Developing roller

Abstract

The developing roller of the present invention is a developing roller used in an image forming apparatus using an electrophotographic method, and includes a metal core material, a rubber elastic layer disposed around the core material, and a surface layer disposed around the elastic layer. The aspect ratio Str of the surface property of the surface layer is 0.55 or more.

Description

Technical Field

[0001] The present invention relates to a developing roller in an image forming apparatus using an electrophotographic method. Background Art

[0002] In an image forming apparatus using an electrophotographic method, a developing device that supplies a developer, i.e., toner, to a photosensitive drum is provided. The developing device includes a toner container and a developing roller. The toner attached to the outer peripheral surface of the developing roller is supplied to the photosensitive drum as the developing roller rotates. An electrostatic latent image is formed on the photosensitive drum, and toner particles are transferred from the developing roller to the electrostatic latent image, thereby generating a toner image (Patent Document 1).

[0003] Prior Art Documents

[0004] Patent Documents

[0005] Patent Document 1: Japanese Patent Application Laid-Open No. 2002-372855 Summary of the Invention

[0006] The quality of an image printed by an image forming apparatus depends on the state of transporting toner by a developing roller. It is desirable that the unevenness of the printed image is less.

[0007] Therefore, the present invention provides a developing roller capable of reducing image unevenness.

[0008] A developing roller according to one aspect of the present invention is used in an image forming apparatus using an electrophotographic method, and includes: a metal core; a rubber elastic layer disposed around the core; and a surface layer disposed around the elastic layer. The aspect ratio Str of the surface property of the surface layer is 0.55 or more.

[0009] In this aspect, the roughness of the surface of the surface layer hardly depends on the direction, and thus fine unevenness periodically generated in the image due to fine roughness changes in the circumferential direction of the surface layer can be reduced. Brief Description of the Drawings

[0010] Figure 1 It is a view showing a usage state of a developing roller according to an embodiment of the present invention.

[0011] Figure 2 It is a cross-sectional view of the developing roller according to the embodiment.

[0012] Figure 3 It is a schematic view showing one process of manufacturing the developing roller according to the embodiment.

[0013] Figure 4 It is an enlarged cross-sectional view of the developing roller according to the embodiment.

[0014] Figure 5 This is a table showing the measurement results of the surface layer indexes of multiple samples of the developing roller and the results of the image quality tests using these samples. Detailed Embodiments

[0015] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. The scale of the drawings is not necessarily accurate, and sometimes some features are exaggerated or omitted.

[0016] As Figure 1 shown, the electrophotographic image forming apparatus has a photosensitive drum 10 and a developing device 11. The photosensitive drum 10 rotates in the direction of the arrow. The developing device 11 supplies toner particles 12 as a developer to the photosensitive drum 10. On the surface of the photosensitive drum 10, an electrostatic latent image is formed by a latent image forming device (not shown in the figure), and the toner particles 12 are transferred from the developing device 11 to the electrostatic latent image, whereby a toner image based on the toner particles 12 is generated on the outer peripheral surface of the photosensitive drum 10.

[0017] The developing device 11 includes: a toner container 13 that stores a toner particle aggregate 14; an elastic roller 15 that is entirely disposed in the toner container 13; a developing roller 20 that is partially disposed in the toner container 13; and a doctor blade 16 (limiting blade) that is supported by the toner container 13. The elastic roller 15 is pressed against the developing roller 20, and the developing roller 20 is pressed against the photosensitive drum 10. The elastic roller 15 and the developing roller 20 rotate in the directions shown by the arrows, and a substantially constant amount of toner particles in the toner container 13 adhere to the developing roller 20. Accordingly, a thin layer of toner particles is formed on the outer peripheral surface of the developing roller 20. As the developing roller 20 rotates, the toner particles adhering to the developing roller 20 are transported toward the photosensitive drum 10. The doctor blade 16 disposed at the toner particle outlet of the toner container 13 is pressed against the outer peripheral surface of the developing roller 20 and limits the amount of toner particles adhering to the developing roller 20 and transported from the toner container 13. In this way, the developing roller 20 contacts each of the photosensitive drum 10, the elastic roller 15, and the doctor blade 16 with a certain degree of force.

[0018] Although not shown in the figure, a component for stirring the toner particle aggregate 14 in the toner container 13, a screw for transporting the toner particles in the toner container 13, etc. may also be provided in the developing device 11.

[0019] As Figure 2 shown, the developing roller 20 includes a cylindrical core material 21 made of metal, an elastic layer 22 made of rubber and having a uniform thickness disposed around the core material 21, and a surface layer 23 made of rubber and having a uniform thickness disposed around the elastic layer 22. The diameter of the core material 21 is several millimeters, the thickness of the elastic layer 22 is 1 - 3 mm, and the thickness of the surface layer 23 is several micrometers to several tens of micrometers.

[0020] Both the elastic layer 22 and the surface layer 23 are formed of rubber. In an embodiment, both the elastic layer 22 and the surface layer 23 are formed of silicone rubber. However, the elastic layer 22 is provided to ensure the elasticity of the developing roller 20, and the surface layer 23 is provided to improve the abrasion resistance of the surface of the developing roller 20. Therefore, the composition of the material of the surface layer 23 is different from the composition of the material of the elastic layer 22.

[0021] The applicant manufactured a plurality of samples of the developing roller 20 as follows.

[0022] First, an iron shaft with an outer diameter of 10 mm was prepared as the core material 21.

[0023] The elastic layer 22 was formed by covering the core material 21 with conductive silicone rubber. The volume resistivity of the conductive silicone rubber was 10 -6 Ω·cm, and the hardness of the conductive silicone rubber measured using a hardness tester (Type A according to "JIS K 6253" and "ISO 7619") was 40.

[0024] Next, as Figure 3 shown, the elastic layer 22 was ground with a grinding wheel 30 of a cylindrical grinding disk so that its outer diameter became 16 mm. Therefore, the thickness of the elastic layer 22 was 3 mm. The main purpose of the grinding was to make the outer diameter of the developing roller 20 uniform in the axial direction, and to improve the roundness, so that the contact width between the developing roller 20 and the photosensitive drum 10 and the contact width between the developing roller 20 and the blade 16 were uniform in the axial direction of the developing roller 20.

[0025] On the other hand, a coating liquid as the material of the surface layer 23 was prepared. First, a reactive silicone oil, an isocyanate compound, its isocyanurate-modified product, and a diluting solvent capable of dissolving these respective components were mixed in a reaction vessel. Then, the mixture was left to carry out a prepolymerization reaction of the components.

[0026] Next, an isocyanate compound, its isocyanurate-modified product, and silicone rubber particles as adhesives were mixed in the solution (solid component concentration 50%) obtained in the prepolymerization reaction to complete the coating liquid (solid component concentration 34%) as the material of the surface layer 23.

[0027] Then, the coating liquid was vigorously stirred with a bead mill to disperse the solid components, and then the coating liquid was stirred with a stirrer for 1 hour.

[0028] On the other hand, a primer was coated around the elastic layer 22 with a sprayer. The primer was "KBP-40" manufactured by Shin-Etsu Chemical Co., Ltd. (Tokyo, Japan).

[0029] Next, the coating liquid was applied around the elastic layer 22 using a sprayer and dried by heat treatment at 160°C for 40 minutes, thereby forming the surface layer 23.

[0030] Figure 4 FIG. 4 is an enlarged cross-sectional view of the developing roller 20 according to the embodiment. The surface layer 23 is fixed to the elastic layer 22 via a primer layer 24 as an adhesive layer. Silicone rubber particles 25 are dispersed inside the surface layer 23.

[0031] As Figure 5 shown, the applicant adjusted the surface roughness of the elastic layer 22 (ten point height of irregularities according to JIS B 0601:1994) R z , the thickness of the surface layer 23, and the material composition of the surface layer 23 to manufacture a plurality of samples with different properties of the surface layer 23. Figure 5 The ten point average roughness R z of the elastic layer in the circumferential direction is a value measured along the circumferential direction of the elastic layer 22 after the above grinding and reflects the unevenness of the grinding.

[0032] As Figure 4 can be seen, if the roughness of the elastic layer 22 is large, the roughness of the outer surface layer 23 is also large. However, if the thickness of the surface layer 23 is large, the influence of the roughness of the elastic layer 22 on the roughness of the surface layer 23 can be mitigated.

[0033] The applicant measured the ten point average roughness R z in the circumferential direction of the elastic layer 22, the aspect ratio Str of the surface properties of the surface layer 23, the ten point average roughness R z in the axial direction of the surface layer 23, the mean length of a roughness curve element RSm of the surface in the axial direction of the surface layer 23, the R z in the circumferential direction of the surface layer 23, and the RSm in the circumferential direction of the surface layer 23 for a plurality of samples of the developing roller 20. The measurement results are shown in Figure 5 .

[0034] The ten point average roughness R z of the elastic layer 22 and the surface layer 23 was measured using a contact surface roughness measuring machine. The measuring instrument was Surf coder "SE500" manufactured by Kosaka Laboratory Ltd. (Tokyo, Japan). The radius of the stylus of the SE500 was 2 μm, the front angle of the stylus was 60 degrees, and the contact force was 0.75 mN. The cut-off value λc for the measurement was 0.8 mm, the measurement length (reference length) of the roughness was 4 mm, and the feed speed of the stylus was 0.5 mm / sec. The measurement site was the central part in the length direction of the sample.

[0035] To measure Str and RSm, the surface of the surface layer 23 at the central part in the length direction of each sample was photographed using a non-contact laser microscope. The laser microscope used was "VK-X250" manufactured by Keyence Corporation (Tokyo, Japan). The magnification was 400 times, and the magnification of the objective lens was 20 times.

[0036] Next, using the multi-document analysis application "VK-H1XM" Version 1.3.0.116 manufactured by Keyence Corporation, quadratic surface correction was performed on the geometric data obtained by photographing. Quadratic surface correction is a process of removing the data component equivalent to the cylindrical surface data in the cylindrical surface of the surface from the geometric data obtained by photographing. In other words, it is a process of transforming the geometric data of the cylindrical surface obtained by photographing into geometric data for a virtual plane.

[0037] Furthermore, using the same application, based on the data obtained by quadratic surface correction, the aspect ratio Str of the surface texture was calculated in the photographed field of view.

[0038] In addition, using the same application, the RSm values in the axial and circumferential directions were calculated in the photographed field of view. The cut-off value λs was set to "none", and the cut-off value λc was set to "none".

[0039] The aspect ratio (texture aspect ratio of the surface) Str of the surface texture is defined by ISO 25178 and is a value from 0 to 1. Str approaching 0 means that the surface roughness has directionality (for example, having multiple grooves extending parallel to the surface). Str approaching 1 means that the surface roughness is independent of direction.

[0040] On the other hand, the ten-point mean roughness R z represents the height of the protrusions on the surface, and the average length RSm of the roughness curve elements represents the spacing of the protrusions on the surface.

[0041] The applicant actually installed these samples in a printer, printed an image on paper, and conducted an experiment to investigate the image quality. The printer was "HL-L8360CDW" manufactured by Brother Industries, Ltd. (Aichi, Japan), and a halftone image with a uniform density was printed on the entire surface of the paper.

[0042] The determination of the image quality was carried out visually as follows. When the periodic fine density unevenness is large, the image quality is judged to be poor. When the periodic fine density unevenness is small, the image quality is judged to be good. When the periodic fine density unevenness is very small, the image quality is judged to be very good.

[0043] Periodic minute density unevenness is considered to be caused by minute circumferential roughness variations of the surface layer 23. When the roughness variations in the circumferential direction of the surface layer 23 (i.e., the developing roller 20) are large, the amount of toner particles supplied from the developing roller 20 to the photosensitive drum 10 becomes uneven in the circumferential direction of the photosensitive drum 10, resulting in periodic density unevenness on the paper.

[0044] Figure 5 Indicates the determination result of the image quality.

[0045] According to Figure 5 the results, when the aspect ratio Str is 0.55 or more, the image quality is good. In addition, the closer the aspect ratio Str is to 1, the better the image quality. That is, it is preferable that the directionality of the roughness of the surface of the surface layer 23 is small. Generally, in order to reduce the directionality of the roughness of the surface of the surface layer 23, it is desirable that the directionality of the roughness of the surface of the elastic layer 22 below the surface layer 23 is small and the thickness of the surface layer 23 is large.

[0046] Particular attention is paid to samples 8 to 13 with very good image quality. The thickness of the surface layer 23 is preferably 20 μm or more and 40 μm or less.

[0047] In addition, according to samples 8 to 13, not only is the aspect ratio Str 0.77 or more, but it is also preferable that the ten-point average roughness R z in the axial direction of the surface layer 23 is 7.6 μm to 10.4 μm, and the ten-point average roughness R z in the circumferential direction of the surface layer 23 is 7.5 μm to 9.7 μm. In addition, it is preferable that the average length RSm of the roughness curve elements of the surface in the axial direction of the surface layer 23 is 88 μm to 118 μm, and the average length RSm of the roughness curve elements of the surface in the circumferential direction of the surface layer 23 is 74 μm to 103 μm.

[0048] As described above, the present invention has been illustrated with reference to the preferred embodiments of the present invention. However, those skilled in the art should understand that changes in form and specific content can be made without departing from the scope of the invention described in the claims. Such changes, alterations, and modifications should be included within the scope of the present invention.

[0049] Symbol description:

[0050] 20 Developing roller

[0051] 21 Core material

[0052] 22 Elastic layer

[0053] 23 Surface layer

[0054] 24 Primer layer

[0055] 25 Silicone rubber particles

Claims

1. A developing roller used in an image forming apparatus employing an electrophotographic method, characterized in that, Comprising: A core material made of metal; An elastic layer made of rubber, which is disposed around the core material; And A surface layer, which is disposed around the elastic layer; Wherein, the aspect ratio Str of the surface property of the surface layer is 0.55 or more.

2. The developing roller according to claim 1, wherein The thickness of the surface layer is 20 μm or more and 40 μm or less.

3. The developing roller according to claim 2, wherein The ten-point average roughness R of the elastic layer in the circumferential direction z is 3 μm or more and 6 μm or less.

4. The developing roller according to any one of claims 1 to 3, wherein The aspect ratio Str of the surface property of the surface layer is 0.77 or more, The ten-point average roughness R in the axial direction of the surface layer z is 7.6 μm or more and 10.4 μm or less, The ten-point average roughness R in the circumferential direction of the surface layer z is 7.5 μm or more and 9.7 μm or less.

5. The developing roller according to claim 4, wherein The average length RSm of the roughness curve elements of the surface in the axial direction of the surface layer is 88 μm or more and 118 μm or less, The average length RSm of the roughness curve elements of the surface in the circumferential direction of the surface layer is 74 μm or more and 103 μm or less.

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