Developing roller

Abstract

To provide a developing roller which improves durability of toner against deterioration.SOLUTION: A developing roller 1 conveys toner to a photoreceptor. The developing roller 1 has a hardness of 0.1 N / mm2 or less as measured when a surface of the developing roller 1 is indented to a depth of 30 μm by an indenter in compliance with ISO14577. A surface roughness of the developing roller 1 is such that the maximum peak height Sp as stipulated by ISO25178 is at least twice an average particle diameter of a toner, and a core void volume ratio as stipulated by ISO25178 is in a range of 59% to 61%, inclusive.SELECTED DRAWING: Figure 2

Description

[Technical Field]

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

[0002] Developing rollers for conveying toner to a photoreceptor are used in, for example, electrophotographic image forming devices. In a conventional technique, the Shore A hardness of the roller body is set to 60 or less, and the surface roughness Rz of the outer circumferential surface is set to 2.5 μm or more and 4.5 μm or less in order to suppress deterioration of image quality due to toner degradation (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-78654 Summary of the Invention [Problem to be solved by the invention]

[0004] However, the above-mentioned conventional techniques still have room for improvement in terms of suppressing the deterioration of the toner and thereby improving the durability of the toner against deterioration.

[0005] SUMMARY OF THE INVENTION An object of the present invention is to provide a developing roller that improves the durability of toner against deterioration. [Means for solving the problem]

[0006] The developing roller according to the present invention is a developing roller for conveying toner to a photosensitive member, and the developing roller has a resistance of 0.1 N / mm when the surface of the developing roller is pressed to a depth of 30 μm by an indenter conforming to ISO 14577. 2The developing roller has a hardness of 0.01 to 0.15, and the surface roughness of the developing roller is such that the maximum peak height Sp, as specified in ISO 25178, is at least twice the average particle size of the toner, and the core void volume ratio, as specified in ISO 25178, is in the range of 59% to 61%. The developing roller according to the present invention improves the durability of the toner against deterioration.

[0007] The developing roller according to the present invention preferably includes a surface layer that forms the surface of the developing roller, and an adjacent layer that is adjacent to and covered by the surface layer, and the adjacent layer preferably has a higher hardness than the surface layer, thereby further improving the durability of the toner against deterioration.

[0008] In the developing roller according to the present invention, the hardness of the adjacent layer is an Asker C hardness measured using an Asker C hardness tester in accordance with JIS K 7312, and the Asker C hardness is preferably in the range of 40° to 80°, inclusive. In this case, the durability of the toner against toner deterioration is further improved. [Effects of the Invention]

[0009] According to the present invention, it is possible to provide a developing roller that improves the durability of the toner against deterioration of the toner. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a diagram schematically illustrating an image forming apparatus in which a developing roller according to an embodiment of the present invention can be used; [Figure 2] FIG. 2 is a diagram schematically illustrating an example of a method for measuring the surface hardness of a developing roller. [Figure 3] 2 is a cross-sectional view schematically illustrating a developing roller taken along a plane including a roller axis. FIG. [Figure 4]This is a graph showing the relationship between a predetermined transfer amount (g) and transfer time (s) for unused new toner, deteriorated toner that was subjected to a durability test using a printer that employs the developing roller of this embodiment, and deteriorated toner that was subjected to a durability test using a printer that employs an existing developing roller as a comparison example. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, a developing roller 1 according to one embodiment of the present invention will be described with reference to the drawings. The developing roller 1 according to one embodiment of the present invention is a non-magnetic developing roller used for non-magnetic toner T that does not contain metal powder.

[0012] 1, reference numeral 10 denotes an image forming apparatus that can use a developing roller 1 according to one embodiment of the present invention. In addition to the developing roller 1, the image forming apparatus 10 includes a toner storage unit 11 that stores toner T, a toner supply roller 12 that supplies toner T to the developing roller 1, a layering blade 13 that arranges the toner T supplied to the developing roller 1 into a uniform thin film, a photosensitive drum (photoconductor) 14 that receives the toner T from the developing roller 1 and can hold an electrostatic latent image, a charging roller 15 that charges the surface of the photosensitive drum 14, an exposure device 16 that exposes image information to the charged surface of the photosensitive drum 14, a transfer unit 17 that transfers the toner image to a recording medium M such as paper, and a cleaning unit 18 that includes a cleaning blade 18a that removes toner T remaining on the surface of the photosensitive drum 14 after transfer.

[0013] In the image forming apparatus 10, the developing roller 1 is disposed between the toner supply roller 12 and the photosensitive drum 14. The image forming apparatus 10 rotates the toner supply roller 12, the developing roller 1, and the photosensitive drum 14 in the directions indicated by the arrows in the figure. As a result, toner T from the toner storage unit 11 is first supplied to the surface of the developing roller 1 by the toner supply roller 12. The toner supplied to the developing roller 1 is then formed into a uniform thin layer by the layering blade 13. The thin layer of toner T adheres from the developing roller 1 to the latent image on the photosensitive drum 14 as the developing roller 1 rotates with the photosensitive drum 14. The latent image is then visualized by the toner T. The surface of the photosensitive drum 14 is charged by the charging roller 15, and then image information is exposed to the charged surface by the exposure device 16. The toner image is transferred to the recording medium M at the transfer unit 17. A desired image can be printed on the recording medium M. In the cleaning unit 18, after the toner image is transferred (printed), the toner T remaining on the surface of the photosensitive drum 14 is removed by a cleaning blade 18a.

[0014] The developing roller 1 of this embodiment can be used in an image forming apparatus (for example, a laser printer) as shown in Fig. 1. Fig. 2 shows an example of a method for measuring the hardness of the developing roller 1.

[0015] 1, the developing roller 1 is a developing roller for conveying toner T to the photosensitive drum 14. As shown in FIG. 2, when the surface F1 of the developing roller 1 is pressed to a depth of 30 μm by an indenter 20 conforming to ISO 14577, the developing roller 1 has a pressure of 0.1 N / mm 2 The developing roller 1 has a surface roughness in which the maximum peak height Sp, as specified by ISO 25178, is at least twice the average particle size Dap of the toner T, and the core void volume ratio, as specified by ISO 25178, is in the range of 59% to 61%.

[0016] [Hardness of developing roller 1 (surface hardness)] In this embodiment, the indenter 20 is a Vickers indenter. In this embodiment, the surface hardness of the developing roller 1 can be measured using, for example, a Fischer hardness tester. That is, in this embodiment, the surface hardness of the developing roller 1 can be defined in terms of the so-called Fischer hardness.

[0017] [Surface roughness of developing roller 1] The maximum peak height Sp is determined based on the average particle diameter Dap of the toner T. A specific value of the average particle diameter Dap of the toner T is, for example, 5 to 30 μm. In this embodiment, the average particle diameter Dap of unused toner T is 6 μm.

[0018] The core void volume ratio can be defined by the following formula (1). Core void volume ratio (%)=Vvc / (Vvc+Vmc)×100...(1) Vvc: Core void volume specified by ISO25178 Vmc: Core material volume as specified in ISO25178

[0019] Incidentally, inorganic external additives (for example, silica and titanium) are added to the surface of the toner T. The external additives are used to control the fluidity of the toner T by, for example, suppressing aggregation of the toner T particles, and also to control the chargeability for adhesion to the photosensitive drum 14. Even if the toner T is supplied to the photosensitive drum 14, the toner T that does not adhere to the photosensitive drum 14 is returned to the toner storage unit 11 as is and is reused.

[0020] However, as described above, the toner Tr that returns as is (hereinafter also referred to as "returned toner Tr") is pressurized between the developing roller 1 and components adjacent to the developing roller 1 (e.g., the toner supply roller 12, the layering blade 13, and the photosensitive drum 14). In other words, stress is applied to the external additives added to the returned toner Tr. This stress may cause the external additives to detach from the surface of the returned toner Tr or to be embedded in the returned toner Tr. This detachment or embedding of the external additives deteriorates the toner T. A specific example of deterioration of the toner T is that the toner T becomes more likely to aggregate with each other. In this example, as printing is repeated, the amount of toner transported by the developing roller 1 increases, causing the image density to become denser over time. Another specific example of deterioration of the toner T is that the charge amount changes. In this example, the charge property of the toner T changes with each printing cycle, resulting in defects in the image.

[0021] In contrast, in this embodiment, the surface hardness of the developing roller 1 is 0.1 N / mm in terms of so-called Fischer hardness. 2 At the same time, the surface roughness of the developing roller 1 is specified so that the maximum peak height Sp is at least twice the average particle size Dap of the toner T and the core void volume ratio is in the range of 59% to 61%. The developing roller 1 can reduce stress applied to the toner T. As a result, the developing roller 1 can suppress the detachment or burial of external additives added to the toner T, which can cause an increase in image density and a decrease in charging performance.

[0022] Therefore, the developing roller 1 according to this embodiment reduces stress that occurs between the toner supply roller 12, the layering blade 13, or the photosensitive drum 14 and the developing roller 1, thereby improving the durability of the toner T against deterioration. Furthermore, existing image forming apparatuses generally have a mechanism (machine) for suppressing deterioration of the toner T. In contrast, if the developing roller 1 according to this embodiment is used as one of the constituent elements of the image forming apparatus, such a mechanism (machine) can be omitted.

[0023] Next, Fig. 3 shows a schematic cross section of a specific example of the developing roller 1, the cross section including the roller axis O. Referring to Fig. 3, the developing roller 1 includes a surface layer 2 that forms the surface of the developing roller 1, and an adjacent layer 3 that is adjacent to the surface layer 2 and is covered by the surface layer 2. The adjacent layer 3 preferably has a higher hardness than the surface layer 2. In this case, the durability of the toner T against deterioration of the toner T is further improved.

[0024] In particular, in the developing roller 1, the hardness of the adjacent layer 3 is an Asker C hardness measured using an Asker C hardness tester in accordance with JIS K 7312, and the Asker C hardness is preferably in the range of 40° to 80°. In this case, the durability of the toner T against deterioration of the toner T is further improved.

[0025] The hardness of the adjacent layer 3 is the hardness (surface hardness) of the surface of the adjacent layer 3 when the surface layer 2 is removed. The surface hardness of the adjacent layer 3 is measured, for example, by directly pressing the surface of the adjacent layer 3. However, the surface hardness of the adjacent layer 3 can also be measured by pressing the surface layer 2 without removing the surface layer 2.

[0026] Here, the developing roller 1 in Fig. 3 will be described. Referring to Fig. 3, in this embodiment, the adjacent layer 3 is located radially outward of the roller shaft 4 and covers the roller shaft 4 over the entire circumference of the roller axis line O. The surface layer 2 is located radially outward of the adjacent layer 3 and covers the adjacent layer 3 over the entire circumference of the roller axis line O.

[0027] The surface hardness of the surface layer 2 is defined to the above surface hardness, and the surface roughness of the surface layer 2 is also defined to the above surface roughness. The surface layer 2 is formed of, for example, polyurethane resin.

[0028] The adjacent layer 3 can be formed from a known rubber or resin, or a foam having air bubbles dispersed therein. Examples of materials for forming the adjacent layer 3 include polyurethane resin (including acrylate polymers having multiple urethane skeletons), and rubber compositions using silicone rubber, butadiene rubber, isoprene rubber, chloroprene rubber, styrene-butadiene rubber, ethylene-propylene rubber, polynorbornene rubber, styrene-butadiene-styrene rubber, epichlorohydrin rubber, etc. as a base rubber, with polyurethane resin being particularly preferred. The expansion ratio of the foam is not particularly limited.

[0029] The roller shaft 4 can be made of a metal material, and the metal material is not particularly limited, but examples thereof include iron, stainless steel, aluminum, and alloys containing these. The roller shaft 4 can also be made of a highly rigid resin material containing a conductive agent. Furthermore, the roller shaft 4 can be a solid shaft as shown in FIG. 3, or a hollow shaft, for example.

[0030] In the developing roller 1, the layers formed on the roller shaft 4 are not limited to the surface layer 2 and the adjacent layer 3. For example, a single layer or multiple layers may be formed between the adjacent layer 3 and the roller shaft 4. Specifically, multiple layers may be provided between the adjacent layer 3 and the roller shaft 4 for the purpose of achieving roller properties such as adhesion and electrical resistance adjustment. [Example]

[0031] The following table shows the toner degradation index of Examples 1-3 of the present invention and the toner degradation index of Comparative Examples 1-6, as measured by using a vibration transfer type flow performance device.

[0032] [Table 1]

[0033] Here, the fluidity of unused toner and the fluidity of used, deteriorated toner are measured, and these values ​​are used as the toner deterioration index.

[0034] [How to make degraded toner] A toner cartridge (Toner Cartridge 046H, manufactured by Canon Inc.) containing unused toner T with an average particle size Dap of 6 μm was installed in a commercially available printer (Laser Beam Printer LBP651C, manufactured by Canon Inc.). The printer was operated until the toner T's durability was reached (e.g., 8,000 prints: durability of 8,000 prints), and the toner remaining in the cartridge at the end was determined as degraded toner. Specifically, the toner cartridge is equipped with a developing roller 1, a toner supply roller 12, and a layering blade 13. The toner cartridge also includes a toner storage section 11 in which unused toner T is pre-stored. When the printer is operating, the toner T in the toner cartridge is placed on the surface of the developing roller 1, but is not used in printing and returns to the toner cartridge. This returned toner Tr is determined as degraded toner.

[0035] [Method for measuring toner deterioration index] The fluidity of unused toner and the fluidity of deteriorated toner are measured using a vibration transfer type fluidity measuring device, and the numerical value is taken as the toner deterioration index (mg / sec). Regarding the developing roller 1, the genuine developing roller attached to the above toner cartridge is removed from the toner cartridge and replaced with the developing roller 1 of this Example 1-4, and a printing durability test is carried out to confirm the performance.

[0036] Specifically, the toner deterioration index (mg / sec) is measured according to the following procedure.

[0037] (1) A certain amount of toner T is loaded into a vibration-transport type fluidity measuring device. Here, the vibration-transport type fluidity measuring device has a spiral tapered portion, and a toner outlet formed by a notch is provided at the top of the tapered portion. Toner T is loaded into the tapered portion. (2) By operating the vibration transfer type fluidity measuring device, the toner T on the tapered portion is discharged to the outside from the toner outlet. Here, by applying vibration to the toner T on the tapered portion, the toner T on the tapered portion rises up, and the toner T is finally discharged to the outside from the toner outlet. (3) The toner T discharged from the toner outlet is collected, the amount of collected toner is measured, and the measured value is used as the toner deterioration index. Here, the toner T discharged from the toner outlet is collected in a container above a weighing machine installed below the toner outlet, and the measured amount of collected toner per unit time is used as the toner deterioration index (mg / sec).

[0038] Referring to Table 1, the surface hardness of Examples 1 to 4 was measured using a Fischer hardness tester and was 0.09 N / mm 2 and 0.1N / mm 2The results are as follows. In Example 1-4, in terms of surface roughness, the maximum peak height Sp is in the range of 9 to 24 μm, which is more than twice the average toner particle size Dap (=6 μm). Furthermore, in terms of surface roughness, in Example 1-4, the core void volume ratio is in the range of 59 to 61%. As is clear from the results in Table 1, in Example 1-4, there was no image defect (blurring) due to deteriorated toner after the durability test (durability printing) using unused toner, and the toner deterioration index was kept to 12.7 to 15.7 (mg / sec).

[0039] On the other hand, in Comparative Example 1-6, at least one of the surface hardness and surface roughness values ​​is outside the range of the developing roller according to the present invention. In Comparative Example 1-6, image defects (blurring) occur due to unused toner that has deteriorated after a durability test (durability printing), and the toner deterioration index is in a higher range of 17.9 to 24.1 (mg / sec) compared to Example 1-4.

[0040] To measure blurring, after a durability test of 8,000 sheets, the image is printed at a solid density (100%) and a determination is made as to whether or not blurring is present.

[0041] As is clear from the results in Table 1, the developing roller of the present invention reduces the stress that occurs between the toner supply roller, layering blade, or photosensitive drum and the developing roller, thereby improving the durability of the toner T against toner deterioration.

[0042] 4 is a graph showing the relationship between a predetermined transport amount (g) and transport time (s) for unused new toner, toner subjected to a durability test using a printer incorporating the developing roller of Example 3, and toner subjected to a durability test using a printer incorporating an existing developing roller (Comparative Example 7). As is clear from this graph, if the point td (s) at which the transport amount (g) of the toner in the durability test using the existing developing roller becomes constant is used as the standard for toner degradation, the toner in the durability test using the developing roller of Example 3 continues to experience a slow increase in transport time (s) at a substantially constant rate. This means that when the existing developing roller is used, the returned toner Tr rapidly deteriorates, causing the deteriorated toner Tr to aggregate rapidly, resulting in a rapid increase in image density. However, when the developing roller of Example 3 is used, the returned toner Tr deteriorates more slowly, resulting in a delayed increase in image density.

[0043] The foregoing describes exemplary embodiments of the present invention, and various modifications can be made without departing from the scope of the claims. [Explanation of symbols]

[0044] 1: developing roller, 2: surface layer, 3: adjacent layer (base layer), 4: roller shaft, 10: image forming device, 11: toner storage section, 12: toner supply roller, 13: layering blade, 14: photosensitive drum (photoconductor), 15: charging roller, 16: exposure device, 17: transfer section, 18: cleaning section, 18a: cleaning blade, 20: indenter, M: recording medium, T: toner, Tr: returned toner

Claims

1. A developing roller for conveying toner to a photosensitive member, the developing roller has a hardness of 0.1 N / mm2 or less when the surface of the developing roller is pressed to a depth of 30 μm with an indenter conforming to ISO 14577; the surface roughness of the developing roller is such that the maximum peak height Sp as specified in ISO 25178 is at least twice the average particle size of the toner, and the core portion void volume ratio as specified by the following formula (1) is in the range of 60.0% or more and 61% or less, using the core portion void volume Vvc as specified in ISO 25178 and the core portion material volume Vmc as specified in ISO 25178; Core void volume ratio (%)=Vvc / (Vvc+Vmc)×100...(1) The developing roller further includes a surface layer that forms a surface of the developing roller, and an adjacent layer that is adjacent to the surface layer and covered by the surface layer, The adjacent layer has a higher hardness than the surface layer.

2. 2. The developing roller according to claim 1, wherein the hardness of the adjacent layer is an Asker C hardness measured using an Asker C hardness tester in accordance with JIS K 7312, and the Asker C hardness is in the range of 40° or more and 80° or less.

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