-magnetic material made of aluminum alloy, and its surface is roughened to improve the transportability of the developer. In other words, in this embodiment, the developing sleeve 28 is made of aluminum alloy. Examples of roughening processes include blasting, which projects fine hard particles onto the surface of the developing sleeve 28 (see, for example, Japanese Patent Publication No. 1-5711 and Japanese Patent Publication No. 1-32506), and knurling, which forms an uneven shape on the surface by cutting or rolling (see, for example, Japanese Patent Publication No. 54-79043). However, with the increasing lifespan of developing devices, knurling, which has excellent wear resistance, has become the mainstream.

[0046] In this embodiment, as shown in Figure 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 transporting the developer are formed parallel to each other on its surface. The plurality of grooves 51 are formed, for example, by knurling. Figure 4 is a perspective view of the developing sleeve 28 of this embodiment, and Figure 5 is a schematic diagram showing a magnified portion of the surface of the developing sleeve 28 in a cross-section taken in a direction perpendicular to the rotation axis direction.

[0047] 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 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, 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 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 region 28S of the outer surface of the developing sleeve 28, on the side of region 50a at one end and on the side of 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.

[0048] 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 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, 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 shape should be such 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.

[0049] Here, we will explain the details of 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 8(a). This is because, as shown in Figure 8(b), 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.

[0050] Furthermore, as shown in Figure 9(a), 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 9(b), 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.

[0051] 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)

[0052] 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.

[0053] 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. The protrusions 52 are non-grooved parts where grooves 51 are not formed.

[0054] Furthermore, as shown in Figure 11, both the developer constrained in the groove 51 and the developer on the protrusion 52 (non-groove portion) 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.

[0055] 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.

[0056] 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 (30-50°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. Therefore, 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.

[0057] [Development area configuration] The developing sleeve 28 is installed opposite the photosensitive drum 1a with a predetermined gap (SD gap) between them to form a developing area, and rotates in the direction of the arrow in the diagram (counterclockwise) during development. The developing sleeve 28 carries a two-component developer whose layer thickness is regulated by a regulating blade 29, and transports this to the developing area opposite the photosensitive drum 1a, thereby supplying the developer to the electrostatic latent image formed on the photosensitive drum 1a. A developing bias voltage, which is a negative polarity DC voltage Vdc superimposed on an AC voltage, is applied to the developing sleeve 28. Due to the potential difference with the photosensitive drum 1a, toner is ejected from the developer carried on the 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 by the toner.

[0058] In the currently dominant digital latent image method, density gradations are created by changing the area ratio (and arrangement pattern) of dots or lines of a certain density. Therefore, the potential Vdr on the photosensitive drum 1a has a latent image potential that forms dots or lines that develop toner on the photosensitive drum 1a (image area latent image potential Vl) and a latent image potential for the white area where toner is not developed on the photosensitive drum 1a (white area latent image potential Vd). The DC voltage component Vdc of the development bias applied to the development sleeve 28 is set between this image area latent image potential Vl and the white area latent image potential Vd. At this time, the AC voltage component of the development bias has the effect of separating the toner from the carrier and supplying toner other than that at the magnetic tip that contacts the photosensitive drum 1a to the development process.

[0059] In this embodiment, the latent image potential Vd of the white area is set to -800V by the charger 2a, and the latent image potential Vl of the image area exposed at a constant intensity by the laser beam scanner 3a is set to -440V. The DC voltage Vdc applied to the developing sleeve 28 is -640V, and an AC voltage with a frequency of 12kHz is applied intermittently for two periods with an amplitude of 1400V. The AC waveform is a square wave, and the time between AC waveforms (hereafter referred to as the blank time) is the voltage of Vdc only, and in this embodiment the blank time was set to 0.3ms.

[0060] Furthermore, the outer diameter of the developing sleeve 28 was set to 20 mm, the outer diameter of the photosensitive drum 1a to 30 mm, and the SD gap to 300 μm. In addition, a drive device such as a motor (not shown) is used to rotate the photosensitive drum 1a at a surface speed of 435 mm / s, and the developing sleeve 28 at a surface speed of 740 mm / s, which is approximately 1.7 times that of the photosensitive drum 1a. Here, the surface speed of the photosensitive drum 1a, 435 mm / s, is approximately equal to the surface speed of the intermediate transfer belt 5 and the transport speed of the recording material S, and is called the image formation speed. The above values ​​for the developing bias waveform, the dimensions of the developing sleeve 28 and the photosensitive drum 1a, and the rotation speed are examples of embodiments and are not limited thereto.

[0061] With the above settings, the toner contained in the developer supported on the surface of the developing sleeve 28 is peeled away from the carrier by the AC voltage in the developing region. The negative polarity DC voltage Vdc makes it relatively positive with respect to the latent image potential Vd of the white area on the photosensitive drum 1a, and relatively negative with respect to the latent image potential Vl of the image area on the photosensitive drum 1a. As a result, it flies onto the photosensitive drum 1a with respect to the latent image potential Vl of the image area, and onto the developing sleeve 28 with respect to the latent image potential Vd of the white area. Here, the potential difference between the latent image potential Vd of the white area and the developing DC voltage Vdc (hereinafter referred to as Vback) is the potential difference necessary to prevent toner from adhering to the white 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 100V or more. In this embodiment, it is set to 160V.

[0062] [Sleeve Ghost] As described above, when toner is released and adheres to the developing sleeve 28 on its own, the amount of toner adhering to the developing sleeve fluctuates depending on the potential difference (Vdr-Vdc, hereafter referred to as 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.

[0063] 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 area as the developing sleeve 28 rotates, the sleeve-adhered toner is subjected to electrostatic force due to the contrast potential difference in the developing area, and the amount of sleeve-adhered toner after passing through the developing area differs from the amount of sleeve-adhered toner before passing through the developing area. 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.

[0064] 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 the toner is a two-component development method with negative polarity, the contrast potential difference (Vl-Vdc) 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.

[0065] 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 rotation axis of the contrast potential difference in the development area, and 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.

[0066] Therefore, by passing through the development area, the amount of toner attached to the development sleeve 28 fluctuates by an amount corresponding to the amount of toner attached to the sleeve at any point on the sleeve and the contrast potential difference, 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, ultimately unevenness in the amount of toner attached to the sleeve occurs in the development area corresponding to the electrostatic latent image.

[0067] Subsequently, the toner attached to the sleeve is transported along with the developer supported on the surface of the developing sleeve 28 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.

[0068] In this embodiment, since the toner is a two-component development method with negative polarity, 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. Therefore, 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.

[0069] Here, we consider an image pattern 200 in which, as shown in Figure 13(a), a solid image patch 201 with the maximum density corresponding to the maximum image signal value (maximum area ratio of the image area; in this case, an image with an area ratio of 100%) 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 one full turn in the sub-scanning direction from the position of these solid image patches 201. Figure 13(a) and Figures 13(b) and 13(c), 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 13(a), unevenness in the amount of toner attached to the sleeve is likely to occur, and this is likely to manifest as density unevenness. Figure 13(b) 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.

[0070] 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 13(b)) 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.

[0071] In recent years, print-on-demand machines, particularly those used in commercial printing, are required not only for high-speed printing and high image quality but also for high stability and energy efficiency in order to achieve higher productivity. First, regarding high stability, efforts have been made to stabilize the amount of developer on the developing sleeve over time, which is one of the important elements due to the nature of the electrophotographic method. Conventionally, in order to transport the developer on the developing sleeve, minute irregularities such as sandblasting were made on the surface of the developing sleeve to give the developing sleeve the ability to transport the developer. However, these minute irregularities wear down between the developing sleeve and the developer during use, and the irregularities become smaller as use progresses. As a result, the developer transport capacity on the developing sleeve decreases, and the amount of developer carried by the developing sleeve decreases.

[0072] To address this, recent image forming apparatuses often employ a configuration, as in this embodiment, in which the outer surface of the developing sleeve is equipped with multiple grooves. These grooves are created by cutting them with a die during processes such as drawing, making it possible to increase the amount of unevenness without deforming the developing sleeve. Because of the increased amount of unevenness in this configuration, the surface unevenness is less affected by durable wear compared to developing sleeves that have undergone sandblasting or other processes, allowing for stable transport of the developer even over long periods of use.

[0073] On the other hand, in terms of energy saving, efforts have been made to improve the low-temperature fixing properties of toner and reduce the energy consumed for image fixing. However, simply lowering the softening point of toner can lead to a decrease in the shelf life of toner affected by heat during transportation and storage, and a decrease in durability, as externally added particles on the toner surface during image printing are more likely to peel off the toner surface or become embedded in the toner, causing toner degradation. Therefore, toners that use crystalline polyester as the binder resin have been proposed as a toner that balances low-temperature fixing properties with shelf life and durability. Compared to conventional toners that use only amorphous polyester as the binder resin, toners that use both amorphous and crystalline polyester have the characteristic of rapidly softening near the softening point, and because crystalline polyester also acts as a plasticizer for amorphous polyester, it is an effective material for low-temperature fixing of toner.

[0074] However, when using the low-melting-point toner described above, the adhesion between the developing sleeve and the toner is high, and it was found that the toner tends to detach from the carrier and adhere to the developing sleeve independently when adjusting the amount of toner carried on the developing sleeve by the layer thickness regulating member, or when the developer is carried on the surface of the developing sleeve and transported. When toner adheres to the developing sleeve independently in this way, it causes sleeve ghosting as described above, depending on the amount of charge of the attached toner (sleeve-attached toner). Based on the above, it is desirable to reduce the difference in the amount of toner attached to the developing sleeve due to the image history as a countermeasure against developing sleeve ghosting caused by this mechanism.

[0075] [Comparative Example] Next, we will describe the results of evaluating the occurrence of sleeve ghosting when test images were printed using a developing sleeve 28 with multiple grooves 51 formed as described above, while changing the type of toner and carrier.

[0076] First, as Comparative Example 1, a toner using amorphous polyester as the binder resin was used. This toner had the viscosity shown by the dashed line in Figure 12. On the other hand, as Comparative Example 2, a toner using the crystalline polyester and amorphous polyester as binder resins was used. This toner had the viscosity shown by the solid line in Figure 12. In Comparative Examples 1 and 2, and Comparative Example 3, which will be described later, the developing sleeve 28 used was a conventional developing sleeve, rather than the configuration of this embodiment in which the outermost layer of the outer surface is a chromium layer. Details of the configuration of this embodiment in which the outermost layer of the outer surface of the developing sleeve 28 is a chromium layer will be described later in Figure 14.

[0077] Using the toners of Comparative Examples 1 and 2 described above, and the toner of Comparative Example 3 described later, a test image was created in accordance with Figure 13(a) above, and the image was output. For the test image, the M0 light source setting of the Xrite eXact Standard was used for image density measurement, and the image density was set to 1.70±0.05 for the image patch with maximum density and 0.50±0.03 for the halftone image area. The image quality of the output image was evaluated according to the criteria in Table 1 for the position described in Figure 13(b). [Table 1]

[0078] For image output, the Bk station of the imagePRESS V1000 electrophotographic image forming machine manufactured by Canon Corporation was used. The environment in which the image forming machine was set up was a room temperature of 23°C and a humidity of 50%, and the paper used was GF-C081 A4 high-whiteness paper sold by Canon Marketing Japan. Table 2 shows the results of the image quality evaluation for Comparative Examples 1 to 3. [Table 2]

[0079] As shown in Table 2, a comparison of test images for sleeve ghosting revealed that no sleeve ghosting occurred when using the toner with amorphous polyester as the binder resin, which is Comparative Example 1. However, it was confirmed that sleeve ghosting occurred over 28 turns of the developing sleeve when using the toner with crystalline and amorphous polyester as the binder resin, which is Comparative Example 2. Considering the mechanism of sleeve ghosting and the viscosity of the toner described above, this indicates that the toner with both crystalline and amorphous polyester in the configuration of Comparative Example 2 is softer at room temperature compared to the toner with amorphous polyester in the configuration of Comparative Example 1, resulting in more toner adhering to the sleeve and making sleeve ghosting more likely to occur.

[0080] Furthermore, from the viewpoint of reducing adhesion between the developing sleeve 28 and the toner, a configuration using a developer that combined the toner of Comparative Example 1 with a carrier containing 20 or more parts silica fine particles as inorganic fine particles in the coating resin layer was used as Comparative Example 3, and the image quality was evaluated. The results are also shown in Table 2. As shown in Table 2, it was found that sleeve ghosting was more pronounced in the configuration of Comparative Example 3 than in the configuration of Comparative Example 2. This indicates that the presence of particles with a charging ability similar to that of the toner on the carrier surface locally reduces the carrier's ability to scrape off the toner, and weakens the ability to resolve image history due to the rotation of the developing sleeve 28.

[0081] [Structure of this embodiment] Based on the results of the examination in Table 2 above, in this embodiment, as shown in Figure 14, a chromium layer 54 is provided on the surface of the developing sleeve 28. That is, the outermost layer of the outer surface of the developing sleeve 28 is the chromium layer 54. The chromium layer is preferably 1 μm or more in thickness, and preferably 5 μm or less.

[0082] As described above, the factor that causes sleeve-adhered toner, which causes sleeve ghosting, to adhere to the developing sleeve 28 is the contrast potential difference, and the amount of sleeve-adhered toner is highly sensitive to the contact resistance near the surface of the developing sleeve 28. In order to reduce sleeve-adhered toner, it is desirable to reduce the contact resistance near the surface of the developing sleeve 28. Also, as mentioned above, stability is required for the developing sleeve 28, so it is desirable that it does not change over time. To stably reduce contact resistance, one can either add a layer of a low-reactivity metal such as gold or platinum, or create a thin layer of a static material such as chromium. The former is expensive and has a relatively soft surface, making it unsuitable for application to the surface of the developing sleeve 28. Therefore, in this embodiment, sleeve-adhered toner is reduced by coating the surface of the developing sleeve 28 with chromium to reduce the contact resistance near the surface of the developing sleeve 28.

[0083] As shown in Figure 14, the outermost layer of the outer surface of the developing sleeve 28 in this embodiment is a chromium layer 54. That is, in this embodiment, the developing sleeve 28 is made by forming a plurality of grooves 51 on the outer surface of an aluminum tube 56 using a die. Then, after appropriate pretreatment and masking, a metal underlayer 53, which is an adhesive layer, is applied to the outer surface of the base tube 56. The metal underlayer 53 is a layer of metal, and nickel or copper is used as the metal. That is, an electroless nickel plating layer (Examples 1a and 1b described later) or a copper plating layer (Example 1c described later) is formed on the outer surface of the tube 56 by electroless plating.

[0084] Subsequently, a chromium layer (metal surface layer) 54 is formed on the outer surface of the metal substrate layer 53. The chromium layer 54 is formed by electrolytic plating on the outer surface of the metal substrate layer 53. As a result of the inventors' studies, improvement in sleeve ghosting has been confirmed when the thickness of the chromium plating layer is 1 μm or more. In this embodiment, the thickness of the chromium plating layer is 1.3 μm (Example 1a) or 4.4 μm (Examples 1b and 1c).

[0085] In this embodiment, a non-destructive X-ray fluorescence analyzer was used to measure the thickness of the chromium layer 54. The measurement was performed by measuring the spectral intensity of CrKα rays using a micro-X-ray fluorescence analyzer (ORBIS PC, manufactured by AMETEK) under the following conditions. • X-ray irradiation area: 30 μmφ • Analysis atmosphere: Atmosphere • Tube voltage: 50kV ·Tube current: 250μA • Filter: None

[0086] Using samples where the thickness of the chromium layer 54 was known in advance by cross-sectional observation with a scanning electron microscope, a calibration curve was created by measuring the spectral intensity of CrKα rays, and the thickness of the chromium layer 54 was estimated from the spectral intensity of CrKα rays of the sample in the example.

[0087] In this embodiment, the thickness of the outermost chromium layer 54 on the outer surface of the protrusions 52 (non-grooved portions) formed between the grooves 51 of the developing sleeve 28 was measured at a total of six locations: three locations in the rotational axis direction of the developing sleeve 28 and three locations on the back side of these three locations. 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 grooves 51 are formed; the center point in the rotational axis direction of region 28S (developer-carrying and transporting section) where the grooves 51 are 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 grooves 51 are formed. In addition, the three locations in the rotational axis direction were measured twice each in the circumferential direction of the developing sleeve 28. Specifically, measurements are taken at the three locations mentioned above along the rotation axis of the developing sleeve 28, and at points rotated 180° in the circumferential direction of the developing sleeve 28, i.e., at points on the back side, for a total of six points. The average value of these measurements is then used as the thickness of the outermost chromium layer 54 on the outer surface of the protrusions 52 (non-grooved portions) formed between the grooves 51 of the developing sleeve 28.

[0088] If the average value calculated from these measured values ​​is 1 μm or more, it can be determined that the thickness of the outermost chromium layer 54 on the outer surface of the protrusion 52 (non-groove portion) formed between the grooves 51 of the developing sleeve 28 is 1 μm or more.

[0089] In this embodiment, a relatively inexpensive and simple plating process was used to create the chromium layer 54, but a vacuum deposition method or the like may also be used. Alternatively, the chromium plating (chromium layer 54) may be applied to the aluminum tube 56, and then multiple grooves 51 may be created on the surface of the developing sleeve 28. Details of the method for applying the chromium plating (chromium layer 54) to the aluminum tube 56 and then creating multiple grooves 51 on the surface of the developing sleeve 28 will be described later in the second embodiment.

[0090] For Examples 1a, 1b, and 1c, which used the developing sleeve 28 of the above embodiment, test images were output under the same conditions as the comparative examples described above. The results are shown in Table 3. In Example 1a, the thickness of the chromium layer 54 is 1.3 μm, and the metal underlayer 53 is an electroless nickel plating layer. In Example 1b, the thickness of the chromium layer 54 is 4.4 μm, and the metal underlayer 53 is an electroless nickel plating layer. In Example 1c, the thickness of the chromium layer 54 is 4.3 μm or less, and the metal underlayer 53 is an electrolytic copper plating layer. [Table 3]

[0091] As shown in Table 3, in the developing sleeve 28 having a chromium layer 54 on the outermost layer, as in this embodiment, sleeve ghosting is reduced compared to Comparative Example 2, regardless of the type of metal underlayment 53 which is the adhesive layer or the thickness of the chromium layer 54. Therefore, as in this embodiment, if the outermost layer of the outer surface of the developing sleeve 28 is a chromium layer 54 and the thickness of the chromium layer 54 is 1 μm or more, the occurrence of sleeve ghosting can be suppressed.

[0092] Table 4 also shows a comparison of the configurations of Comparative Example 3 and Example 1d described above. Example 1d is a configuration of Example 1b, but with a carrier containing 20 or more parts of silica nanoparticles as inorganic fine particles with the same polarity as the toner and a number-average particle size of 50 nm or more and 200 nm or less in the coating resin layer. Comparative Example 3 also uses a carrier containing 20 or more parts of silica nanoparticles as inorganic fine particles in the coating resin layer, as described above. [Table 4]

[0093] As shown in Table 4, when a carrier containing 20 or more parts silica fine particles as inorganic fine particles in the coating resin layer was used, sleeve ghosting was easily apparent in Comparative Example 3, but it can be seen that the occurrence of sleeve ghosting can be suppressed in Example 1d. Therefore, as in this embodiment, if the outermost layer of the outer surface of the developing sleeve 28 is a chromium layer 54, the occurrence of sleeve ghosting can be suppressed even when a carrier containing 20 or more parts silica fine particles as inorganic fine particles in the coating resin layer is used.

[0094] As described above, by making the outermost layer of the outer surface of the developing sleeve 28 a chromium layer 54, the adhesion of toner to the developing sleeve 28 can be suppressed, thereby suppressing the occurrence of sleeve ghosting. In addition, since chromium plating is used, an increase in manufacturing costs can be suppressed. From the viewpoint of suppressing the occurrence of sleeve ghosting, it is preferable that the thickness of the chromium layer provided on the outermost layer (outer surface) of the outer surface of the developing sleeve 28 be 1 μm or more. On the other hand, according to the inventors' studies, if the thickness of the chromium layer provided on the outer surface of the developing sleeve 28 is 5 μm, the effect of suppressing the occurrence of sleeve ghosting can be sufficiently achieved. From this point of view, from the viewpoint of suppressing manufacturing costs due to chromium plating, it is preferable that the thickness of the chromium layer provided on the outer surface of the developing sleeve 28 be 5 μm or less. Therefore, in this embodiment, the thickness of the chromium layer provided on the outer surface of the developing sleeve 28 is 1 μm or more and 5 μm.

[0095] Therefore, according to this embodiment, toner adhesion to the developing sleeve 28 can be suppressed at low cost. In particular, according to this embodiment, even when a low-melting-point toner using crystalline polyester as the toner binder resin is used, sleeve ghosting can be suppressed with a simple and inexpensive configuration.

[0096] <Second Embodiment> A second embodiment will be described with reference to Figure 15. In the configuration of the first embodiment described above, the chromium layer 54 was provided on both the grooves 51 (grooved portion) and the protrusions 52 (non-grooved portion) on the surface of the developing sleeve 28. In contrast, in the configuration of the second embodiment, the chromium layer 54 is provided only on the protrusions 52 (non-grooved portion) on the surface of the developing sleeve 28. The other configurations and operations of the second embodiment 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.

[0097] In this embodiment, since the groove 51 (groove portion) does not have a chromium layer 54, the chromium layer 54 does not affect the groove shape, and the developer is transported appropriately by the groove 51 (groove portion). In addition, in this embodiment, only the convex portion 52 (non-groove portion) is chromium plated, and since the convex portion 52 (non-groove portion) has fewer irregularities than the groove 51 (groove portion), it becomes easier to set the conditions during chromium plating.

[0098] On the other hand, if the portion that is chrome-plated is only the protruding portion 52 (non-grooved portion), the effect of reducing toner adhering to the sleeve is slightly smaller compared to the case where both the groove 51 (grooved portion) and the protruding portion 52 (non-grooved portion) are chrome-plated. However, the ratio of the area of ​​the groove 51 (grooved portion) to the area of ​​the protruding portion 52 (non-grooved portion) is about 10% to 40%, and the protruding portion 52 (non-grooved portion) occupies the majority of the outermost layer (outer surface) of the outer circumferential surface of the developing sleeve 28. Therefore, even if the portion that is chrome-plated is only the protruding portion 52 (non-grooved portion), it is still possible to sufficiently reduce toner adhering to the sleeve.

[0099] Furthermore, since the groove 51 (grooved portion) is further away from the photosensitive drum 1a than the protrusion 52 (non-grooved portion), the groove 51 (grooved portion) is less affected by potential changes due to toner adhering to the sleeve than the protrusion 52 (non-grooved portion). For these reasons, the effect of reducing sleeve ghosting can be ensured even with the configuration of this embodiment.

[0100] As shown in Figure 15, the surface of the developing sleeve 28 in the second embodiment has a chromium layer 54 on the outer surface of the protrusions 52 (non-grooved portions), but the outer surface of the grooves 51 (grooved portions) does not have a chromium layer 54.

[0101] In the second embodiment, the developing sleeve 28 is prepared by applying appropriate pretreatment and masking to an aluminum base tube 56, and then providing a metal underlayer 53, which is an adhesive layer, to the outer surface of the base tube 56. The metal underlayer 53 is a layer of metal, and nickel is used as the metal. That is, an electroless nickel plating layer is formed on the outer surface of the base tube 56 by electroless plating. Multiple grooves 51 are formed on the outer surface of the developing sleeve 28 using a die, according to the conditions described above, on the base tube 56 having this plating layer. At this time, the processability with the die was not easy when the thickness of the chromium plating layer (thickness of the chromium layer) was greater than 5 μm. Therefore, from the viewpoint of processability, it is preferable that the thickness of the chromium layer provided on the outer surface of the protrusions 52 (non-grooved parts) of the developing sleeve 28 is 5 μm or less.

[0102] On the other hand, from the viewpoint of suppressing the occurrence of sleeve ghosting, it is preferable that the thickness of the chromium layer provided on the outer surface of the protrusion 52 (non-groove portion) of the developing sleeve 28 be 1 μm or more. Therefore, in the second embodiment, it is preferable that the thickness of the chromium layer provided on the outer surface of the protrusion 52 (non-groove portion) of the developing sleeve 28 be 1 μm or more and 5 μm or less.

[0103] In Example 2, which uses the developing sleeve 28 of the second embodiment described above, test images were output under the same conditions as the comparative examples described above. The results are shown in Table 4. In Example 2, the thickness of the chromium layer 54 provided on the outer surface of the protrusion 52 (non-grooved portion) of the developing sleeve 28 is 4.2 μm. As can be seen from the results in Table 4, in Example 2, the occurrence of sleeve ghosting was suppressed, similar to Example 1d.

[0104] As described above, in the second embodiment, even if the chromium layer 54 is only present on the protrusions 52 (non-groove portions) as the outermost layer of the outer circumferential surface of the developing sleeve 28, toner adhesion to the developing sleeve 28 can be suppressed, and the occurrence of sleeve ghosting can be suppressed. Furthermore, in the second embodiment (Example 2), sleeve ghosting can be suppressed with a simple and inexpensive configuration, similar to the first embodiment (Example 1).

[0105] <Third Embodiment> A third embodiment will be described with reference to Figure 16. This embodiment has a low-phosphorus electrolytic layer below the chromium layer 54, compared to the configuration of the first embodiment described above. 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 components, and their description and illustration are omitted or simplified. The following description will focus on the differences from the first embodiment.

[0106] The cause of sleeve ghosting is the image history of the amount of toner attached to the sleeve. In the first embodiment, the total amount of toner attached to the sleeve was reduced using a chromium layer 54. In contrast, in this embodiment, the effect of eliminating the image history of the amount of toner attached to the sleeve is increased by giving the developing sleeve 28 a minute magnetic field.

[0107] As shown in Figure 16, the surface of the developing sleeve 28A in this embodiment has a chromium layer 54 as the outermost layer of the outer circumferential surface, and a metal intermediate layer 55, which is a layer of phosphorus-containing metal, between the aluminum tube 56, which is the base layer, and the chromium layer 54. That is, in this embodiment, the developing sleeve 28A is made by forming a plurality of grooves 51 on the outer circumferential surface of the aluminum tube 56 using a die. Then, after appropriate pretreatment and masking, a metal underlayer 53, which is an adhesive layer, is provided on the outer circumferential surface of the base tube 56. The metal underlayer 53 is a metal plating layer, and nickel or copper is used as the metal. That is, an electroless nickel plating layer is applied to the outer circumferential surface of the tube 56 by electroless plating, or a copper plating layer is formed by electrolytic plating.

[0108] Next, a metal intermediate layer 55 is formed on the outer surface of the metal substrate layer 53. The metal intermediate layer 55 is formed by electroplating an electrolytic nickel plating layer containing 1% or more (1% by weight or more) and 4% or less (4% by weight or less) of phosphorus on the outer surface of the metal substrate layer 53. Subsequently, a chromium layer (metal surface layer) 54 is formed on the outer surface of the metal intermediate layer 55. The chromium layer 54 is formed by electroplating a chromium plating layer on the outer surface of the metal substrate layer 53. In this embodiment, the thickness of the chromium plating layer is 4.2 μm. In the first embodiment, the processing method for the chromium layer 54 was not specified, but in this embodiment, since it is necessary to have an electrolytic nickel layer on the metal intermediate layer 55, plating is a preferred processing method.

[0109] Test images were output under the same conditions as described above for Comparative Example 3 and Example 1d, as well as for Example 3 using the developing sleeve 28A of this embodiment, as described in the first embodiment above. The results are shown in Table 5. In Example 3, the thickness of the chromium layer 54 is 4.2 μm, the metal underlayer 53 is an electroless nickel plating layer, and the metal intermediate layer 55 is an electrolytic nickel plating layer. Comparative Example 3 and Example 1d do not have a metal intermediate layer 55. As described above, Comparative Example 3, Example 1d, and Example 3 use a carrier containing 20 or more parts of silica fine particles as inorganic fine particles with a number average particle size of 50 nm or more and 200 nm or less in the coating resin layer. [Table 5]

[0110] As shown in Table 5, when a carrier containing 20 parts or more of silica fine particles as inorganic fine particles in the coating resin layer was used, sleeve ghosting was easily apparent in Comparative Example 3, but it can be seen that the occurrence of sleeve ghosting can be suppressed in Example 1d. Furthermore, it can be seen that the occurrence of sleeve ghosting can be suppressed even more in Example 3 than in Example 1d.

[0111] Therefore, as in this embodiment, by having a chromium layer 54 as the outermost layer of the outer surface of the developing sleeve 28, and providing a metal intermediate layer 55 which is a layer of phosphorus-containing metal below the chromium layer 54, the occurrence of sleeve ghosting can be sufficiently suppressed even when using a carrier containing 20 or more parts silica fine particles as inorganic fine particles in the coating resin layer. In this embodiment, although the surface structure of the developing sleeve is more complex compared to the first embodiment, developing sleeve ghosting can be suppressed more effectively. Therefore, in this embodiment as well, the adhesion of toner to the developing sleeve 28A can be suppressed at low cost. In particular, according to this embodiment, even when using a low-melting-point toner with crystalline polyester as the toner binder resin, and even when using a carrier containing 20 or more parts silica fine particles as inorganic fine particles in the coating resin layer, it is possible to suppress sleeve ghosting with a simple and inexpensive configuration.

[0112] <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.

[0113] Furthermore, in the embodiments described above, drum-shaped organic photoreceptors, specifically photosensitive drums 1a to 1d, were used as image carriers. However, inorganic photoreceptors such as amorphous silicon photoreceptors can also be used. It is also possible to use belt-shaped photoreceptors. The charging method, transfer method, cleaning method, and fixing method are not limited to those described above.

[0114] Furthermore, while the first, second, and third embodiments described above describe the application of the present disclosure to a developing apparatus 4a in which the developing chamber 23 and agitation chamber 24 are arranged vertically, the developing apparatus is not limited to this. 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. [Explanation of Symbols]

[0115] 4a, 4b, 4c, 4d...developing device 22. Developing container 28, 28A... Developing sleeve (developer carrier) 28m... Magnetic roller (magnet) 28S... Area (Developer carrying and transport section) 51, 51a, 51b...Groove (groove) 52...Convex portion (non-grooved portion) 54. Chromium layer

Claims

1. A rotatable sleeve, A developer carrying and transport unit for carrying and transporting a developer containing toner and carrier to a developing position, the unit having a grooved portion where grooves are formed and a non-grooved portion where grooves are not formed. Equipped with, If 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, then D > R and W > 2R are satisfied. The non-groove portion is provided with a chromium layer on the outer surface of the sleeve. The thickness of the chromium layer is 1 μm or more and 5 μm or less. A sleeve characterized by the following features.

2. The non-groove portion comprises a metal underlayer, which is a layer of metal, between the base layer of the sleeve and the chromium layer. The sleeve according to feature 1.

3. The aforementioned metal underlayer is a nickel plating layer. The sleeve according to feature 2.

4. The aforementioned metal underlayer is a copper plating layer. The sleeve according to feature 2.

5. The non-groove portion comprises a metal intermediate layer, which is a layer of metal containing phosphorus, between the base layer and the chromium layer of the sleeve, and a metal underlayer, which is a layer of metal, between the base layer and the metal intermediate layer. The sleeve according to feature 1.

6. The aforementioned metal intermediate layer is a nickel plating layer containing phosphorus. The aforementioned metal underlayer is a nickel plating layer. The sleeve according to feature 5.

7. A rotatable sleeve, A developer carrying and transport unit for carrying and transporting a developer containing toner and carrier to a developing position, the unit having a grooved portion where grooves are formed and a non-grooved portion where grooves are not formed. Equipped with, If 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, then D > R and W > 2R are satisfied. Each of the grooved portion and the non-grooved portion is provided with a chromium layer on the outer surface of the sleeve. A sleeve characterized by the following features.

8. The thickness of the chromium layer is 1 μm or more and 5 μm or less. The sleeve according to feature 7.

9. Each of the grooved and non-grooved portions includes a metal underlayer, which is a layer of metal, between the base layer of the sleeve and the chromium layer. The sleeve according to feature 7.

10. The aforementioned metal underlayer is a nickel plating layer. The sleeve according to feature 9.

11. The aforementioned metal underlayer is a copper plating layer. The sleeve according to feature 9.

12. Each of the grooved and non-grooved portions comprises a metal intermediate layer, which is a layer of phosphorus-containing metal, between the base layer and the chromium layer of the sleeve, and a metal underlayer, which is a layer of metal, between the base layer and the metal intermediate layer. The sleeve according to feature 7.

13. The aforementioned metal intermediate layer is a nickel plating layer containing phosphorus. The aforementioned metal underlayer is a nickel plating layer. The sleeve according to feature 12.

14. A developer carrier, Rotatable sleeve and A magnet placed inside the sleeve, Equipped with, The aforementioned sleeve is A developer carrying and transport unit for carrying and transporting a developer containing toner and carrier to a developing position, the unit having a grooved portion where grooves are formed and a non-grooved portion where grooves are not formed. Equipped with, If 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, then D > R and W > 2R are satisfied. The non-groove portion is provided with a chromium layer on the outer surface of the sleeve. The thickness of the chromium layer is 1 μm or more and 5 μm or less. A developer carrier characterized by the following features.

15. A developer carrier, Rotatable sleeve and A magnet placed inside the sleeve, Equipped with, The aforementioned sleeve is A developer carrying and transport unit for carrying and transporting a developer containing toner and carrier to a developing position, the unit having a grooved portion where grooves are formed and a non-grooved portion where grooves are not formed. Equipped with, If 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, then D > R and W > 2R are satisfied. Each of the grooved portion and the non-grooved portion is provided with a chromium layer on the outer surface of the sleeve. A developer carrier characterized by the following features.

16. The thickness of the chromium layer is 1 μm or more and 5 μm or less. The developer carrier according to feature 15.

17. A developing device, A developing container containing a developer including toner and carrier, A developer carrier having a rotatable sleeve and a magnet disposed inside the sleeve, Equipped with, The aforementioned sleeve is A developer carrying and transporting unit for carrying and transporting the developer to a developing position, comprising 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. Equipped with, If 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, then D > R and W > 2R are satisfied. The non-groove portion is provided with a chromium layer on the outer surface of the sleeve. The thickness of the chromium layer is 1 μm or more and 5 μm or less. A developing apparatus characterized by the following features.

18. A developing device, A developing container containing a developer including toner and carrier, A developer carrier having a rotatable sleeve and a magnet disposed inside the sleeve, Equipped with, The aforementioned sleeve is A developer carrying and transporting unit for carrying and transporting the developer to a developing position, comprising 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. Equipped with, If 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, then D > R and W > 2R are satisfied. Each of the grooved portion and the non-grooved portion is provided with a chromium layer on the outer surface of the sleeve. A developing apparatus characterized by the following features.

19. The thickness of the chromium layer is 1 μm or more and 5 μm or less. The developing apparatus according to feature 18.

Images