CN112882362A - Developing roller - Google Patents

Abstract

The invention provides a developing roller which has a laminated structure and can form an image with more excellent image quality than the current situation. The developing roller (1) comprises an inner layer (2) and an outer layer (4), wherein the inner layer (2) is composed of a rubber composition containing epichlorohydrin rubber in a proportion of 21 parts by mass or more per 100 parts by mass of the total amount of rubber, and the surface resistance value logR of the outer peripheral surface (8) is determined₁Setting the roll resistance value logR of the whole roll body (5) to 7.0-8.5₂The number of the grooves is 6.3 to 8.5.

Description

Developing roller

Technical Field

The present invention relates to a developing roller to be mounted in an image forming apparatus using an electrophotographic method.

Background

Recently, as a developing roller, a developing roller including a roller body having a laminated structure including: a cylindrical inner layer made of a crosslinked rubber composition, and an outer layer covering the outer peripheral surface of the inner layer and constituting the outer peripheral surface of the roller body (see patent document 1 and the like).

[ Prior art documents ]

[ patent document ]

[ patent document 1] Japanese patent laid-open No. 2016-95455

Disclosure of Invention

[ problems to be solved by the invention ]

The invention aims to provide a developing roller which has a laminated structure and can form an image with better image quality than the current situation.

[ means for solving problems ]

The invention is a developing roller comprising a roller body including a cylindrical inner layer and a cylindrical outer layer, the cylindrical inner layer being composed of a crosslinked product of a rubber composition containing epichlorohydrin rubber and diene rubber as rubbers, the cylindrical outer layer covering the outer periphery of the inner layer, the epichlorohydrin rubber being present in a proportion of 21 parts by mass or more based on 100 parts by mass of the total amount of the rubbers, and a surface resistance value R of the outer peripheral surface of the roller body as the outer peripheral surface of the outer layer₁(Ω, when 10V is applied), the formula (1) is satisfied:

7.0≦logR₁≦8.5 (1)

and the roll resistance value R of the whole roll body₂(Ω, when 400V is applied), the following formula (2) is satisfied:

6.3≦logR₂≦8.5 (2)。

[ Effect of the invention ]

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

Drawings

Fig. 1 (a) is a perspective view showing the entire appearance of an example of the developing roller of the present invention, and fig. 1 (b) is an end view of the developing roller of the example.

Fig. 2 is a diagram illustrating a method of measuring a roller resistance value of the roller main body.

Fig. 3 is a diagram illustrating a method of measuring a contact angle of water on the outer circumferential surface of the roller main body.

[ description of symbols ]

1: developing roller

2: inner layer

3. 8: peripheral surface

4: outer layer

5: roller body

6: through hole

7: shaft

9: oxide film

10: aluminum roller

12: direct current power supply

13: resistance (RC)

14: measuring circuit

15: liquid droplet

F: load(s)

V: detecting voltage

θ_W: contact angle

h: height

r: a radius.

Detailed Description

Examples of the image forming apparatus to which the developing roller is attached include a laser printer, an electrostatic copier, a plain paper facsimile machine, and a multi-function machine of these.

As one of the criteria for evaluating an image of an image forming apparatus such as a laser printer, a solid black density and a 2-dot (dot) density of a formed image are known.

The solid black density is a density of a so-called solid black image in which at least a part of the paper surface is filled with black, and an image with a higher contrast can be formed as the solid black density is higher.

The 2dot density is a density of an image of circles arranged in a square lattice having a lattice length of about 80 μm, which is called isolated 2dot, and as the 2dot density is higher, the reproducibility and gradation of a thin line can be improved to form a fine image.

However, the two image densities are in an inverse relationship and hardly coexist.

Namely, there is a tendency that: the pure black concentration is higher as the roller resistance value of the developing roller is lowered, but the 2dot concentration is higher as the roller resistance value of the developing roller is higher, and it is difficult to make the two opposite characteristics coexist in the conventional developing roller having a single-layer structure.

As described above, it is considered that the roller body of the developing roller has a structure including two layers, i.e., the inner layer and the outer layer, each of which is formed of a crosslinked rubber composition, and the resistance values of the two layers are adjusted so that the two opposite characteristics are compatible with each other.

That is, the pure black density is related to the resistance value near the surface of the roller body, and if the resistance value near the surface is decreased, the pure black density can be increased.

On the other hand, the 2dot concentration is related to the roll resistance value of the entire roll body, and the 2dot concentration can be increased as the roll resistance value is increased.

Therefore, if

As described above, the roller body has a structure including both the inner layer and the outer layer each formed of a crosslinked rubber composition,

wherein the outer layer is in a low resistance state for adjusting the resistance value near the surface of the roller body to a range capable of increasing the pure black concentration, and

the inner layer below the outer layer is set to a high resistance state in order to adjust the roll resistance value of the entire roll body combined with the outer layer to a range capable of increasing the 2dot concentration,

the pure black concentration can be made to coexist with the 2dot concentration.

However, according to the studies of the inventors, in the conventional developing roller including the roller main body having a laminated structure described in patent document 1 and the like, the setting of the range of the resistance value in the vicinity of the surface and the roller resistance value, the composition of the rubber composition forming the two layers, and the like are not definite.

Therefore, in the initial stage of image formation, the solid black density (initial solid black density) or the 2dot density (initial 2dot density) may be insufficient, or the 2dot density may be greatly reduced when image formation is repeated.

Further, when image formation is repeated, density unevenness depending on the density of an image adjacent in a lateral direction perpendicular to a paper passing direction of the paper may occur in the formed image.

Further, when image formation is repeated, especially when a solid black image (solid black image on the entire surface) is formed on the entire surface of a region of paper on which image formation is possible, white streaks are likely to occur, and a clean solid black image having a uniform density may not be formed.

Therefore, the inventors have further studied, in particular, the optimum ranges of the surface resistance value of the outer peripheral surface of the roller body and the roller resistance value of the roller body, which define the resistance value in the vicinity of the surface of the roller body, and the composition of the rubber composition forming the inner layer.

As a result, as described above, the inventors have found that

The inner layer is formed of a crosslinked product of a rubber composition containing epichlorohydrin rubber and a diene rubber, and the proportion of the epichlorohydrin rubber is 21 parts by mass or more based on 100 parts by mass of the total amount of the rubber,

surface resistance R of the outer peripheral surface of the roller body₁(Ω, when 10V is applied) is set to satisfy formula (1):

7.0≦logR₁≦8.5 (1)

and is in the range of

The roll resistance value R of the entire roll body₂(Ω, when 400V is applied) is set to satisfy formula (2):

6.3≦logR₂≦8.5 (2)

the above range may be used.

That is, the developing roller of the present invention includes: a roller body comprising a cylindrical inner layer and a cylindrical outer layer, the cylindrical inner layer being composed of a crosslinked product of a rubber composition containing epichlorohydrin rubber and a diene rubber as rubbers, the cylindrical outer layer covering the outer periphery of the inner layer, the epichlorohydrin rubber being present in a proportion of 21 parts by mass or more based on 100 parts by mass of the total amount of the rubbers, and a surface resistance value R of the outer peripheral surface of the roller body as the outer peripheral surface of the outer layer₁(omega, when 10V is applied) satisfies the above formula (1), and the roll resistance value R of the entire roll body₂(Ω, when 400V is applied) satisfies the formula (2).

According to the developing roller of the present invention, by adopting the above configuration, both the pure black density and the 2dot density can be increased at the same time, and an image excellent in contrast and reproducibility of a thin line or gradation can be formed.

Further, it is possible to suppress density unevenness in an image depending on the density of images adjacent in the lateral direction, or to suppress a decrease in 2dot density, that is, a decrease in durable 2dot density when image formation is repeated.

Further, it is possible to prevent the occurrence of white streaks in the entire solid black image when the image formation is repeated, and to make the entire solid black image in a clean state with a uniform density.

The presence or absence of the occurrence of the blooming can be evaluated by the density of the portion having the lowest density in the entire solid black image, that is, the entire solid black density.

These cases are also clear from the results of the examples, comparative examples, and previous examples described below.

Fig. 1 (a) is a perspective view showing the entire appearance of an example of the developing roller of the present invention, and fig. 1 (b) is an end view of the developing roller of the example.

Referring to fig. 1 (a) and 1 (b), the developing roller 1 of the example includes a roller main body 5 having a two-layer structure in which an outer layer 4 made of an elastic material is directly laminated on an outer circumferential surface 3 of a cylindrical inner layer 2 made of an elastic material in the roller main body 5 having a two-layer structure.

A shaft 7 is inserted and fixed into a through hole 6 in the center of the inner layer 2.

The shaft 7 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 7 is electrically joined to the roller main body 5 and mechanically fixed, for example, by an adhesive having conductivity, or by pressing a shaft having an outer diameter larger than the inner diameter of the through hole 6 into the through hole 6, and is electrically joined to the roller main body 5 and mechanically fixed.

In addition, the shaft 7 and the roller body 5 may be electrically joined and mechanically fixed by the above two methods in combination.

The surface of the outer layer 4, i.e., the outer circumferential surface 8 of the roll body 5, is covered with an oxide film 9 as shown in enlarged views in both figures.

By covering the outer circumferential surface 8 with the oxide film 9, the oxide film 9 functions as a dielectric layer, whereby the dielectric loss tangent tan δ of the developing roller 1 can be reduced, and the oxide film 9 functions as a low friction layer, whereby adhesion of toner can be favorably suppressed.

Further, the oxide film 9 can be formed simply by, for example, simply oxidizing the rubber in the vicinity of the outer peripheral surface 8 by irradiating the outer peripheral surface 8 with ultraviolet rays or the like, and therefore, a decrease in productivity of the developing roller 1 or an increase in manufacturing cost can be suppressed.

But the oxide film 9 may be omitted.

The inner layer 2 and the outer layer 4 are preferably formed of a single non-porous layer in order to simplify the structure of each layer and improve durability.

The "single layer" of the inner layer 2 and the outer layer 4 means that the number of layers including the elastic material is a single layer.

The "two layers" of the roller main body 5 also means that the number of layers including the elastic material of both the inner layer 2 and the outer layer 4 is two, and in any case, the oxide film 9 formed by irradiation of ultraviolet rays or the like is not included in the number of layers.

In the present invention, the surface resistance R of the outer peripheral surface 8 of the roller body 5 is set to be equal to₁(omega, when 10V is applied) and the roll resistance value R of the entire roll main body 5₂The reason why (Ω, 400V applied) is limited to the range satisfying the above formulas (1) and (2) is as follows.

That is, the surface resistance value R of the outer peripheral surface 8 of the roller body 5₁(omega, 10V applied) logR is the usual logarithm₁If the resistance value is less than 7.0, the resistance value near the surface of the roller body 5 may be too low, and an image failure due to an overcurrent may occur in an image.

On the other hand, the surface resistance value R of the outer peripheral surface 8 of the roller body 5₁(omega, 10V applied) logR is the usual logarithm₁When the amount exceeds 8.5, the resistance value near the surface of the roller body 5 cannot be sufficiently reduced to a range in which the pure black density can be increased.

Therefore, the contrast of the image may be reduced due to insufficient initial pure black density, or the whole pure black density may be reduced due to the occurrence of white blur in the whole pure black image.

In addition, the roll resistance value R of the entire roll body 5₂(omega, 400V applied) logR is the usual logarithm₂When the average value is less than 6.3, the initial 2dot density may be insufficient, the durable 2dot density may be significantly reduced, the reproducibility or gradation of thin lines may be reduced, and the fineness of an image may be reduced.

On the other hand, the roll resistance value R of the entire roll main body 5₂(omega. application400V) in the usual log R₂When the number exceeds 8.5, density unevenness depending on the density of an image adjacent in the lateral direction perpendicular to the paper passing direction of the paper may occur in the image.

The reason why the proportion of the 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 the rubber is as follows.

That is, if the proportion of epichlorohydrin rubber is less than 21 parts by mass, the roll resistance value R of the entire roll body 5 is obtained₂(omega, when 400V is applied), the initial 2dot concentration may be insufficient or the durable 2dot concentration may be significantly reduced.

In contrast, the surface resistance value R is set to₁(omega, when applying 10V) to satisfy the formula (1) range, the roller resistance value R₂The generation of the various defects can be suppressed by setting the range satisfying the formula (2) (Ω, 400V applied) and the ratio of epichlorohydrin rubber in the rubber composition forming the inner layer 2 to the above range.

Further, a developing roller capable of forming an image having a better image quality than the present image over a long period of time can be provided.

The developing roller 1 of the present invention is also dependent on the composition of the rubber composition forming the outer layer 4 constituting the outer peripheral surface 8 of the roller body 5, but the contact angle θ of water on the outer peripheral surface 8 is preferably set to be larger than the contact angle θ of water on the outer peripheral surface 8_W(°) is 50 ° or more.

The contact angle theta of water on the outer peripheral surface 8 of the roller body 5_WWhen the water repellency of the outer peripheral surface 8 is within the above range, the releasability of the toner can be improved.

Therefore, the initial solid black density can be further increased, and the entire solid black image can be more effectively prevented from being whitened and from being lowered in the entire solid black density.

Further, if the effect is further improved, the contact angle θ of water is increased_WThe degree of (°) is also preferably 60 ° or more within the above range.

In order to adjust the contact angle theta of water on the outer peripheral surface 8 of the roller body 5_WAdjusted to the above range, for example, to form oxygen to coat the outer peripheral surface 8The chemical film 9 may be formed by adjusting the cumulative amount of ultraviolet light (mJ/cm) irradiated to the outer peripheral surface 8²) And (4) finishing.

Specifically, the cumulative light quantity (mJ/cm) is decreased²) The larger the contact angle theta of water can be_W(°)。

So-called cumulative light quantity (mJ/cm)²) Means the intensity of irradiation per unit area (mW/cm) by the ultraviolet ray irradiated to the outer peripheral surface 8 of the roller body 5²) The total amount of ultraviolet light irradiated to the outer peripheral surface 8 is determined by multiplying the irradiation time (seconds).

Furthermore, the contact angle of water θ_WThe upper limit of (°) is not particularly limited, and includes the contact angle θ of water to the outer peripheral surface 8 not coated with the oxide film 9 because ultraviolet light is not irradiated_W(°) up to.

< measurement of cumulative quantity of ultraviolet light >

Cumulative amount of light (mJ/cm)²) The measurement was performed using an integrated light quantity measuring apparatus.

Specifically, for example, an integrated light amount measuring device is actually provided at a position where the roller body 5 is provided in a device (UV treatment device) for irradiating the outer peripheral surface 8 of the roller body 5 with ultraviolet rays.

Subsequently, the UV treatment device was operated in the same manner as when the outer peripheral surface 8 of the roll main body 5 was irradiated with ultraviolet light, and the light receiving portion of the integrated light quantity measuring device was irradiated with ultraviolet light to determine the integrated light quantity (mJ/cm) measured by the integrated light quantity measuring device²) The operating conditions of the UV treatment device required to reach the target value.

As the operation conditions, for example, in the case of a UV treatment apparatus that irradiates the outer peripheral surface 8 with ultraviolet rays while rotating the roller main body 5, in addition to the wavelength, irradiation intensity, and irradiation time of the irradiated ultraviolet rays, the rotation speed of the roller main body 5 and the like can be cited.

Further, if the roll main body 5 is installed in the same UV treatment apparatus and operated under the operation conditions determined by the previous measurement, the same integrated light amount (mJ/cm) can be used²) The outer peripheral surface 8 of the installed roller body 5 is irradiated with ultraviolet rays.

Rubber composition for inner layer 2

As described above, the inner layer 2 is formed of a crosslinked product of a rubber composition containing epichlorohydrin rubber and diene rubber as rubbers and having imparted thereto ionic conductivity.

< Epichlorohydrin 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.

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 exerts an effect of reducing the resistance value of the inner layer 2, and further reducing the roll resistance value R of the roll body 5 as a whole₂(omega, when 400V was applied).

However, if the ethylene oxide content is less than the above range, the above-described effect cannot be sufficiently obtained, and therefore the roll resistance value R of the entire roll main body 5 may not be sufficiently reduced₂(omega, when 400V is applied).

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 roll resistance value R of the entire roll body 5 is rather present₂(omega, when 400V was applied) increased.

In addition, the inner layer 2 after crosslinking may be too hard, or the viscosity of the rubber composition before crosslinking may increase during heating and melting, 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.

The allyl glycidyl ether functions to secure a free volume as a side chain, thereby suppressing crystallization of ethylene oxide and reducing the roll resistance R of the roll main body 5 as a whole₂(omega, when 400V was applied).

However, if the allyl glycidyl ether content is less than the above range, the above-described effect cannot be sufficiently obtained, and therefore the roll resistance value R of the entire roll main body 5 may not be sufficiently reduced₂(omega, when 400V is applied).

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 chain motion of the molecular chain is inhibited, and the roll resistance value R of the entire roll main body 5 is adversely affected₂(omega, when 400V was applied) 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.

As the epichlorohydrin rubber, GECO is particularly preferable.

Since GECO has a double bond in the main chain functioning as a crosslinking point due to allyl glycidyl ether, the compression set after crosslinking can be reduced by crosslinking between the main chains.

Therefore, the compression set of the inner layer 2 can be reduced and collapse is less likely to occur.

One or two or more of these epichlorohydrin rubbers may be used.

< diene rubber >

The diene rubber functions to impart good processability to the rubber composition, to improve mechanical strength and durability of the inner layer 2, or to impart good properties as a rubber, that is, properties of softness, small compression set and low tendency to collapse to the inner layer 2.

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, it is preferable to use a nonpolar 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 in combination.

In addition, CR and/or NBR may be used in combination in the combination system.

(IR)

As IR, various kinds of IR having a polyisoprene structure which artificially reproduces the structure of natural rubber can be used.

Further, as the IR, there are oil-filled type IR in which flexibility is adjusted by adding an extender oil, and non-oil-filled type IR in which the extender oil is not added, but in the present invention, it is preferable to use non-oil-filled type IR which does not contain extender oil that may be a bleeding substance in order to prevent contamination of the photoreceptor.

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

(BR)

As BR, various types of BR having a polybutadiene structure in the molecule and having a crosslinking property can be used.

Particularly preferred is a high cis BR having a cis-1, 4 bond content of 95% or more, which can exhibit favorable properties as a rubber in a wide temperature range from a low temperature to a high temperature.

Further, as BR, there are oil-filled BR to which extender oil is added to adjust flexibility and non-oil-filled BR to which extender oil is not added, but in the present invention, it is still preferable to use non-oil-filled BR which does not contain extender oil that may become exudative substances in order to prevent contamination of the photoreceptor.

One or two or more of these BR may 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.

As the SBR, any of high styrene type, medium styrene type, and low styrene type SBRs classified according to the styrene content can be used.

Further, as the SBR, there are oil-filled SBR in which flexibility is adjusted by adding an extender oil, and non-oil-filled SBR in which no extender oil that may be a bleeding substance is contained, but in the present invention, it is still preferable to use non-oil-filled SBR in which an extender oil that may be a bleeding substance is not contained, in order to prevent contamination of the photoreceptor and the like.

One or two or more of these SBRs can be used.

(CR)

CR is a polar diene rubber and is a value of a roll resistance R for the roll body 5 as a whole₂(omega, when 400V is applied) is finely adjusted to function.

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, it is still preferable to use non-oil-filled CR not containing filling oil that may become a bleeding substance in order to prevent contamination of the photoreceptor.

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

(NBR)

The NBR is also a polar diene rubber, and has a roll resistance value R for the roll body 5 as a whole₂(omega, when 400V is applied) is finely adjusted to function.

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 proportion of the rubber may be determined by various characteristics required for the inner layer 2, particularly the resistance value of the inner layer 2 and the roll resistance value R of the entire roll body 5₂(omega, when 400V is applied), flexibility of the inner layer 2, and the like.

However, the proportion of the epichlorohydrin rubber must be 21 parts by mass or more per 100 parts by mass of the total amount of the rubber.

The reasons are as described above.

Also, the proportion of the epichlorohydrin rubber within the above range is preferably 30 parts by mass or less of 100 parts by mass of the total amount of the rubber.

When the epichlorohydrin rubber content exceeds the above range, the roll resistance value R of the entire roll body 5 may be determined depending on the composition of the rubber composition and the like₂(omega, when 400V is applied) is less than the range of the formula (2), the initial 2dot concentration is insufficient, or the durable 2dot concentration is greatly reduced.

In contrast, 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 a decrease in 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, of the total 100 parts by mass of the rubber.

If the ratio of CR and/or NBR is less than the above range, the above-described effects of blending these rubbers, that is, the roll resistance value R of the roll body 5 as a whole may not be sufficiently obtained₂(omega, when 400V is applied) fine adjustment.

On the other hand, when the ratio of these rubbers exceeds the above range, the epichlorohydrin rubber may be relatively reduced, and the roll resistance value R of the entire roll main body 5 may not be able to be set₂(Ω, when 400V was applied) was sufficiently reduced to a range satisfying the above formula (2).

The proportion of the nonpolar diene rubber other than CR and/or NBR is the residual amount of epichlorohydrin rubber or epichlorohydrin rubber and CR and/or NBR.

That is, when the epichlorohydrin rubber or the ratio of the epichlorohydrin rubber to CR and/or NBR is set to a predetermined value within the above range, the ratio of the nonpolar diene rubber may be set so that the total amount of the rubber is 100 parts by mass.

< crosslinking component >

A crosslinking component for crosslinking the rubber is blended in the rubber composition for the inner layer 2.

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 ratio is the ratio of the sulfur itself as the active ingredient 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 (5):

(C_nH_2n+1NH)₂C＝S (5)

[ 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.

< Ionic conductive agent >

An ion conductive agent may be further formulated in the rubber composition for the inner layer 2.

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.

By blending the ion conductive agent, the ion conductivity of the rubber composition can be further improved, and the roll resistance value R of the roll body 5 as a whole can be further reduced₂(omega, when 400V is applied).

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.

Wherein the ionic conductivity of the rubber composition is improved and the roll resistance value R of the whole roll body 5 is reduced₂(omega, when 400V is applied), it is preferable that (CF)₃SO₂)₂NLi [ lithium bis (trifluoromethanesulfonyl) imide Li-TFSI]And/or (CF)₃SO₂)₂NK [ Potassium bis (trifluoromethanesulfonyl) imide, K-TFSI]。

The proportion 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, relative to 100 parts by mass of the total amount of the rubber.

< carbon Black >

Carbon black may be further blended as a filler in the rubber composition for the inner layer 2.

The mechanical strength of the developing roller can be improved by blending carbon black.

Examples of the carbon black include SAF, ISAF, HAF, and FEF.

When conductive carbon black is used as carbon black, electron conductivity can be imparted to the inner layer 2.

Examples of the conductive carbon black include acetylene black.

The proportion 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 the rubber.

< Others >

Various additives may be further compounded as necessary in the rubber composition for the inner layer 2.

Examples of additives include: crosslinking promoting aids, acid acceptors, plasticizers, processing aids, etc.

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

The proportion of the crosslinking accelerating 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-based gas generated from epichlorohydrin rubber or CR during crosslinking from remaining in the inner layer 2, or from causing crosslinking inhibition or contamination of the photoreceptor.

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 can be further reliably prevented.

The proportion of the acid scavenger 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 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, and 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.

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

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

< preparation of rubber composition >

The rubber composition for the inner layer 2 containing the above-described components can be prepared in the same manner as in the conventional case.

First, the rubber composition for the inner layer 2 can be obtained by masticating the rubber, adding and kneading the components other than the crosslinking component, and finally adding and kneading the crosslinking component.

The kneading may be carried out by, for example, a kneader, a Banbury mixer, an extruder, or the like.

Rubber composition for outer layer 4

The outer layer 4 can be formed by the surface resistance R of the outer peripheral surface 8 of the roller body 5₁(omega, when 10V is applied) to the range of the elastic material formation.

In particular, the outer layer 4 is preferably formed of a crosslinked product of a rubber composition containing epichlorohydrin rubber and diene rubber.

< Epichlorohydrin rubber >

As the epichlorohydrin rubber, one or two or more of the same epichlorohydrin rubbers as used in the inner layer 2 can be used.

Among these, ECO and/or GECO are preferable, and GECO is particularly preferable.

The reason for this is the same as in the case of the inner layer 2.

That is, by using GECO as the epichlorohydrin rubber, the compression set of the outer layer 4 can be reduced and the collapse is less likely to occur.

< diene rubber >

The diene rubber functions to impart good processability to the rubber composition, to improve mechanical strength, durability, and the like of the outer layer 4, or to impart good properties as a rubber to the outer layer 4.

The diene rubber is also oxidized by the ultraviolet irradiation to form an oxide film 9 on the surface of the outer layer 4, that is, the outer circumferential surface 8 of the roller body 5.

As the diene rubber, one or two or more of the same diene rubbers as 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, the diene rubber is preferably a nonpolar diene rubber, specifically at least one of three types of IR, BR, and SBR, and particularly SBR.

In addition, the surface resistance value R of the outer peripheral surface 8 of the roller body 5 is adjusted₁(omega, when 10V is applied), CR and/or NBR may be used in combination with the nonpolar diene rubber.

Specific examples of these diene rubbers are as described above.

(proportion of rubber)

The proportion of the rubber may be varied depending on various characteristics required for the outer layer 4, particularly, the surface resistance value R of the outer peripheral surface 8 of the roller body 5₁(Ω, 10V applied), flexibility of the outer layer 4, and the like.

However, the proportion of the epichlorohydrin rubber is 20 parts by mass or more, preferably 25 parts by mass or more, and preferably 50 parts by mass or less, of the total 100 parts by mass of the rubber.

If the epichlorohydrin rubber content is less than the above range, the surface resistance value R of the outer peripheral surface 8 of the roller body 5 may be determined depending on the composition of the rubber composition and the like₁(Ω, when 10V is applied) exceeds the range of the formula (1).

Further, the initial pure black density may be insufficient to lower the contrast of the image, or the whole pure black image may be whitened to lower the whole pure black density.

On the other hand, when the proportion of epichlorohydrin rubber exceeds the above range, the surface resistance value R of the outer peripheral surface 8 of the roller body 5 may be set to be higher than the above range₁(Ω, when 10V is applied) is smaller than the range of the above formula (1), the resistance value near the surface of the roller body 5 is too low, and image defects due to overcurrent occur in an image.

On the other hand, the surface resistance value R of the outer peripheral surface 8 of the roller body 5 is set to be within the above range by setting the ratio of epichlorohydrin rubber to be within the above range₁The range of formula (1) (Ω, when 10V is applied) can suppress the deterioration of these characteristics.

The ratio of CR and/or NBR is preferably 1 part by mass or more, particularly 2.5 parts by mass or more, and preferably 10 parts by mass or less, of the total 100 parts by mass of the rubber.

If the ratio of CR and/or NBR is less than the above range, the above-described effects of blending these rubbers, that is, the surface resistance value R to the outer peripheral surface 8 of the roller body 5 may not be sufficiently obtained₁(omega, when 10V is applied) fine adjustment.

On the other hand, when the ratio of these rubbers exceeds the above range, epichlorohydrin rubber may be relatively decreased, and the surface resistance value R of the outer peripheral surface 8 of the roller body 5 may not be able to be set to be relatively low₁(Ω, when 10V is applied) is sufficiently reduced to a range satisfying the formula (1).

The proportion of the nonpolar diene rubber other than CR and/or NBR is the residual amount of epichlorohydrin rubber or epichlorohydrin rubber and CR and/or NBR.

That is, when the epichlorohydrin rubber or the ratio of the epichlorohydrin rubber to CR and/or NBR is set to a predetermined value within the above range, the ratio of the nonpolar diene rubber may be set so that the total amount of the rubber is 100 parts by mass.

< crosslinking component >

As the crosslinking component, it is preferable to use the same crosslinking agent and crosslinking accelerator as those used for the inner layer 2 in combination.

That is, the crosslinking agent is preferably a sulfur-based crosslinking agent, particularly sulfur, and the crosslinking accelerator combined with the sulfur-based crosslinking agent is preferably a combination of four of a thiuram-based accelerator, a thiazole-based accelerator, a thiourea-based accelerator, and a guanidine-based accelerator.

The proportions of the sulfur-based crosslinking agent and the four crosslinking accelerators are also preferably the same as in the case of the inner layer 2.

< Ionic conductive agent >

An ion conductive agent may be further formulated in the rubber composition for the outer layer 4.

By blending the ion conductive agent, the ion conductivity of the rubber composition can be further improved, and the surface resistance value R of the outer peripheral surface 8 of the roller body 5 can be further reduced₁(Ω, when 10V was applied).

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, the same as those used in the inner layer 2.

The proportion of the ion conductive agent is also preferably the same as in the case of the inner layer 2.

< Others >

Various additives may be further compounded as necessary in the rubber composition for the outer layer 4.

Examples of the additives include the same additives as those used in the inner layer 2, for example, crosslinking acceleration aids, acid absorbers, fillers, plasticizers, processing aids, deterioration inhibitors, scorch retarders, lubricants, pigments, antistatic agents, flame retardants, neutralizing agents, nucleating agents, co-crosslinking agents, and the like.

The filler is preferably carbon black such as thermal carbon black.

The proportion of the additive is also preferably the same as in the case of the inner layer 2.

< preparation of rubber composition >

The rubber composition for the outer layer 4 containing the above-described components can be prepared in the same manner as in the conventional case.

That is, the rubber composition for the outer layer 4 can be obtained by kneading the rubber, adding the components other than the crosslinking component, and kneading the kneaded mixture, and finally adding the crosslinking component.

The kneading may be carried out by, for example, a kneader, a Banbury mixer, an extruder, or the like.

Production of developing roller 1

In order to produce the developing roller 1 shown in fig. 1 (a) and 1 (b) using the rubber compositions for the inner layer 2 and the outer layer 4, for example, both the rubber compositions are supplied to a two-layer extruder, are co-extruded into a cylindrical shape having a two-layer structure, and are then integrally crosslinked to form the inner layer 2 and the outer layer 4.

Alternatively, the rubber composition for the inner layer 2 is extruded into a cylindrical 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, and is formed into a cylindrical shape by press molding or the like, 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 using an oven or the like, subjected to secondary crosslinking, cooled, and then polished so as to have a predetermined outer diameter, thereby forming a roller body 5 including the laminate.

The thickness of the inner layer 2 can be arbitrarily set according to the structure, size, and the like of the image forming apparatus to be mounted.

The thickness of the outer layer 4 may be set arbitrarily, but is preferably 0.1mm or more, and preferably 2mm or less.

By setting the thickness of the outer layer 4 within the above range, the surface resistance value R of the outer peripheral surface 8 of the roller body 5 can be set when the inner layer 2 and the outer layer 4 each containing the predetermined rubber composition are combined₁(omega, when 10V is applied) and the overall roll resistance R₂(omega, when 400V was applied) was adjusted to fall within the above-mentioned range.

Therefore, the pure black density and the 2dot density are both increased at the same time, and an image having excellent contrast and reproducibility of thin lines or excellent gradation can be formed.

Further, it is possible to suppress the occurrence of density unevenness in an image depending on the density of images adjacent in the lateral direction, or to suppress the reduction of the durable 2dot density or the entire surface solid black density.

As the polishing method, various polishing methods such as dry longitudinal polishing can be used, or finish polishing can be performed by mirror polishing at the end of the polishing step.

In this case, the releasability of the outer peripheral surface 8 is improved, the oxide film 9 is not formed, or the adhesion of the toner can be more favorably suppressed by a synergistic effect with the formation of the oxide film 9, and the contamination of the photoreceptor and the like can be effectively prevented.

The shaft 7 can be inserted and fixed into the through hole 6 at any time from the cutting of the cylindrical body serving as the base of the roller body 5 to the polishing.

However, after the cutting, the shaft 7 is preferably first subjected to secondary crosslinking and polishing in a state of being inserted into the through hole 6. This can suppress the warping or deformation of the roller body 5 due to expansion and contraction at the time of secondary crosslinking.

Further, by polishing while rotating about the shaft 7, the polishing workability can be improved and the run-out of the outer peripheral surface 8 can be suppressed.

As described above, the shaft 7 may be inserted into the through hole 6 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 the shaft having an outer diameter larger than the inner diameter of the through hole 6 may be pressed into the through hole 6.

In the former case, the thermosetting adhesive is cured while the cylindrical body is secondarily crosslinked by heating in the oven, and the shaft 7 is electrically and mechanically engaged with the roller body 5.

In the latter case, the electrical joining and the mechanical fixing are completed simultaneously with the press-fitting.

As described above, the shaft 7 and the roller body 5 may be electrically joined and mechanically fixed by the above-described two methods.

As described above, the oxide film 9 is preferably formed by irradiating the outer peripheral surface 8 of the roller main body 5, which is the surface of the outer layer 4, with ultraviolet rays.

That is, the outer peripheral surface 8 of the roller body 5 is irradiated with ultraviolet rays of a predetermined wavelength for a predetermined time, and only the rubber constituting the vicinity of the outer peripheral surface 8 is oxidized to form the oxide film 9.

Therefore, the oxide film 9 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.

In addition, as described above, the cumulative amount of ultraviolet light (mJ/cm) was adjusted²) The contact angle θ of water on the outer peripheral surface 8 covered with the formed oxide film 9 can be adjusted_W(°)。

The oxide film 9 formed by the irradiation of ultraviolet rays does not have a problem as a coating film formed by applying a coating agent in the past, and is excellent in thickness uniformity, adhesion to the roller main body 5, and the like.

The wavelength of the ultraviolet rays to be irradiated is preferably 100nm or more, preferably 400nm or less, and particularly 300nm or less, in consideration of efficiently oxidizing the diene rubber in the rubber composition for the outer layer 4 to form the oxide film 9 having the excellent function.

In addition, the irradiation time may be based on the cumulative amount of ultraviolet light (mJ/cm)²) Contact angle theta of water_W(°) is set arbitrarily so as to fall within the predetermined range.

However, the oxide film 9 may be formed by another method, or may not be formed as described above.

One or more optional intermediate layers may be interposed between the inner layer 2 and the outer layer 4.

However, considering the simplification of the structure of the roller body 5, the roller body 5 preferably has a two-layer structure in which the inner layer 2 and the outer layer 4 are directly laminated as shown in fig. 1 (a) and 1 (b).

The developing roller 1 of the present invention can be used by being attached to various image forming apparatuses 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 described below based on examples and comparative examples, but the constitution of the present invention is not necessarily limited to these examples.

Preparation of rubber composition

< rubber composition (A) for inner layer 2 >

As the rubber, 16 parts by mass of eico (epoon) (registered trademark) 301L, EO/EP/AGE ═ 73/23/4 (molar ratio) manufactured by GECO [ OSAKA dada (OSAKA SODA) (stock) ], nibo (Nipol) (registered trademark) IR2200 manufactured by IR [ ZEON (stock) ], non-oil-extended ]77 parts by mass, zeya (JSR)1502 manufactured by SBR [ zeya (JSR) (stock) ], bound styrene: 23.5% and non-oil-extended 6 parts by mass, and CR 1 part by mass of Shoprene (Shoprene) (registered trademark) WRT and non-oil-extended manufactured by Showa Denko (Ltd.).

While kneading the total amount of the rubber 100 parts by mass using a banbury mixer, the following ingredients were blended and kneaded.

[ Table 1]

Composition (I)	Mass portion of
		Ionic salts	0.1
Crosslinking-promoting assistants	2.5
		Filler	5.0
Acid-absorbing agent	3.0
		Processing aid	0.5

The components in table 1 are as follows, and parts by mass in the table is parts by mass with respect to 100 parts by mass of the total amount of the rubber.

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

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

Filling agent: carbon black FEF [ Seast (registered trademark) SO manufactured by Toyo carbon (stock) ]

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

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

Subsequently, while continuing the kneading, the following crosslinking components were blended and further kneaded to prepare a rubber composition (a) for the inner layer 2.

[ Table 2]

Composition (I)	Mass portion of
		Crosslinking agent	1.05
Accelerator DM	1.5
		Accelerant TS	0.5
Accelerator 22	0.3
		Accelerant DT	0.2

The components in table 2 are as follows, and parts by mass in the table is parts by mass with respect to 100 parts by mass of the total amount of the rubber.

A crosslinking agent: oil-treated powdered sulfur [ crane see chemical industry (stock) made golden print 5% oil-immersed micropowder sulfur ]

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

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

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 [ Nocceler DT (Nocceler) manufactured by Innova chemical industry (Strand Co., Ltd.) ]

< rubber composition (B) for inner layer 2 >

A 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 >

A 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 >

A 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 >

A 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 >

A 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 >

A 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 >

A 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 the rubber, GECO [ Epin (EPION)301L manufactured by OSAKA dada (OSAKA SODA) (stock) mentioned above ]26 parts by mass, BR [ Uspro (UBEPOL) (registered trademark) BR130B manufactured by yuba co (stock), non-oil-extended ]59 parts by mass, CR [ Shorelin (SHOPRENE) WRT (stock) mentioned above) 10 parts by mass, and NBR [ nipo (Nipol) DN401LL manufactured by nippon (stock)), acrylonitrile content: rubber composition (I) for inner layer 2 was prepared in the same manner as rubber composition (a) except that 18.0% and 5 parts by mass of non-oil extended oil were used and no ionic salt was added.

< rubber composition (J) > < for inner layer 2

Rubber composition (J) for inner layer 2 was prepared in the same manner as rubber composition (a) except that GECO [ Elaine (EPION)301L ]17.5 parts by mass manufactured by OSAKA SODA (stock) proposed above, IR [ nipy (Nipol) IR2200]36.25 parts by mass manufactured by nippon (ZEON) (stock) proposed above, SBR [ Jacobia (JSR)1502]36.25 parts by mass manufactured by Jacobia (JSR) (stock) proposed above, CR [ showa and jun (SHOPRENE) WRT ]5 parts by mass manufactured by shogao and electrician (stock) proposed above, and ethylene propylene diene rubber [ EPDM ] as a non-diene rubber, Esprene (Esprene) (registered trademark) 505A ]5 parts by mass.

< rubber composition (K) for inner layer 2 >

Rubber composition (K) for inner layer 2 was prepared in the same manner as rubber composition (a) except that GECO [ EPION 301L manufactured by OSAKA dada (OSAKA SODA) (stock) mentioned above ]5 parts by mass, IR [ nibo (Nipol) IR2200 manufactured by nippon (stock) mentioned above ]45 parts by mass, BR [ usperlo (ubeplol) BR130B manufactured by yawako (stock) mentioned above ]40 parts by mass, and CR [ Shoplan (SHOPRENE) WRT manufactured by showa electrician (stock) mentioned above ]10 parts by mass and the amount of the ionic salt was 1 part by mass.

< rubber composition (L) > for inner layer 2

A rubber composition (L) for the inner layer 2 was prepared in the same manner as the rubber composition (K) except that the amount of GECO was 10 parts by mass, the amount of IR was 42.5 parts by mass, and the amount of BR was 37.5 parts by mass.

< rubber composition (M) for inner layer 2 >

A rubber composition (M) for the inner layer 2 was prepared in the same manner as the rubber composition (K) except that the amount of GECO was 12.5 parts by mass, the amount of IR was 41.25 parts by mass, and the amount of BR was 36.25 parts by mass.

< rubber composition (N) for inner layer 2 >

A 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.

< rubber composition (O) for inner layer 2 >

A rubber composition (O) for the inner layer 2 was prepared in the same manner as the rubber composition (K) except that the amount of GECO was 20 parts by mass, the amount of IR was 37.5 parts by mass, and the amount of BR was 32.5 parts by mass.

< rubber composition (P) > for inner layer 2

A rubber composition (P) for the inner layer 2 was prepared in the same manner as the rubber composition (K) except that the amount of GECO was 30 parts by mass, the amount of IR was 32.5 parts by mass, and the amount of BR was 27.5 parts by mass.

< rubber composition (Q) for inner layer 2 >

Rubber composition (Q) for inner layer 2 was prepared in the same manner as rubber composition (a) except that GECO [ Elaine (EPION)301L ]28 parts by mass manufactured by OSAKA dada (OSAKA SODA) (stock) mentioned above ], IR [ nibo (Nipol) IR2200 parts by IR [ nippo (ZEON) (stock) mentioned above ], SBR [ Jacobia (JSR)1502 parts by abra (JSR) stock mentioned above ], CR [ Shoplilin (SHOPRENE) WRT ]1 parts by mass manufactured by showa electrician (stock) mentioned above ] and EPDM [ Esprene (Esprene)505A ]5 parts by mass manufactured by sumitomo chemistry (stock) mentioned above ] were used as rubbers.

< rubber composition (i) > < for outer layer 4

As the rubber, 15 parts by mass of GECO [ Elaine (EPION)301L manufactured by OSAKA dada (OSAKA SODA) (stock) proposed above ], 75 parts by mass of SBR [ Jaceya (JSR)1502 manufactured by Jaceya (JSR) (stock) proposed above ], and 10 parts by mass of CR [ SHOPRENE (SHOPRENE) WRT manufactured by showa electrician (stock) proposed above ] were used.

While kneading the total amount of the rubber 100 parts by mass using a banbury mixer, the following ingredients were blended and kneaded.

[ Table 3]

Composition (I)	Mass portion of
		Ionic salts	1.0
Crosslinking-promoting assistants	2.5
		Filler	5.0
Acid-absorbing agent	3.0
		Processing aid	0.5

The components in table 3 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 made by the electronization (Strand) of Mitsubishi material as proposed above ]

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

Filling agent: carbon Black [ thermal carbon Black, Asahi #15 manufactured by Asahi carbon Black (stock) ]

Acid-absorbing agent: hydrotalcite (DHT-4A-2 made by the cooperative chemical industry (Strand) as set forth above)

Processing aid: zinc stearate [ SZ-2000 made by Sakai chemical industry (Strand) as set forth above ]

Subsequently, while continuing the kneading, the following crosslinking components were blended and further kneaded to prepare a rubber composition (i) for the outer layer 4.

[ Table 4]

Composition (I)	Mass portion of
		Crosslinking agent	1.05
AcceleratorDM	1.5
		Accelerant TS	0.5
Accelerator 22	0.3
		Accelerant DT	0.2

The components in table 4 are as follows. In addition, the mass part in the table is relative to the total amount of rubber 100 mass parts of mass.

A crosslinking agent: oil-treated powdered sulfur [ the above-mentioned sulfur is 5% oil-immersed micropowder of golden print manufactured by chemical industry (stock) ]

Accelerator DM: di-2-benzothiazolyl disulfide [ Nocceler DM, thiazole-based accelerator, produced by the emerging chemical industry (Strand) as set forth above ]

Accelerator TS: tetramethylthiuram monosulfide [ SANCELER TS, thiuram series accelerator from Sanxin chemical industries (Ltd.) as mentioned above ]

Accelerator 22: ethylenethiourea [ 2-mercaptoimidazoline, Ishel (acell) 22-S produced by Katsu chemical industry (Strand) and thiourea accelerator ]

Accelerator DT: 1, 3-di-o-tolylguanidine [ Nocceler DT (Nocceler) produced by the Innova chemical industry (Strand) as set forth above ]

< rubber composition (ii) > for outer layer 4

A 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 (iii) > for outer layer 4

A 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 (iv) for outer layer 4 >

A 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 (v) > for outer layer 4

Rubber composition (v) for outer layer 4 was prepared in the same manner as 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 (vi) > < for outer layer 4

A rubber composition (vi) for the outer layer 4 was prepared in the same manner as in the rubber composition (i) except that the amount of GECO was 30 parts by mass, the amount of SBR was 67.5 parts by mass, and the amount of CR was 2.5 parts by mass.

< rubber composition (vii) > < for outer layer 4

The rubber composition (vii) for the outer layer 4 was prepared in the same manner as the rubber composition (vi) except that the ion salt was not blended.

< rubber composition for outer layer 4 (viii) >)

Rubber composition (viii) for outer layer 4 was prepared in the same manner as 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 to 9 and comparative examples 1 to 10

The rubber compositions (B) to (P) for the inner layer 2 and the rubber compositions (i) to (v) for the outer layer were fed to a two-layer extruder in the combinations shown in tables 5 to 8, extruded into a two-layer structure having an outer diameter of 16mm and an inner diameter of 6.5mm in a cylindrical shape, mounted on 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 7 having an outer diameter of 7.5mm and coated with a conductive thermosetting adhesive on the outer peripheral surface thereof, and heated in an oven to 160 ℃ to be bonded to the shaft 7.

Next, both ends of the cylindrical body were shaped, the outer circumferential surface 8 was longitudinally polished using a cylindrical polishing machine, and then mirror-polished as a finish to an outer diameter of 16mm, thereby forming a roller body 5 having a two-layer structure of the inner layer 2 and the outer layer 4 and integrated with the shaft 7.

The thickness of the outer layer 4 after grinding is about 0.1mm to 2 mm.

Next, after the outer peripheral surface 8 of the formed roller main body 5 was wiped with alcohol, the distance from the outer peripheral surface 8 to the UV lamp was set to 50mm, and the roller main body was set in an ultraviolet irradiation apparatus [ PL21-200 manufactured by special light Source (SEN) of Seine (SEN) ].

Then, ultraviolet rays having wavelengths of 184.9nm and 253.7nm were irradiated while rotating around the axis at 90 ° units, thereby coating the outer circumferential surface 8 with the oxide film 9, and the developing roller 1 was manufactured.

The cumulative quantity of ultraviolet light was 100mJ/cm²。

(determination of characteristics)

The developing roller 1 manufactured in each of the above examples and comparative examples was subjected to the following tests, and the characteristics thereof were obtained.

Each test was carried out at a temperature of 23 ℃ and a relative humidity of 55%.

< surface resistance value R₁Measurement of

Hiresta (registered trademark) UP MCP-HT800 manufactured by Mitsubishi Chemical analysis (Mitsubishi Chemical Analytich) (Inc.) using a resistivity meter]The surface resistance value R of the outer peripheral surface 8 of the roller body 5 was measured in the surface resistance mode using a special MCP probe (UA type) manufactured by the same company₁(Ω, when 10V was applied).

That is, a load of 480g was applied to the MCP probe, the MCP probe was pressed against the axial center of the outer peripheral surface 8 of the roller body 5, and the value after 10 seconds had elapsed was defined asThe surface resistance R of the outer peripheral surface 8 of the roller body 5₁(Ω, when 10V was applied).

The conditions of the measurement were RCF (S): 1.050, applied voltage: 10V.

With respect to the surface resistance value R₁(Ω, 10V applied), as described above, logR will be used commonly₁When the number is 7.0 or more and 8.5 or less, it is determined as pass (o), and otherwise it is determined as fail (x).

< roll resistance value R₂Measurement of

The roll resistance value R of the entire roll main body 5 was measured by the method shown in FIG. 2₂(omega, when 400V is applied).

That is, referring to fig. 1 (a), 1 (b), and 2, first, an aluminum drum 10 rotatable at a fixed rotational speed is prepared, and the outer circumferential surface 8 of the roller main body 5 is brought into contact with the outer circumferential surface 11 of the prepared aluminum drum 10 from above.

Further, a direct current power supply 12 and a resistor 13 are connected in series between the shaft 7 and the aluminum drum 10 to constitute a measurement circuit 14.

The (-) side of the dc power supply 12 is connected to the shaft 7, the (+) side is connected to the resistor 13, and the resistance r' of the resistor 13 is set to 100 Ω.

Subsequently, a load F of 450g was applied to both end portions of the shaft 7, and the aluminum drum 10 was rotated at 40rpm in a state where the roller body 5 was pressed against the aluminum drum 10.

Then, while the rotation is continued, when an applied voltage E of 400V dc is applied from the dc power supply 12 between the roller main body 5 and the aluminum drum 10, a detection voltage V applied to the resistor 13 is measured.

Based on the detected voltage V and the applied voltage E (400V), the roll resistance value R of the entire roll body 5 is set to be equal to₂Substantially using formula (3):

R₂＝r’×E/V-r’ (3)

and then the result is obtained.

However, since one term of-r' in the formula (3) can be regarded as minute, the formula (3 a):

R₂＝r’×E/V (3a)

the value thus obtained is the roll resistance value of the entire roll body 5R₂(omega, when 400V is applied).

With respect to the roll resistance value R₂(Ω, 400V applied), as described above, logR will be used as a common logarithm₂A value of 6.3 or more and 8.5 or less is defined as pass (o), and is otherwise defined as fail (x).

Contact Angle of < Water θ_WMeasurement of

Contact angle θ of water on outer circumferential surface 8 of roller body 5_W(°) automatic contact Angle Meter [ science of synergetic interface DMo-501]In the droplet amount: 2 μ L, measurement start time after dropping: measured under 1000ms conditions.

Specifically, referring to fig. 3, first, 2 μ L of pure water filled in a micro syringe was dropped on the outer circumferential surface 8 of the roller main body 5, and the shape of the droplet 15 after 1000ms from the dropping was determined by the formula (4):

θ_W＝2arctan(h/r) (4)

the contact angle theta of water was determined_W(°)。

In the formula (4), h is the height of the liquid droplets 15 dropped on the outer peripheral surface 8 of the roller body 5, and r is the radius of the liquid droplets 15, as shown in fig. 3.

The measurement was carried out by dropping the droplets 15 onto the outer peripheral surface 8 of the roller main body 5 of the same sample at positions 5cm from both ends in the axial direction and at three positions in total in the center in the axial direction, and the average value was taken as a measurement value.

Contact angle theta of water_WThe values (° below) are poor (x), good (Δ) are 50 ° or more and less than 60 °, and particularly good (o) are 60 ° or more.

Experimental on machine

The manufactured developing roller 1 was mounted on a laser printer (HL-2240D manufactured by brother industry (stock)), and the following tests were performed to evaluate the image quality of the formed image.

Each test was carried out at a temperature of 23.5 ℃ and a relative humidity of 55%.

< measurement of initial pure Black concentration >

Immediately after images of 1% density were continuously formed on 30 plain papers, 1 solid black image of 3cm square was formed.

Then, the image density was measured at an arbitrary 5 points on the formed solid black image using a reflection density meter manufactured by Videojet X-Rite (jet), and the average value thereof was determined as the initial solid black density. The initial pure black concentration of 1.30 or more was defined as pass (o), and the initial pure black concentration of less than 1.30 was defined as fail (x).

< measurement of initial 2dot concentration >

Immediately after images of 1% density were continuously formed on 30 plain papers, 1 isolated 2dot image of circles arranged in a square lattice having a lattice length of about 80 μm was formed.

Then, image densities were measured using the same reflection density meter at arbitrary 5 points on the formed isolated 2dot image, and the average value thereof was determined as the initial 2dot density.

When the initial 2dot concentration exceeds 0.02, it is determined as "pass" (o), and when the initial 2dot concentration is 0.02 or less, it is determined as "fail" (x).

< measurement of concentration unevenness >

Immediately after images of 1% density were continuously formed on 3000 plain papers, a 3cm wide halftone portion and a lateral direction of the halftone portion orthogonal to the paper passing direction were adjacent to each other at a distance of 5mm, and 13 cm square image having a solid black portion was formed.

Then, when the halftone portion of the formed image was observed, the obtained image was evaluated as good (o) and poor (x), and the subsequent test was not performed.

In addition, the subsequent tests were not performed for those having an initial pure black concentration of 1.1 or less and/or an initial 2dot concentration of 0.01 or less.

< determination of durable 2dot concentration >

Immediately after images of 1% density were continuously formed on 3000 plain papers, 1 isolated 2dot image was formed in the same manner as in the initial 2dot density measurement.

Then, the image density was measured at an arbitrary 5 points on the formed isolated 2dot image using the same reflection density meter, and the average value thereof was determined as the durable 2dot density.

The durability 2dot concentration exceeding 0.02 is regarded as pass (o), and 0.02 or less is regarded as fail (x).

The difference between the initial 2dot concentration and the durable 2dot concentration is obtained as a change amount (Δ 2dot concentration), and it is assumed that the Δ 2dot concentration is 0.03 or less and is acceptable (o), and that the Δ 2dot concentration exceeds 0.03 and is unacceptable (x).

< measurement of the concentration of pure Black throughout the surface >

After images of 1% density were continuously formed on 3000 plain papers, 1 entire surface solid black image was formed immediately.

Then, the density of the portion where the density of the formed entire pure black image is the lowest is measured by using the same reflection density meter, and the entire pure black density is set.

The whole-surface pure black concentration was defined as "poor" (x) to be less than 1.13, as "good" (Δ) to be 1.13 or more and less than 1.2, and as "particularly good" (o) to be 1.2 or more.

The results are shown in tables 5 to 8.

[ Table 5]

[ Table 6]

[ Table 7]

[ Table 8]

According to Table 5-Table8, it is found that the rubber composition has a two-layer structure of the inner layer 2 and the outer layer 4, and the epichlorohydrin rubber in the inner layer 2 is contained in an amount of 21 parts by mass or more based on 100 parts by mass of the total amount of the rubber, and the surface resistance value logR of the outer peripheral surface 8 is₁The roll resistance value logR of the whole roll body 5 is set to 7.0-8.5₂The developing roller is set to 6.3-8.5, and an image with better image quality than the current image can be formed.

Examples 10 to 19 and 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 were fed to a two-layer extruder in the combinations shown in tables 9 to 11, extruded into a two-layer structure having an outer diameter of 16mm and an inner diameter of 6.5mm in a cylindrical shape, mounted on a temporary shaft for crosslinking, and crosslinked in a vulcanization tank at 160 ℃ for 1 hour.

Subsequently, the crosslinked tubular body was mounted on a metal shaft 7 having an outer diameter of 7.5mm and coated with a conductive thermosetting adhesive on the outer peripheral surface thereof, and heated in an oven to 160 ℃ to be bonded to the shaft 7.

Next, both ends of the cylindrical body were shaped, the outer circumferential surface 8 was longitudinally polished using a cylindrical polishing machine, and then mirror-polished as a finish to an outer diameter of 16mm, thereby forming a roller body 5 having a two-layer structure of the inner layer 2 and the outer layer 4 and integrated with the shaft 7.

The thickness of the outer layer 4 after grinding is about 0.1mm to 2 mm.

Next, after the outer peripheral surface 8 of the formed roller main body 5 was wiped with alcohol, the distance from the outer peripheral surface 8 to the UV lamp was set to 50mm, and the roller main body was set in an ultraviolet irradiation apparatus [ PL21-200 manufactured by special light Source (SEN) of Seine (SEN) ].

Then, ultraviolet rays having wavelengths of 184.9nm and 253.7nm were irradiated while rotating around the axis at 90 ° units, thereby coating the outer circumferential surface 8 with the oxide film 9, and the developing roller 1 was manufactured.

The cumulative amounts of ultraviolet light were set to the values shown in tables 9 to 11, respectively.

The developing roller 1 manufactured in each of the examples and comparative examples was subjected to the above tests, and the characteristics thereof were evaluated.

The results are shown in tables 9 to 11.

[ Table 9]

[ Table 10]

[ Table 11]

As is apparent from the results in tables 9 to 11, the developing roller having the above-described configuration can form an image having an image quality superior to that of the present state.

From the results of examples 1 to 19 and comparative examples 1 to 14, it is further understood that the contact angle θ of water on the outer peripheral surface 8 of the roller body 5 is larger than the contact angle θ of water on the outer peripheral surface 8 of the roller body_WThe degree of (°) is preferably 50 ° or more, particularly 60 ° or more.

Claims (5)

1. A developing roller comprises a roller body including a cylindrical inner layer and a cylindrical outer layer, the cylindrical inner layer being composed of a crosslinked product of a rubber composition containing epichlorohydrin rubber and diene rubber as rubbers, the cylindrical outer layer covering the outer periphery of the inner layer, the epichlorohydrin rubber being present in a proportion of 21 parts by mass or more based on 100 parts by mass of the total amount of the rubbers, and a surface resistance value R when 10V is applied to the outer peripheral surface of the roller body as the outer peripheral surface of the outer layer₁Satisfying formula (1):

7.0≦logR₁≦8.5 (1)

and a roll resistance value R when 400V is applied to the whole roll body₂Satisfying formula (2):

6.3≦logR₂≦8.5 (2)。

2. the developing roller according to claim 1, wherein the outer layer is constituted by a crosslinked product of a rubber composition containing epichlorohydrin rubber and diene rubber as rubbers.

3. 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-based rubber.

4. The developing roller according to any one of claims 1 to 3, wherein an outer circumferential surface of the roller body is coated with an oxide film.

5. The developing roller according to any one of claims 1 to 4, wherein a contact angle θ of water of an outer peripheral surface of the roller body_WIs more than 50 degrees.

Images