JP2021086112A - Developing roller - Google Patents

Abstract

To provide a developing roller which has a laminated structure and is capable of forming images with better image quality compared with conventional products.SOLUTION: A developing roller 1 is provided, comprising an inner layer 2 and an outer layer 4, the inner layer 2 being made of a rubber composition containing 21 pts.mass or more of epichlorohydrin rubber per 100 pts.mass of total rubber. A surface resistance logR1 of an outer peripheral surface 8 is in a range of 7.0-8.5, and a roller resistance logR2 of the entire roller body 5 is in a range of 6.3-8.5.SELECTED DRAWING: Figure 1

Description

The present invention relates to a developing roller used by incorporating it into an image forming apparatus using an electrophotographic method.

Recently, as a developing roller, the roller body includes a roller body, and the roller body is covered with a tubular inner layer made of a crosslinked product of a rubber composition and an outer peripheral surface of the inner layer to form an outer peripheral surface of the roller body. A laminated structure including an outer layer is being studied (see Patent Document 1 and the like).

Japanese Unexamined Patent Publication No. 2016-95455

An object of the present invention is to provide a developing roller having a laminated structure and capable of forming an image having a higher image quality than the current state.

The present invention includes a tubular inner layer made of a crosslinked product of a rubber composition containing epichlorohydrin rubber as a rubber and a diene-based rubber, and a roller body including a tubular outer layer covering the outer periphery of the inner layer, and the epichlorohydrin rubber. The ratio of is 21 parts by mass or more out of 100 parts by mass of the total amount of the rubber, and the surface resistance value R ₁ (when Ω and 10 V is applied) of the outer peripheral surface of the roller body, which is the outer peripheral surface of the outer layer, is expressed by 1):
7.0 ≤ logR ₁ ≤ 8.5 (1)
The roller resistance value R ₂ (when Ω, 400 V is applied) of the entire roller body is expressed by the equation (2):
6.3 ≤ log R ₂ ≤ 8.5 (2)
It is a developing roller that satisfies.

According to the present invention, it is possible to provide a developing roller having a laminated structure and capable of forming an image having a higher image quality than the current state.

FIG. (A) is a perspective view showing the overall appearance of an example of the developing roller of the present invention, and FIG. (B) is an end view of the developing roller of the above example. It is a figure explaining the method of measuring the roller resistance value of a roller main body. It is a figure explaining the method of measuring the contact angle of water on the outer peripheral surface of a roller body.

Examples of the image forming apparatus incorporating the developing roller include a laser printer, an electrostatic copying machine, a plain paper facsimile machine, and a combination machine thereof.
As one of the image evaluation criteria of an image forming apparatus such as a laser printer, a solid black density and a 2 dot density of a formed image are known.
The solid black density is the density of a so-called solid black image in which at least a part of the paper surface is filled with a solid black color, and the higher the solid black density, the higher the contrast of the image can be formed.

The 2dot density is the density of an image in which circles are lined up on a square grid with a grid length of about 80 μm, which is called isolated 2dot. The higher the 2dot density, the better the reproducibility and gradation of fine lines, and the finer the image. Images can be formed.
However, these two image densities are in a reciprocal relationship, and it is difficult to achieve both.
That is, the solid black density tends to increase as the roller resistance value of the developing roller decreases, but the 2dot density tends to increase as the roller resistance value of the developing roller increases. It is difficult to achieve both of the two contradictory characteristics.

As described above, the roller body of the developing roller has a structure including two layers, an inner layer and an outer layer, both of which are crosslinked products of the rubber composition, and the resistance values of both layers are adjusted to have the above-mentioned two contradictory characteristics. It is conceivable to achieve both.
That is, the black solid density is related to the resistance value near the surface of the roller body, and the black solid density can be improved by lowering the resistance value near the surface.

On the other hand, the roller resistance value of the entire roller body is related to the 2dot concentration, and the higher the overall roller resistance value, the higher the 2dot concentration can be.
so that,
-As described above, the roller body has a structure including two layers, an inner layer and an outer layer, both of which are crosslinked rubber compositions.
・ Of these, the outer layer is in a low resistance state in order to adjust the resistance value near the surface of the roller body to a range where the black solid density can be improved, and the inner layer below it is the roller body combined with the outer layer. If the overall roller resistance value is set to a high resistance state in order to adjust the 2dot concentration within a range that can be improved,
It is possible to achieve both a solid black density and a 2 dot density.

However, according to the study of the inventor, in the conventional developing roller provided with the roller body having a laminated structure described in Patent Document 1 and the like, the range of the resistance value and the roller resistance value near the surface can be set, or both layers can be set. The composition of the rubber composition that forms the above is not yet appropriate.
Therefore, in the initial stage of image formation, the black solid density (initial black solid density) and the 2 dot density (initial 2 dot density) may be insufficient, or the 2 dot density may be significantly reduced when the image formation is repeated.

Further, when the image formation is repeated, the formed image may have uneven density depending on the density of the image adjacent in the horizontal direction orthogonal to the paper passing direction.
Further, when the image formation is repeated, blurring is likely to occur especially when a solid black image (solid black image) is formed on the entire surface of the area where the image can be formed on the paper, and the entire surface is solid black with a uniform density. It may not be possible to form an image.

Therefore, the inventor specifically defines the resistance value near the surface of the roller body, the surface resistance value of the outer peripheral surface of the roller body, the optimum range of the roller resistance value of the roller body, and the rubber composition forming the inner layer. The composition was further investigated.
As a result, as mentioned above
-The inner layer is formed of a crosslinked product of a rubber composition containing epichlorohydrin rubber and a diene-based rubber, and the proportion of epichlorohydrin rubber is set to 21 parts by mass or more in 100 parts by mass of the total amount of rubber.
_{・ The surface resistance value R 1} (when Ω and 10 V is applied) of the outer peripheral surface of the roller body is expressed by Eq. (1):
7.0 ≤ logR ₁ ≤ 8.5 (1)
It was set in a range satisfying the, yet roller roller resistance value of the entire body R _{2 (Omega,} at 400V applied), the formula (2):
6.3 ≤ log R ₂ ≤ 8.5 (2)
I found that it should be set in the range that satisfies.

That is, the developing roller of the present invention includes a tubular inner layer made of a crosslinked product of a rubber composition containing epichlorohydrin rubber as rubber and a diene rubber, and a roller body including a tubular outer layer covering the outer periphery of the inner layer. Including, the proportion of the epichlorohydrin rubber is 21 parts by mass or more in 100 parts by mass of the total amount of rubber, and the surface resistance value R ₁ (when Ω, 10 V is applied) of the outer peripheral surface of the roller body, which is the outer peripheral surface of the outer layer, is the above. The feature is that the formula (1) is satisfied, and the roller resistance value R ₂ (when Ω, 400 V is applied) of the entire roller body satisfies the above formula (2).

According to the developing roller of the present invention, with the above configuration, both the solid black density and the 2 dot density are simultaneously improved, and an image having excellent contrast and fine line reproducibility and gradation is formed. be able to.
Further, it is necessary to suppress the occurrence of density unevenness depending on the density of images adjacent in the lateral direction in the image, or to suppress the decrease in the 2 dot density when the image formation is repeated, that is, the decrease in the durable 2 dot density. You can also.

Further, it is possible to suppress blurring of the entire black solid image when the image formation is repeated, and to bring the entire black solid image into a clean state with uniform density.
The presence or absence of blurring can be evaluated by the density of the portion having the lowest density in the full black solid image, that is, the full black solid density.
These facts are clear from the results of Examples, Comparative Examples, and Conventional Examples described later.

FIG. 1A is a perspective view showing the overall appearance of an example of the developing roller of the present invention, and FIG. 1B is an end view of the developing roller of the above example.
With reference to FIGS. 1 (a) and 1 (b), in the developing roller 1 of this example, the outer layer 4 made of an elastic material is directly laminated on the outer peripheral surface 3 of the tubular inner layer 2 made of an elastic material. It includes a roller body 5 having a two-layer structure.

A shaft 7 is inserted and fixed in the through hole 6 at the center of the inner layer 2.
The shaft 7 is integrally formed of a material having good conductivity, for example, a metal such as iron, aluminum, an aluminum alloy, or stainless steel.
The shaft 7 is, for example, electrically joined to the roller body 5 via a conductive adhesive and mechanically fixed, or a through hole having an outer diameter larger than the inner diameter of the through hole 6. By press-fitting into 6, it is electrically joined to the roller body 5 and mechanically fixed.

Further, both methods may be used in combination to electrically join the shaft 7 to the roller body 5 and mechanically fix the shaft 7.
The surface of the outer layer 4, that is, the outer peripheral surface 8 of the roller body 5, is covered with an oxide film 9 as shown in both drawings in an enlarged manner.
By covering the outer peripheral surface 8 with the oxide film 9, the oxide film 9 can function as a dielectric layer to reduce the dielectric loss tangent tan δ of the developing roller 1, and the oxide film 9 can function as a low friction layer. Therefore, the adhesion of the toner can be suppressed satisfactorily.

Moreover, since the oxide film 9 can be easily formed by, for example, irradiating the outer peripheral surface 8 with ultraviolet rays to oxidize the rubber in the vicinity of the outer peripheral surface 8, the productivity of the developing roller 1 may decrease. It is also possible to suppress the high manufacturing cost.
However, the oxide film 9 may be omitted.
The inner layer 2 and the outer layer 4 are preferably formed into a non-porous single layer in order to simplify the respective structures and improve durability and the like.

The "single layer" of the inner layer 2 and the outer layer 4 means that the number of layers made of the elastic material is both single layers.
Further, the "two layers" of the roller body 5 also indicate that the number of layers made of elastic materials in both the inner layer 2 and the outer layer 4 is two, and in each case, an oxide film formed by irradiation with ultraviolet rays or the like. 9 is not included in the number of layers.

In the present invention, the surface resistance value R ₁ (when Ω, 10 V is applied) _{of the outer peripheral surface 8 of the roller body 5 and the roller resistance value R 2} (when Ω, 400 V are applied) of the entire roller body 5 are described above. The reason why the range satisfying the equations (1) and (2) is limited is as follows.
That is, when the surface resistance value R ₁ (when Ω, 10 V is applied) _{of the outer peripheral surface 8 of the roller body 5 is less than 7.0 represented by the common logarithmic value log R 1} , the resistance value near the surface of the roller body 5 becomes low. Therefore, for example, the image may have image defects due to overcurrent.

On the other hand, when the surface resistance value R ₁ (when Ω, 10 V is applied) _{of the outer peripheral surface 8 of the roller body 5 exceeds 8.5 in terms of the common logarithmic value log R 1} , the resistance value near the surface of the roller body 5 Cannot be sufficiently reduced to the extent that the solid black density can be improved.
Therefore, the initial black solid density may be insufficient and the contrast of the image may be lowered, or the entire black solid image may be blurred and the black solid density may be lowered.

Further, (at Omega, 400V applied) roller resistance value _{R 2} of the entire roller body 5 is less than 6.3 expressed in common logarithm logR _2, or insufficient initial 2dot concentration, greater durability 2dot concentration In some cases, the fineness of the image may be deteriorated due to the deterioration of the reproducibility and gradation of fine lines.
On the other hand, the roller resistance value of the entire roller body 5 _{R 2} (Omega, at 400V applied) is, when it exceeds 8.5, expressed in common logarithm logR ₂ is an image, a paper feeding direction of the paper orthogonal In some cases, uneven density may occur depending on the density of images adjacent to each other in the horizontal direction.

Further, the ratio of epichlorohydrin rubber in the rubber composition forming the inner layer 2 is limited to 21 parts by mass or more in 100 parts by mass of the total amount of rubber for the following reasons.
At below the proportion of the epichlorohydrin rubber is 21 parts by weight, the roller resistance value _{R 2} (Omega, at 400V applied) on the entire roller body 5 regardless, or insufficient initial 2dot concentration, endurance 2dot concentration greatly reduced May be done.

On the other hand, the surface resistance value R ₁ (when Ω and 10 V is applied) is within the range satisfying the equation (1), and the roller resistance value R ₂ (when Ω and 400 V is applied) is within the range satisfying the equation (2). By setting the proportion of epichlorohydrin rubber in the rubber composition forming the inner layer 2 within the above range, it is possible to suppress the occurrence of the various defects described above.
Then, it becomes possible to provide a developing roller capable of forming an image having better image quality than the current state for a long period of time.

_{Further, in the developing roller 1 of the present invention, the contact angle θ W} (°) of water on the outer peripheral surface 8 is different depending on the composition of the rubber composition forming the outer layer 4 forming the outer peripheral surface 8 of the roller main body 5. It is preferably 50 ° or more.
_{When the contact angle θ W} (°) of water on the outer peripheral surface 8 of the roller main body 5 is within the above range, the outer peripheral surface 8 exhibits water repellency, so that the releasability of the toner can be improved.

Therefore, the initial solid black density can be further improved, and it is possible to more effectively suppress the decrease in the solid black density due to blurring of the solid black image on the entire surface.
Considering that the effect is further improved, the contact angle θ _W (°) of water is more preferably 60 ° or more even in the above range.
_{In order to adjust the contact angle θ W} (°) of water on the outer peripheral surface 8 of the roller body 5 within the above range, for example, in order to form an oxide film 9 covering the outer peripheral surface 8, the outer peripheral surface 8 is formed. The integrated amount of ultraviolet rays to be irradiated (mJ / cm ² ) may be adjusted.

Specifically, the smaller the integrated light intensity (mJ / cm ² ), the larger the contact angle θ _{W (°) of water.}
The integrated light intensity (mJ / cm ^{2 ) is the outer circumference obtained by the product of the irradiation intensity (mW / cm 2} ) per unit area and the irradiation time (seconds) of the ultraviolet rays irradiating the outer peripheral surface 8 of the roller body 5. It is the total amount of ultraviolet rays irradiated to the surface 8.

The upper limit of the contact angle θ _W (°) of water is not particularly limited, and includes up to _{the contact angle θ W} (°) of water on the outer peripheral surface 8 which is not irradiated with ultraviolet rays and is therefore not covered with the oxide film 9. And.
<Measurement of integrated light intensity of ultraviolet rays>
The integrated light intensity (mJ / cm ² ) is measured using an integrated light intensity measuring device.

Specifically, for example, the integrated light amount measuring device is set at the position where the roller body 5 is set in the device (UV processing device) that actually irradiates the outer peripheral surface 8 of the roller body 5 with ultraviolet rays.
Next, the UV processing device is operated in the same manner as when the outer peripheral surface 8 of the roller main body 5 is irradiated with ultraviolet rays, the light receiving portion of the integrated light amount measuring machine is irradiated with ultraviolet rays, and the integrated light amount measured by the integrated light amount measuring machine. The operating conditions of the UV processing device required for (mJ / cm ^{2) to reach the target value are obtained.}

The operating conditions include, for example, the wavelength, irradiation intensity, and irradiation time of the ultraviolet rays to be irradiated, and in the case of a UV processing device that irradiates the outer peripheral surface 8 with ultraviolet rays while rotating the roller body 5, the rotation speed of the roller body 5. And so on.
Then, when the roller body 5 is set in the same UV processing device and operated under the operating conditions obtained by the above measurement, ultraviolet rays ^{are applied to the outer peripheral surface 8 of the set roller body 5 with the same integrated light amount (mJ / cm 2).} Can be irradiated.

<< Rubber composition for inner layer 2 >>
As described above, the inner layer 2 contains epichlorohydrin rubber and a diene-based rubber as rubber, and is formed by a crosslinked product of a rubber composition imparted with ionic conductivity.
<Epichlorohydrin rubber>
Examples of the epichlorohydrin rubber include epichlorohydrin homopolymer, epichlorohydrin-ethylene oxide binary copolymer (ECO), epichlorohydrin-propylene oxide binary copolymer, epichlorohydrin-allyl glycidyl ether binary copolymer, and epichlorohydrin-ethylene oxide. Examples thereof include -allyl glycidyl ether ternary copolymer (GECO), epichlorohydrin-propylene oxide-allyl glycidyl ether ternary copolymer, epichlorohydrin-ethylene oxide-propylene oxide-allyl glycidyl ether quaternary copolymer and the like.

Of these, copolymers containing ethylene oxide, particularly ECO and / or GECO, are preferred.
The ethylene oxide content in ECO and / or GECO is preferably 30 mol% or more, particularly preferably 50 mol% or more, and preferably 80 mol% or less.

Ethylene oxide has a function of lowering the resistance value of the inner layer 2, and by extension, the roller resistance value R ₂ (when Ω, 400 V is applied) of the entire roller body 5.
However, if the ethylene oxide content is less than the above range, such an action cannot be sufficiently obtained, so that the roller resistance value R ₂ (when Ω, 400 V is applied) of the entire roller body 5 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 segment movement of the molecular chain is hindered. Therefore, on the contrary, the roller resistance value R ₂ (Ω, (When 400V is applied) tends to increase.
In addition, the inner layer 2 after cross-linking may become too hard, or the viscosity of the rubber composition before cross-linking at the time of heating and melting may increase, resulting in a decrease in processability of the rubber composition.

The epichlorohydrin content in ECO is the remaining amount of ethylene oxide content.
That is, the epichlorohydrin content is preferably 20 mol% or more, preferably 70 mol% or less, and particularly preferably 50 mol% or less.
The allyl glycidyl ether content in GECO is preferably 0.5 mol% or more, particularly preferably 2 mol% or more, and preferably 10 mol% or less, particularly 5 mol% or less.

The allyl glycidyl ether itself functions as a side chain to secure a free volume, thereby suppressing the crystallization of ethylene oxide, and the roller resistance value R ₂ (Ω, 400 V) of the entire roller body 5 as a whole. It works to reduce (when applied).
However, if the allyl glycidyl ether content is less than the above range, such an action cannot be sufficiently obtained, so that the roller resistance value R ₂ (when Ω, 400 V is applied) of the entire roller body 5 may not be sufficiently reduced. ..

On the other hand, allyl glycidyl ether functions as a cross-linking point when cross-linking GECO.
Therefore, when the allyl glycidyl ether content exceeds the above range, the cross-linking density of GECO becomes too high and the segment movement of the molecular chain is hindered. On the contrary, the roller resistance value R _{2 of the entire roller body 5 is used.} (When Ω, 400V is applied) tends to increase.

The epichlorohydrin content in GECO is the remaining amount of ethylene oxide content and allyl glycidyl ether content.
That is, the epichlorohydrin content is preferably 10 mol% or more, particularly preferably 19.5 mol% or more, and preferably 69.5 mol% or less, particularly 60 mol% or less.
As GECO, in addition to the copolymer in a narrow sense obtained by copolymerizing the three types of monomers described above, epichlorohydrin-ethylene oxide copolymer (ECO) was modified with allyl glycidyl ether. Denatured products are also known.

In the present invention, any of these GECOs can be used.
As the epichlorohydrin rubber, GECO is particularly preferable.
Since GECO has a double bond in the main chain that functions as a cross-linking point due to the allyl glycidyl ether, the compression set after cross-linking can be reduced by cross-linking between the main chains.

Therefore, the inner layer 2 can be made to have a small compression set and less likely to be settled.
One or more of these epichlorohydrin rubbers can be used.
<Diene rubber>
The diene-based rubber imparts good workability to the rubber composition, improves the mechanical strength and durability of the inner layer 2, or gives the inner layer 2 good properties as rubber, that is, flexible and compressible. It functions to give the property that the permanent strain is small and the settling is hard to occur.

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).
Among them, as the diene rubber, non-polar diene rubber, specifically, at least one of three types of IR, BR, and SBR, particularly two types of IR and BR, or two types of IR and SBR. It is preferable to use them together.

Further, CR and / or NBR may be further used in combination with the above-mentioned combination system.
(IR)
As the IR, various IRs having a polyisoprene structure, which artificially reproduces the structure of natural rubber, can be used.
Further, as IR, there are an oil-extending type in which extensibility oil is added to adjust the flexibility and a non-oil-extending type in which no spreading oil is added. In the present invention, bleeding is performed in order to prevent contamination of the photoconductor. It is preferable to use a non-oil-extending type IR that does not contain spreading oil that can be a substance.

One or more of these IRs can be used.
(BR)
As the BR, various BRs having a polybutadiene structure in the molecule and having crosslinkability can be used.
In particular, a high cis BR having a cis-1,4 bond content of 95% or more, which can exhibit good properties as a rubber in a wide temperature range from low temperature to high temperature, is preferable.

Further, there are two types of BR, one is an oil-extending type in which the flexibility is adjusted by adding spreading oil, and the other is a non-oil-extending type in which no spreading oil is added. In the present invention, in order to prevent contamination of the photoconductor, It is preferable to use a non-oil-extending type BR that does not contain a spreading oil that can be a bleeding substance.
One or more of these BRs can be used.
(SBR)
As the SBR, various SBRs synthesized by copolymerizing styrene and 1,3-butadiene by various polymerization methods such as an emulsion polymerization method and a solution polymerization method can be used.

Further, as the SBR, there are a high styrene type, a medium styrene type, and a low styrene type SBR classified according to the styrene content, and any of these can be used.
Further, as the SBR, there are an oil-extending type in which the flexibility is adjusted by adding a spreading oil and a non-oil-extending type in which no spreading oil is added. In the present invention, in order to prevent contamination of the photoconductor and the like. , It is preferable to use a non-oil-extending type SBR that does not contain a spreading oil that can be a bleeding substance.

One or more of these SBRs can be used.
(CR)
CR is a polar diene rubber, _{and functions to finely adjust the roller resistance value R 2} (when Ω, 400 V is applied) of the entire roller body 5.
CR is synthesized by emulsion polymerization of chloroprene, and is classified into a sulfur-modified type and a non-sulfur-modified type according to the type of molecular weight modifier used at that time.

Of these, the sulfur-modified type CR is synthesized by plasticizing a polymer obtained by copolymerizing chloroprene and sulfur as a molecular weight modifier with thiuram disulfide or the like to adjust the viscosity to a predetermined value.
Further, the non-sulfur-modified type CR is classified into, for example, a mercaptan-modified type, a xanthate-modified type, and the like.

Of these, the mercaptan-modified type CR is synthesized in the same manner as the sulfur-modified type CR except that alkyl mercaptans such as n-dodecyl mercaptan, tert-dodecyl mercaptan, and octyl mercaptan are used as molecular weight modifiers. ..
Further, the xanthate-modified type CR is also synthesized in the same manner as the sulfur-modified type CR except that the alkylxanthate compound is used as a molecular weight modifier.

Further, CR is classified into a slow crystallization rate type, a moderate crystallization rate type, and a high crystallization rate type based on the crystallization rate.
In the present invention, any type of CR may be used, but among them, a non-sulfur-modified type CR having a slow crystallization rate is preferable.
Further, as CR, a copolymer of chloroprene and another copolymerization component may be used. Other copolymerization components include, for example, 2,3-dichloro-1,3-butadiene, 1-chloro-1,3-butadiene, styrene, acrylonitrile, methacrylonitrile, isoprene, butadiene, acrylic acid, acrylic acid ester. , Methacrylic acid, and methacrylic acid ester and the like.

Further, as the CR, there are an oil-extending type in which the flexibility is adjusted by adding spreading oil and a non-oil-extending type in which no spreading oil is added. In the present invention, also in order to prevent contamination of the photoconductor. , It is preferable to use a non-oil-extending type CR that does not contain spreading oil that can be a bleeding substance.
One or more of these CRs can be used.
(NBR)
NBR is also a diene rubber having polarity, _{and functions to finely adjust the roller resistance value R 2} (when Ω, 400 V is applied) of the entire roller body 5.

The NBR includes low nitrile NBR having an acrylonitrile content of 24% or less, medium nitrile NBR having 25 to 30%, medium and high nitrile NBR having 31 to 35%, and high nitrile NBR having 36 to 42%, and 43% or more. Any ultra-high nitrile NBR can be used.
Further, as NBR, there are an oil-extending type in which extensibility oil is added to adjust the flexibility and a non-oil-extending type in which no spreading oil is added. In the present invention, in order to prevent contamination of the photoconductor and the like. , It is preferable to use a non-oil-extending type NBR that does not contain spreading oil that can be a bleeding substance.

One or more of these NBRs can be used.
<Rubber ratio>
The ratio of rubber depends on various characteristics required for the inner layer 2, especially the resistance value of the inner layer 2, the roller resistance value R ₂ (when Ω, 400 V is applied) of the entire roller body 5, the flexibility of the inner layer 2, and the like. It can be set arbitrarily according to the situation.

However, the proportion of epichlorohydrin rubber needs to be 21 parts by mass or more in 100 parts by mass of the total amount of rubber.
The reason for this is as explained above.
Even in the above range, the proportion of epichlorohydrin rubber is preferably 30 parts by mass or less based on 100 parts by mass of the total amount of rubber.

When the proportion of epichlorohydrin rubber exceeds this range, the roller resistance value R ₂ (when Ω, 400 V is applied) of the entire roller body 5 is in the range of the formula (2), although it depends on the composition of the rubber composition and the like. If it is less than, the initial 2dot concentration may be insufficient, or the durable 2dot concentration may be significantly lowered.
On the other hand, by setting the proportion of epichlorohydrin rubber to 30 parts by mass or less in 100 parts by mass of the total amount of rubber, it is possible to suppress deterioration of these characteristics.

The ratio of CR and / or NBR is preferably 1 part by mass or more, and preferably 15 parts by mass or less in the total amount of 100 parts by mass of rubber.
When the ratio of CR and / or NBR is less than this range, the above-mentioned effect of blending these rubbers, that is, the effect _{of finely adjusting the roller resistance value R 2} (when Ω, 400 V is applied) of the entire roller body 5 is applied. May not be obtained sufficiently.

On the other hand, when the ratio of these rubbers exceeds the above range, the epichlorohydrin rubber is relatively reduced, and the roller resistance value R ₂ (when Ω, 400 V is applied) of the entire roller body 5 is described above. It may not be possible to sufficiently reduce the equation (2) to a satisfactory range.
The proportion of non-polar diene rubber other than CR and / or NBR is epichlorohydrin rubber, or the remaining amount of epichlorohydrin rubber and CR and / or NBR.

That is, the ratio of the non-polar diene rubber is set so that the total amount of rubber is 100 parts by mass when the ratio of epichlorohydrin rubber or epichlorohydrin rubber to CR and / or NBR is set to a predetermined value within the above-mentioned range. You can set it.
<Crosslink component>
The rubber composition for the inner layer 2 contains a cross-linking component for cross-linking the rubber.

As the cross-linking component, it is preferable to use a cross-linking agent for cross-linking the rubber and a cross-linking accelerator for promoting the cross-linking of the rubber by the cross-linking agent in combination.
Among these, examples of the cross-linking agent include sulfur-based cross-linking agents, thiourea-based cross-linking agents, triazine derivative-based cross-linking agents, peroxide-based cross-linking agents, various monomers, and the like, and sulfur-based cross-linking agents are particularly preferable.

(Sulfur-based cross-linking agent)
Examples of the sulfur-based cross-linking agent include sulfur such as powdered sulfur, oil-treated powdered sulfur, precipitated sulfur, colloidal sulfur, and dispersible sulfur, and organic sulfur-containing compounds such as tetramethylthium disulfide and N, N-dithiobismorpholine. Etc., and sulfur is particularly preferable.
The proportion of sulfur is preferably 0.5 parts by mass or more per 100 parts by mass of the total amount of rubber, and preferably 2 parts by mass or less, in consideration of imparting good characteristics as rubber to the roller body. preferable.

When oil-treated powdered sulfur, dispersible sulfur, or the like is used as sulfur, the above ratio is the ratio of sulfur itself as an active ingredient contained therein.
When an organic sulfur-containing compound is used as the cross-linking agent, the ratio thereof is preferably adjusted so that the ratio of sulfur contained in the molecule per 100 parts by mass of the total amount of rubber is within the above range.

(Crosslink accelerator)
Examples of the cross-linking accelerator for promoting the cross-linking of rubber include a thiuram-based accelerator, a thiazole-based accelerator, a thiourea-based accelerator, a guanidine-based accelerator, a sulfenamide-based accelerator, a dithiocarbamate-based accelerator, and the like. 1 type or 2 or more types of.
Of these, it is preferable to use a thiuram-based accelerator, a thiazole-based accelerator, a thiourea-based accelerator, and a guanidine-based accelerator in combination.

Examples of the thiuram-based accelerator include one or more of tetramethylthiuram monosulfide, tetramethylthiuram disulfide, tetraethylthiuram disulfide, tetrabutylthiuram disulfide, dipentamethylenethiuram tetrasulfide, and the like, and in particular, tetramethyl. Thiram monosulfide is preferred.
Examples of the thiazole-based accelerator include 2-mercaptobenzothiazole, di-2-benzothiazolyl disulfide, zinc salt of 2-mercaptobenzothiazole, cyclohexylamine salt of 2-mercaptobenzothiazole, 2- (4'-). One or more of morpholinodithio) benzothiazole and the like can be mentioned, and di-2-benzothiazolyl disulfide is particularly preferable.

As the thiourea accelerator, various thiourea compounds having a thiourea structure in the molecule can be used.
Examples of the thiourea accelerator include ethylene thiourea, N, N'-diphenyl thiourea, trimethyl thiourea, and formula (5):
(C _n H _{2n + 1} NH) ₂ C = S (5)
[In the formula, n represents an integer of 1-12. ], One or more of thiourea, tetramethylthiourea and the like, and ethylene thiourea is particularly preferable.

Examples of the guanidine-based accelerator include one or more of 1,3-diphenylguanidine, 1,3-di-o-tolylguanidine, 1-o-tolylbiguanide and the like, and particularly 1,3-. Di-o-tolylguanidine is preferred.
Considering that the effect of promoting the cross-linking of rubber is sufficiently exhibited in the above four types of combined systems, the ratio of the thiuram-based accelerator is 0.3 parts by mass or more per 100 parts by mass of the total amount of rubber. Is preferable, and it is preferably 1 part by mass or less.

The ratio of the thiazole-based accelerator is preferably 0.3 parts by mass or more and preferably 2 parts by mass or less per 100 parts by mass of the total amount of rubber.
The ratio of the thiourea accelerator is preferably 0.3 parts by mass or more and preferably 1 part by mass or less per 100 parts by mass of the total amount of rubber.
Further, the ratio of the guanidine-based accelerator is preferably 0.2 parts by mass or more and preferably 1 part by mass or less per 100 parts by mass of the total amount of rubber.

The thiourea-based accelerator also functions as an ECO cross-linking agent having no sulfur cross-linking property, and the guanidine-based accelerator also functions as an ECO cross-linking accelerator by the thiourea-based accelerator.
<Ion conductive agent>
An ionic conductive agent may be further added to the rubber composition for the inner layer 2.
As the ionic conductive agent, a salt (ion salt) of an anion having a fluoro group and a sulfonyl group in the molecule and a cation is preferable.

By blending the ionic conductive agent, the ionic conductivity of the rubber composition can be further improved, and the roller resistance value R ₂ (when Ω, 400 V is applied) of the entire roller body 5 can be further reduced. ..
Examples of the anion having a fluoro group and a sulfonyl group in the molecule constituting the ionic salt include one or two such as fluoroalkyl sulfonic acid ion, bis (fluoroalkylsulfonyl) imide ion, and tris (fluoroalkylsulfonyl) methide ion. More than seeds can be mentioned.

Among these, examples of the fluoroalkyl sulfonic acid ion include one or more of _{CF 3} SO ₃ ⁻ , C ₄ F ₉ SO ₃ ^{− and the like.}
Examples of the bis (fluoroalkylsulfonyl) imide ion include (CF ₃ SO ₂ ) ₂ N ⁻ , (C ₂ F ₅ SO ₂ ) ₂ N ⁻ , and (C ₄ F ₉ SO ₂ ) (CF ₃ SO ₂ ) N. ⁻ , (FSO ₂ C ₆ F ₄ ) (CF ₃ SO ₂ ) N ⁻ , (C ₈ F ₁₇ SO ₂ ) (CF ₃ SO ₂ ) N ⁻ , (CF ₃ CH ₂ OSO ₂ ) ₂ N ⁻ , (CF) ₃ CF ₂ CH ₂ OSO ₂ ) ₂ N ⁻ , (HCF ₂ CF ₂ CH ₂ OSO ₂ ) ₂ N ⁻ , [(CF ₃ ) ₂ CHOSO ₂ ] ₂ N ^−, etc.

Further, as the tris (fluoroalkylsulfonyl) methide ion, for example, one kind or two or more kinds such as _{(CF 3} SO ₂ ) ₃ C ⁻ and (CF ₃ CH ₂ OSO ₂ ) ₃ C ^{− can be mentioned.}
The cations include, for example, alkali metal ions such as sodium, lithium and potassium, Group 2 element ions such as beryllium, magnesium, calcium, strontium and barium, transition element ions, amphoteric element cations and cations. Examples thereof include one or more of quaternary ammonium ions and imidazolium cations.

As the ionic salt, a lithium salt using lithium ion as a cation or a potassium salt using potassium ion is particularly preferable.
Above all, in terms of the effect of improving the ionic conductivity of the rubber composition _{and lowering the roller resistance value R 2} (when Ω, 400 V is applied) of _{the entire roller body 5, (CF 3} SO ₂ ) ₂ NLi [lithium] -Bis (trifluoromethanesulfonyl) imide Li-TFSI] and / or (CF ₃ SO ₂ ) ₂ NK [potassium bis (trifluoromethanesulfonyl) imide, K-TFSI] are preferred.

The ratio of the ionic conductive agent such as an ionic salt is preferably 0.1 part by mass or more and preferably 2 parts by mass or less per 100 parts by mass of the total amount of rubber.
<Carbon black>
Carbon black may be further blended as a filler in the rubber composition for the inner layer 2.
By blending carbon black, the mechanical strength of the developing roller can be improved.

Examples of carbon black include SAF, ISAF, HAF, FEF and the like.
Further, when conductive carbon black is used as the carbon black, electron conductivity can be imparted to the inner layer 2.
Examples of the conductive carbon black include acetylene black and the like.

The ratio of carbon black is preferably 3 parts by mass or more and preferably 10 parts by mass or less per 100 parts by mass of the total amount of rubber.
<Others>
If necessary, various additives may be further added to the rubber composition for the inner layer 2.
Examples of the additive include a cross-linking accelerator, an acid receiving agent, a plasticizer, a processing aid and the like.

Among these, examples of the cross-linking promoting aid include metal compounds such as zinc oxide; fatty acids such as stearic acid, oleic acid, and cottonseed fatty acid, and one or more of conventionally known cross-linking promoting aids.
The proportion of the cross-linking accelerator is preferably 0.1 part by mass or more, and preferably 7 parts by mass or less, individually per 100 parts by mass of the total amount of rubber.

The antacid functions to prevent the chlorine-based gas generated from epichlorohydrin rubber and CR during cross-linking from remaining in the inner layer 2 and thereby inhibiting cross-linking and contaminating the photoconductor.
As the acid receiving agent, various substances that act as acid receptors can be used, and among them, hydrotalcites or magsalats having excellent dispersibility are preferable, and hydrotalcites are particularly preferable.

Further, when hydrotalcites and the like are used in combination with magnesium oxide and potassium oxide, a higher acid receiving effect can be obtained, and contamination of the photoconductor can be prevented more reliably.
The ratio of the acid receiving agent is preferably 0.1 part by mass or more, and preferably 7 parts by mass or less per 100 parts by mass of the total amount of rubber.
Examples of the plasticizer include various plasticizers such as dibutyl phthalate, dioctyl phthalate, and tricresyl phosphate, and various waxes such as polar wax. Examples of the processing aid include fatty acid metals such as zinc stearate. Examples include salt.

The ratio of the plasticizer and / or the processing aid is preferably 3 parts by mass or less per 100 parts by mass of the total amount of rubber.
In addition, as additives, various additives other than carbon black, deterioration inhibitors, scorch inhibitors, lubricants, pigments, antistatic agents, flame retardants, neutralizers, nucleating agents, co-crosslinking agents, etc. are added. The agent may be blended in any proportion.

Examples of the filler other than carbon black include one or more of zinc oxide, silica, talc, calcium carbonate, magnesium carbonate, aluminum hydroxide and the like.
<Preparation of rubber composition>
The rubber composition for the inner layer 2 containing each component described above can be prepared in the same manner as before.

First, the rubber is kneaded, then each component other than the cross-linking component is added and kneaded, and finally the cross-linking component is added and kneaded to obtain a rubber composition for the inner layer 2.
For kneading, for example, a kneader, a Bambali mixer, an extruder and the like can be used.
<< Rubber composition for outer layer 4 >>
The outer layer 4 can be formed of various elastic materials capable of adjusting _{the surface resistance value R 1} (when Ω and 10 V is applied) of the outer peripheral surface 8 of the roller body 5 within the above-mentioned range.

In particular, the outer layer 4 is preferably formed by a crosslinked product of a rubber composition containing epichlorohydrin rubber and a diene-based rubber.
<Epichlorohydrin rubber>
As the epichlorohydrin rubber, one or more of the same epichlorohydrin rubbers used in the inner layer 2 can be used.

Of these, ECO and / or GECO are preferable, and GECO is particularly preferable.
The reason is the same as in the case of the inner layer 2.
That is, by using GECO as the epichlorohydrin rubber, the outer layer 4 can be made to have a small compression set and less likely to be settled.
<Diene rubber>
The diene rubber is used to impart good workability to the rubber composition, improve the mechanical strength and durability of the outer layer 4, or impart good properties as rubber to the outer layer 4. Function.

Further, the diene rubber is also a material that is oxidized by ultraviolet irradiation to form an oxide film 9 on the surface of the outer layer 4, that is, the outer peripheral surface 8 of the roller body 5.
As the diene-based rubber, one or more of the same diene-based rubbers used in the inner layer 2 can be used.
That is, examples of the diene rubber include natural rubber, IR, NBR, SBR, BR, CR and the like.

Among them, as the diene-based rubber, it is preferable to use a non-polar diene-based rubber, specifically, at least one of three types of IR, BR, and SBR, particularly SBR.
_{Further, in order to finely adjust the surface resistance value R 1} (when Ω and 10 V is applied) of the outer peripheral surface 8 of the roller main body 5, CR and / or NBR may be further used together with the non-polar diene rubber.

Specific examples of these diene-based rubbers are as described above.
(Rubber ratio)
Proportion of rubber, various properties required for the outer layer 4, can be particularly surface resistance value R ₁ of the outer peripheral surface 8 of the roller body 5 _(Omega, when 10V is applied) and, optionally set depending on the flexibility of the outer layer 4 or the like ..
However, the proportion of epichlorohydrin rubber is preferably 20 parts by mass or more, particularly preferably 25 parts by mass or more, and preferably 50 parts by mass or less in the total amount of 100 parts by mass of rubber.

If the proportion of epichlorohydrin rubber is less than this range, the surface resistance value R ₁ (when Ω and 10 V is applied) of the outer peripheral surface 8 of the roller body 5 is within the range of the above-mentioned formula (1), although it depends on the composition of the rubber composition and the like. May exceed.
Then, the initial black solid density may be insufficient and the contrast of the image may be lowered, or the entire black solid image may be blurred and the entire black solid density may be lowered.

On the other hand, when the proportion of epichlorohydrin rubber exceeds the above range, the surface resistance value R ₁ (when Ω and 10 V is applied) of the outer peripheral surface 8 of the roller body 5 becomes less than the range of the above-mentioned formula (1), and the roller body The resistance value near the surface of No. 5 may become too low, causing image defects or the like due to overcurrent in the image.
On the other hand, by setting the proportion of epichlorohydrin rubber in the above range, the surface resistance value R ₁ (when Ω and 10 V is applied) of the outer peripheral surface 8 of the roller body 5 is set in the range of the equation (1), and these characteristics are exhibited. It can be suppressed from decreasing.

The ratio of CR and / or NBR is preferably 1 part by mass or more, particularly preferably 2.5 parts by mass or more, and preferably 10 parts by mass or less in the total amount of 100 parts by mass of rubber.
When the ratio of CR and / or NBR is less than this range, the above-mentioned effect of blending these rubbers, that is, the surface resistance value R ₁ (when Ω and 10 V is applied) of the outer peripheral surface 8 of the roller body 5 is finely adjusted. It may not be possible to obtain a sufficient effect.

On the other hand, when the ratio of these rubbers exceeds the above range, the epichlorohydrin rubber is relatively reduced, and the surface resistance value R ₁ (when Ω and 10 V is applied) of the outer peripheral surface 8 of the roller body 5 is set as described above. In some cases, it may not be possible to sufficiently reduce the above equation (1) to a satisfactory range.
The proportion of non-polar diene rubber other than CR and / or NBR is epichlorohydrin rubber, or the remaining amount of epichlorohydrin rubber and CR and / or NBR.

That is, the ratio of the non-polar diene rubber is set so that the total amount of rubber is 100 parts by mass when the ratio of epichlorohydrin rubber or epichlorohydrin rubber to CR and / or NBR is set to a predetermined value within the above-mentioned range. You can set it.
<Crosslink component>
As the cross-linking component, it is preferable to use a combination of a cross-linking agent and a cross-linking accelerator similar to those used in the inner layer 2.

That is, the cross-linking agent is preferably a sulfur-based cross-linking agent, particularly sulfur, and the cross-linking accelerator to be combined with the sulfur-based cross-linking agent is a thiuram-based accelerator, a thiazole-based accelerator, a thiourea-based accelerator, and a guanidine-based accelerator. It is preferable to use 4 types in combination.
The proportions of the sulfur-based cross-linking agent and the four types of cross-linking accelerators are also preferably about the same as in the case of the inner layer 2.

<Ion conductive agent>
An ionic conductive agent may be further added to the rubber composition for the outer layer 4.
By blending the ionic conductive agent, the ionic conductivity of the rubber composition can be further improved, and the surface resistance value R ₁ (when Ω and 10 V is applied) of the outer peripheral surface 8 of the roller body 5 can be further lowered. it can.

As the ionic conductive agent, a salt (ion salt) of an anion having a fluoro group and a sulfonyl group in the molecule and a cation, which is the same as that used in the inner layer 2, is preferable.
The ratio of the ionic conductive agent is also preferably about the same as in the case of the inner layer 2.
<Others>
If necessary, various additives may be further added to the rubber composition for the outer layer 4.

As the additive, the same additives as those used in the inner layer 2, for example, a cross-linking accelerator, an acid receiving agent, a filler, a plasticizer, a processing aid, a deterioration inhibitor, a deterioration inhibitor, a scorch inhibitor, etc. Examples include lubricants, pigments, antistatic agents, flame retardants, neutralizers, nucleating agents, co-crosslinking agents and the like.
As the filler, for example, carbon black such as thermal black is preferable.
The ratio of the additive is also preferably about the same as in the case of the inner layer 2.

<Preparation of rubber composition>
The rubber composition for the outer layer 4 containing each component described above can be prepared in the same manner as before.
That is, the rubber composition for the outer layer 4 is obtained by first kneading the rubber, then adding each component other than the cross-linking component and kneading, and finally adding the cross-linking component and kneading.

For kneading, for example, a kneader, a Bambali mixer, an extruder and the like can be used.
<< Manufacturing of developing roller 1 >>
In order to manufacture the developing roller 1 shown in FIGS. 1A and 1B using the rubber compositions for the inner layer 2 and the outer layer 4, for example, both rubber compositions are supplied to a two-layer extruder. Then, after coextrusion molding into a tubular shape having a laminated two-layer structure, the entire layer is crosslinked to form an inner layer 2 and an outer layer 4.

Alternatively, the rubber composition for the inner layer 2 is extruded into a tubular shape and crosslinked to form the inner layer 2, and then a sheet of the rubber composition for the outer layer 4 is wound around the outer peripheral surface 3 thereof and press-molded or the like. It is formed into a tubular shape, crosslinked, and integrated with the inner layer 2 to form the outer layer 4.
Next, the formed laminate of the inner layer 2 and the outer layer 4 is heated by using an oven or the like for secondary cross-linking, cooled, and then polished to have a predetermined outer diameter. It is formed.

The thickness of the inner layer 2 can be arbitrarily set according to the structure, dimensions, and the like of the image forming apparatus to be incorporated.
Further, although the thickness of the outer layer 4 can be arbitrarily set, it is preferably 0.1 mm or more, and preferably 2 mm or less.
_{By setting the thickness of the outer layer 4 in this range, the surface resistance value R 1} (Ω, Ω,) of the outer peripheral surface 8 of the roller body 5 when the inner layer 2 and the outer layer 4 made of the above-mentioned predetermined rubber compositions are combined. Both (when 10 V is applied) and the overall roller resistance value R ₂ (when Ω, 400 V is applied) can be adjusted within the above-mentioned range.

Therefore, both the solid black density and the 2 dot density can be improved at the same time to form an image having excellent contrast and fine line reproducibility and gradation.
In addition, it is possible to suppress the occurrence of density unevenness depending on the density of images adjacent to each other in the lateral direction, and it is also possible to suppress a decrease in the durability 2 dot density and the entire black solid density.
As the polishing method, for example, various polishing methods such as dry traverse polishing can be adopted, and mirror polishing may be performed at the end of the polishing step to finish.

In that case, the releasability of the outer peripheral surface 8 is improved, and the adhesion of the toner is further suppressed by the synergistic effect of not forming the oxide film 9 or forming the oxide film 9. In addition, it is possible to effectively prevent contamination of the photoconductor and the like.
The shaft 7 can be inserted into the through hole 6 and fixed at any time from after cutting to after polishing the tubular body that is the basis of the roller body 5.

However, after cutting, it is preferable to first perform secondary cross-linking and polishing with the shaft 7 inserted through the through hole 6. As a result, warpage and deformation of the roller body 5 due to expansion and contraction during secondary cross-linking can be suppressed.
Further, by polishing while rotating around the shaft 7, the workability of the polishing can be improved and the deflection of the outer peripheral surface 8 can be suppressed.

As described above, the shaft 7 is inserted into the through hole 6 of the tubular body before the secondary cross-linking through a conductive adhesive, particularly a conductive thermosetting adhesive, and then the shaft 7 is subjected to the secondary cross-linking. Alternatively, a material having an outer diameter larger than the inner diameter of the through hole 6 may be press-fitted into the through hole 6.
In the former case, the tubular body is secondarily crosslinked by heating in the oven, and at the same time, the thermosetting adhesive is cured, and the shaft 7 is electrically bonded to the roller body 5 and mechanically. Is fixed to.

In the latter case, electrical joining and mechanical fixing are completed at the same time as press fitting.
Further, as described above, both methods may be used in combination to electrically join the shaft 7 to the roller body 5 and mechanically fix the shaft 7.
As described above, the oxide film 9 is preferably formed by irradiating the outer peripheral surface 8 of the roller body 5, which is the surface of the outer layer 4, with ultraviolet rays.

That is, the oxide film 9 can be formed only by irradiating the outer peripheral surface 8 of the roller body 5 with ultraviolet rays having a predetermined wavelength for a predetermined time to oxidize the rubber constituting the vicinity of the outer peripheral surface 8.
Therefore, the process of forming the oxide film 9 is simple and efficient, and it is possible to suppress a decrease in the productivity of the developing roller 1 and a high production cost.
_{Further, as described above, the contact angle θ W} (°) of water on the outer peripheral surface 8 coated with the formed oxide film 9 can be adjusted by adjusting the integrated light amount (mJ / cm ^{2) of ultraviolet rays.} it can.

Moreover, the oxide film 9 formed by irradiation with ultraviolet rays does not cause problems like the conventional coating film formed by applying a coating agent, and has a uniform thickness and a roller body 5. It is also excellent in adhesion.
The wavelength of the ultraviolet rays to be irradiated is preferably 100 nm or more in consideration of efficiently oxidizing the diene-based rubber in the rubber composition for the outer layer 4 to form the oxide film 9 having the above-mentioned excellent function. , 400 nm or less, particularly preferably 300 nm or less.

The irradiation time can be arbitrarily set so that the contact angle θ _W (°) of water based on the integrated amount of ultraviolet rays (mJ / cm ² ) is within the predetermined range described above.
However, the oxide film 9 may be formed by another method, or may not be formed as described above.
Any intermediate layer may be interposed between the inner layer 2 and the outer layer 4 in one layer or two or more layers.

However, in consideration of simplifying the structure of the roller body 5, the roller body 5 has a two-layer structure in which the inner layer 2 and the outer layer 4 are directly laminated as shown in FIGS. 1A and 1B. Is preferable.
The developing roller 1 of the present invention can be used by being incorporated into various image forming devices using an electrophotographic method, such as a laser printer, an electrostatic copier, a plain paper facsimile machine, and a multifunction device thereof. ..

Hereinafter, the present invention will be described based on Examples and Comparative Examples, but the configuration of the present invention is not necessarily limited to these examples.
<< Preparation of rubber composition >>
<Rubber composition for inner layer 2 (A)>
As rubber, GECO [Epion (registered trademark) 301L manufactured by Osaka Soda Corporation, EO / EP / AGE = 73/23/4 (molar ratio)] 16 parts by mass, IR [Nipol manufactured by Nippon Zeon Co., Ltd.] (Registered trademark) IR2200, non-oil spread] 77 parts by mass, SBR [JSR 1502 manufactured by JSR Corporation, bonded styrene: 23.5%, non-oil spread] 6 parts by mass, and CR [manufactured by Showa Denko KK] Styrene (registered trademark) WRT, non-oil-extended] 1 part by mass was used.

While kneading 100 parts by mass of the total amount of the rubber using a Bambali mixer, the following components were mixed and kneaded.

Each component in Table 1 is as follows, and the mass part in the table is the mass part per 100 mass parts of the total amount of rubber.
Ionic salt: Potassium bis (trifluoromethanesulfonyl) imide [K-TFSI, EF-N112 manufactured by Mitsubishi Materials Electronics Chemical Co., Ltd.]
Crosslinking accelerator: Zinc oxide 2 types [manufactured by Sakai Chemical Industry Co., Ltd.]
Filler: Carbon Black FEF [Seast (registered trademark) SO manufactured by Tokai Carbon Co., Ltd.]
Antacid: Hydrotalcites [DHT-4A (registered trademark) -2 manufactured by Kyowa Chemical Industry Co., Ltd.]
Processing aid: Zinc stearate [SZ-2000 manufactured by Sakai Chemical Industry Co., Ltd.]
Next, while continuing kneading, the following cross-linking components were blended and further kneaded to prepare a rubber composition (A) for the inner layer 2.

Each component in Table 2 is as follows, and the mass part in the table is the mass part per 100 mass parts of the total amount of rubber.
Cross-linking agent: Oil-treated powdered sulfur [Kinka-in 5% oil-containing fine powder sulfur manufactured by Tsurumi Chemical Industry Co., Ltd.]
Accelerator DM: Di-2-benzothiazolyl disulfide [Noxeller (registered trademark) DM manufactured by Ouchi Shinko Kagaku Kogyo Co., Ltd., thiazole-based accelerator]
Accelerator TS: Tetramethylthiuram Monosulfide [Sunceller (registered trademark) TS manufactured by Sanshin Chemical Industry Co., Ltd., thiuram-based accelerator]
Accelerator 22: Ethylene thiourea [2-mercaptoimidazoline, Axel (registered trademark) 22-S manufactured by Kawaguchi Chemical Industry Co., Ltd., thiourea accelerator]
Accelerator DT: 1,3-di-o-tolylguanidine [Noxeller DT manufactured by Ouchi Shinko Kagaku Kogyo Co., Ltd., guanidine-based accelerator]
<Rubber composition for inner layer 2 (B)>
The rubber composition (B) for the inner layer 2 was prepared in the same manner as the rubber composition (A) except that the amount of GECO was 18 parts by mass and the amount of IR was 75 parts by mass.

<Rubber composition (C) for inner layer 2>
The rubber composition (C) for the inner layer 2 was prepared in the same manner as the rubber composition (A) except that the amount of GECO was 21 parts by mass and the amount of IR was 72 parts by mass.
<Rubber composition (D) for inner layer 2>
The rubber composition (D) for the inner layer 2 was prepared in the same manner as the rubber composition (A) except that the amount of GECO was 23 parts by mass and the amount of IR was 70 parts by mass.

<Rubber composition (E) for inner layer 2>
The rubber composition (E) for the inner layer 2 was prepared in the same manner as the rubber composition (A) except that the amount of GECO was 26 parts by mass and the amount of IR was 67 parts by mass.
<Rubber composition (F) for inner layer 2>
The rubber composition (F) for the inner layer 2 was prepared in the same manner as the rubber composition (A) except that the amount of GECO was 28 parts by mass and the amount of IR was 65 parts by mass.

<Rubber composition (G) for inner layer 2>
The rubber composition (G) for the inner layer 2 was prepared in the same manner as the rubber composition (A) except that the amount of GECO was 30 parts by mass and the amount of IR was 63 parts by mass.
<Rubber composition (H) for inner layer 2>
The rubber composition (H) for the inner layer 2 was prepared in the same manner as the rubber composition (A) except that the amount of GECO was 32 parts by mass and the amount of IR was 61 parts by mass.

<Rubber composition (I) for inner layer 2>
As rubber, GECO [Epion 301L manufactured by Osaka Soda Co., Ltd.] 26 parts by mass, BR [UBEPOL (registered trademark) BR130B manufactured by Ube Industries, Ltd., non-oil exhibition] 59 parts by mass, CR [mentioned above Showa Denko Co., Ltd.'s Showpren WRT] 10 parts by mass and NBR [Nippon Zeon Co., Ltd. Nipol DN401LL, acrylonitrile content: 18.0%, non-oil spread] 5 parts by mass, and ionic salt The rubber composition (I) for the inner layer 2 was prepared in the same manner as the rubber composition (A) except that it was not blended.

<Rubber composition for inner layer 2 (J)>
As rubber, GECO [Epion 301L manufactured by Osaka Soda Co., Ltd. mentioned above] 17.5 parts by mass, IR [Nipol IR2200 manufactured by Nippon Zeon Co., Ltd. mentioned above] 36.25 parts by mass, SBR [mentioned above JSR 1502 manufactured by JSR Corporation] 36.25 parts by mass, CR [Showpren WRT manufactured by Showa Denko Co., Ltd. mentioned above] 5 parts by mass, and ethylene propylene diene rubber [EPDM, Sumitomo Chemical] which is a non-diene rubber. Esprene (registered trademark) 505A manufactured by JSR Corporation] A rubber composition (J) for the inner layer 2 was prepared in the same manner as the rubber composition (A) except that 5 parts by mass was used.

<Rubber composition (K) for inner layer 2>
As rubber, GECO [Epion 301L manufactured by Osaka Soda Co., Ltd. mentioned above] 5 parts by mass, IR [Nipol IR2200 manufactured by Nippon Zeon Co., Ltd. mentioned above] 45 parts by mass, BR [Ube Kosan Co., Ltd. mentioned above] ) UBEPOL BR130B] 40 parts by mass and CR [Showa Denko Co., Ltd. showprene WRT] 10 parts by mass, and the amount of ionic salt was 1 part by mass. The rubber composition (K) for the inner layer 2 was prepared in the same manner as in A).

<Rubber composition (L) for inner layer 2>
The rubber composition for the inner layer 2 is the same as the rubber composition (K) except that the amount of GECO is 10 parts by mass, the amount of IR is 42.5 parts by mass, and the amount of BR is 37.5 parts by mass. (L) was prepared.
<Rubber composition (M) for inner layer 2>
The rubber for the inner layer 2 is the same as the rubber composition (K) except that the amount of GECO is 12.5 parts by mass, the amount of IR is 41.25 parts by mass, and the amount of BR is 36.25 parts by mass. The composition (M) was prepared.

<Rubber composition (N) for inner layer 2>
The rubber composition (N) for the inner layer 2 was prepared in the same manner as the rubber composition (K) except that the amount of GECO was 15 parts by mass, the amount of IR was 40 parts by mass, and the amount of BR was 35 parts by mass. Prepared.
<Rubber composition (O) for inner layer 2>
The rubber composition for the inner layer 2 is the same as the rubber composition (K) except that the amount of GECO is 20 parts by mass, the amount of IR is 37.5 parts by mass, and the amount of BR is 32.5 parts by mass. (O) was prepared.

<Rubber composition (P) for inner layer 2>
The rubber composition for the inner layer 2 is the same as the rubber composition (K) except that the amount of GECO is 30 parts by mass, the amount of IR is 32.5 parts by mass, and the amount of BR is 27.5 parts by mass. (P) was prepared.
<Rubber composition for inner layer 2 (Q)>
As rubber, GECO [Epion 301L manufactured by Osaka Soda Co., Ltd. mentioned above] 28 parts by mass, IR [Nipol IR2200 manufactured by Nippon Zeon Co., Ltd. mentioned above] 60 parts by mass, SBR [JSR Corporation mentioned above] JSR 1502] 6 parts by mass, CR [Showa Denko Co., Ltd. Showa Plen WRT] 1 part by mass, and EPDM [Sumitomo Chemical Co., Ltd. Esplen 505A] 5 parts by mass were used. A rubber composition (Q) for the inner layer 2 was prepared in the same manner as the rubber composition (A) except for the above.

<Rubber composition (i) for outer layer 4>
As rubber, GECO [Epion 301L manufactured by Osaka Soda Co., Ltd. mentioned above] 15 parts by mass, SBR [JSR 1502 manufactured by JSR Corporation mentioned above] 75 parts by mass, and CR [Showa Denko mentioned above (Showa Denko) Showa Plen WRT manufactured by JSR Corporation] 10 parts by mass was used.
While kneading 100 parts by mass of the total amount of the rubber using a Bambali mixer, the following components were mixed and kneaded.

Each component in Table 3 is as follows. The parts by mass in the table are parts by mass per 100 parts by mass of the total amount of rubber.
Ionic salt: Potassium bis (trifluoromethanesulfonyl) imide [K-TFSI, EF-N112 manufactured by Mitsubishi Materials Denshi Kasei Co., Ltd.]
Crosslinking accelerator: Zinc oxide 2 types [manufactured by Sakai Chemical Industry Co., Ltd.]
Filler: Carbon Black [Thermal Black, Asahi # 15 manufactured by Asahi Carbon Co., Ltd.]
Antacid: Hydrotalcites [DHT-4A-2 manufactured by Kyowa Chemical Industry Co., Ltd. mentioned above]
Processing aid: Zinc stearate [SZ-2000 manufactured by Sakai Chemical Industry Co., Ltd. mentioned above]
Next, while continuing kneading, the following cross-linking components were blended and further kneaded to prepare a rubber composition (i) for the outer layer 4.

Each component in Table 4 is as follows. The parts by mass in the table are parts by mass per 100 parts by mass of the total amount of rubber.
Cross-linking agent: Oil-treated powdered sulfur [Kinka-in 5% oil-containing fine powder sulfur manufactured by Tsurumi Chemical Industry Co., Ltd.]
Accelerator DM: Di-2-benzothiazolyl disulfide [Noxeller DM manufactured by Ouchi Shinko Kagaku Kogyo Co., Ltd., thiazole-based accelerator]
Accelerator TS: Tetramethylthiuram monosulfide [Sunceller TS manufactured by Sanshin Chemical Industry Co., Ltd., thiuram-based accelerator]
Accelerator 22: Ethylene thiourea [2-mercaptoimidazoline, accelerator 22-S manufactured by Kawaguchi Chemical Industry Co., Ltd., thiourea accelerator]
Accelerator DT: 1,3-di-o-tolylguanidine [Noxeller DT manufactured by Ouchi Shinko Kagaku Kogyo Co., Ltd., guanidine-based accelerator]
<Rubber composition for outer layer 4 (ii)>
The rubber composition (ii) for the outer layer 4 was prepared in the same manner as the rubber composition (i) except that the amount of GECO was 20 parts by mass and the amount of SBR was 70 parts by mass.

<Rubber composition for outer layer 4 (iii)>
The rubber composition (iii) for the outer layer 4 was prepared in the same manner as the rubber composition (i) except that the amount of GECO was 25 parts by mass and the amount of SBR was 65 parts by mass.
<Rubber composition for outer layer 4 (iv)>
The rubber composition (iv) for the outer layer 4 was prepared in the same manner as the rubber composition (i) except that the amount of GECO was 30 parts by mass and the amount of SBR was 60 parts by mass.

<Rubber composition for outer layer 4 (v)>
The rubber composition (v) for the outer layer 4 was prepared in the same manner as the rubber composition (i) except that the amount of GECO was 50 parts by mass and the amount of SBR was 40 parts by mass.
<Rubber composition for outer layer 4 (vi)>
The rubber composition for the outer layer 4 is the same as the rubber composition (i) except that the amount of GECO is 30 parts by mass, the amount of SBR is 67.5 parts by mass, and the amount of CR is 2.5 parts by mass. (vii) was prepared.

<Rubber composition for outer layer 4 (vii)>
A rubber composition (viii) for the outer layer 4 was prepared in the same manner as the rubber composition (vi) except that an ionic salt was not blended.
<Rubber composition for outer layer 4 (viii)>
A rubber composition (viii) for the outer layer 4 was prepared in the same manner as the rubber composition (vii) except that the amount of GECO was 40 parts by mass and the amount of SBR was 57.5 parts by mass.

<Rubber composition for outer layer 4 (ix)>
A rubber composition (ix) for the outer layer 4 was prepared in the same manner as the rubber composition (vii) except that the amount of GECO was 25 parts by mass and the amount of SBR was 72.5 parts by mass.
<< Examples 1-9, Comparative Examples 1-10 >>
The rubber compositions (B) to (P) for the inner layer 2 and the rubber compositions (i) to (V) for the outer layer are supplied to the two-layer extruder in the combinations shown in Tables 5 to 8 to the outside. It was extruded into a tubular shape having a two-layer structure with a diameter of φ16 mm and an inner diameter of φ6.5 mm, mounted on a temporary shaft for cross-linking, and cross-linked in a vulcanization can at 160 ° C. for 1 hour.

Next, the crosslinked tubular body is reattached to a metal shaft 7 having an outer diameter of φ7.5 mm coated with a conductive thermosetting adhesive on the outer peripheral surface, and heated to 160 ° C. in an oven. It was adhered to the shaft 7.
Next, both ends of the tubular body are shaped, and the outer peripheral surface 8 is traverse-polished using a cylindrical grinding machine and then mirror-polished to have an outer diameter of φ16 mm. A roller body 5 having a layered structure and integrated with the shaft 7 was formed.

The thickness of the outer layer 4 after polishing was about 0.1 to 2 mm.
Next, after wiping the outer peripheral surface 8 of the formed roller body 5 with alcohol, the distance from the outer peripheral surface 8 to the UV lamp is set to be 50 mm, and the ultraviolet irradiation device [PL21-manufactured by Sen Special Light Source Co., Ltd. 200] was set.
Then, the outer peripheral surface 8 was covered with the oxide film 9 by irradiating ultraviolet rays having wavelengths of 184.9 nm and 253.7 nm while rotating by 90 ° about the shaft to manufacture the developing roller 1.

The integrated amount of ultraviolet rays was 100 mJ / cm ² in each case.
《Characteristic measurement》
The following tests were carried out on the developing rollers 1 manufactured in each of the above Examples and Comparative Examples to determine their characteristics.
Each test was carried out in an environment with a temperature of 23 ° C. and a relative humidity of 55%.

<Measurement of surface resistance value R _{1>
The surface resistance value R 1} (when Ω, 10 V is applied) of the outer peripheral surface 8 of the roller body 5 is set to the resistivity meter [High Restor (registered trademark) UP MCP-HT800 manufactured by Mitsubishi Chemical Analytech Co., Ltd.] and the company's exclusive use. Measurements were made in surface resistivity mode using an MCP probe (UA type).
That is, the MCP probe is applied with a load of 480 g and pressed against the central portion of the outer peripheral surface 8 of the roller body 5 in the axial direction, and the value after 10 seconds has passed is the surface resistance value R of the outer peripheral surface 8 of the roller body 5. _{It was set to 1} (when Ω and 10 V were applied).

The measurement conditions were RCF (S): 1.050 and applied voltage: 10V.
As for the surface resistance value R ₁ (when Ω and 10 V is applied), as described above, those having a common logarithmic value log R ₁ of 7.0 or more and 8.5 or less are passed (○), and others are rejected (○). ×).
<Measurement of roller resistance value R _{2>
The roller resistance value R 2} (when Ω, 400 V was applied) of the entire roller body 5 was measured by the method shown in FIG.

That is, with reference to FIGS. 1 and 2, an aluminum drum 10 capable of rotating at a constant rotation speed is first prepared, and the outer peripheral surface 8 of the roller body 5 is placed on the outer peripheral surface 11 of the prepared aluminum drum 10 from above. Was brought into contact.
Further, a DC power supply 12 and a resistor 13 are connected in series between the shaft 7 and the aluminum drum 10 to form a measurement circuit 14.

In the DC power supply 12, the (−) side was connected to the shaft 7 and the (+) side was connected to the resistor 13, and the resistance value r of the resistor 13 was set to 100Ω.
Next, a load F of 450 g was applied to both ends of the shaft 7, and the aluminum drum 10 was rotated at 40 rpm with the roller body 5 pressed against the aluminum drum 10.

Then, while continuing the rotation, when the applied voltage E of DC 400 V was applied from the DC power supply 12 between the roller main body 5 and the aluminum drum 10, the detected voltage V applied to the resistor 13 was measured.
Since the detection voltage V and the applied voltage E (= 400V), the roller resistance value R ₂ of the entire roller body 5 is basically the formula (3):
R ₂ = r × E / V-r (3)
Demanded by.

However, since the term -r in the formula (3) can be regarded as a minute amount, in the present invention, the formula (3a):
R ₂ = r × E / V (3a)
_{The roller resistance value R 2} (when Ω, 400 V was applied) of the entire roller body 5 was set as the value obtained by.
As for the roller resistance value R ₂ (when Ω, 400 V is applied), as described above, the one in which the common log value log R ₂ is 6.3 or more and 8.5 or less is passed (○), and the others are rejected (○). ×).

<Measurement of water contact angle θ _{W>
The contact angle θ W} (°) of water on the outer peripheral surface 8 of the roller body 5 was determined by using an automatic contact angle meter [DMo-501 of Kyowa Interface Science Co., Ltd.] with a droplet amount of 2 μL and after dropleting. Measurement start time: Measurement was performed under the condition of 1000 ms.
Specifically, referring to FIG. 3, first, 2 μL of pure water filled in the microsyringe is dropped onto the outer peripheral surface 8 of the roller body 5, and the shape of the droplet 15 1000 ms after the dropping is based on the formula (4). :
θ _W = 2 arctan (h / r) (4)
The contact angle of water θ _W (°) was determined by.

As shown in FIG. 3, h is the height of the droplet 15 dropped on the outer peripheral surface 8 of the roller body 5, and r is the radius of the droplet 15.
The measurement was carried out by dropping the droplets 15 on the outer peripheral surface 8 of the roller body 5 of the same sample at a position 5 cm from both ends in the axial direction and at a total of three locations in the center in the axial direction, and calculating the average value. It was used as a measured value.

Regarding the water contact angle θ _W (°), less than 50 ° was regarded as defective (×), 50 ° or more and less than 60 ° was regarded as good (Δ), and 60 ° or more was regarded as particularly good (◯).
《Actual machine test》
The manufactured developing roller 1 was incorporated into a laser printer [HL-2240D manufactured by Brother Industries, Ltd.], and the following tests were carried out to evaluate the image quality of the formed image.

Each test was carried out in an environment with a temperature of 23.5 ° C. and a relative humidity of 55%.
<Measurement of initial solid black density>
Immediately after 30 consecutive 1% density images were formed on plain paper, one 3 cm square black solid image was formed.
Then, the image density was measured at any five points on the formed black solid image using a reflection densitometer manufactured by Videojet X-Light Co., Ltd., and the average value was obtained to obtain the initial black solid density. The initial solid black density was 1.30 or higher as a pass (◯) and less than 1.30 as a failure (x).

<Measurement of initial 2dot concentration>
Immediately after 30 consecutive 1% density images were formed on plain paper, one isolated 2dot image in which circles were lined up on a square grid having a grid length of about 80 μm was formed.
Then, the image density was measured at any five points on the formed isolated 2 dot image using the same reflection densitometer, and the average value was obtained and used as the initial 2 dot density.

The initial 2dot concentration of more than 0.02 was regarded as acceptable (◯), and the initial 2dot concentration of 0.02 or less was regarded as rejected (x).
<Measurement of density unevenness>
Immediately after 3000 sheets of 1% density images are continuously formed on plain paper, a 3 cm wide halftone part and the halftone part are adjacent to each other with a 5 mm gap in the horizontal direction orthogonal to the paper passing direction. Then, one image having a solid black portion of 3 cm square was formed.

Then, by observing the halftone portion of the formed image, those without unevenness are evaluated as good (○), those with unevenness are evaluated as defective (×), and the evaluation is defective (×). No further testing was done.
Further, those having an initial solid black concentration of 1.1 or less and / or those having an initial 2dot concentration of 0.01 or less were not subjected to the subsequent tests.

<Measurement of durable 2dot concentration>
Immediately after 3000 consecutive 1% density images were formed on plain paper, one isolated 2dot image, which was the same as the initial 2dot density measurement, was formed.
Then, the image density was measured at any five points on the formed isolated 2 dot image using the same reflection densitometer, and the average value was obtained to obtain the durable 2 dot density.

Those having a durable 2dot concentration of more than 0.02 were evaluated as acceptable (◯), and those having a durability of 0.02 or less were evaluated as rejected (x).
Further, the difference between the initial 2 dot concentration and the durable 2 dot concentration is obtained as the amount of change (Δ2 dot concentration), and the one having the Δ2 dot concentration of 0.03 or less is passed (○), and the one exceeding 0.03 is rejected (○). ×).

<Measurement of solid black density on the entire surface>
Immediately after 3000 consecutive 1% density images were formed on plain paper, one solid black image was formed on the entire surface.
Then, the density of the portion having the lowest density of the formed solid black image was measured using the same reflection densitometer to obtain the solid black density of the entire surface.

The overall black solid density was defined as poor (x) when it was less than 1.13, good (Δ) when it was 1.13 or more and less than 1.2, and particularly good (◯) when it was 1.2 or more.
The above results are shown in Tables 5 to 8.

From the results of Tables 5 to 8, it has a two-layer structure of an inner layer 2 and an outer layer 4, and the inner layer 2 has an epichlorohydrin rubber ratio of 21 parts by mass or more in 100 parts by mass of the total amount of rubber, and has an outer peripheral surface 8 of the outer layer 8. By setting the surface resistance value log R ₁ to 7.0 to 8.5 and the roller resistance value log R ₂ of the entire roller body 5 to 6.3 to 8.5, an image having better image quality than the current state can be formed. It was found that a developing roller could be obtained.

<< Examples 10 to 19, Comparative Examples 11 to 14 >>
The rubber compositions (A) to (H) (Q) for the inner layer 2 and the rubber compositions (vi) to (ix) for the outer layer are supplied to the two-layer extruder in the combinations shown in Tables 9 to 11. Then, it was extruded into a tubular shape having a two-layer structure with an outer diameter of φ16 mm and an inner diameter of φ6.5 mm, mounted on a temporary shaft for cross-linking, and cross-linked in a vulcanization can at 160 ° C. for 1 hour.

Next, the crosslinked tubular body is reattached to a metal shaft 7 having an outer diameter of φ7.5 mm coated with a conductive thermosetting adhesive on the outer peripheral surface, and heated to 160 ° C. in an oven. It was adhered to the shaft 7.
Next, both ends of the tubular body are shaped, and the outer peripheral surface 8 is traverse-polished using a cylindrical grinding machine and then mirror-polished to have an outer diameter of φ16 mm. A roller body 5 having a layered structure and integrated with the shaft 7 was formed.

The thickness of the outer layer 4 after polishing was about 0.1 to 2 mm.
Next, after wiping the outer peripheral surface 8 of the formed roller body 5 with alcohol, the distance from the outer peripheral surface 8 to the UV lamp is set to be 50 mm, and the ultraviolet irradiation device [PL21-manufactured by Sen Special Light Source Co., Ltd. 200] was set.
Then, the outer peripheral surface 8 was covered with the oxide film 9 by irradiating ultraviolet rays having wavelengths of 184.9 nm and 253.7 nm while rotating by 90 ° about the shaft to manufacture the developing roller 1.

The integrated light amount of ultraviolet rays was set to the values shown in Tables 9 to 11, respectively.
Each of the above-mentioned tests was carried out on the developing rollers 1 manufactured in each of the above Examples and Comparative Examples to evaluate their characteristics.
The results are shown in Tables 9 to 11.

From the results of Tables 9 to 11, it was found that a developing roller capable of forming an image having better image quality than the current state can be obtained by the above-described configuration.
Further, from the results of Examples 1 to 19 and Comparative Examples 1 to 14, _{it is preferable that the outer peripheral surface 8 of the roller body 5 has a water contact angle θ W} (°) of 50 ° or more, particularly 60 ° or more. I found out.

1 Development roller 2 Inner layer 3 Outer layer 4 Outer layer 5 Roller body 6 Through hole 7 Shaft 8 Outer surface 9 Oxide film 10 Aluminum drum 12 DC power supply 13 Resistance 14 Measuring circuit 15 Droplet F Load V Detection voltage r Resistance value θ _W Contact angle h height r radius

Claims (5)

The rubber includes epichlorohydrin rubber, a tubular inner layer made of a crosslinked product of a rubber composition containing a diene rubber, and a roller body including a tubular outer layer covering the outer periphery of the inner layer, and the proportion of the epichlorohydrin rubber is _{The surface resistance value R 1} (when Ω and 10 V is applied) of the outer peripheral surface of the roller body, which is 21 parts by mass or more in the total amount of 100 parts of the rubber and is the outer peripheral surface of the outer layer, is expressed by the formula (1):
7.0 ≤ logR ₁ ≤ 8.5 (1)
The roller resistance value R ₂ (when Ω, 400 V is applied) of the entire roller body is expressed by the equation (2):
6.3 ≤ log R ₂ ≤ 8.5 (2)
Are satisfied with the developing roller. The developing roller according to claim 1, wherein the outer layer is a crosslinked product of a rubber composition containing epichlorohydrin rubber as rubber and a diene-based rubber. The developing roller according to claim 1 or 2, wherein the rubber composition forming the inner layer contains at least one selected from the group consisting of isoprene rubber and butadiene rubber as the diene rubber. The developing roller according to any one of claims 1 to 3, wherein the outer peripheral surface of the roller body is covered with an oxide film. The developing roller according to any one of claims 1 to 4, wherein the outer peripheral surface of the roller body has a water contact angle θ _{W (°) of 50 ° or more.}

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