阅读说明：本技术 显影辊 (Developing roller ) 是由 黒田贤一 于 2019-12-20 设计创作，主要内容包括：本发明提供一种显影辊,调色剂难以从辊本体的端部泄漏而污染图像,而且图像耐久性也优异,并且可成本廉价地制造。显影辊(1)中,由轴向的两个端部(5)与所述两个端部间的中间部(6)构成筒状的辊本体(2),所述轴向的两个端部(5)由橡胶组合物的交联物构成,热传导率超过0.47W/m·K,所述两个端部间的中间部(6)由橡胶组合物的交联物构成,橡胶硬度比端部小。(The invention provides a developing roller, which is difficult to cause toner leakage from the end part of a roller body to pollute an image, has excellent image durability and can be manufactured at low cost. In the developing roller (1), a cylindrical roller body (2) is formed by two axial end parts (5) and a middle part (6) between the two end parts, the two axial end parts (5) are formed by a cross-linked product of a rubber composition, the heat conductivity exceeds 0.47W/m.K, the middle part (6) between the two end parts is formed by the cross-linked product of the rubber composition, and the rubber hardness is smaller than that of the end parts.)

1. A developing roller comprising a cylindrical roller body, the roller body comprising:

both ends in the axial direction are composed of a crosslinked rubber composition, and the heat conductivity is more than 0.47W/m.K; and

the intermediate portion between the two end portions is formed of a crosslinked product of a rubber composition, and has a rubber hardness smaller than that of the end portions.

2. The developing roller according to claim 1, wherein the type a durometer hardness of the intermediate portion is less than 60.

3. The developing roller according to claim 1 or 2, wherein the end portion is composed of a rubber composition containing a rubber and 30 parts by mass or more of at least one heat transfer component selected from the group consisting of graphite powder and scale-like boron nitride powder with respect to 100 parts by mass of the total amount of the rubber.

4. A developing roller according to claim 3, wherein said intermediate portion is composed of a rubber composition containing rubber and less than 30 parts by mass of said heat transfer component with respect to 100 parts by mass of the total amount of said rubber, or from which said heat transfer component is removed.

5. The developing roller according to claim 1 or 2, wherein the roller body contains an oxide film composed of an oxide of the crosslinked material on an outer circumferential surface.

6. The developing roller according to claim 3, wherein the roller body contains an oxide film composed of an oxide of the crosslinked material on an outer circumferential surface.

7. The developing roller according to claim 4, wherein the roller body contains an oxide film composed of an oxide of the crosslinked material on an outer circumferential surface.

Technical Field

The present invention relates to a developing roller.

Background

In an image forming apparatus using an electrophotographic method, such as a laser printer, an electrostatic copier, a plain paper facsimile machine, or a multifunction machine thereof, a developing roller is used to develop an electrostatic latent image formed on a surface of a photoreceptor into a toner image.

As the developing roller, for example, a developing roller including a roller main body formed by molding a rubber composition having conductivity into a cylindrical shape and crosslinking the same and a shaft made of metal or the like inserted through a through hole fixed to the center of the roller main body is used.

In development using a developing roller, the developing roller is provided in a developing portion provided in the vicinity of a photoreceptor and accommodating toner in an image forming apparatus, and the developing roller is rotated in a state where a tip end portion of a quantity regulating blade (charging blade) is brought into contact with an outer peripheral surface of a roller body of the developing roller.

In this way, the toner in the developing portion is charged when passing between the outer peripheral surface of the roller body and the leading end portion of the quantity regulating blade, and adheres to the outer peripheral surface, and the amount of adhesion is regulated by the quantity regulating blade, and a toner layer having a substantially constant thickness is formed on the outer peripheral surface.

In addition, an electrostatic latent image is simultaneously formed by uniformly charging on the surface of the photoreceptor and then exposing.

When the developing roller is further rotated in this state and the toner layer formed on the outer peripheral surface of the roller main body is brought close to the surface of the photoreceptor, the toner in the toner layer selectively moves to the surface of the photoreceptor in accordance with the electrostatic latent image formed on the surface of the photoreceptor, and the electrostatic latent image is developed into a toner image.

In order to prevent the toner adhering to the outer circumferential surface of the roller body from leaking out of the developing portion, the axial end portion of the roller body of the developing roller is generally sealed by a sealing member.

The sealing member is formed of, for example, felt, and is slidably connected to an outer peripheral surface of an end portion of the roller body of the rotating developing roller in a state fixed to a frame of the developing portion or the like.

In recent years, in order to reduce power consumption of an image forming apparatus, a fixing temperature of toner tends to be set low, and a low melting point toner that can be fixed well even at a low temperature has been widely used.

However, toner having a lower melting point tends to be easily fused to the outer peripheral surface of the end portion of the roller body or to the sealing member slidably connected to the end portion.

That is, when the developing roller is rotated, frictional heat is generated between the outer peripheral surface of the end portion of the roller body of the developing roller and the sealing member, and the temperature rises, but the toner having a lower melting point tends to be more easily welded to these members even if the temperature rises a little.

Further, the sealing of the sealing member may be inhibited by the fused toner, or the outer peripheral surface of the end portion of the roller main body may be worn by the fused toner when image formation is repeated, and a gap may be formed between the outer peripheral surface and the sealing member, so that the toner may leak from the end portion.

The leaked toner causes contamination in the image forming apparatus or contamination of the formed image.

Therefore, it has been studied to increase the thermal conductivity of the entire roller body as compared with the conventional one, and to suppress the temperature rise of the roller body and the seal member by rapidly dissipating heat from the roller body and the shaft even if frictional heat is generated with the rotation of the developing roller, thereby suppressing the fusion of toner (see patent documents 1 to 3, etc.).

In addition, it has been proposed to add a heat transfer component such as graphite powder to a rubber composition that is a base of a roller body.

[ Prior art documents ]

[ patent document ]

[ patent document 1] Japanese patent application laid-open No. 2002-189341

[ patent document 2] Japanese patent laid-open No. 2016-142367

[ patent document 3] Japanese patent laid-open No. 2016-142333

Disclosure of Invention

[ problems to be solved by the invention ]

However, in the conventional developing roller in which the entire roller body is integrally formed of the crosslinked product of the rubber composition containing the heat transfer component such as graphite powder, good image durability may not be obtained.

The image durability is an index as follows: this shows that the developing roller can suppress the deterioration of toner when repeatedly performing image formation, and can maintain the quality of the formed image well for how many times the image is formed.

In primary image formation, only a very small part of the toner accommodated in the developing portion is used, and most of the remaining toner is repeatedly circulated in the developing portion.

Therefore, how much damage or not, which is caused to the circulating toner, is caused to the roller body of the developing roller that is provided in the developing portion and repeatedly contacts the toner is a key to improving the image durability of the developing roller.

However, if the entire roller body is integrally formed of the rubber composition containing the heat transfer component, the entire roller body becomes hard and easily damages the toner.

Therefore, in the conventional developing roller including the roller body, there are: when image formation is repeated, the quality of the formed image deteriorates early, and good image durability cannot be obtained.

Further, the heat transfer component such as graphite powder is less easily available and expensive than, for example, a filler and the like which are generally blended in a rubber composition such as carbon black.

Therefore, the conventional developing roller in which the heat transfer component is mixed in the entire roller body has a problem of an increase in manufacturing cost.

The invention aims to provide a developing roller, which is difficult to cause toner leakage from the end part of a roller body to pollute an image, has excellent image durability and can be manufactured at low cost.

[ means for solving the problems ]

The present invention is a developing roller including a cylindrical roller body, the roller body including: both ends in the axial direction are composed of a crosslinked rubber composition, and the heat conductivity is more than 0.47W/m.K; and an intermediate portion between the end portions, which is formed of a crosslinked product of a rubber composition and has a rubber hardness smaller than that of the end portions.

[ Effect of the invention ]

According to the present invention, it is possible to provide a developing roller which is less likely to cause toner leakage from the end of the roller body to contaminate an image, has excellent image durability, and can be manufactured at low cost.

Drawings

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

[ description of symbols ]

1: developing roller

2: roller body

3: through hole

4: shaft

5: end part

6: intermediate section

7. 8: peripheral surface

9: oxide film

Detailed Description

Development roller

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

Referring to fig. 1, a developing roller 1 of the above example includes a cylindrical roller body 2, and a shaft 4 is inserted through a through hole 3 fixed to the center of the roller body 2.

The roller body 2 includes two axial end portions 5 and an intermediate portion 6 between the two end portions 5, and the entire intermediate portion 6 between the two axial end portions 5 and the two end portions 5 is formed in a non-porous, single-layer-structured cylindrical shape from a cross-linked rubber composition.

In the drawing, the outer diameters of the end portions 5 and the intermediate portions 6 are the same as the inner diameter of the through-hole 3, and the outer peripheral surfaces 7 and 8 of the end portions 5 and the intermediate portions 6 are concentric with the through-hole 3.

The end portion 5 and the intermediate portion 6 are fixed to each other by a shaft 4 inserted through the through hole 3 at the center thereof.

In the fixed state, the end portion 5 and the intermediate portion 6 are in close contact with each other without a gap in the axial direction over the entire circumference of the outer circumferential surface 7 and the outer circumferential surface 8, respectively, and the outer circumferential surface 7 and the outer circumferential surface 8 are continued without a step in the radial direction over the entire circumference thereof.

As shown in fig. 1 in an enlarged manner, an oxide film 9 made of an oxide of a crosslinked product of each rubber composition may be formed on the entire outer peripheral surface 7 of the end portion 5 and the outer peripheral surface 8 of the intermediate portion 6 constituting the outer peripheral surface of the roller body 2.

The "single-layer structure" of the end portions 5 and the intermediate portion 6 means that the number of layers made of rubber or the like is a single layer, and the oxide film 9 formed by ultraviolet irradiation or the like is not included in the number of layers.

The end portion 5 is made of a crosslinked material of a rubber composition containing a heat transfer component such as graphite powder, for example, and the thermal conductivity is limited to a range exceeding 0.47W/m.K.

Therefore, even if frictional heat is generated between the outer peripheral surface 7 of the end portion 5 and a sealing member, not shown, as the developing roller 1 rotates, the heat can be rapidly dissipated through the end portion 5 and the shaft 4, and the temperature rise of these members can be suppressed.

Therefore, even with a low melting point toner, fusion to the outer peripheral surface 7 of the end portion 5 of the roller body 2 or to the sealing member can be suppressed, and leakage of toner from the end portion 5 and contamination of an image due to fusion of toner and a decrease in sealability associated therewith can be suppressed.

On the other hand, the intermediate portion 6, which is mainly in repeated contact with the toner, is made of, for example, a rubber composition containing a small amount of the heat transfer component or containing no heat transfer component (removed), and has a rubber hardness smaller than that of the end portion 5.

Therefore, the intermediate portion 6 is provided with good flexibility, and when image formation is repeated, a state in which toner is less likely to be damaged can be formed, and the image durability of the developing roller 1 can be improved.

Further, by forming the intermediate portion 6 from a rubber composition containing little or no heat transfer component as described above, the amount of heat transfer component in the entire roller body 2 can be reduced, and the manufacturing cost of the developing roller can be reduced.

The end portions 5 and the intermediate portions 6 can be formed by, for example, respectively molding and crosslinking rubber compositions as bases into a cylindrical shape, and the end portions 5 and the intermediate portions 6 can be fixed to the shaft 4 to form the roller body 2.

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

The shaft 4 is electrically, thermally, and mechanically fixed to the end portion 5 and the intermediate portion 6 constituting the roller body 2 via, for example, an adhesive having conductivity.

Alternatively, the shaft 4 having an outer diameter larger than the inner diameter of the through-hole 3 of the end portion 5 and the intermediate portion 6 is pressed into the through-hole 3, whereby the shaft 4 is electrically, thermally, and mechanically fixed to the end portion 5 and the intermediate portion 6.

The shaft 4 may be electrically, thermally and mechanically fixed to the end portion 5 and the intermediate portion 6 by a combination of the above two methods.

< end 5 >

The end portion 5 is composed of a crosslinked rubber composition as described above, and the thermal conductivity is limited to a range exceeding 0.47W/m.K.

The thermal conductivity of the end portion 5 is limited to the above range because the following effects cannot be obtained if the thermal conductivity is within the range: the frictional heat generated between the toner and the sealing member is rapidly dissipated to suppress the temperature rise of the end portion 5 or the sealing member, thereby suppressing the toner from being welded to these members.

On the other hand, when the thermal conductivity of the end portion 5 is in the above range, the frictional heat generated between the end portion 5 and the sealing member can be quickly dissipated, and the temperature rise of the end portion 5 or the sealing member can be suppressed, thereby suppressing the toner from being welded to these members.

Further, it is possible to suppress toner leakage from the end portion 5 and contamination of an image due to fusion of toner and a decrease in sealability accompanying the fusion.

In view of further improving the above effect, the thermal conductivity of the end portion 5 is preferably 0.49W/m · K or more, and particularly preferably 0.50W/m · K or more within the above range.

In the configuration in which the heat transfer component is blended to increase the thermal conductivity of the end portion 5, the thermal conductivity can be increased as the proportion of the heat transfer component blended in the rubber composition is increased.

However, as the proportion of the heat transfer component increases, the rubber hardness of the end portion 5 increases, which may reduce the sealing property with the sealing member, or may cause the sealing member to be worn significantly and reduce the sealing property when image formation is repeated.

Further, the toner may leak from the end portion 5 to contaminate the image due to the decrease in the sealing property.

Therefore, in view of suppressing the occurrence of these problems by excessively increasing the rubber hardness of the end portion 5, it is preferable to limit the proportion of the heat transfer component using the thermal conductivity as an index so that the thermal conductivity is 1.20W/m · K or less, particularly 1.01W/m · K or less.

The rubber hardness of the end portion 5 is not limited to this, and is preferably 60 or more, and preferably 80 or less in type a durometer hardness.

The end portion 5 having a rubber hardness smaller than the above range may have a low proportion of heat transfer components, and may not satisfy a range in which the thermal conductivity exceeds 0.47W/m · K, and may not quickly dissipate the frictional heat generated between the end portion and the sealing member to suppress the temperature rise.

In addition, fusion of the toner having a low melting point is particularly likely to occur, and the toner leaks from the end portion 5 due to the decrease in sealing property caused by the fusion, which may cause image contamination.

On the other hand, when the rubber hardness exceeds the above range, the end portion 5 becomes too hard, and the sealing property with the sealing member may be lowered, or the sealing member may be greatly worn and the sealing property may be lowered when the image formation is repeated.

Further, the toner may leak from the end portion 5 due to the decrease in the sealing property, which may cause image contamination.

On the other hand, by setting the rubber hardness of the end portion 5 in the above range, it is possible to prevent leakage of toner caused by the above various causes, and to suppress image contamination.

< intermediate part 6 >

The intermediate portion 6 is composed of a crosslinked rubber composition as described above, and is set to have a rubber hardness smaller than that of the end portion 5.

By setting the rubber hardness of the intermediate portion 6 to a range smaller than the end portion 5, it is possible to maintain good flexibility of the intermediate portion 6 which repeatedly comes into contact with the toner, and it is difficult to damage the toner when image formation is repeated, and it is possible to improve the image durability of the developing roller 1.

The intermediate portion 6 may be formed of a crosslinked rubber composition having a smaller proportion of heat transfer components than the end portions 5 or having heat transfer components removed.

Therefore, the amount of the heat transfer component in the entire roller body 2 can be reduced, and the manufacturing cost of the developing roller can be reduced.

The rubber hardness of the intermediate portion 6 is not limited to this, and is preferably within a range of type a durometer hardness of less than 60, particularly 50 or less, and is further less than the type a durometer hardness of the end portion 5.

When the rubber hardness of the intermediate portion 6 exceeds the above range, good flexibility cannot be imparted to the intermediate portion 6, and thus good image durability cannot be imparted to the developing roller 1 in some cases.

On the other hand, by setting the rubber hardness of the intermediate portion 6 within the above range, more favorable flexibility can be imparted to the intermediate portion 6, and the image durability of the developing roller 1 can be further improved.

However, when the rubber hardness of the intermediate portion 6 is too low, the compression set of the intermediate portion 6 becomes large, and collapse is likely to occur.

In addition, in recent years, in order to improve image quality of an image, when the toner is combined with a toner having a fine, uniform, or spherical shape, charging failure may occur, which may reduce image density or cause fogging in a blank portion of the image.

Therefore, in view of suppressing the occurrence of these problems and forming an image with good image quality, the rubber hardness of the intermediate portion 6 is preferably 30 or more as represented by type a durometer hardness within the above range.

The thermal conductivity of the intermediate portion 6 is not particularly limited.

However, when the intermediate portion 6 is formed of a rubber composition having a smaller proportion of heat transfer components than the end portions 5 or having heat transfer components removed, the thermal conductivity of the intermediate portion 6 may not be in a range exceeding 0.47W/m · K.

Specifically, the thermal conductivity of the intermediate portion 6 may be about 0.47W/mK or less, of which 0.40W/mK or less, particularly about 0.30W/mK or less.

The lower limit of the thermal conductivity of the intermediate portion 6 is not particularly limited, but is preferably 0.10W/mK or more, and particularly 0.20W/mK or more.

Even in this case, by maintaining the thermal conductivity of the end portion 5 in the range exceeding 0.47W/m · K, fusion of the toner having a low melting point can be suppressed, and leakage of the toner from the end portion 5 due to a decrease in sealing property accompanying the fusion can be prevented, thereby suppressing image contamination.

In the present invention, the thermal conductivity and the type a durometer hardness of the end portion 5 and the intermediate portion 6 are each expressed by values measured by the following method.

< measurement of thermal conductivity >

The same rubber composition as that forming the end portions 5 and the middle portion 6 was press-molded at 160 ℃ for 30 minutes to prepare a sheet having a length of 150mm × a width of 50mm × a thickness of 4mm, and the sheet was allowed to stand at 23 ± 2 ℃ for 24 hours or more in a standard test environment having a relative humidity of 55 ± 2%, and then measured by a probe method under the same environment, and the obtained value was regarded as the thermal conductivity (W/m · K).

< type A durometer hardness measurement >

Under the standard test environment, the shaft 4 protruding from both ends of the roller body 2 is fixed to the support table from both ends thereof, and is measured from above in accordance with JIS K6253_：2012Method for determining hardness of vulcanized rubber and thermoplastic rubber-section 3: the pressing pin of a type a durometer specified in durometer hardness ″ abuts against the center portion in the axial direction of the end portion 5 and the center portion in the axial direction of the intermediate portion 6 of the roller body 2, and when a load: 1kg, measurement time: the measurement was carried out under the condition of 3 seconds (standard measurement time for vulcanized rubber), and the obtained value was taken as type a durometer hardness.

< oxide film 9 >

The oxide film 9 is formed by irradiating the outer circumferential surface 7 and the outer circumferential surface 8 with ultraviolet rays having a predetermined wavelength for a predetermined time, for example, to oxidize a cured product of the rubber composition exposed on the outer circumferential surface 7 and the outer circumferential surface 8.

When the oxide film 9 is formed, the oxide film 9 functions as a dielectric layer, and the dielectric tangent of the developing roller 1 can be reduced.

Further, since the oxide film 9 functions as a low-friction layer, friction of the end portion 5 against the sealing member can be reduced, generation of frictional heat can be suppressed, and particularly, leakage of toner from the end portion 5 due to fusion of toner having a low melting point and contamination of an image can be more effectively suppressed.

Further, the oxide film 9 functions as a low friction layer, thereby suppressing toner from remaining or accumulating on the outer peripheral surfaces 7 and 8, and suppressing the toner from affecting the formed image.

Further, the oxide film 9 is an extremely thin film compared to a conventional coating layer formed by applying a coating agent, for example, and does not harden the entire roll main body 2 and the intermediate portion 6 thereof as in the case of the coating layer.

Therefore, when the tip end portion of the amount regulation blade is brought into contact with the outer peripheral surface 8 of the intermediate portion 6, the intermediate portion 6 is easily deformed by being sandwiched therebetween, and a toner layer having a uniform thickness can be formed on the outer peripheral surface 8.

However, the oxide film 9 may not be formed.

< method for manufacturing developing roller >

In order to manufacture the developing roller 1, the rubber composition for forming the end portion 5 is first extruded into a cylindrical shape using, for example, an extruder, then cut into a predetermined length, and crosslinked by pressurizing and heating with pressurized steam in a vulcanizing tank.

Similarly, the rubber composition for forming the intermediate portion 6 is extruded into a cylindrical shape using, for example, an extruder, then cut into a predetermined length, and crosslinked by pressurization and heating with pressurized steam in a vulcanizing tank.

Next, the crosslinked tubular body serving as the base of the end portions 5 and the intermediate portion 6 is sequentially arranged, heated in an oven or the like, secondarily crosslinked, cooled, and further ground to a predetermined outer diameter, thereby forming the roller body 2 including the two end portions 5 in the axial direction and the intermediate portion 6 between the two end portions 5.

The shaft 4 may be inserted through the through-holes 3 fixed to the end portions 5 and the intermediate portion 6 at any time from after the cutting of the cylindrical body to after the polishing, but it is preferable that the shaft 4 is first subjected to secondary crosslinking and polishing in a state of being inserted through the through-holes 3 of the end portions 5 and the intermediate portion 6 arranged in this order after the cutting.

This can suppress warpage, deformation, and the like of the cylindrical body due to expansion and contraction during secondary crosslinking, and polishing can be performed while rotating around the shaft 4, thereby improving the workability of polishing and suppressing the run-out of the outer peripheral surfaces 7 and 8.

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

In the former case, the tubular body is secondarily crosslinked by heating in the oven, and at the same time, the thermosetting adhesive is cured, and the shaft 4 is electrically and thermally bonded to the end portion 5 and the intermediate portion 6 constituting the roller main body 2 and mechanically fixed.

In addition, in the latter case, electrical, thermal bonding and mechanical fixing are accomplished while being pressed in.

As described above, the shaft 4 may be electrically, thermally and mechanically fixed to the end portion 5 and the intermediate portion 6 of the roller body 2 by a combination of the above-described two methods.

As described above, the oxide film 9 is preferably formed by irradiating the end portion 5 and the outer peripheral surface 7 and the outer peripheral surface 8 of the intermediate portion 6 constituting the roller main body 2 with ultraviolet rays.

That is, the outer circumferential surface 7 and the outer circumferential surface 8 are irradiated with ultraviolet rays having a predetermined wavelength for a predetermined time, and a cured product of the rubber composition constituting the vicinity of the outer circumferential surface 7 and the outer circumferential surface 8, particularly a diene rubber therein is oxidized, whereby the oxide film 9 can be formed.

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.

Further, the oxide film 9 formed by irradiation with ultraviolet rays does not have the problems of the coating film formed by applying the coating agent, and is excellent in uniformity of thickness, adhesion to the end portion 5 and the intermediate portion 6, and the like.

When the cured product of the rubber composition is oxidized efficiently to form the oxide film 9 having an excellent function, the wavelength of the ultraviolet ray to be irradiated is preferably 100nm or more, preferably 400nm or less, and particularly 300nm or less.

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

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

Rubber composition

Both the end portions 5 and the intermediate portion 6 are preferably formed of a crosslinked product of a rubber composition having crosslinkability and conductivity.

This can impart conductivity to the end portions 5 and the intermediate portion 6, set the roller resistance value within an appropriate range, and charge the toner with an appropriate charge amount during development.

In order to set the thermal conductivity of the end portion 5 to a range exceeding 0.47W/m.K, it is preferable to mix a heat transfer component as described above in the rubber composition that is the base of the end portion 5.

< Heat transfer component >

Examples of the heat transfer component include: one or more of graphite powder, boron nitride powder, carbon black, graphene, carbon fiber and the like.

Among these, graphite powder and/or boron nitride powder which can provide good thermal conductivity with a small amount of the powder and which is relatively inexpensive and easily available as compared with graphene and the like are preferable, and graphite powder is particularly preferable.

(graphite powder)

Since the graphite powder functions as a filler or an electron conductive agent, as with carbon black, the blending of carbon black or the like may be omitted when the graphite powder is used as a heat transfer component.

In this case, the graphite powder may be blended so that the thermal conductivity of the end portion 5 is in the range of more than 0.47W/m.K, and the flexibility of the end portion 5 may be improved by omitting the blending of carbon black or the like.

As the graphite powder, either artificial graphite powder or natural graphite powder can be used, and particularly, artificial graphite powder having less impurities and stable quality is preferable.

The artificial graphite powder is not limited to this, and for example, UF-G5 (particle size: 3 μm, specific surface area: 40m²/g]UF-G10[ particle size: 5 μm, specific surface area: 35m²/g]UF-G30[ particle size: 10 μm, specific surface area: 15m²/g]And the like, or two or more thereof.

(boron nitride powder)

The boron nitride powder is preferably a highly-crystallized hexagonal boron nitride powder.

The boron nitride powder is not limited to this, and any one or two or more of various grades of boron nitride powders such as UHP-1K, UHP-EX, UHP-30, UHP-2, UHP-S1, UHP-G1, UHP-G1H, UHP-G3, UHP-10, UHP-S2, UHP-FM, UHP-15 and UHP-S3 in Showa Denko (registered trademark) UHP series which is a hexagonal boron nitride powder can be used.

Among these, particularly, scaly boron nitride powders such as UHP-1K, UHP-2, UHP-S1 and UHP-15 are preferably used because they are excellent in the effect of improving the thermal conductivity by blending a smaller amount than granular boron nitride powders and the like.

< proportion of Heat transfer component-end 5 >

The ratio of the heat transfer component in the end portion 5 may be set to any range that can set the thermal conductivity of the end portion 5 within a range exceeding 0.47W/m · K depending on the kind of the heat transfer component.

(graphite powder)

The proportion of the graphite powder such as the artificial graphite powder in the end portion 5 is preferably 25 parts by mass or more, particularly 30 parts by mass or more, with respect to 100 parts by mass of the total amount of the rubber.

By setting the ratio of the graphite powder to the above range, the thermal conductivity of the end portion 5 can be set to a range exceeding 0.47W/m · K, and temperature rise of the end portion 5 or the sealing member, particularly fusion bonding of the low melting point toner can be suppressed.

Therefore, it is possible to suppress toner leakage from the end portion 5 and contamination of an image due to fusion of toner and a decrease in sealability accompanying the fusion.

However, the proportion of the graphite powder is preferably 80 parts by mass or less, particularly 70 parts by mass or less, relative to 100 parts by mass of the total amount of the rubber.

When the ratio of the graphite powder exceeds the above range, the type a durometer hardness of the end portion 5 exceeds 80, and the end portion 5 becomes too hard, so that the toner may leak from the end portion 5 to cause image contamination due to the reduction in sealing property as described above.

On the other hand, by setting the ratio of the graphite powder to the above range, it is possible to maintain appropriate flexibility of the end portion 5, prevent toner from leaking from the end portion 5 due to a decrease in sealing property, and suppress image contamination.

(boron nitride powder)

The appropriate range of the proportion of the boron nitride powder differs depending on the particle shape of the boron nitride powder and the like.

For example, when the scaly boron nitride powder is used alone (including a case where two or more scaly boron nitride powders are used in combination, the same applies hereinafter), the ratio thereof is preferably 25 parts by mass or more, particularly 30 parts by mass or more, relative to 100 parts by mass of the total amount of the rubber.

For example, when a scale-like boron nitride powder and a particulate boron nitride powder are used in combination, the total ratio varies depending on the combination ratio of the two powders, but is, for example, a ratio of 1: 1, the amount is preferably 25 parts by mass or more, particularly 30 parts by mass or more, based on 100 parts by mass of the total amount of the rubber.

Further, the proportion of the particulate boron nitride powder used alone is preferably 35 parts by mass or more, particularly 40 parts by mass or more, relative to 100 parts by mass of the total amount of the rubber.

By setting the ratio of the boron nitride powder to the above range, the thermal conductivity of the end portion 5 can be set to a range exceeding 0.47W/m · K, and temperature rise of the end portion 5 or the sealing member, particularly fusion bonding of the low melting point toner can be suppressed.

Therefore, it is possible to suppress toner leakage from the end portion 5 and contamination of an image due to fusion of toner and a decrease in sealability accompanying the fusion.

However, when boron nitride is used as the heat transfer component, carbon black or the like as a filler or an electron conductive agent cannot be omitted.

Therefore, in order to maintain appropriate flexibility by setting the type a durometer hardness of the end portion 5 to 80 or less, prevent leakage of toner from the end portion 5 due to a decrease in sealing property, and suppress image contamination, the proportion of the boron nitride powder is preferably smaller than that of the graphite powder.

Specifically, the proportion of the boron nitride powder is preferably 60 parts by mass or less, particularly 50 parts by mass or less, relative to 100 parts by mass of the total amount of the rubber.

< proportion of Heat transfer component-intermediate portion 6 >

The ratio of the heat transfer component in the intermediate portion 6 may be set to any range that can make the rubber hardness of the intermediate portion 6 smaller than that of the end portion 5.

Specifically, the rubber hardness of the intermediate portion 6 can be made smaller than that of the end portions 5 by making the proportion of the heat transfer component smaller than that of the end portions 5.

However, it is important to make the type a durometer hardness of the intermediate portion 6 less than 60 to impart good flexibility to the intermediate portion 6 and improve the image durability of the developing roller 1.

Therefore, the ratio of the intermediate portion 6 is preferably less than 30 parts by mass, more preferably less than 25 parts by mass, and particularly preferably 0 part by mass, which is a ratio without blending (removing) the heat transfer component, with respect to 100 parts by mass of the total amount of the rubber, in any of the heat transfer components.

< rubber >

As the rubber used in the rubber composition forming the end portions 5 and the intermediate portion 6, in the rubber composition, as described above, it is preferable to use an ion conductive rubber in order to impart conductivity.

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

By using these rubbers in combination, it is possible to impart good processability to the rubber composition, and to improve the mechanical strength, durability, and the like of the end portion 5 or the intermediate portion 6 constituting the roller body 2.

The end portions 5 and the intermediate portion 6 may be provided with excellent properties as rubber, that is, properties of softness, small compression set, and resistance to collapse.

(ion-conductive rubber)

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

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

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

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

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

The ethylene oxide plays a role of reducing the roller resistance value of the developing roller 1.

However, if the ethylene oxide content is less than the above range, the above-described effect cannot be sufficiently obtained, and therefore, the roller resistance value of the developing roller 1 may not be sufficiently reduced.

On the other hand, when the ethylene oxide content exceeds the above range, crystallization of ethylene oxide occurs, and the chain motion of the molecular chain is inhibited, so that the roller resistance value of the developing roller 1 tends to increase on the contrary.

In addition, the end portions 5 and the intermediate portions 6 after crosslinking become too hard, or the viscosity of the rubber composition before crosslinking at the time of heating and melting increases, and the processability of the rubber composition may be lowered.

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

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

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

The allyl glycidyl ether functions to secure a free volume as a side chain, thereby playing a role of suppressing crystallization of ethylene oxide and reducing the roller resistance value of the developing roller 1.

However, if the allyl glycidyl ether content is less than the above range, the above effect cannot be sufficiently obtained, and therefore the roller resistance value of the developing roller 1 may not be sufficiently reduced.

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

Therefore, when the allyl glycidyl ether content exceeds the above range, the crosslinking density of the GECO becomes too high, and the segmental motion of the molecular chain is inhibited, and the roller resistance value of the developing roller 1 tends to be increased.

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

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

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

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

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

(diene rubber)

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

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

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

·BR

BR functions particularly to impart excellent properties as rubber to the end portions 5 and the intermediate portion 6.

Further, BR functions to improve the charging characteristics of the positively chargeable toner, or to improve the fluidity or moldability of the rubber composition before crosslinking, in particular.

Further, BR is oxidized by the irradiation of ultraviolet rays, and functions as a material for forming the oxide film 9 on the outer peripheral surfaces 7 and 8 of the end portion 5 and the intermediate portion 6.

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 high temperature to a low 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 preferable to use non-oil-filled BR 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 BR may be used.

·CR

CR functions to improve flexibility of the end portions 5 and the intermediate portion 6 and improve image durability of the developing roller 1.

CR functions to improve the charging characteristics of positively chargeable toner, or to finely adjust the roller resistance value of the developing roller 1 because it is a polar rubber.

Further, CR is oxidized by irradiation with ultraviolet rays, and functions as a material for forming oxide films 9 on the outer peripheral surfaces 7 and 8 of the end portions 5 and the intermediate portion 6.

CR is synthesized by, for example, emulsion polymerization of chloroprene, and is classified into sulfur-modified type and non-sulfur-modified type according to the type of molecular weight modifier used at that 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.

On the other hand, 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.

Further, CR is classified into the slow crystallization rate type, the medium crystallization rate type, and the 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 rubber of chloroprene and other copolymerization components may also be used.

Examples of the 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 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 has a dissolution parameter (SP value) similar to that of any of epichlorohydrin rubber plasma-conductive rubbers, BR and CR, and therefore functions as a so-called compatibilizer for these rubbers to assist in the micro dispersion between the respective rubbers and improve the integrity of the rubber composition.

Further, the rubber composition functions to improve the fluidity during heating and to ensure good moldability.

The NBR also functions to further improve the flexibility of the end portions 5 and the intermediate portions 6 after molding, to further improve the image durability of the developing roller 1, and to improve the elastic modulus of the outer peripheral surfaces 7 and 8 on which the oxide films 9 are formed.

The NBR functions to improve the charging characteristics of the positively chargeable toner, or to finely adjust the roller resistance value of the developing roller 1 because it is a polar rubber.

Furthermore, the NBR is still oxidized by the irradiation of ultraviolet rays, and functions as a material for forming an oxide film 9 on the outer peripheral surfaces 7 and 8 of the end portions 5 and the intermediate portion 6.

The NBR may be any of a low-nitrile NBR having a bonded acrylonitrile amount 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%, or a very high-nitrile NBR of 43% or more.

In addition, it is preferable to select and use NBR having a low mooney viscosity as the NBR in order to improve the fluidity of the rubber composition during heating and to obtain better moldability even when the NBR is formulated without a softener.

In particular, Mooney viscosity ML of NBR₍₁₊₄₎The temperature of 100 ℃ is preferably 35 or less.

However, the lower limit of the mooney viscosity is not particularly limited, and NBR of various solids up to NBR of the minimum mooney viscosity that can be obtained can be used.

Alternatively, a liquid NBR that is liquid at room temperature may be used instead of the solid NBR.

Furthermore, as the NBR, there are oil-filled NBR in which an extender oil is added to adjust flexibility and non-oil-filled NBR in which an extender oil is not added, but in the present invention, it is still preferable to use non-oil-filled NBR which does not contain an extender oil that may be a bleeding substance in order to prevent contamination of the photoreceptor.

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

(proportion of rubber)

The proportion of the ion conductive rubber is preferably 10 parts by mass or more and preferably 50 parts by mass or less in 100 parts by mass of the total amount of the rubber.

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

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

In the case where the ratio of the ion conductive rubber is less than the above range or exceeds the above range, in either case, the roller resistance value of the developing roller 1 cannot be adjusted to a range suitable for the developing roller 1.

When the proportion of the ion conductive rubber exceeds the above range, the proportion of the diene rubber may be relatively small, and favorable characteristics as the rubber may not be imparted to the end portions 5 or the intermediate portion 6.

On the other hand, by setting the ratio of the ion conductive rubber to the above range, it is possible to provide favorable characteristics as rubber to the end portion 5 or the intermediate portion 6 constituting the roller main body 2 while adjusting the roller resistance value of the developing roller 1 to an appropriate range.

< crosslinking component >

A crosslinking component for crosslinking the rubber is blended in the rubber composition forming the end portions 5 and the intermediate portion 6.

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 end portions 5 or the intermediate portion 6, the proportion of sulfur is preferably 0.5 parts by mass or more, and preferably 2 parts by mass or less, per 100 parts by mass of the total amount of rubber.

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

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

(crosslinking accelerator)

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

Among them, four types of thiuram-based accelerators, thiazole-based accelerators, thiourea-based accelerators and guanidine-based accelerators are preferably used in combination.

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

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

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

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

(C_nH_2n+1NH)₂C＝S (1)

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

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

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

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

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

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

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

< Others >

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

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

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

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

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

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

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

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

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

Further, by using conductive carbon black which also functions as a filler or an electron conductive agent, electron conductivity can be imparted to the roller body.

Examples of the conductive carbon black include acetylene black.

The proportion of the conductive carbon black is preferably 5 parts by mass or more, and preferably 15 parts by mass or less, relative to 100 parts by mass of the total amount of the rubber.

However, since the graphite powder functions as a filler and an electron conductive agent as described above, when the graphite powder is used as a heat transfer component, the blending of the filler such as conductive carbon black and the electron conductive agent can be omitted (eliminated).

For example, when the end portions 5 containing graphite powder as a heat transfer component are combined with the intermediate portion 6 not containing graphite powder, it is considered that the conductive carbon black is not blended in the end portions 5 but only in the intermediate portion 6.

On the other hand, when the end portion 5 containing boron nitride powder as a heat transfer component and the intermediate portion 6 containing no graphite powder are combined, it is considered that conductive carbon black is blended in both the end portion 5 and the intermediate portion 6.

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

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

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

Examples of the deterioration inhibitor include various antioxidants and antioxidants.

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

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

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

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

In the example of fig. 1, both the end portion 5 and the intermediate portion 6 constituting the roller main body 2 have a single-layer structure, but at least one of them may have a laminated structure of two or more layers.

However, when the end portion 5 has a laminated structure, it is preferable that each layer constituting the laminated structure has a thermal conductivity exceeding 0.47W/m · K in order to quickly dissipate heat.

On the other hand, when the intermediate portion 6 has a laminated structure, the outermost layer thereof may be a layer having a rubber hardness smaller than that of the end portion 5.

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