Cylindrical developer carrier and production method thereof

Abstract

A cylindrical developer carrier capable of fully charging a toner compound on a developing sleeve via frictional force even after being used repeatedly. The cylindrical developer carrier includes an electrically conductive substrate having an evenly roughened surface, and an alumite layer formed on the roughened surface, wherein the alumite layer has a uniform distribution of minute holes that reach the substrate surface. A method for manufacturing the cylindrical developer carrier includes roughening the electrically conductive substrate surface by blasting it with spherical fine particles, forming the alumite layer on the roughened surface by an anodizing method, and blasting the surface of the alumite-layer with amorphous fine particles that a diameter greater than that of the spherical fine particles.

Description

FIELD OF THE INVENTION

The invention relates to a cylindrical developer carrier loaded on an electrophotographic apparatus such as an electrophotographic printer, copying machine, or fax machine.

DESCRIPTION OF BACKGROUND ARTS

Conventionally, any electrophotographic apparatus, such as a laser printer, LED printer, or copying machine using normal paper, executes the formation of images through application of a so-called Carlson process. The Carlson process is a method for forming an image via the output of a toner image transcribed and fixed on copy paper or the like every cycle of an electrophotographic process executed via components for performing an electrification (i.e., charging), an exposure, a toner development, an image transcription, and an electrical discharge. Such components respectively are disposed on the circumferential surface of a cylindrical photoconductor provided with a photosensitive layer.

In the course of executing the above processes, when a static latent image formed on the surface of the photoconductor via the above electrifying and exposing steps is converted into a positive image in the following toner developing step, toner compound stored in a developer unit is held and carried to an area close to the surface of the photoconductor through the application of a static electrical force via a cylindrical developer carrier, i.e., via a developing sleeve, before the static latent image present on the surface of the photoconductor is eventually developed into a positive image. In order to secure a satisfactory image via the above developing method, it is extremely important that the toner compound on the developing sleeve be held and carried as a leveled layer free from the generation of deflection.

Likewise, when an excessively thick or thin toner layer is formed on the developing sleeve, in terms of developing density, a satisfactory image cannot be obtained. To prevent this, aside from the need to separately provide the system with a specific member for regulating toner thickness on the developing sleeve, in uniformly distributing toner compound over the entire developing sleeve, surface conditions of the developing sleeve are also quite important. A fully smoothed surface is not always the optimal choice. It is, rather, conventionally considered to be more advantageous to provide the surface of the developing sleeve with projections and recesses each having appropriate magnitude so as to enable optimum friction force to be generated between the developing sleeve and the toner compound. On the other hand, depending on the hardness of the developing sleeve, these projections and recesses are subject to wear after repeated use. This causes the quality of images to be gradually degraded, thus leading to a problem. To cope with this problem, an improvement in wear-resistance properties has been sought by those concerned. In cases in which a developing sleeve is made of an aluminum alloy, its Vickers hardness is rated to be as low as approximately 70 Hv. Thus, it is known that wear-resistance properties can be improved through the formation of an alumite surface layer generated by anodization with a Vickers hardness as high as approximately 200 to 400 Hv after completing formation of projections and recesses on its surface (refer to the Laid-Open Japanese Patent Publication No. HEISEI 5-46008/1993).

On the other hand, in cases in which an alumite layer has been formed on the surface of the developing sleeve, due to the insulation characteristics of the alumite layer, its surface resistance rises. However, in the case of a high surface resistance value, the charge borne by the toner compound in the area corresponding to the spot for forming an image applied during the preceding developing process is apt to remain as it is without fully shifting onto the surface of the photoconductor from the developing sleeve. As a result, the amount of charge in a specific area of the developing sleeve corresponding to the above-described spot becomes greater than the amount of charge in those areas without the formation of images. As a result, when another image is formed in the ensuing developing step, in the above specific area of the developing sleeve corresponding to the spot at which the last image was formed, developing-agent is further drawn toward another specific area of the developing sleeve containing a higher charge. Thereby, the toner compound becomes more difficult to shift onto the surface of the photoconductor. This in turn leads to another problem in that a difference in depth is apt to be generated on the developed image of the photoconductor through the generation of a specific pattern corresponding to the image generated during the last developing process. In other words, a so-called “ghost image” is apt to be generated. In summary, the above symptom of a defect may be defined as the difference in the developing capability in correspondence with the toner development history (hereinafter also referred to as “memory”).

In consideration of the technical problems described thus far, the invention aims at providing a novel cylindrical developer carrier and a method for manufacturing it, wherein the cylindrical developer carrier is capable of fully charging a toner compound on a developing sleeve via friction force even after being used repeatedly. The invention also aims to provide a cylindrical developer carrier wherein toner compound in the form of a leveled (even) layer can be properly held and carried, and the cylindrical developer carrier does not generate even the slightest difference in developing capability in correspondence with the toner development history.

SUMMARY OF THE INVENTION

According to the invention, the above-specified object has been achieved through the provision of a novel cylindrical developer carrier incorporating an alumite layer coated on a uniformly roughened surface of an electrically conductive substrate. The alumite layer uniformly incorporates minute holes reaching the above-described conductive substrate.

According to another aspect of the invention, the cylindrical developer carrier is provided with an electrically conductive substrate consisting primarily of an aluminum-group metallic material. According to a further aspect of the invention, the cylindrical developer carrier is composed of an alumite layer formed through the application of an anodizing method. According to still another aspect of the invention, the cylindrical developer carrier is composed of an alumite layer having minute holes sealed with nickel acetate. The alumite layer may have a thickness of 2 μm to 5 μm. According to a further aspect of the invention, the minute holes account for 10% to 50% of the total area of the formed alumite layer that constitutes the cylindrical developer carrier.

According to an embodiment of the invention, a first method for manufacturing the inventive cylindrical developer carrier includes the following steps: Initially, the surface of an electrically conductive substrate is roughened uniformly by blasting spherical fine particles onto the surface. An alumite layer is formed using anodization. The surface is blasted with amorphous fine particles, each having a diameter greater than that of said spherical fine particles.

According to another embodiment of the invention, a second method for manufacturing the cylindrical developer carrier includes the following steps: Initially, spherical fine particles, including glass beads, are blasted onto the surface of an electrically conductive substrate. An alumite layer is formed by anodization. Then the surface is blasted with amorphous fine particles consisting primarily of aluminum oxide, with each particle having a diameter greater than that of the spherical fine particles.

According to a further embodiment of the invention, a third method for manufacturing the cylindrical developer carrier includes the following steps: Initially, spherical fine particles, including glass beads, are blasted onto the surface of an electrically conductive substrate. Projections and recesses are formed each being provided with a mean surface roughness in a specific range expressed in terms of Ra=0.8 μm to 1.5 μm. An alumite layer is formed by anodization. Lastly, the surface is blasted with amorphous fine particles consisting primarily of aluminum oxide, and each particle has a diameter greater than that of said spherical fine particles.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIG. 1 is a perspective view of the cylindrical developer carrier according to an embodiment of the invention;

FIG. 2 is a partially enlarged cross-sectional view of a cylindrical developer carrier according to an embodiment of the invention; and

FIG. 3 is a schematic cross-sectional view of an image forming apparatus loaded with a cylindrical developer carrier according to an embodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

With reference to the accompanying drawings, preferred embodiments of the cylindrical developer carrier according to the invention are described below. However, it should be understood that the scope of the invention is by no means limited to the embodiments described below.

FIG. 1 is a perspective view of a cylindrical developer carrier, i.e., a developing sleeve 11, according to an embodiment of the invention. FIG. 2 is a partially enlarged cross-sectional view of the developing sleeve 11. FIG. 3 is a schematic cross-sectional view of an image forming apparatus 100 loaded with the developing sleeve 11 according to an embodiment of the invention.

Referring to FIG. 3, the image forming apparatus 100 includes a variety of electrophotographic processing members, including a toner developing unit (consisting of a roller electrifying (charging) member 3, an image exposing means 4, including an image exposing light source, a developing-agent storage tank 5, and a developing sleeve 1, an image transcribing unit 6, and a discharging member 7. These members respectively are disposed on the external circumferential surface of a cylindrical electrophotographic organic photoconductor 10.

The image forming apparatus 100, which is based on the contact (roller) charging system shown in FIG. 3, serially executes electrophotographic processes through application of the above-described developing members, before eventually forming a predetermined image. A method of forming an image is described below. Initially, a predetermined voltage is added to the roller charging member 3 disposed in contact with the surface of the photoconductor 10. This electrifies the entire surface of the photoconductor 10. Next, through the application of the image exposing means 4, an image corresponding to a predetermined document is exposed to the surface of the photoconductor 10, thus forming a static latent image. Next, a toner compound, previously stirred and electrified in the developing-agent storage tank 5, is statically transferred and adhered to the circumferential surface of the photoconductor 10 via the developing sleeve 11, before the static latent image on the photoconductor 10 is converted to a visible positive image. Next, the toner image formed on the surface of the photoconductor 10 is transferred or transcribed onto an image material such as paper fed via a paper-feeding roller and a paper-feeding guide member. The transfer is performed through the application of the transcribing unit 6. Finally, residual toner compound remaining on the photoconductor 10 without having been transcribed onto the sheet is collected by a cleaning member 12. In the event that a residual charge still remains inside the photoconductor 10, it is suggested that the residual charge be eliminated through the application of an adequate voltage or light beams to the photoconductor 10 via the discharging means 7. On the other hand, the sheet material onto which a transcribed toner image is formed is transferred to a fixing unit (not shown) via a conveying unit, thus enabling the toner image to be fixed before eventually being output as a visible positive image.

In the image forming apparatus 100, the light source for the image exposing means 4 may consist of a halogen lamp, a fluorescent lamp, laser beams, or the like. It is also permissible to add any auxiliary processing step, as required. In addition to copying machines, the image forming apparatus 100 may also be applied to a wide variety of applicable electrophotographic devices, such as a laser printer or an electronic photoengraving system, for example.

As shown in the perspective view illustrated in FIG. 1, the developing sleeve 11 consists of a 20 mm-diameter sleeve-shaped electrically conductive substrate 1 fitted with a pair of shaft holders on both sides, which is made entirely of aluminum alloy. The actual diameter may be adjusted according to the type of component loaded. Normally, the diameter will be in a range from 10 mm to 25 mm. In the above-cited example, the aluminum alloy is made entirely of the composition corresponding to the JIS-A6063 standard. However, an aluminum alloy conforming to the JIS-A5056 or JIS-A3003 standard may also be used. The aluminum sleeve substrate 1 is formed in accordance with the below-described series of steps. Initially, the original pipe is manufactured by processing an aluminum-alloy ingot using an extruding machine and a drawing machine. Next, the surface of the formed original pipe is planed or ground using a cutting tool or a grindstone until the pipe surface is completely smoothed. Next, through the application of a number of spherical glass beads, having a maximum mean particle size of 44 μm (#600), the surface of the sleeve substrate 1 is treated using a blasting process until recesses and projections created thereby produce a mean surface roughness value Ra in a predetermined range, from 0.8 μm to 1.5 μm. It should be noted that, if the mean surface roughness value exceeds 1.5 μm, toner compound will remain in the recessed portions. Conversely, if the mean surface roughness value is less than 0.8 μm, the effect of the frictional charge that can be borne by the toner compound will become insufficient, resulting in a poor density of the toner compound. This latter circumstance may lead to a failure to achieve proper density in images. Further, inadequate mean surface roughness leads to slippage of the toner compound. Therefore as a result of which the toner layer will not be uniform due to uneven propagation of the toner.

Next, through the application of an anode-oxidizing process against the roughened surface of the sleeve substrate 1, an alumite layer 2 is formed and then sealed. The sealing process preferably is executed through the application of nickel acetate. However, the invention also is realizable with the use of sealing methods. It is preferred that the alumite layer 2 be provided with a thickness in the range from 2 μm to a maximum of 5 μm. If the thickness exceeds 5 μm, it will become quite difficult uniformly to form a plurality of minute holes 21 reaching the aluminum substrate 1 according to the invention, as described below. Conversely, if the above thickness is less than 2 μm, the alumite layer 2 will wear quickly.

After the above alumite layer 2 has been formed, a plurality of minute holes 21 are formed by blasting the layer surface with fine particles of amorphous aluminum oxide (alumina), each having a hardness value greater than that of alumite. Insofar as the hardness value is greater than that of alumite, it is also possible to use fine particles of another material. The particle size (such as #320) of the usable alumina fine particles shall be greater than the particle size (such as #600) of the above-described glass beads.

The object of the blasting process following the formation of the alumite layer 2, and the details of the process are described below. Initially, among the projections and recesses formed on the alumite layer 2, only the alumite layer 2 immediately above the projections is removed. Then, a plurality of uniformly distributed minute holes 21 reaching the aluminum substrate 1 are provided so as to provide a plurality of uniformly distributed leakage sites for allowing leakage from the charge borne by the toner compound. Thereby, the surface resistance value of the alumite layer 2 is minimized, which solves the above-described technical problem arising from a difference in the developing capability in correspondence with the surface's toner development history.

EXAMPLE

In order to accurately determine the relationship of quality of images to the ratio of the area of the minute holes formed immediately above the projections on the alumite layer 2 to the area shared by the formed alumite layer 2, the inventors conducted experiments. Initially, actual samples of the developing sleeve 11 were prepared, and were individually provided with ratios 5%, 10%, 20%, 40%, 50%, 60%, 70%, and 100% of the total area of the minute holes 21 to the actual area shared by the alumite layer 2 (hereinafter total ratios). The total area ratios were computed based on the difference in the light reflection ratios as between the alumite-layer formed portions and the minute holes 21. More particularly, a light-reflection rating instrument was used, with which the total area ratios of the minute holes 21 were computed based on a calibration curve prepared from a previously known sample. Alternatively, it is also allowable to compute area ratios by referring to an enlarged photographic view of the sleeve surface. The computed results are shown in TABLE 1.

Then, the actual quality of the formed images and actual service life of the developing sleeves 11 were respectively evaluated. Through the application of a Macbeth densiometer, the density of images was evaluated, with ratings of 1.3 and above 1.3 designated by circular symbols (o), ratings of 1.2 to 1.3 designated by triangular symbols (Δ), and ratings below 1.2 designated by a cross symbol (x), as shown in TABLE 1 below. It is understood from the results of evaluation of the density of images that the toner compound was fully subjected to friction, and the subsequent charge was applied to the developing sleeve 11 before being formed into a level layer of toner compound, which was then properly held and carried without generating any deflection.

Following evaluation of an image memory (toner development history) to check for a difference in the toner developing capability, the results showing non-occurrence of a difference in the developing capability were designated by circular symbols (o) in TABLE 1 below. The results showing the occurrence of some difference in the toner developing capability were designated by a triangular symbol (Δ). The results showing the actual occurrence of a difference in the toner developing capability were designated by cross symbols (x). It is thus understood from the results of evaluation of the image memory shown in TABLE 1 that the developing sleeve 11 retained a proper surface condition through the preservation of appropriate leakage sites, without generating any difference in the toner developing capability in correspondence with the toner development history.

To evaluate the actual service life of the developing sleeves 11, up to more than 20,000 copies were prepared with each sleeve. Those sleeves found to be sufficiently durable after the processing of more than 20,000 copies were designated by circular symbols (o). Those sleeves found to be sufficiently durable for processing only 10,000 to 20,000 copies were designated by triangular symbols (Δ), whereas those sleeves found to be insufficiently durable to process even 10,000 copies were designated by cross symbols (x) in TABLE 1 below. Thus, the results of evaluation of the actual service life of the developing sleeves corresponding to the former two groups enabled the inventors to detect the presence or absence of variations in (or degradation of) the physical characteristics of the developing sleeves as between an initial state and after use to prepare a predetermined number of copies.

To define the overall results of the evaluations of the groups of sleeves with the respective minute hole area ratios, results evaluated as (o) in all three categories were rated with a designation (o). In the event that even a single characteristic was rated with a cross symbol (x), the overall evaluation result for the group of sleeves was designated by the cross symbol (x) as well. Those sleeve groups for which at least one characteristic was designated by the triangular symbol (Δ), without the presence of a designation with the cross symbol (x), were identified with the triangular symbol (Δ) in the designation of their overall evaluation result.

TABLE 1
Minute hole	Image	Image	Sleeve	Overall
area ratio (%)	density	memory	life	evaluation
5	∘	x	∘	x
10	∘	∘	∘	∘
20	∘	∘	∘	∘
40	∘	∘	∘	∘
50	∘	∘	∘	∘
60	∘	∘	Δ	Δ
70	Δ	∘	x	x
100	x	∘	x	x

With reference to TABLE 1, the above three characteristics (image density, image memory, and sleeve life) were evaluated as (o) when the area ratio of minute holes to the area shared by the alumite layer formed on the surface of the developing sleeve ranged from 10% to 50%, and it is thus clear that the overall evaluation result for these developing sleeves was favorably designated to be (o) as well.

Thus, according to the invention, an alumite layer is provided by coating over the entire surface of an electrically conductive substrate that has been uniformly roughened, wherein the alumite layer itself constitutes a cylindrical developer carrier evenly incorporating minute holes respectively reaching the surface of the above-described substrate. Due to this construction, even after repeated use, toner compound can be subjected to and hold a full, evenly propagated frictional charge on the developing sleeve, thereby enabling the invention to provide a novel cylindrical developer carrier without generating any difference in the toner developing capability in correspondence with the toner development history.

Claims

1-12. (canceled)

13. A cylindrical developer carrier comprising

an electrically conductive substrate having an evenly roughened surface; and

an alumite layer formed on said surface, wherein said alumite layer has a uniform distribution of minute holes respectively reaching said substrate surface.

14. A cylindrical developer carrier according to claim 13, wherein said electrically conductive substrate is formed primarily of an aluminum-group metallic material.

15. A cylindrical developer carrier according to claim 13, wherein said alumite layer comprises an alumite layer formed by an anodizing method.

16. A cylindrical developer carrier according to claim 15, further comprising nickel acetate sealing said alumite layer.

17. A cylindrical developer carrier according to claim 13, further comprising nickel acetate sealing said alumite layer.

18. A cylindrical developer carrier according to claim 17, wherein said alumite layer has a thickness in the range of 2 μm to 5 μm.

19. A cylindrical developer carrier according to claim 13, wherein said alumite layer has a thickness in the range of 2 μm to 5 μm.

20. A cylindrical developer carrier according to claim 19, wherein said minute holes, as a whole, account for 10% to 50% of the total area of the alumite layer.

21. A cylindrical developer carrier according to claim 13, wherein said minute holes, as a whole, account for 10% to 50% of the total area of the alumite layer.

22. A method for manufacturing a cylindrical developer carrier comprising the steps of:

roughening an electrically conductive substrate surface by blasting spherical fine particles onto the substrate surface;

forming an alumite layer on the roughened surface by an anodizing method; and

blasting the surface of the alumite-layer with amorphous fine particles each having a diameter greater than that of the spherical fine particles.

23. A method for manufacturing a cylindrical developer carrier according to claim 22, wherein

the blasting the spherical fine particles includes blasting the electrically conductive substrate surface with glass beads, and

the blasting the surface of the alumite layer with amorphous fine particles includes blasting the alumite layer surface with amorphous fine particles formed primarily of aluminum oxide, each of the amorphous fine particles having a diameter greater than that of the spherical fine particles.

24. A method for manufacturing a cylindrical developer carrier according to claim 23, wherein

the step of blasting said electrically conductive substrate surface with spherical fine particles includes a step of blasting the substrate surface with spherical fine particles consisting solely of glass beads, so as to form a number of projections and recesses each having a mean surface roughness rated at Ra=0.8 μm to 1.5 μm, and

the blasting the surface of the alumite layer with amorphous fine particles includes blasting the alumite layer surface with amorphous fine particles formed primarily of aluminum oxide, each of the amorphous fine particles having a diameter greater than that of the spherical fine particles.