Developing device

Abstract

To provide a developing device capable of preventing aggregation toner from occurring.SOLUTION: A developing device 44 includes a cylindrical developing roller 22, a regulation member 30, a magnetic member 60 and a synthetic resin member 70. The regulation member 30 includes a first opposing surface 32 facing an outer circumferential surface 26 of the developing roller 22. The synthetic resin member 70 is arranged on a side surface of the magnetic member 60 on an upstream side in a rotating direction of the developing roller 22. The first opposing surface 32 controls thickness of a toner image formed, by magnetic toner, on the circumferential surface 26 of the developing roller 22. The synthetic resin member 70 includes a second opposing surface 71 facing the outer circumferential surface 26 of the developing roller 22. The second opposing surface 71 is tilted at 40° or more and 60° or less with respect to the first opposing surface 32 to be increasingly distant from the outer circumferential surface 26 of the developing roller 22 toward the upstream side in the rotating direction of the developing roller 22. A solubility parameter of a material of the synthetic resin member 70 is 23 (J / cm3)1 / 2 or more. The magnetic toner includes toner and resin fine particles.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a developing device. [Background technology]

[0002] The developing device described in Patent Document 1 has an elastic member disposed in the upstream space where toner tends to accumulate. The elastic member is disposed so as to occupy the upstream space while being in close contact with the upstream surface of the regulating blade as viewed from the direction of rotation of the developing roller. In this way, the upstream space is occupied by the elastic member, which prevents toner from accumulating.

[0003] The elastic member also has a transport amount control surface that faces the circumferential surface of the developing roller. The transport amount control surface is designed to gradually move away from the developing roller as it moves upstream in the direction of rotation of the developing roller. Therefore, toner that has adhered to the circumferential surface of the developing roller from the developer storage section is gradually pushed back into the developer storage section by the transport amount control surface as it moves through the upstream space due to the rotation of the developing roller. This prevents a large amount of toner from accumulating upstream of the control blade in the direction of rotation of the developing roller. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007-147915 Summary of the Invention [Problem to be solved by the invention]

[0005] However, in the developing device described in Patent Document 1, toner is attracted to the transport amount control surface of the elastic member. The attracted toner is difficult to separate from the elastic member and aggregates around the transport amount control surface to form aggregated toner. The aggregated toner causes clogging and results in image contamination.

[0006] The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide a developing device that can suppress the generation of toner aggregation. [Means for solving the problem]

[0007] The developing device of the present invention comprises a cylindrical developing roller, a regulating member, a magnetic body, and a synthetic resin member. The developing roller contains a magnetic field generating member and rotates. The regulating member has a first opposing surface that faces the outer peripheral surface of the developing roller. The magnetic body is disposed on a side surface of the regulating member that is upstream in the direction of rotation of the developing roller. The synthetic resin member is disposed on a side surface of the magnetic body that is upstream in the direction of rotation of the developing roller. The first opposing surface regulates the thickness of a toner image formed by magnetic toner on the outer peripheral surface of the developing roller. The synthetic resin member has a second opposing surface that faces the outer peripheral surface of the developing roller. The second opposing surface is inclined at an angle of 40° to 60° with respect to the first opposing surface, and moves away from the outer peripheral surface of the developing roller toward the upstream side in the direction of rotation of the developing roller. The solubility parameter of the material of the synthetic resin member is 23 (J / cm 3 ) 1 / 2 The magnetic toner contains toner and resin fine particles. [Effects of the Invention]

[0008] According to the developing device of the present invention, the generation of toner aggregation can be suppressed. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a diagram illustrating a configuration of an image forming apparatus according to an embodiment of the present invention. [Figure 2] FIG. 2 is an enlarged view of the developing device according to the embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In the drawings, the same or corresponding parts are designated by the same reference numerals, and description thereof will not be repeated. In this embodiment, the X-axis, Y-axis, and Z-axis are mutually orthogonal, the X-axis and Y-axis are parallel to a horizontal plane, and the Z-axis is parallel to a vertical line.

[0011] First, the configuration of an image forming apparatus 1 according to the first embodiment will be described with reference to Fig. 1. Fig. 1 is a diagram showing the configuration of the image forming apparatus 1. The image forming apparatus 1 is, for example, a monochrome printer.

[0012] As shown in FIG. 1, the image forming apparatus 1 includes an image forming unit 4, a fixing unit 5, a paper discharge tray 12, a conveying path 6, a manual feed tray 3, a paper feed cassette 7, and an operation unit (not shown).

[0013] The paper feed cassette 7 stores paper sheets P. The paper sheets P may be, for example, plain paper, copy paper, recycled paper, thin paper, thick paper, glossy paper, or OHP (Overhead Projector) paper. The paper sheets P are discharged onto the paper discharge tray 12.

[0014] The conveying path 6 conveys the paper P from the paper feed cassette 7 to the paper discharge tray 12 via the image forming unit 4 and the fixing unit 5 .

[0015] The manual feed tray 3 is provided on the right side of the image forming apparatus 1 in FIG.

[0016] The operation unit has a plurality of menu setting keys and the like for setting various menus.

[0017] Image forming unit 4 forms a toner image on paper (sheet) P based on image data from an external device (for example, a personal computer). Specifically, image forming unit 4 includes photosensitive drum (image carrier) 10, charger 42, exposure unit 43, developing device 44, toner cartridge 45, transfer roller (transfer member) 46, and toner remover 47. When viewed from the rotation direction of photosensitive drum 10 (clockwise in FIG. 1), charger 42, developing device 44, transfer roller 46, and toner remover 47 are arranged in this order along the circumferential direction of photosensitive drum 10. Exposure unit 43 is arranged above charger 42.

[0018] The photosensitive drum 10 is, for example, a drum having a photosensitive body in which an amorphous silicon layer, which is a positively chargeable photoconductor, is vapor-deposited on the surface of an aluminum cylinder. The thickness of the amorphous silicon layer and the linear velocity of the photosensitive drum 10 are set appropriately.

[0019] The charger 42 charges the photosensitive drum 10. Specifically, the charger 42 includes, for example, a charging roller 50. The charging roller 50 is composed of a core metal and an epichlorohydrin rubber layer covering the core metal. The charging roller 50 is of a contact charging type in which the circumferential surface of the charging roller 50 comes into approximate point contact with the drum surface of the photosensitive drum 10, and applies a predetermined reference charging voltage (reference charging bias) in which a DC voltage and an AC voltage are superimposed to the drum surface, thereby uniformly charging the surface potential of the drum surface.

[0020] The exposure unit 43 irradiates the charged photosensitive drum 10 with laser light L to form an electrostatic latent image. Specifically, the exposure unit 43 has a polygon mirror (not shown) that directs the laser light L based on image data input from an external PC (personal computer) or the like to the drum surface of the photosensitive drum 10. The polygon mirror, while rotated by a predetermined drive source, scans the laser light L over the drum surface of the photosensitive drum 10 to form an electrostatic latent image on the drum surface.

[0021] The developing device 44 electrostatically attaches toner to the electrostatic latent image formed on the photosensitive drum 10, thereby visualizing the toner image. The toner cartridge 45 supplies the toner filled therein to the developing device 44.

[0022] Transfer roller 46 transfers the developed toner image onto paper P. More specifically, transfer roller 46 is pressed against the drum surface of photosensitive drum 10 in transport path 6, and a nip N is formed between transfer roller 46 and the drum surface. A voltage of opposite polarity to the surface potential of the drum surface is applied to transfer roller 46, so that the toner image on the drum surface is transferred onto paper P as it passes through nip N. Paper P that has passed through nip N is transported to fixing unit 5 via transport path 6.

[0023] The toner remover 47 removes and collects the toner remaining on the surface of the photosensitive drum 10 .

[0024] The fixing unit 5 heats the toner image formed on the paper P to fix it onto the paper P. After the toner image on the paper P is heated and fixed onto the paper P in the fixing unit 5, the paper P is transported to the paper output tray 12 through the transport path 6.

[0025] The configuration of the developing device 44 will be described with reference to Figures 1 and 2. Figure 2 is an enlarged view of the developing device 44. As shown in Figure 2, the developing device 44 uses a magnetic one-component developer (magnetic toner) to develop the electrostatic latent image on the photosensitive drum 10.

[0026] The magnetic one-component developer (magnetic toner) contains toner, magnetic powder, and resin particles. The resin particles include, for example, particles of styrene acrylic resin. Examples of styrene acrylic resin include a copolymer of styrene, methyl methacrylate, and divinylbenzene, and a copolymer of styrene, methyl methacrylate, and ethylene glycol methacrylate diester. The average primary particle diameter of the particles is, for example, 30 nm or more and 150 nm or less, and preferably 35 nm or more and 125 nm or less. The solubility parameter of the resin particles is, for example, 18.4 (J / cm3 ) 1 / 2 More than 19.6(J / cm 3 ) 1 / 2 The following is preferable: The magnetic one-component developer (magnetic toner) may contain silica particles, a binder resin, a charge control agent, and a release agent.

[0027] The developing device 44 includes a developing container (housing) 21, a developer storage section 11, a developing roller 22, a regulating member 30, and a magnet 60. The developing container 21 defines the internal space of the developing device 44. The magnet 60 is an example of a "magnetic body."

[0028] The developer storage section 11 is formed on the bottom wall of the developing container 21. Specifically, the developer storage section 11 is composed of two adjacent developer storage chambers 14, 15 extending in the longitudinal direction of the developing device 44 (the direction perpendicular to the paper surface of FIG. 1). The developer storage chambers 14, 15 are separated from each other in the longitudinal direction by a partition plate 17 made of a metal such as aluminum, but are connected to each other at both corners in the longitudinal direction.

[0029] Rotatably mounted in each of the developer storage chambers 14 and 15 are screw feeders 18 and 19, which convey the magnetic toner while stirring it as they rotate. The screw feeders 18 and 19 are set to convey the magnetic toner in opposite directions, so that the magnetic toner is conveyed while being stirred between the developer storage chambers 14 and 15. The developer storage section 11 receives toner from a toner cartridge 45 through a supply port (not shown).

[0030] The developing roller 22 is disposed in the developing opening 23 of the developing container 21. The developing roller 22 is made of a non-magnetic material such as aluminum, and is a roller member that includes a cylindrical developing sleeve 24 that extends in the longitudinal direction of the developing device 44 (i.e., the axial direction of the photosensitive drum 10), and a rotation shaft (not shown) that rotates the developing sleeve 24 counterclockwise in FIG.

[0031] The developing sleeve 24 is disposed opposite the photosensitive drum 10, with a gap of 0.2 mm to 0.4 mm formed between the outer peripheral surface 26 of the developing sleeve 24 and the surface of the photosensitive drum 10. The developing sleeve 24 contains a magnetic field generating member. The magnetic field generating member is configured so that the pole facing the regulating member 30 is an S pole (S2), and the following poles are disposed along the circumferential direction of the developing sleeve 24 in this order downstream of the S pole (S2): an N pole (N1), an S pole (S1), an N pole (N2), an S pole (S3), and an N pole (N3).

[0032] The regulating member 30 is disposed above the developing roller 22 in FIG. 2 and is a plate-shaped member made of a magnetic material extending along the axial direction of the developing sleeve 24. The regulating member 30 has a tip portion 31 extending toward the outer peripheral surface 26 of the developing sleeve 24. The tip portion 31 has a first opposing surface 32 facing the outer peripheral surface 26. A gap G of a predetermined dimension is set between the first opposing surface 32 and the outer peripheral surface 26 of the developing sleeve 24. The regulating member 30 regulates the layer thickness of the magnetic toner on the outer peripheral surface 26 of the developing sleeve 24 by means of the first opposing surface 32.

[0033] The magnet 60 is disposed on the side surface of the regulating member 30 on the upstream side in the rotation direction of the developing sleeve 24. The magnet 60 is also affixed to the side surface of the regulating member 30 with an adhesive so that the pole facing the developing sleeve 24 is the south pole and so that the end of the magnet 60 on the developing sleeve 24 side does not protrude beyond the end of the regulating member 30 on the developing sleeve 24 side.

[0034] The magnetic toner on the outer peripheral surface 26 of the developing sleeve 24 is carried toward the drum surface of the photosensitive drum 10 as the developing sleeve 24 rotates, and adheres to the electrostatic latent image on the drum surface of the photosensitive drum 10 due to the potential difference between the developing bias applied to the developing sleeve 24 and the drum bias applied to the photosensitive drum 10. This forms a toner image on the drum surface.

[0035] The developing device 44 further includes a synthetic resin member 70. The synthetic resin member 70 is disposed on the upstream side of the magnet 60 in the rotation direction of the developing sleeve 24. The synthetic resin member 70 extends along the axial direction of the developing sleeve 24. Specifically, the synthetic resin member 70 has a second opposing surface 71 that faces the outer peripheral surface 26 of the developing sleeve 24.

[0036] The second opposing surface 71 is located upstream of the first opposing surface 32 of the regulating member 30 when viewed from the rotation direction of the developing sleeve 24, and is configured to gradually move away from the developing sleeve 24 as it moves upstream in the rotation direction. In other words, the second opposing surface 71 is configured so that the space S between the second opposing surface 71 and the outer peripheral surface 26 of the developing sleeve 24 gradually increases as it moves from the first opposing surface 32 to the upstream side in the rotation direction of the developing sleeve 24. A portion of the transported magnetic toner is gradually pushed back by the second opposing surface 71 in the direction opposite to the rotation direction of the developing sleeve 24. In this way, the second opposing surface 71 regulates the amount of magnetic toner transported to the first opposing surface 32. This prevents a large amount of magnetic toner from accumulating in the gap G upstream in the rotation direction.

[0037] The second opposing surface 71 is inclined at an angle of 40° to 60° relative to the first opposing surface 32. If the angle is less than 40°, the magnetic toner receives too much stress from the regulating member 30, reducing the charge on the magnetic toner and resulting in a decrease in image density on the sheet. This decrease in image density is particularly significant in high-temperature environments. On the other hand, if the angle is greater than 60°, the magnetic toner accumulates around the regulating member 30, causing aggregation, weakening the regulating force on the magnetic toner in the aggregation region, resulting in an increase in the amount of magnetic toner transported and an insufficient charge, resulting in toner streaks (vertical stripes) on the sheet.

[0038] The solubility parameter of the material of the synthetic resin member 70 is 23 (J / cm 3 ) 1 / 2The synthetic resin member 70 may be made of, for example, ABS resin, polyamide resin, etc. Furthermore, the difference between the solubility parameter of the synthetic resin member 70 material and the solubility parameter of the resin particles is 5 (J / cm 3 ) 1 / 2 It is preferable that this is equal to or greater than this.

[0039] As described above with reference to FIGS. 1 and 2, the second opposing surface 71 of the synthetic resin member 70 has an inclination of 40° to 60° with respect to the first opposing surface 32, and the solubility parameter of the material of the synthetic resin member 70 is 23 (J / cm 3 ) 1 / 2 As described above, since the magnetic toner contains resin fine particles, it is possible to prevent the magnetic toner from being adsorbed to the second opposing surface 71 of the synthetic resin member 70. As a result, it is possible to prevent the generation of toner aggregation. [Example]

[0040] The present invention will be described in more detail below using examples, but the present invention is not limited to the scope of the examples.

[0041] [Preparation of silica particles] First, 30 g of dimethylpolysiloxane and 15 g of 3-aminopropyltrimethoxysilane (both manufactured by Shin-Etsu Chemical Co., Ltd.) were dissolved in 200 g of toluene and diluted 10-fold. Next, while stirring 200 g of fumed silica particles ("AERSIL® 130" manufactured by Nippon Aerosil Co., Ltd.), the diluted solution was gradually added dropwise, and the mixture was ultrasonically irradiated and stirred for 30 minutes to obtain a mixture. This mixture was heated in a thermostatic chamber at 150°C, after which the toluene was removed using a rotary evaporator. The resulting solid was dried in a vacuum dryer at a set temperature of 50°C until no weight loss was observed. This was then subjected to a heat treatment in an electric furnace under a nitrogen stream at 200°C for 3 hours. The resulting powder was crushed using a jet mill and collected using a bag filter to obtain silica particles.

[0042] [Preparation of resin microparticles] (Preparation of Resin Particles A) 200 g of ion-exchanged water and 3 g of sodium lauryl sulfate were placed in a 500 ml flask equipped with a dropping funnel, a stirrer, a nitrogen gas inlet tube, a thermometer, and a reflux condenser. While heating to 80°C under a nitrogen gas atmosphere, 1 g of ammonium persulfate was added, and a monomer mixture consisting of 42 g of styrene, 40 g of methyl methacrylate, and 26 g of divinylbenzene was then added dropwise over 1 hour, followed by stirring for another 1 hour. The resulting reaction solution was cooled to room temperature and filtered through a 300-mesh sieve to obtain an emulsion. The resulting emulsion was dried to obtain a mean particle size of 80 nm and a solubility parameter (SP value) of 18.4 (J / cm). 3 ) 1 / 2 Thus, resin fine particles A were obtained.

[0043] (Preparation of resin particles B) The same procedure as for resin fine particles A was repeated except that 1 g of sodium lauryl sulfate was added instead of 3 g, and the average particle diameter was 125 nm and the solubility parameter was 18.4 (J / cm 3 ) 1 / 2 Thus, resin fine particles B were obtained.

[0044] (Preparation of resin particles C) The same procedure as for resin fine particles A was repeated except that 10 g of sodium lauryl sulfate was added instead of 3 g, and the average particle diameter was 35 nm and the solubility parameter was 18.4 (J / cm 3 ) 1 / 2 Thus, resin fine particles C were obtained.

[0045] (Preparation of Resin Particles D) The average particle diameter was 80 nm and the solubility parameter was 19.6 (J / cm) in the same manner as Resin Fine Particle A, except that styrene was changed from 42 g to 31 g, methyl methacrylate from 40 g to 30 g, and divinylbenzene was changed to 26 g with ethylene glycol dimethacrylate at 79 g. 3 ) 1 / 2 Resin fine particles D were obtained.

[0046] Example 1 The magnetic toner of Example 1 was produced as follows: 1100 g of polyester binder resin (manufactured by Kao Corporation, Mw: 6500, acid value: 8.2 mgKOH / g, Tm: 96.3°C, Tg: 54.4°C), 1090 g of binder resin (manufactured by Kao Corporation, acid value: 11.8 mgKOH / g, Tm: 118.5°C, Tg: 59.6°C, gel content: 36%), 1450 g of magnetic powder X (2 x 105 Ωcm, Toda Kogyo Co., Ltd. "MRO-15A"), 200 g of charge control agent (Fujikura Kasei Co., Ltd. "FCA-482PLV"), and 160 g of release agent (Kato Yoko Co., Ltd. "Carnauba Wax Characteristic No. 1") were mixed in a mixer (Nippon Coke Company, Ltd. "FM-20B") at 2000 rpm for 5 minutes.

[0047] The resulting mixture was melt-kneaded using a twin-screw extruder (Toshiba Machine Co., Ltd., "TEM-26SS") at a cylinder temperature of 120°C, a shaft rotation speed of 100 rpm, and a mass of 75 g / min. The resulting kneaded mixture was cooled and then coarsely pulverized using a grinder (Hosokawa Micron Corporation, "Rotoplex 16 / 8"). The coarsely pulverized mixture was then finely pulverized using a Powder Turbo Mill TA (Freund-Turbo). The mixture was then fed into a jet mill (Hosokawa Micron Corporation, "MJT-1") for fine pulverization and classification, yielding toner base particles Tn1.

[0048] 12 g of the silica particles obtained by the above-mentioned method and 1 g of resin fine particles A were added as external additives to 1 kg of the obtained toner base particles, and mixed and adhered for 5 minutes at 3200 rpm using a mixer ("FM-10C" manufactured by Nippon Coke & Engineering Co., Ltd.). Then, the mixture was sieved through a 100 mesh (opening 150 μm) sieve to obtain the magnetic toner according to Example 1.

[0049] In addition, the developing device contains a solvent with a solubility parameter of 23.7 (J / cm 3 ) 1 / 2 A synthetic resin member (mount blade) was manufactured from ABS resin and was disposed so that the second opposing surface was inclined at 50° with respect to the first opposing surface. As a result, the developing device according to Example 1 was obtained.

[0050] <Example 2> Example 2 is the same as Example 1 except that resin particles B are used in place of resin particles A in the toner.

[0051] Example 3 Example 3 is the same as Example 1 except that resin particles C are used in place of resin particles A in the toner.

[0052] Example 4 Example 4 is the same as Example 1 except that resin particles D are used in place of resin particles A in the toner.

[0053] <Example 5> In Example 5, the synthetic resin members of the developing device were made of ABS resin, and the solubility parameter was 27.8 (J / cm 3 ) 1 / 2 The procedure is the same as in Example 1, except that the synthetic resin member was manufactured from a polyamide resin.

[0054] <Comparative Example 1> Comparative Example 1 is the same as Example 1 except that no synthetic resin members were used in the developing device.

[0055] <Comparative Example 2> In Comparative Example 2, the synthetic resin members of the developing device were made of ABS resin, and the solubility parameter was 18.4 (J / cm 3 ) 1 / 2 The same as in Example 1, except that the synthetic resin member was manufactured from high-density polystyrene resin.

[0056] <Comparative Example 3> Comparative Example 3 is the same as Example 1 except that the developing device is arranged so that the second opposing surface is inclined at 35° with respect to the first opposing surface.

[0057] <Comparative Example 4> Comparative Example 4 is the same as Example 1 except that the developing device is arranged so that the second opposing surface is inclined at 65° with respect to the first opposing surface.

[0058] <Comparative Example 5> Comparative Example 5 is the same as Example 1 except that the fine resin particles A were not used in the toner.

[0059] Table 1 shows the configurations of the toner and developing device according to Examples 1 to 5 and Comparative Examples 1 to 5.

[0060] [Table 1]

[0061] <Evaluation of actual printing durability> Using the toners and developing devices according to Examples 1 to 5 and Comparative Examples 1 to 5, a monochrome printer ECOSYS (registered trademark) P2040dw manufactured by Kyocera Document Solutions, Inc. was used to output 100,000 and 5,000 images of an original image with a print ratio of 2% at a 23°C, 65% humidity environment and at a 28°C, 80% humidity environment, respectively, with two-page intermittent output. The image density was evaluated initially and after outputting 100,000 images at a 23°C, 65% humidity environment and after outputting 5,000 images at a 28°C, 80% humidity environment, as well as the presence or absence of vertical streaks when outputting 100,000 images at a 23°C, 65% humidity environment. ◯: No vertical streaks (white streaks and black streaks) were observed during output of 100,000 sheets. ×: Vertical streaks (white streaks and black streaks) were observed during output of 100,000 sheets. The results are shown in Table 2.

[0062] [Table 2]

[0063] From the above, in Comparative Examples 1 to 3 and 5, the magnetic toner accumulated around the regulating member, causing aggregation, and the regulating force of the magnetic toner in the aggregation area weakened, leading to an increase in the amount of magnetic toner transported and an insufficient amount of charge, resulting in the appearance of toner streaks (vertical streaks) on the sheet. Also, in Comparative Example 4, the stress on the magnetic toner from the regulating member became too great, causing the amount of charge on the magnetic toner to decrease, resulting in a decrease in image density on the sheet. The decrease in image density was particularly significant in high-temperature environments.

[0064] On the other hand, in Examples 1 to 5, no toner streaks (vertical streaks) were generated on the sheet, and the decrease in image density was suppressed even in a high temperature environment. [Industrial Applicability]

[0065] The developing device according to the present invention can be used in an image forming apparatus. [Explanation of symbols]

[0066] 22 Developing roller 26 Outer surface 30 Regulatory components 32 First opposing surface 44 Developing device 60 Magnet (magnetic material) 70 Synthetic resin components 71 Second opposing surface

Claims

1. A cylindrical developing roller that includes a magnetic field generating member and rotates; a regulating member having a first opposing surface facing the outer circumferential surface of the developing roller; a magnetic body disposed on a side surface of the regulating member on an upstream side in a rotation direction of the developing roller; a synthetic resin member disposed on a side surface of the magnetic body on the upstream side in the rotation direction of the developing roller; Equipped with the first opposing surface regulates a thickness of a toner image formed by magnetic toner on the outer circumferential surface of the developing roller, the synthetic resin member has a second opposing surface that faces the outer circumferential surface of the developing roller, the second opposing surface is inclined at an angle of 40° to 60° with respect to the first opposing surface, and moves away from the outer circumferential surface of the developing roller toward an upstream side in a rotation direction of the developing roller, The solubility parameter of the synthetic resin material is 23 (J / cm 3 ) 1 / 2 That's all. The magnetic toner contains a toner and fine resin particles.

2. The resin fine particles include particles of a styrene-acrylic resin, 2. The developing device according to claim 1, wherein the particles have an average primary particle diameter of 30 nm or more and 150 nm or less.

3. The difference between the solubility parameter of the resin fine particles and the solubility parameter of the material of the synthetic resin member is 5 (J / cm 3 ) 1 / 2 The developing device according to claim 1 .

4. 2. The developing device according to claim 1, wherein the synthetic resin member is made of ABS resin or polyamide resin.

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