CN112305880A

CN112305880A - Developing roller and method for manufacturing the same

Info

Publication number: CN112305880A
Application number: CN202010424435.4A
Authority: CN
Inventors: 今瀬悠太
Original assignee: Sumitomo Rubber Industries Ltd
Current assignee: Sumitomo Rubber Industries Ltd
Priority date: 2019-07-31
Filing date: 2020-05-19
Publication date: 2021-02-02
Also published as: JP2021026035A

Abstract

The invention provides a developing roller capable of forming an image with better image quality than the current state while maintaining a simple structure without a coating film and a manufacturing method thereof. In the developing roller (1), the arithmetic mean curvature Spc defining the peak apex of the surface shape of the outer peripheral surface (5) of the roller body (2) is set to 20000/mm or less, and the minimum autocorrelation length Sal is set to 10 [ mu ] m or more. The manufacturing method comprises a step of performing laser processing on the outer peripheral surface (5) after grinding to finish the outer peripheral surface into the surface shape.

Description

Developing roller and method for manufacturing the same

Technical Field

The present invention relates to a developing roller and a method of manufacturing the same.

Background

In an image forming apparatus using an electrophotographic method, a developing roller including a roller main body made of a crosslinked rubber is used. Various studies have been made on the surface shape of the outer peripheral surface of the roller body of the developing roller (patent documents 1 to 3, etc.).

[ Prior art documents ]

[ patent document ]

[ patent document 1] Japanese patent laid-open No. 2006-243374

[ patent document 2] Japanese patent laid-open publication No. 2013-73130

[ patent document 3] Japanese patent laid-open No. 2016-183997

Disclosure of Invention

[ problems to be solved by the invention ]

The invention aims to provide a developing roller capable of forming an image with better image quality than the current situation and a manufacturing method thereof.

[ means for solving problems ]

The invention provides a developing roller, comprising a roller body, wherein the arithmetic mean curvature Spc of a peak top point specified in the international Standardization organization standard ISO (International Standardization organization)25178-2:2012 of the outer peripheral surface of the roller body is 20000/mm or less, and the minimum autocorrelation length Sal is 10 mu m or more.

Further, the present invention is a method for manufacturing a developing roller, the developing roller of the present invention is manufactured, and the manufacturing method includes: grinding the outer peripheral surface of the roller body; and a step of performing laser processing on the outer peripheral surface of the roller body after polishing, and finishing the arithmetic mean curvature Spc of the peak top and the minimum autocorrelation length Sal to be within the ranges.

[ Effect of the invention ]

According to the present invention, a developing roller capable of forming an image having an image quality superior to that of the current state and a method for manufacturing the same can be provided.

Drawings

Fig. 1 is a perspective view showing an example of an embodiment of a developing roller of the present invention.

[ description of symbols ]

1: developing roller

2: roller body

3: through hole

4: shaft

5: peripheral surface

6: and (5) oxidizing the film.

Detailed Description

The outer peripheral surface of the roller body is usually polished or coated with a coating film after polishing, for example, in order to adjust the surface state.

The coating film is formed by applying a liquid coating agent as a base thereof to the outer peripheral surface of the roller body by a coating method such as a spraying method or a dipping method and then drying the coating agent.

However, the coating film has various problems such as mixing of foreign matters such as dust and generation of thickness unevenness, which are likely to occur during the formation.

Further, an organic solvent is required for preparing a coating agent, but the use of an organic solvent imposes a large burden on the environment, and the trend toward the formation of low Volatile Organic Compounds (VOC) is also being counter-acted in recent years.

The inventions described in patent documents 1 to 3 propose a method of polishing the outer peripheral surface of a roller body made of a crosslinked rubber product and finishing the outer peripheral surface to a predetermined surface shape by various kinds of machining.

With these configurations, it is considered that the structure of the roller body can be simplified by omitting the coating film.

However, according to the studies of the inventors, it is still impossible to say that the outer peripheral surface of the roller body is sufficiently uniformized and optimized in the surface shapes proposed in patent documents 1 to 3 at present.

In particular, when the coating film is omitted, the amount of toner that can be carried on the outer peripheral surface tends to vary, or the amount of toner tends to be insufficient, or conversely tends to be excessive.

If the amount of toner that can be carried on the outer peripheral surface varies, there is a concern that density unevenness occurs in the formed image, and if the amount of toner is insufficient, there is a concern that the density decreases, whereas if the amount of toner is excessive, there is a concern that so-called fogging occurs in a blank portion where the image is formed.

For example, the outer peripheral surface of a conventional roll main body finished by polishing has a surface shape in which a surface roughness component composed of a plurality of fine irregularities and a surface waviness component composed of a plurality of irregularities having a periodicity longer than that of the surface roughness component are superposed.

According to the studies of the inventors, it is important to control these components in order to uniformize and optimize the surface state of the outer peripheral surface of the roller body of the developing roller to the outer peripheral surface for the developing roller.

Thus, the inventors studied the Geometric Product Specifications (GPS) -surface properties-part 2 of the article, which specifies the international standardization organization standard ISO25178-2: 2012: the arithmetic mean curvature Spc and the minimum autocorrelation length Sal of the peak apex defined in the wording, definition, and surface property parameters "are new indicators of the surface roughness.

That is, the arithmetic mean curvature Spc of the peak top represents the principal curvature of the convex portion (mountain) per unit area, and serves as an index representing the sharpness of the peak of the convex portion.

Specifically, the smaller the arithmetic mean curvature Spc of the peak top, the more convex portions with gentle peaks are present, and conversely, the larger the arithmetic mean curvature Spc of the peak top, the more convex portions with sharp peaks are present.

The autocorrelation is a measure of how well an image matches an image in which the coordinates of the image itself are offset during image processing, and the minimum autocorrelation length Sal is an index indicating whether or not there is a sharp step on the outer peripheral surface when the outer peripheral surface has a surface shape.

Specifically, the smaller the minimum autocorrelation length Sal, the more steep steps are indicated, and conversely, the larger the minimum autocorrelation length Sal, the less steep steps are indicated.

Therefore, the ratio of the surface roughness component composed of a plurality of fine irregularities constituting the irregularities of the outer peripheral surface to the surface waviness component composed of a plurality of irregularities having a longer periodicity than the surface roughness component can be specified according to the magnitude of the arithmetic mean curvature Spc of the peak top and the minimum autocorrelation length Sal.

Therefore, the inventors have further studied the range between the arithmetic mean curvature Spc of the peak top and the minimum autocorrelation length Sal, and as a result, have found that the arithmetic mean curvature Spc of the peak top is defined to be 20000/mm or less and the minimum autocorrelation length Sal is defined to be 10 μm or more.

In the case where the arithmetic mean curvature Spc of the peak top exceeds 20000/mm, or the minimum autocorrelation length Sal is less than 10 μm, in either case, the proportion of the surface roughness component becomes large, and the amount of toner carried on the outer peripheral surface of the roller main body is liable to be ununiformed.

Further, the amount of toner carried is not uniform, and thus the density of the formed image is not uniform, or the amount of toner carried on the outer peripheral surface is excessive, and thus fog is generated in a blank portion where the image is formed, or conversely, the amount of toner carried on the outer peripheral surface is insufficient, and thus the density of the formed image is reduced.

In contrast, by defining the arithmetic mean curvature Spc and the minimum autocorrelation length Sal of the peak apex within the above ranges, it is possible to provide a developing roller capable of forming an image having an image quality superior to the current image quality while maintaining a simple structure in which a coating film is omitted.

That is, since the surface state of the outer peripheral surface is made uniform and optimized, it is possible to provide a developing roller in which density unevenness, reduction, fogging, and the like of an image to be formed are less likely to occur.

In consideration of further improving the above effect, the arithmetic mean curvature Spc of the peak top is preferably 4000/mm or more, particularly 4300/mm or more, preferably 15000/mm or less, particularly 7000/mm or less within the above range.

The minimum autocorrelation length Sal is also preferably 15 μm or more, particularly 16 μm or more, preferably 40 μm or less, particularly 35 μm or less within the above range.

In the present invention, the arithmetic mean curvature Spc of the peak top and the minimum autocorrelation length Sal are expressed by values obtained in accordance with the ISO standard, for example, based on the result of measuring the surface shape of the outer peripheral surface of the roller body within a predetermined observation area using a shape analysis laser microscope.

The outer peripheral surface of the roller main body having the specific surface shape is not limited thereto, and for example, the arithmetic average height Sa defined in the ISO standard is preferably 0.5 μm or more, and preferably 2 μm or less.

The maximum height Sz defined in the ISO standard is preferably 8 μm or more, and preferably 16 μm or less.

Further, the depth of the concave portions constituting the irregularities of the surface waviness component is preferably 1 μm or more, and preferably 50 μm or less.

When the height direction dimension of the irregularities is smaller than these ranges, the amount of toner carried on the outer peripheral surface of the roller body may be insufficient, and the density of the formed image may be reduced.

On the other hand, when the height direction dimension of the irregularities is larger than the above range, the amount of toner carried on the outer peripheral surface of the roller main body may not be uniform, resulting in uneven density of an image to be formed, or the amount of toner carried on the outer peripheral surface may be excessive, resulting in fogging in a blank portion where an image is formed.

Developing roller and method for manufacturing the same

Fig. 1 is a perspective view showing an example of an embodiment of a developing roller 1 according to the present invention.

Referring to fig. 1, the developing roller 1 of this example includes a roller main body 2 formed in a non-porous single-layer cylindrical shape from a rubber composition to which conductivity is imparted. The shaft 4 is inserted through and fixed to the through hole 3 in the center of the roller body 2.

The shaft 4 is integrally formed of a material having good electrical conductivity, for example, a metal such as iron, aluminum, an aluminum alloy, or stainless steel.

The shaft 4 is electrically joined to the roller main body 2 through, for example, an electrically conductive adhesive and mechanically fixed thereto, or the shaft 4 having an outer diameter larger than the inner diameter of the through hole 3 is pressed into the through hole 3 and electrically joined to the roller main body 2 and mechanically fixed thereto.

In addition, the shaft 4 and the roller body 2 may be electrically joined and mechanically fixed by the above two methods in combination.

On the outer circumferential surface 5 of the roller body 2, an oxide film 6 is formed as enlarged in the drawing.

When the oxide film 6 is formed, the oxide film 6 functions as a dielectric layer, and the dielectric loss tangent of the developing roller 1 can be reduced. Further, the oxide film 6 can function as a low-friction layer, and adhesion of toner can be favorably suppressed.

Further, the oxide film 6 can be easily formed by simply oxidizing the rubber in the vicinity of the outer peripheral surface 5 by, for example, irradiating the outer peripheral surface 5 with ultraviolet rays or the like, and thus, a decrease in productivity of the developing roller 1 or an increase in manufacturing cost can be suppressed.

However, the oxide film 6 may be omitted.

The term "single layer" of the roller body 2 means that the number of layers made of rubber or the like is a single layer, and the extremely thin oxide film 6 formed by irradiation of ultraviolet rays or the like is not included in the number of layers.

In order to manufacture the developing roller 1, the rubber composition prepared is extruded into a cylindrical shape using an extruder, for example, and then cut into a predetermined length, and the rubber is crosslinked by applying pressure and heat in a vulcanizing tank.

Next, the crosslinked cylindrical body is heated in an oven or the like to be secondarily crosslinked, and after cooling, the outer peripheral surface 5 is polished so as to have a predetermined outer diameter (polishing step).

As the polishing method, various polishing methods such as dry longitudinal polishing can be used. Further, it is preferable that the outer circumferential surface 5 is finely polished at the end of the polishing step.

By performing the finish polishing, the height-direction dimension of the irregularities constituting the surface waviness component can be reduced.

The finish polishing may be mirror polishing using a polishing film.

In mirror polishing, the more precise the polishing film is used, the smaller the dimension in the height direction of the irregularities constituting the surface waviness component can be.

Next, the outer circumferential surface 5 after polishing is finished by laser processing or the like into a specific surface shape in which the arithmetic mean curvature Spc of the peak point and the minimum autocorrelation length Sal both satisfy the above-described range, thereby forming the roller body 2.

That is, only the outer peripheral surface 5 to be polished is in a state where the size in the height direction of fine irregularities constituting the surface roughness component is large and the number thereof is large.

When the outer peripheral surface 5 in the above-described state is further subjected to laser processing or the like, it is possible to reduce the irregularities finer than the irregularities constituting the surface roughness component while newly forming the irregularities constituting the surface waviness component and having a longer period than the surface roughness component.

Further, the roller body 2 having the outer peripheral surface 5 having the above-described specific surface shape, that is, satisfying the range in which the arithmetic mean curvature Spc of the peak top is 20000/mm or less and the minimum autocorrelation length Sal is 10 μm or more can be formed.

The laser processing is performed by, for example, irradiating the polished outer circumferential surface 5 with laser light whose irradiation size is limited to a predetermined irradiation size while moving the irradiation position at a predetermined pitch.

In the laser processing, the crosslinked material of the rubber composition forming the outer circumferential surface 5 is selectively melted by heat generated by irradiation of the laser, and at least a part thereof is evaporated.

As a result, a plurality of irregularities constituting the surface waviness component can be formed on the outer peripheral surface 5, and minute irregularities constituting the surface roughness component can be reduced.

In order to form the outer peripheral surface of the roller main body into the specific surface shape by laser processing, for example, the output of laser light, the irradiation size of laser light irradiated to the outer peripheral surface, the movement pitch of irradiation positions, the degree of overlapping of adjacent irradiation positions, or the like may be adjusted.

The pitch may be set in any range that can form a specific surface shape, but the pitch in the axial direction of the roller body is preferably 125 μm or less, particularly 110 μm or less.

The pitch in the circumferential direction of the roller body 2 is preferably 105 μm or less, particularly 95 μm or less.

The shaft 4 can be inserted and fixed in the through hole 3 at any time from the cutting of the cylindrical body to the finish machining.

However, after the cutting, the shaft 4 is preferably first subjected to secondary crosslinking, polishing, and finishing in a state of being inserted into the through hole 3.

This can suppress the bending or deformation of the roller body 2 caused by the expansion and contraction at the time of secondary crosslinking.

Further, by performing polishing and finish machining while rotating about the shaft 4, workability of the polishing and finish machining can be improved and the run-out of the outer peripheral surface 5 can be suppressed.

As described above, the shaft 4 may be inserted into the through hole 3 of the tubular body before the secondary crosslinking via an adhesive having conductivity, particularly a thermosetting adhesive having conductivity, and then the secondary crosslinking is performed, or a shaft having an outer diameter larger than the inner diameter of the through hole 3 may be press-fitted into the through hole 3.

In the former case, the thermosetting adhesive is cured while the cylindrical body is secondarily crosslinked by heating in the oven, and the shaft 4 is electrically and mechanically engaged with the roller body 2.

In the latter case, the electrical engagement and the mechanical fixation are completed simultaneously with the press-fitting of the shaft 4.

As described above, the shaft 4 and the roller body 2 may be electrically joined and mechanically fixed by the above-described two methods.

As described above, the oxide film 6 is preferably formed by irradiating the outer peripheral surface 5 of the roll main body 2 with ultraviolet rays.

That is, the outer peripheral surface 5 after being subjected to the finishing such as laser processing is irradiated with ultraviolet rays of a predetermined wavelength for a predetermined time to oxidize the rubber in the vicinity of the outer peripheral surface 5, thereby forming the oxide film 6.

Therefore, the oxide film 6 can be formed in a simple and efficient manner, and a reduction in productivity of the developing roller 1 and an increase in manufacturing cost can be suppressed.

The oxide film 6 formed by the irradiation of ultraviolet rays does not cause a problem such as a coating film formed by coating a coating agent, and is excellent in uniformity of thickness, adhesion to the roll main body 2, and the like.

In view of forming the oxide film 6 having excellent functions by oxidizing the diene rubber in the rubber composition with good equivalent efficiency, the wavelength of the ultraviolet rays to be irradiated is preferably 100nm or more, preferably 400nm or less, and particularly 300nm or less.

The irradiation time is preferably 30 seconds or more, particularly 1 minute or more, preferably 30 minutes or less, particularly 20 minutes or less.

However, the oxide film 6 may be formed by another method or may not be formed.

Rubber composition

The rubber composition forming the roller body 2 is prepared by compounding a crosslinking ingredient or various additives for crosslinking the rubber in the rubber.

In order to impart conductivity to the rubber composition, the roller resistance value of the developing roller 1 is adjusted to be within an appropriate range, and the following description will be made of an ion-conductive rubber composition.

< rubber >

As described above, in order to impart ionic conductivity to the rubber composition, it is preferable to use an ionic conductive rubber as the rubber.

Further, as the rubber, it is preferable to use a diene rubber together with the ion conductive rubber.

By using the diene rubber in combination, it is possible to impart good processability to the rubber composition and to improve mechanical strength and durability of the roller body.

Further, by using the diene rubber in combination, the roll body can be provided with excellent properties as a rubber, that is, softness, small compression permanent strain, and resistance to collapse.

(ion-conductive rubber)

Examples of the ion conductive rubber include epichlorohydrin rubber and polyether rubber.

Examples of the epichlorohydrin rubber include epichlorohydrin homopolymers, epichlorohydrin-ethylene oxide binary copolymers (ECO), epichlorohydrin-propylene oxide binary copolymers, epichlorohydrin-allyl glycidyl ether binary copolymers, epichlorohydrin-ethylene oxide-allyl glycidyl ether ternary copolymers (GECO), epichlorohydrin-propylene oxide-allyl glycidyl ether ternary copolymers, epichlorohydrin-ethylene oxide-propylene oxide-allyl glycidyl ether quaternary copolymers, and epichlorohydrin-ethylene oxide-propylene oxide-allyl glycidyl ether quaternary copolymers.

Examples of the polyether rubber include ethylene oxide-allyl glycidyl ether binary copolymers and ethylene oxide-propylene oxide-allyl glycidyl ether ternary copolymers.

Among these, ethylene oxide-containing copolymers, in particular ECO and/or GECO, are preferred.

The ethylene oxide content in the ECO and/or GECO is preferably 30 mol% or more, particularly 50 mol% or more, and preferably 80 mol% or less.

The ethylene oxide plays a role of reducing the roller resistance value of the developing roller.

However, if the ethylene oxide content is less than the above range, the above-described effect cannot be sufficiently obtained, and therefore, the roller resistance value of the developing roller may not be sufficiently reduced.

On the other hand, when the ethylene oxide content exceeds the above range, crystallization of ethylene oxide occurs, and the chain motion of the molecular chain is inhibited, so that the roller resistance value of the developing roller tends to be increased.

Further, the roller body after crosslinking becomes too hard, or the viscosity of the rubber composition before crosslinking at the time of heating and melting increases, and the processability of the rubber composition may be lowered.

The epichlorohydrin content in the ECO is the remainder of the ethylene oxide content.

That is, the epichlorohydrin content is preferably 20 mol% or more, preferably 70 mol% or less, and particularly 50 mol% or less.

The allyl glycidyl ether content in the GECO is preferably 0.5 mol% or more, particularly 2 mol% or more, preferably 10 mol% or less, particularly 5 mol% or less.

Allyl glycidyl ether functions to secure a free volume as a side chain, thereby playing a role of suppressing crystallization of ethylene oxide and reducing a roller resistance value of a developing roller.

However, if the allyl glycidyl ether content is less than the above range, the above effect cannot be sufficiently obtained, and therefore, the roller resistance value of the developing roller may not be sufficiently reduced.

On the other hand, allyl glycidyl ether functions as a crosslinking point at the time of crosslinking of GECO.

Therefore, when the allyl glycidyl ether content exceeds the above range, the crosslinking density of the GECO becomes too high, whereby the segmental motion of the molecular chain is inhibited, and the roller resistance value of the developing roller tends to be increased.

The epichlorohydrin content in the GECO is the remainder of the ethylene oxide content and the allyl glycidyl ether content.

That is, the epichlorohydrin content is preferably 10 mol% or more, particularly 19.5 mol% or more, preferably 69.5 mol% or less, particularly 60 mol% or less.

Further, as the GECO, in addition to the copolymer in the narrow sense of the above-described copolymerization of three monomers, a modified product obtained by modifying an epichlorohydrin-ethylene oxide copolymer (ECO) with allyl glycidyl ether is known.

In the present invention, any of the above-mentioned GECOs may be used.

One or two or more of these ion conductive rubbers may be used.

(diene rubber)

Examples of the diene rubber include natural rubber, Isoprene Rubber (IR), acrylonitrile butadiene rubber (NBR), Styrene Butadiene Rubber (SBR), Butadiene Rubber (BR), and Chloroprene Rubber (CR).

In particular, as the diene rubber, it is preferable to use both of CR and NBR in combination.

However, two or more kinds of rubbers may be used in combination.

·CR

CR functions to improve the flexibility of the roller body and improve the image durability of the developing roller.

The image durability is an index indicating how long the quality of an image formed can be maintained well while suppressing deterioration of the same toner when the toner is repeatedly used for image formation.

That is, only a very small part of the toner contained in the developing unit of the image forming apparatus is used in one image formation, and most of the remaining toner is repeatedly circulated in the developing unit.

Therefore, how much or no damage is caused to the toner by the roller body of the developing roller that is provided in the developing portion and that repeatedly contacts the toner is a key in improving the durability of the image.

When the flexibility of the roller main body is reduced and the image durability is reduced, the quality of the formed image tends to be gradually reduced in the repeated image formation.

Therefore, the developing roller is required to have excellent flexibility of the roller body in order to improve image durability.

CR functions to improve the charging characteristics of positively chargeable toner, or to finely adjust the roller resistance value of the developing roller because it is a polar rubber.

Further, CR is oxidized by irradiation with ultraviolet rays, and functions as a material for forming an oxide film on the outer circumferential surface of the roller main body.

CR is synthesized by emulsion polymerization of chlorobutadiene, and is classified into sulfur-modified type and non-sulfur-modified type according to the kind of molecular weight modifier used at this time.

Among them, sulfur-modified CR can be synthesized by plasticizing a polymer obtained by copolymerizing chloroprene and sulfur as a molecular weight modifier with thiuram disulfide or the like and adjusting the plasticized polymer to a predetermined viscosity.

Further, the non-sulfur-modified CR is classified into, for example, a thiol-modified CR and a xanthane-modified CR.

Among them, the thiol-modified CR is synthesized in the same manner as the sulfur-modified CR, except that alkylthiols such as n-dodecylthiol, t-dodecylthiol, and octylthiol are used as a molecular weight modifier.

Further, the xanthate-modified CR was synthesized in the same manner as the sulfur-modified CR, except that an alkylxanthate compound was used as a molecular weight modifier.

CR is classified into a slow crystallization rate type, a medium crystallization rate type, and a fast crystallization rate type based on its crystallization rate.

Any type of CR may be used in the present invention, but among them, a CR that is not sulfur-modified and has a slow crystallization rate is preferable.

Further, as CR, a copolymer of chloroprene and another copolymerization component may also be used.

Examples of other copolymerizable components include: 2, 3-dichloro-1, 3-butadiene, 1-chloro-1, 3-butadiene, styrene, acrylonitrile, methacrylonitrile, isoprene, butadiene, acrylic acid, acrylic ester, methacrylic acid, methacrylic ester, and the like.

Further, as CR, there are oil-filled CR in which filling oil is added to adjust flexibility and non-oil-filled CR in which filling oil is not added, but in the present invention, in order to prevent contamination of the photoreceptor, it is preferable to use non-oil-filled CR not containing filling oil that may become a bleeding substance.

One or two or more of these CR may be used.

·NBR

The NBR is still oxidized by the irradiation of ultraviolet rays, and functions as a material for forming an oxide film on the outer circumferential surface of the roller main body. Further, since the NBR is a polar rubber, it also functions to finely adjust the roller resistance value of the developing roller.

The NBR may be any of a low-nitrile NBR having an acrylonitrile content of 24% or less, a medium-nitrile NBR of 25% to 30%, a medium-nitrile NBR of 31% to 35%, a high-nitrile NBR of 36% to 42%, and a very high-nitrile NBR of 43% or more.

The NBR may be an oil-filled NBR in which an extender oil is added to adjust flexibility, or an oil-unfilled NBR in which an extender oil is not added.

One or two or more of these NBRs may be used.

(proportion of rubber)

The ratio of the rubber can be arbitrarily set according to various characteristics required for the developing roller, particularly, the roller resistance value, the flexibility of the roller body, and the like.

However, the proportion of the epichlorohydrin rubber plasma-conductive rubber is preferably 15 parts by mass or more, particularly 30 parts by mass or more, preferably 80 parts by mass or less, particularly 70 parts by mass or less, of the total 100 parts by mass of the rubber.

In the case where the ratio of the ion conductive rubber is less than the above range or exceeds the above range, in either case, the roller resistance value of the developing roller cannot be adjusted to a range suitable for the developing roller.

When the proportion of the ion conductive rubber exceeds the above range, the proportion of the diene rubber may be relatively small, and favorable characteristics as the rubber may not be imparted to the roller body.

On the other hand, by setting the ratio of the ion conductive rubber to the above range, the roller body can be provided with excellent characteristics as rubber while adjusting the roller resistance value of the developing roller to an appropriate range.

The proportion of the diene rubber is the residual amount of the ionic conductive rubber.

That is, when the proportion of the ion conductive rubber is set to a predetermined value within the above range, the proportion of the diene rubber may be set so that the total amount of the rubber becomes 100 parts by mass.

< crosslinking component >

As the crosslinking component, it is preferable to use a crosslinking agent for crosslinking the rubber and a crosslinking accelerator for accelerating crosslinking of the rubber by the crosslinking agent in combination.

Among these, examples of the crosslinking agent include a sulfur-based crosslinking agent, a thiourea-based crosslinking agent, a triazine derivative-based crosslinking agent, a peroxide-based crosslinking agent, and various monomers, and particularly, a sulfur-based crosslinking agent is preferable.

(Sulfur-based crosslinking agent)

Examples of the sulfur-based crosslinking agent include: powdered sulfur, oil-treated powdered sulfur, precipitated sulfur, colloidal sulfur, dispersible sulfur, or an organic sulfur-containing compound such as tetramethylthiuram disulfide or N, N-dithiodimorpholine, and the like, and sulfur is particularly preferable.

In view of imparting good properties as rubber to the roller body, the proportion of sulfur is preferably 0.5 parts by mass or more, and preferably 2 parts by mass or less, per 100 parts by mass of the total amount of rubber.

In the case where oil-treated powdered sulfur, dispersed sulfur, or the like is used as the sulfur, the above-mentioned ratio is a ratio of the sulfur itself as an effective component contained in each.

In the case where the organic sulfur-containing compound is used as the crosslinking agent, the proportion thereof is preferably adjusted so that the proportion of sulfur contained in the molecule with respect to 100 parts by mass of the total amount of the rubber falls within the above-mentioned range.

(crosslinking accelerator)

Examples of the crosslinking accelerator for accelerating crosslinking of the rubber include one or two or more of thiuram accelerators, thiazole accelerators, thiourea accelerators, guanidine accelerators, sulfenamide accelerators, and dithiocarbamate accelerators.

Among them, it is preferable to use a thiuram-based accelerator, a thiazole-based accelerator, a thiourea-based accelerator and a guanidine-based accelerator in combination.

The thiuram-based accelerator includes, for example, one or more of tetramethylthiuram monosulfide, tetramethylthiuram disulfide, tetraethylthiuram disulfide, tetrabutylthiuram disulfide, dipentamethylenethiuram tetrasulfide, and the like, and tetramethylthiuram monosulfide is particularly preferable.

Examples of the thiazole accelerator include one or more of 2-mercaptobenzothiazole, di-2-benzothiazolyl disulfide, zinc salt of 2-mercaptobenzothiazole, cyclohexylamine salt of 2-mercaptobenzothiazole, and 2- (4' -morpholinodithio) benzothiazole, and di-2-benzothiazolyl disulfide is particularly preferable.

As the thiourea-based accelerator, various thiourea compounds having a thiourea structure in the molecule can be used.

Examples of the thiourea-based accelerator include ethylenethiourea, N' -diphenylthiourea, trimethylthiourea, and compounds represented by formula (1):

(C_nH_2n+1NH)₂C＝S (1)

[ in the formula, n represents an integer of 1 to 12] and one or more of thiourea, tetramethylthiourea and the like, and ethylene thiourea is particularly preferable.

Examples of the guanidine-based accelerator include one or two or more of 1, 3-diphenylguanidine, 1, 3-di-o-tolylguanidine, 1-o-tolylbiguanidine, and the like, and 1, 3-di-o-tolylguanidine is particularly preferable.

In the above-described four-use system, the proportion of the thiuram-based accelerator is preferably 0.3 parts by mass or more, and preferably 1 part by mass or less, relative to 100 parts by mass of the total amount of the rubber, in view of the effect of accelerating crosslinking of the rubber, and the like.

The proportion of the thiazole accelerator is preferably 0.3 part by mass or more, and preferably 2 parts by mass or less, based on 100 parts by mass of the total amount of the rubber.

The proportion of the thiourea-based accelerator is preferably 0.3 parts by mass or more, and preferably 1 part by mass or less, relative to 100 parts by mass of the total amount of the rubber.

Further, the proportion of the guanidine-based accelerator is preferably 0.2 parts by mass or more, and preferably 1 part by mass or less, relative to 100 parts by mass of the total amount of the rubber.

The thiourea-based accelerator also functions as a crosslinking agent for ECO that does not have sulfur crosslinking properties, and the guanidine-based accelerator also functions as an accelerator for crosslinking ECO that is caused by the thiourea-based accelerator.

< conductive agent >

The rubber composition may further contain an ionic conductive agent.

By blending the ion conductive agent, the ion conductivity of the rubber composition can be further improved, and the roller resistance value of the developing roller 1 can be further reduced.

The ion conductive agent is preferably a salt (ionic salt) of an anion and a cation having a fluorine group and a sulfonyl group in the molecule.

Examples of the anion having a fluoro group and a sulfonyl group in the molecule, which constitutes the ionic salt, include one or two or more kinds of a fluoroalkyl sulfonate ion, a bis (fluoroalkylsulfonyl) imide ion, a tris (fluoroalkylsulfonyl) methide ion, and the like.

Among them, as the fluoroalkyl sulfonate ion, for example, CF is cited₃SO₃ ^-、C₄F₉SO₃ ^-And the like, or two or more thereof.

Further, the bis (fluoroalkylsulfonyl) imide ion may be, for example, (CF)₃SO₂)₂N^-、(C₂F₅SO₂)₂N^-、(C₄F₉SO₂)(CF₃SO₂)N^-、(FSO₂C₆F₄)(CF₃SO₂)N^-、(C₈F₁₇SO₂)(CF₃SO₂)N^-、(CF₃CH₂OSO₂)₂N^-、(CF₃CF₂CH₂OSO₂)₂N^-、(HCF₂CF₂CH₂OSO₂)₂N^-、[(CF₃)₂CHOSO₂]₂N^-And the like, or two or more thereof.

Further, the tris (fluoroalkylsulfonyl) methide ion may be, for example, (CF)₃SO₂)₃C^-、(CF₃CH₂OSO₂)₃C^-And the like, or two or more thereof.

Examples of the cation include one or more of alkali metal ions such as sodium, lithium, and potassium, ions of group 2 elements such as beryllium, magnesium, calcium, strontium, and barium, ions of transition elements, cations of amphoteric elements, quaternary ammonium ions, and imidazolium cations.

As the ionic salt, a lithium salt using a lithium ion as a cation, or a potassium salt using a potassium ion is particularly preferable.

Among them, (CF) is preferable in terms of the effect of improving the ionic conductivity of the rubber composition and reducing the resistance value of the outer layer₃SO₂)₂NLi [ lithium-bis (trifluoromethanesulfonyl)Imide compound]And/or (CF)₃SO₂)₂NK [ Potassium bis (trifluoromethanesulfonyl) imide]。

The proportion of the ionic conductive agent such as an ionic salt is preferably 0.5 parts by mass or more, and preferably 5 parts by mass or less, relative to 100 parts by mass of the total amount of the rubber.

< Others >

Various additives may be further compounded in the rubber composition as required. Examples of additives include: crosslinking aids, acid-absorbing agents, fillers, plasticizers, processing aids, deterioration inhibitors, and the like.

Among them, examples of the crosslinking assistant include: metal compounds such as zinc oxide (zinc white); one or more of fatty acids such as stearic acid, oleic acid, and cottonseed fatty acid, and other known crosslinking aids.

The proportion of the crosslinking assistant is preferably 0.1 part by mass or more, and preferably 7 parts by mass or less, respectively, based on 100 parts by mass of the total amount of the rubber.

The acid-absorbing agent functions to prevent chlorine-containing gas generated from epichlorohydrin rubber, CR, or the like during crosslinking from remaining in the roller body, or to prevent crosslinking inhibition or contamination of the photoreceptor due to chlorine-containing gas.

As the acid acceptor, various substances which function as acid acceptors can be used, but among them, hydrotalcite and magarat (magaraat) having excellent dispersibility are preferable, and hydrotalcite is particularly preferable.

Further, when hydrotalcite or the like is used in combination with magnesium oxide or potassium oxide, a higher acid absorption effect can be obtained, and contamination of the photoreceptor or the like can be more reliably prevented.

The proportion of the acid scavenger is preferably 0.2 parts by mass or more, particularly 0.5 parts by mass or more, and preferably 7 parts by mass or less, per 100 parts by mass of the total amount of the rubber.

Examples of the filler include one or more of zinc oxide, silica, carbon black, talc, calcium carbonate, magnesium carbonate, and aluminum hydroxide.

The mechanical strength of the roll body can be improved by blending the filler.

Further, by using conductive carbon black as a filler, electron conductivity can be imparted to the roller body.

Examples of the conductive carbon black include acetylene black.

The proportion of the conductive carbon black is preferably 1 part by mass or more, and preferably 30 parts by mass or less, relative to 100 parts by mass of the total amount of the rubber.

Examples of the plasticizer include various plasticizers such as dibutyl phthalate, dioctyl phthalate, and tricresyl phosphate, and various waxes such as polar waxes.

Examples of the processing aid include fatty acid metal salts such as zinc stearate.

The proportion of the plasticizer and/or the processing aid is preferably 3 parts by mass or less with respect to 100 parts by mass of the total amount of the rubber.

Examples of the deterioration inhibitor include various antioxidants and antioxidants.

The aging inhibitor plays a role of reducing environmental dependency of the roller resistance value of the developing roller and suppressing an increase in the roller resistance value when continuously energized.

Examples of the age resister include nickel diethyldithiocarbamate and nickel dibutyldithiocarbamate.

The proportion of the antioxidant is preferably 0.1 part by mass or more, and preferably 1 part by mass or less, per 100 parts by mass of the total amount of the rubber.

Further, as the additive, various additives such as a scorch retarder, a lubricant, a pigment, an antistatic agent, a flame retardant, a neutralizer, a nucleating agent, a co-crosslinking agent, and the like may be further blended at an arbitrary ratio.

In the example of fig. 1, the roller body 2 has a single-layer structure, but the roller body 2 may have a laminated structure of two or more layers.

The roller body 2 is not limited to a roller body formed of a rubber composition containing the above-described components. For example, the roller body 2 may be formed of various materials satisfying requirements that an appropriate roller resistance value can be imparted to the developing roller 1, the roller body 2 having excellent mechanical strength and durability can be formed, and characteristics that the roller body 2 is soft, has a small compression permanent strain, and is less likely to collapse can be imparted.

In either case, by forming the outer peripheral surface 5 of the roller main body 2 into the specific surface shape, the surface state of the outer peripheral surface 5 is made uniform and optimized more than it is, while maintaining a simple structure in which a coating film is omitted, and therefore, the developing roller 1 in which density unevenness, reduction, fogging, and the like of an image to be formed are less likely to occur can be obtained.

The developing roller 1 of the present invention can be used in an image forming apparatus using an electrophotographic method, such as a laser printer, an electrostatic copier, a plain paper facsimile machine, and a multifunction machine thereof.

[ examples ]

The present invention will be further described below based on examples and comparative examples, but the constitution of the present invention is not necessarily limited to these examples.

The arithmetic mean curvature Spc, the minimum autocorrelation length Sal, the arithmetic mean height Sa, and the maximum height Sz of the peaks of the outer peripheral surface of the roller main body of the developing roller manufactured in examples and comparative examples were obtained by the following measurement methods.

< method of measurement >

VK-X150/160 manufactured by using a shape-resolving laser microscope (Keyence) (Strand)]In the observation area: 55625 μm²The measurement result of the surface shape of the outer peripheral surface measured in the range of (3) is obtained in accordance with the ISO standard.

Further, the arithmetic mean curvature Spc of the peak top was 20000/mm or less and evaluated as "o", and the arithmetic mean curvature Spc exceeding 20000/mm was evaluated as "x".

In addition, a minimum autocorrelation length Sal of 10 μm or more was evaluated as "O", and a length of less than 10 μm was evaluated as "X".

< example 1 >

(preparation of rubber composition)

As the rubber, 20 parts by mass of ECO [ epidekoleman (epichlome) (registered trademark) D, EO/EP 61/39 (molar ratio) manufactured by OSAKA dada (OSAKA SODA) (stock.), 40 parts by mass of eichen (epilon) (registered trademark) 301 (js type) manufactured by GECO [ OSAKA dada (OSAKA SODA) (stock.), EO/EP/AGE 73/23/4 (molar ratio) ] CR [ shochu Shorelin (SHOPRENE) (registered trademark) WRT and non-oil-filled ]10 parts by mass, and also, anchoray (r) N250SL manufactured by NBR [ anchoray (r) (stock ], low-nitrile NBR, acrylonitrile content: 20% and non-oil-extended ]30 parts by mass.

Then, the following ingredients were blended and kneaded while masticating 100 parts by mass of the total of the four types of rubber using a banbury mixer.

[ Table 1]

Composition (I)	Mass portion of
		Ionic salts	3.40
Crosslinking aid	5.00
		Acid-absorbing agent	5.00
Filler	2.00
		Processing aid	1.00
Anti-aging agent	0.50

The components in table 1 are as follows. In addition, the mass part in the table is relative to the total amount of rubber 100 mass parts of mass.

Ionic salt: potassium bis (trifluoromethanesulfonyl) imide [ K-TFSI, EF-N112 manufactured by Mitsubishi Material Electron Synthesis (Strand) ]

Crosslinking assistant agent: zinc oxide made by Sakai chemical industry (Strand)

Acid-absorbing agent: hydrotalcite (DHT-4A (registered trademark) -2 manufactured by Kyowa chemical industry (Strand)

Filling agent: conductive carbon BLACK [ acetylene BLACK, superconducting acetylene BLACK (DENKA BLACK) (registered trademark) manufactured by the electrochemical industry (Strand), granular ]

Processing aid: zinc stearate [ Sakai made by chemical industry (steam) SZ-2000]

Anti-aging agent: nickel dibutyldithiocarbamate [ Noclark (Nocrac) (registered trademark) NBC manufactured by Innova chemical industry (David Co., Ltd.) ]

Subsequently, while continuing the kneading, the following crosslinking components were blended and further kneaded to prepare a rubber composition.

[ Table 2]

Composition (I)	Mass portion of
		Dispersible sulfur	1.50
Accelerant TS	0.50
		Accelerator DM	1.50
Accelerator 22	0.60
		Accelerant DT	0.54

The components in table 2 are as follows. In addition, the mass part in the table is relative to the total amount of rubber 100 mass parts of mass.

Dispersive sulfur: crosslinking agent [ crane, trade name Suforai (SULFAX) PS manufactured by chemical industry (stock.), sulfur component: 99.5% ]

Accelerator TS: tetramethylthiuram monosulfide [ SANCELER (registered trademark) TS manufactured by Sanxin chemical industries (Ltd.), thiuram series accelerator ]

Accelerator DM: di-2-benzothiazolyl disulfide [ Noccelar (registered trademark) DM, thiazole-based accelerator, manufactured by Noccelar (R) chemical industry, Innova chemical industries, Ltd ]

Accelerator 22: ethylene thiourea [ 2-mercaptoimidazoline, Abserve (acell) 22-S, thiourea accelerator, produced by Chuankou chemical industry (Strand) ]

Accelerator DT: 1, 3-di-o-tolylguanidine [ Su xi le (SANCELER) DT, guanidine-based accelerator manufactured by Sanxin chemical industries (Ltd.) ]

(production of developing roller)

The prepared rubber composition was fed to an extruder, extruded into a cylindrical shape having an outer diameter of 14.0mm and an inner diameter of 6.5mm, cut and attached to a temporary shaft for crosslinking, and crosslinked at 160 ℃ for 1 hour in a vulcanizing tank.

Subsequently, the crosslinked tubular body was mounted on a metal shaft having an outer diameter of 6.0mm and coated with a conductive thermosetting adhesive (polyamide-based) on the outer peripheral surface thereof, heated to 160 ℃ in an oven, and then bonded to the metal shaft, and then both ends were reshaped.

Next, the outer peripheral surface of the cylindrical body was longitudinally polished using a cylindrical grinder, and then mirror-polished using a #1000 polishing film [ a mirror film (registered trademark) manufactured by triax chemistry (jet), as finish polishing, to finish the outer diameter to phi 13.00 mm.

Next, after alcohol wiping of the polished outer peripheral surface, laser processing was performed using a laser beam machine [ fiber laser beam machine ML-7320DL manufactured by amantamiyagi (AMADA MIYACHI) (thigh) ]. The movement pitch of the irradiation position of the laser during laser processing is axial: 50 μm, circumferential direction: the output was adjusted to 45 μm by setting the degree of overlap between adjacent irradiation positions to 30%.

After alcohol wiping of the outer peripheral surface after laser processing was performed again, the outer peripheral surface was set to a distance of 50mm from the UV light source, set in a UV treatment apparatus, and irradiated with ultraviolet light for 15 minutes while rotating at 300rpm, thereby forming an oxide film, and a developing roller was manufactured.

The arithmetic mean curvature Spc of the peak apex of the outer peripheral surface of the roller body of the produced developing roller was 14872/mm (. smallcircle.), the minimum autocorrelation length Sal was 15.6 μm (. smallcircle.), the arithmetic mean height Sa was 1.3 μm, and the maximum height Sz was 13.9 μm.

< example 2 >

Except that the movement pitch of the irradiation position of the laser beam during laser processing is set as the axial direction: 55 μm, circumferential direction: a developing roller was produced in the same manner as in example 1, except that the thickness of the developing roller was 50 μm and the overlap degree of the adjacent irradiation positions was set to 30%, and the output was adjusted accordingly.

The arithmetic mean curvature Spc of the peak apex of the outer peripheral surface of the roller body of the produced developing roller was 4928/mm (° c), the minimum autocorrelation length Sal was 20.6 μm (° c), the arithmetic mean height Sa was 1.2 μm, and the maximum height Sz was 13.3 μm.

< example 3 >

Except that the movement pitch of the irradiation position of the laser beam during laser processing is set as the axial direction: 60 μm, circumferential direction: a developing roller was produced in the same manner as in example 1, except that the 60 μm was used and the degree of overlap between adjacent irradiation positions was set to 30%, and the output was adjusted accordingly.

The arithmetic mean curvature Spc of the peak apex of the outer peripheral surface of the roller body of the produced developing roller was 5629/mm (. smallcircle.), the minimum autocorrelation length Sal was 16.8 μm (. smallcircle.), the arithmetic mean height Sa was 1.8 μm, and the maximum height Sz was 13.7 μm.

< example 4 >

Except that the movement pitch of the irradiation position of the laser beam during laser processing is set as the axial direction: 70 μm, circumferential direction: a developing roller was produced in the same manner as in example 1, except that the overlap degree of the adjacent irradiation positions was set to 30% and the output was adjusted accordingly, 65 μm.

The arithmetic mean curvature Spc of the peak apex of the outer peripheral surface of the roller body of the produced developing roller was 4325/mm (. smallcircle.), the minimum autocorrelation length Sal was 20.8 μm (. smallcircle.), the arithmetic mean height Sa was 1.4 μm, and the maximum height Sz was 11.1 μm.

< example 5 >

Except that the movement pitch of the irradiation position of the laser beam during laser processing is set as the axial direction: 100 μm, circumferential direction: a developing roller was produced in the same manner as in example 1, except that the overlap of the adjacent irradiation positions was set to 30% and the output was adjusted accordingly, which was 90 μm.

The arithmetic mean curvature Spc of the peak apex of the outer peripheral surface of the roller body of the produced developing roller was 6922/mm (. smallcircle.), the minimum autocorrelation length Sal was 30.0 μm (. smallcircle.), the arithmetic mean height Sa was 1.2 μm, and the maximum height Sz was 11.7 μm.

< example 6 >

Except that the movement pitch of the irradiation position of the laser beam during laser processing is set as the axial direction: 120 μm, circumferential direction: a developing roller was produced in the same manner as in example 1, except that the overlap degree of the adjacent irradiation positions was set to 30% and the output was adjusted accordingly, to 100 μm.

The arithmetic mean curvature Spc of the peak apex of the outer peripheral surface of the roller body of the produced developing roller was 7565/mm (. smallcircle.), the minimum autocorrelation length Sal was 37.5 μm (. smallcircle.), the arithmetic mean height Sa was 1.9 μm, and the maximum height Sz was 15.8 μm.

< comparative example 1 >

A developing roller was produced in the same manner as in example 1, except that the outer peripheral surface mirror-polished with the polishing film of #1000 was further mirror-polished with the polishing film of #3000 [ mirror film produced by triax chemistry (strand) ], and laser processing was omitted.

The arithmetic mean curvature Spc of the peak apex of the outer peripheral surface of the roller body of the produced developing roller was 13841/mm (. smallcircle.), the minimum autocorrelation length Sal was 3.4 μm (x), the arithmetic mean height Sa was 0.4 μm, and the maximum height Sz was 10.9 μm.

< comparative example 2 >

A developing roller was produced in the same manner as in example 1, except that laser processing of the outer peripheral surface mirror-polished using the polishing film of #1000 was omitted.

The arithmetic mean curvature Spc of the peak apex of the outer peripheral surface of the roller body of the produced developing roller was 22558/mm (x), the minimum autocorrelation length Sal was 3.6 μm (x), the arithmetic mean height Sa was 1.0 μm, and the maximum height Sz was 13.1 μm.

< comparative example 3 >

A developing roller was produced in the same manner as in example 1, except that mirror polishing and laser processing for the longitudinally polished outer circumferential surface were omitted.

The arithmetic mean curvature Spc of the peak apex of the outer peripheral surface of the roller body of the produced developing roller was 22571/mm (x), the minimum autocorrelation length Sal was 19.9 μm (∘), the arithmetic mean height Sa was 2.1 μm, and the maximum height Sz was 21.5 μm.

< practical machine test >

The developing rollers manufactured in examples and comparative examples were mounted in place of a genuine developing roller including a toner container for storing toner, a photoreceptor, and a developing roller in contact with the photoreceptor, and a new black toner cartridge detachably mounted on a main body of a color laser printer (HL-L8360 CDW manufactured by brother industries).

Then, the assembled ink cartridges were loaded into the color laser printer, 30 images of pure black and halftone (2 spaces per 1 dot) were formed successively, and the density of the first formed image was measured using a reflection densitometer (model 939 manufactured by alice (X-Rite)) and evaluated by the following criteria.

(pure black)

O: the concentration is more than 1.3. Is good.

And (delta): the concentration is 1.2 or more and less than 1.3. The middle level.

X: the concentration is less than 1.2. It is not good.

(halftone)

O: the concentration is above 0.65. Is good.

And (delta): the concentration is 0.6 or more and less than 0.65. The middle level.

X: the concentration is less than 0.6. It is not good.

(unevenness)

In addition, in 30 formed pure black images, even if unevenness in density was observed in one sheet, the image was evaluated as poor (x), and no unevenness was observed as good (o).

The results are shown in tables 3 to 5.

[ Table 3]

[ Table 4]

[ Table 5]

As is clear from the results of examples 1 to 6 and comparative examples 1 to 3 in tables 3 to 5, a developing roller capable of forming an image having an image quality more excellent than the current state while maintaining a simple structure in which a coating film is omitted can be obtained by setting the arithmetic mean curvature Spc of the peak top of the outer peripheral surface of the roller body to 20000/mm or less and the minimum autocorrelation length Sal to 10 μm or more.

Claims

1. A developing roller includes a roller body, an arithmetic mean curvature Spc of a peak apex defined in International standards organization ISO25178-2:2012 of an outer peripheral surface of the roller body is 20000/mm or less, and a minimum autocorrelation length Sal is 10 [ mu ] m or more.

2. The developing roller according to claim 1, wherein the outer circumferential surface comprises: a surface roughness component composed of a plurality of irregularities, and a surface waviness component composed of a plurality of irregularities having a longer periodicity than the surface roughness component.

3. The developing roller according to claim 1 or 2, wherein an arithmetic mean curvature Spc of the peak top is 4300/mm or more and 7000/mm or less.

4. The developing roller according to any one of claims 1 to 3, wherein the minimum autocorrelation length Sal is 16 μm or more and 35 μm or less.

5. The developing roller according to any one of claims 1 to 4, wherein the outer peripheral surface is constituted by a crosslinked product of rubber, including an oxide film.

6. A method of manufacturing a developing roller, the developing roller according to any one of claims 1 to 5 being manufactured, and the method of manufacturing a developing roller comprising:

grinding the outer peripheral surface of the roller body; and

and a step of performing laser processing on the outer peripheral surface of the roll main body after polishing, and finishing the arithmetic mean curvature Spc of the peak top and the minimum autocorrelation length Sal to within a predetermined range.

7. The method for manufacturing a developing roller according to claim 6, wherein the outer circumferential surface of the roller body is constituted by a crosslinked product of rubber, further comprising after the step of finishing

And irradiating the outer peripheral surface with ultraviolet rays to oxidize the rubber to form an oxide film.