JP2014157287A - Conductive roller and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a conductive roller that has a stable initial resistance value as well as a stable resistance value over time, and an image forming apparatus capable of forming high-quality images for a long period.SOLUTION: There is provided a conductive roller 1 including a non-foaming conductive elastic layer 3 that is arranged on an outer peripheral surface of a shaft body 2 and has an annular flange part 5 protruding in a radial direction provided at both ends in an axial direction, and a foaming conductive elastic layer 12 that is arranged on an outer peripheral surface of the non-foaming conductive elastic layer 3 and in a gap with the annular flange part 5 and has a larger outer diameter than that of the annular flange part 5; and an image forming apparatus including the conductive roller 1 as at least one roller selected from the group consisting of a charging roller, a developing roller, a developer supply roller, and a cleaning roller.

Description

  The present invention relates to a conductive roller and an image forming apparatus. More specifically, the present invention forms a conductive roller and a high-quality image over a long period of time that have not only initial hardness and resistance values but also stable hardness and resistance values over time. The present invention relates to a possible image forming apparatus.

  Various image forming apparatuses using an electrophotographic system are employed in printers such as laser printers and video printers, copiers, facsimiles, and multi-function machines thereof. An image forming apparatus using an electrophotographic system includes various types of rollers. Examples of such various rollers include a conductive roller having conductivity or semi-conductivity, and an elastic roller having a relatively low hardness. Specifically, the conductive roller includes a charging roller for uniformly charging an image carrier such as a photoconductor, a developing roller for carrying and transporting the developer and supplying the developer to the image carrier, and a developer on the developing roller. Examples thereof include a developer supply roller that is supplied while being charged, a cleaning roller that removes the developer remaining on the image carrier or various belts, and the like.

  As a conductive roller, Patent Document 1 states that “an insulating silicone rubber foam layer having a rubber hardness of 18 ° Hs to 36 ° Hs (JISA) is formed on the outer peripheral surface of a conductive core, and further its outer peripheral surface. A two-layer silicone rubber roll having a conductive silicone rubber layer formed thereon, in contact with both end faces of the insulating silicone rubber foam layer, and both end faces projecting from the insulating silicone rubber foam layer A pair of ring-shaped semiconductive silicone rubbers having a thickness of 5 mm to 10 mm formed in advance between the inner peripheral surface of the projecting portion of the formed conductive silicone rubber layer and the outer peripheral surface of the conductive core. Is formed integrally, and the maximum value / minimum value of the average resistance value is in the range of 1.1 to 1.2 ”.

  Various rollers mounted on the image forming apparatus may be reduced in hardness in order to secure a pressure contact width (also referred to as a nip width) with a member to which it is pressed. Examples of such rollers include rollers for fixing devices described in Patent Document 2 and Patent Document 3. Specifically, Patent Document 2 states that “a silicone rubber layer, a silicone sponge layer, and a fluororesin tube layer are sequentially laminated in the order from the central core to the surface layer, and the silicone rubber layer and the silicone are laminated. A pressure roller characterized in that the wall thickness ratio with the sponge layer is in the range of 2: 1 to 7: 1 ”is disclosed in Patent Document 3 as“ a non-foamed silicone rubber layer is coated on the outer periphery of the core metal, Furthermore, a fixing roll characterized in that the non-foamed silicone rubber layer is coated with a foamed silicone rubber layer to form a two-layer coating structure is described.

Japanese Patent No. 3765431 Japanese Utility Model Publication No. 5-59474 JP 2002-156857 A

  By the way, reduction in hardness of a roller mounted on an image forming apparatus and reduction in change in hardness / resistance value are also required for a conductive roller. The reason is to obtain better print image quality by reducing the influence on the contact toner.

  In particular, in order to reduce the hardness of the conductive roller, it is effective to form the elastic layer with a foam like the roller for the fixing device.

  However, as described in the column 0007 of Patent Document 1, when the elastic layer is formed of a foam, “just to adjust the resistance value of the roll to this semiconductive region, such as conductive carbon black, etc. It is very difficult to adjust the amount of conductive filler added, and especially when this is used as a sponge roll, the resistance value increases due to foaming, and the rate of increase varies greatly depending on the foaming ratio. In general, it is very difficult to control the resistance value.

  Furthermore, the elastic layer made of a foam is likely to be physically affected, and as a result, the hardness is lowered and the resistance value of the initial semiconductive region is generally changed. Note that the rollers for the fixing devices of Patent Document 2 and Patent Document 3 usually do not have electrical conductivity, and therefore it is not necessary to adjust the resistance value.

  Since the conductive roller mounted on the image forming apparatus is usually arranged in contact with or pressed against other members, the resistance value of the conductive roller itself is of course the end and center of the conductive roller in the axial direction. It may be difficult to adjust the resistance value to approximately the same. In particular, when the conductive roller is mounted in a state where it is in contact with or pressed against another member, the resistance value fluctuates over time, and even if the initial resistance value is adjusted uniformly, the uniformity of the resistance value gradually deteriorates. This is a strong factor that deteriorates the quality of an image formed by the image forming apparatus.

  Accordingly, an object of the present invention is to provide a conductive roller that has not only initial hardness and resistance value but also stable hardness and resistance value over time and can maintain elasticity for a long period of time.

  Another object of the present invention is to provide an image forming apparatus capable of forming a high-quality image over a long period of time.

Means for solving the problems are as follows:
(1) a non-foamed conductive elastic layer having a central portion disposed on the outer peripheral surface of the shaft body and an annular flange formed so as to protrude in the radial direction at both ends in the axial direction of the central portion; A foamed conductive elastic layer formed on the outer peripheral surface of the non-foamed conductive elastic layer so as to cover the central portion between the annular flange and having a larger outer radius than the annular flange. Conductive roller,
(2) The dimensional difference A between the outer radius of the annular flange and the outer radius of the central portion has a ratio of 25% to 95% with respect to the thickness C of the foamed conductive elastic layer. The conductive roller according to claim 1, wherein the minimum thickness B is 0.5 mm.
(3) The non-foamed conductive elastic layer contains carbon black and has an electric resistance value of 1 × 10 ⁴ to 1 × 10 ⁸ Ω.
The foamed conductive elastic layer is the conductive roller according to (1) or (2), which contains carbon black and has an electric resistance value of 1 × 10 ⁵ to 1 × 10 ⁹ Ω.
(4) The foamed conductive elastic layer according to any one of (1) to (3), wherein each of both end portions has an annular tapered portion in which an outer radius gradually decreases toward each end edge. An elastic roller according to claim 1,
(5) The non-foamed conductive elastic layer has a JIS A hardness of 20 to 70, and the foamed conductive elastic layer has an Asker F hardness of 40 or more and an Asker C hardness of 50 or less. ), The elastic roller according to any one of
(6) The conductive roller according to any one of (1) to (5) is provided as at least one roller selected from the group consisting of a charging roller, a developing roller, a developer supply roller, and a cleaning roller. The image forming apparatus.

  The conductive roller according to the present invention includes a non-foamed conductive elastic layer that is disposed on the outer peripheral surface of the shaft body and has an annular flange projecting radially at both ends in the axial direction, and the non-foamed conductive elastic layer Each of the both ends of the foamed conductive elastic layer is non-foamed. Excessive deformation in the axial direction is suppressed by the annular flange of the conductive elastic layer. As a result, both ends of the foamed conductive elastic layer are reduced or prevented from excessive deformation and destruction of the foamed structure with time, and the network of carbon blacks in the foamed conductive elastic layer is maintained for a long period of time.

  The image forming apparatus according to the present invention includes at least one conductive roller according to the present invention as at least one roller selected from the group consisting of a charging roller, a developing roller, a developer supply roller, and a cleaning roller. The roller exhibits stable electrical characteristics.

  Therefore, according to the present invention, it is possible to provide a conductive roller having not only initial hardness and resistance value but also stable hardness and resistance over time, and an image forming apparatus capable of forming a high-quality image over a long period of time. .

FIG. 1 is a schematic sectional view showing a conductive roller as an example of the conductive roller according to the present invention. FIG. 2 is a schematic sectional view showing a conductive roller as another example of the conductive roller according to the present invention. FIG. 3 is a schematic explanatory view showing the fixing device according to the present invention and the image forming apparatus according to the present invention.

  The conductive roller according to the present invention is a conductive roller mounted on an image forming apparatus, such as a charging roller, a developing roller, a developer supply roller, and a cleaning roller, and the outer peripheral surface of the shaft body. A non-foamed conductive elastic layer and a foamed conductive elastic layer disposed on the outer peripheral surface of the non-foamed conductive elastic layer. The non-foamed conductive elastic layer has an annular flange projecting in the radial direction at both ends in the axial direction, and the foamed conductive elastic layer has an outer radius larger than the annular collar, It is arranged between the parts. The electroconductive roller which concerns on this invention should just have the said structure, and may be provided with the adhesive bond layer, the surface layer, etc. in addition to the non-foaming electroconductive elastic layer and the foaming electroconductive elastic layer.

The conductive roller according to the present invention has conductivity, particularly semi-conductivity. In this invention, “semi-conductive” means an electric resistance value (100 V) described later of 1 × 10 ⁴ to 1 × 10 ^9. Electrical characteristics within the Ω range.

  As shown in FIG. 1, a conductive roller 1 as an example of the conductive roller according to the present invention includes a shaft body 2, a non-foamed conductive elastic layer 3 disposed on the outer peripheral surface of the shaft body 2, And a foamed conductive elastic layer 4 disposed on the outer peripheral surface of the foamed conductive elastic layer 3.

  The shaft body 2 only needs to have good conductive properties, and is usually a so-called “core” composed of iron, aluminum, stainless steel, brass, or the like. Further, the shaft body 2 may be a shaft body that is made conductive by plating an insulating core body such as a thermoplastic resin or a thermosetting resin. Furthermore, the shaft body 2 may be a thermoplastic resin or a thermosetting resin. The shaft body may be formed of a conductive resin in which carbon black or metal powder is blended as a conductivity imparting agent.

  The non-foamed conductive elastic layer 3 is formed on the outer peripheral surface of the shaft body 2 and has annular flanges 5 projecting in the radial direction at both ends in the axial direction. Specifically, the non-foamed conductive elastic layer 3 extends in the axial direction, and preferably has a cylindrical central portion 6 having a constant outer radius B and an end portion of the central portion 6 that are preferably integrally connected to each other. The cross-sectional shape including the axial line which is provided and has an annular flange portion 5 protruding in the radial direction from the outer peripheral surface of the central portion 6 is a substantially H shape having a wide width. Thus, the non-foamed conductive elastic layer 3 is formed in a tubular shape having the annular flanges 5 at both ends.

  As shown in FIG. 2A, the inner end surface 7 facing the central portion 6 of the annular flange 5 and the outer peripheral surface 8 of the central portion 6 may be connected substantially vertically (in other words, the inner end surface). 7 may rise in the radial direction at right angles from the outer peripheral surface 8 of the central portion 6). However, the pressure applied when the roller is pressed against the object is relieved and uniformed as shown in FIG. As shown in the drawing, it is preferable that the curved surface is continuous from the inner end surface 7 to the outer peripheral surface 8 and is continuously formed from the annular flange 5 to the central portion 6 or, although not shown, the inner end surface 7 and the outer peripheral surface. 8 is preferably connected through a plane intersecting at an acute angle. Examples of such a curved surface include an R surface in a cross section including the axis of the non-foamed conductive elastic layer 3. Further, as surfaces intersecting at an acute angle, for example, inclined surfaces disposed in the vicinity of the outer peripheral surface 8 side of the inner end surface 7 and in the vicinity of the inner end surface 7 side of the outer peripheral surface 8 in the cross section including the axis of the non-foamed conductive elastic layer 3, for example C surface etc. are mentioned. Here, the radius of curvature of the R surface is not particularly limited, and can be arbitrarily changed depending on the outer radius of the manufactured conductive roller and the total thickness of the foamed conductive elastic layer and the foamed elastic layer.

  As described above, the non-foamed conductive elastic layer in the conductive roller according to the present invention is not only shown in FIGS. 2 (a) and (b), but as long as the object of the present invention can be achieved, It can take the form as shown below. As shown in FIG. 2 (c), the inner end surface 7 facing the central portion 6 of the annular flange 5 may be a frustoconical surface as shown by a straight line having a gentle slope in a cross section passing through the axis. Further, as shown in FIG. 2 (d), the outer peripheral surface 10 sandwiched between the inner end surface 7 and the outer end surface 9 of the annular flange 5 is inclined from the inner end surface 7 to the outer end surface 9. It may be formed on the surface.

  The non-foamed conductive elastic layer 3 is a so-called “solid elastic layer” that does not substantially have hollow portions that open to the inner and outer surfaces thereof. Here, “substantially does not have” means that the hollow part formed by foaming of the foaming agent and the hollow part due to the presence of the hollow filler are not positively present and inevitably exist. It does not mean that it does not even have a hollow part.

  The non-foamed conductive elastic layer 3 preferably has a JIS A hardness of 20 to 70 in that the foamed structure of the foamed conductive elastic layer 4 can be significantly or highly reduced or prevented from breaking. Particularly preferred is a JIS A hardness of 60. The JIS A hardness is a value obtained by measuring a plurality of locations in accordance with JIS K6253 and arithmetically averaging the measured values.

The non-foamed conductive elastic layer 3 preferably has an electric resistance value (100 V) of 1 × 10 ⁴ to 1 × 10 ⁸ Ω, particularly preferably 1 × 10 ^{5 to} 5 × 10 ⁷ Ω. When the electrical resistance value of the non-foamed conductive elastic layer 3 is within the above range, the electrical resistance value of the conductive roller 1 can be easily adjusted to a semiconductive region, and the resistance value of the foamed conductive elastic layer is set to 1. When it is set to × 10 ⁴ to 1 × 10 ⁸ Ω, the effect of reducing the influence on the foamed elastic layer when energized for a long time is obtained by a synergistic effect. The electrical resistance value of the non-foamed conductive elastic layer 3 can be measured using, for example, an electrical resistance meter (trade name: ULTRA HIGH RESISTANCE METER R8340A, manufactured by Advantest Co., Ltd.) in an environment of a temperature of 20 ° C. and a relative humidity of 50%. . Specifically, in the method described in detail below, before coating the foamed conductive elastic layer, the entire roller ground to the annular flange diameter is placed in the state of only the manufactured non-foamed conductive elastic layer. A gold-plated plate having a length that can be used is an electrode, and a load of 500 g is supported on each end of the shaft body 2 in the conductive roller 1 (total load 1000 g), between the shaft body 2 and the electrode. DC100V is applied to the electrode, the value of the electric resistance meter after 1 second is read, and measurement is performed in accordance with a method of setting this value as the electric resistance value. The electric resistance value of the non-foamed conductive elastic layer 3 can be adjusted by the content of carbon black or the like.

  The non-foamed conductive elastic layer 3 is adjusted to have an arbitrary length and thickness depending on the application, but preferably has dimensions and shapes described below.

  The annular jaw 5 has a length in the axial direction of preferably 1.0 mm or more and 20 mm or less, and is preferably 2.0 mm or more and 10 mm or less in that the deformation of the end of the foamed conductive elastic layer 4 can be highly prevented. It is particularly preferred. Further, the shape may be inclined regardless of the foamed conductive elastic layer side and the outside thereof, regardless of the vertical direction.

  A preferable minimum thickness B of the columnar central portion 6 formed between the pair of annular flanges 5 in the non-foamed conductive elastic layer 3 is 0.5 mm. When the thickness B of the central portion 6 is 0.5 mm or more, there is an advantage that the deformation of the end portion can be highly prevented.

  The ratio of the dimensional difference A between the outer radius of the pair of annular flanges 5 and the outer radius of the central portion 6 in the non-foamed conductive elastic layer 3 to the thickness C of the foamed conductive elastic layer 4 is 25% or more and 95%. It is preferable that: When the dimensional difference A is in the above range, it indicates that the outer radius of the foamed conductive elastic layer is larger than the outer radius of the annular flange, and there is an advantage that the deformation of the end portion can be highly prevented.

  The non-foamed conductive elastic layer 3 contains rubber, a conductivity imparting agent, and various additives as desired. Examples of the rubber include silicone or silicone-modified rubber, nitrile rubber, ethylene propylene rubber (including ethylene propylene diene rubber), styrene butadiene rubber, butadiene rubber, isoprene rubber, natural rubber, acrylic rubber, chloroprene rubber, butyl rubber, and epichlorohydrin. Examples thereof include rubbers such as rubber, urethane rubber, and fluorine rubber. Silicone or silicone-modified rubber or urethane rubber is preferable, and silicone or silicone-modified rubber is particularly preferable in terms of excellent heat resistance and charging characteristics. These rubbers may be liquid or millable.

  Examples of the conductivity imparting agent include a conductive powder and an ion conductive material. Specific examples of the conductive powder include carbon for rubber such as SAF, ISAF, HAF, FEF, GPF, SRF, FT, and MT, in addition to carbon black such as ketjen black and acetylene black. Examples thereof include metals such as titanium oxide, zinc oxide, nickel, copper, silver, and germanium. Examples of the ionic conductive material include inorganic ionic conductive materials such as sodium perchlorate, lithium perchlorate, calcium perchlorate, and lithium chloride.

  The conductivity imparting agent is added alone or in combination of two or more in an appropriate content so that the non-foamed conductive elastic layer 3 has an electric resistance value in the above range. For example, the content of the conductivity imparting agent is set within a range of 2 to 80 parts by mass with respect to 100 parts by mass of the rubber.

  Examples of the additives include various additives contained in rubber compositions or resin compositions, for example, auxiliary agents such as chain extenders and crosslinking agents, catalysts, dispersants, foaming agents, anti-aging agents, and antioxidants. , Fillers, pigments, colorants, processing aids, softeners, plasticizers, emulsifiers, heat resistance improvers, flame retardant improvers, acid acceptors, thermal conductivity improvers, mold release agents, solvents, etc. It is done. These various additives may be commonly used additives or may be specially used additives depending on applications.

  The rubber composition forming the non-foamed conductive elastic layer 3 may be a composition containing rubber, a conductivity-imparting agent, and various additives as desired. For example, foaming forming the foamed conductive elastic layer 4 Among the rubber compositions, a rubber composition from which the foaming agent has been removed can be suitably used.

  Of the foamed rubber composition forming the foamed conductive elastic layer 4, the rubber composition from which the foaming agent has been removed is preferably a conductive silicone rubber composition, a foamed conductive urethane rubber composition, or the like.

  As the conductive silicone rubber composition, for example, an addition reaction type foamed conductive silicone rubber composition is particularly preferable.

  The addition reaction type foamed conductive silicone rubber composition contains a vinyl group-containing silicone raw rubber, a silica-based filler, an addition reaction crosslinking agent, an addition reaction catalyst, a reaction control agent, and a conductivity imparting agent. If desired, it further contains an organic peroxide crosslinking agent, a heat resistance improver (excluding those that function as the conductivity-imparting agent), and various additives.

  Examples of the vinyl group-containing silicone raw rubber include millable silicone rubber and heat-crosslinked silicone rubber (HTV: High Temperature Vulcanizing). These vinyl group-containing silicone raw rubbers have the property that a foaming agent and an addition reaction cross-linking agent can be easily kneaded with a roll mill or the like in a later step, and are used singly or in combination of two or more. be able to. Examples of the vinyl group-containing silicone raw rubber include trade name “KE-77VBS” manufactured by Shin-Etsu Chemical Co., Ltd.

Examples of the silica-based filler include reinforcing fumed silica or precipitated silica, and surface treatment with a silane coupling agent represented by the general formula RSi (OR ′) _3, which has a high reinforcing effect. Silica-based fillers are preferred. Here, R in the general formula is a glycidyl group, vinyl group, aminopropyl group, methacryloxy group, N-phenylaminopropyl group, mercapto group or the like, and R ′ in the general formula is a methyl group or an ethyl group. . Examples of the silane coupling agent represented by the above general formula include trade names “KBM1003” and “KBE402” manufactured by Shin-Etsu Chemical Co., Ltd., and trade names “Celite Super Floss” manufactured by Toshin Kasei Co., Ltd. It can be easily obtained. Such a silica-based filler surface-treated with a silane coupling agent can be obtained by treating the surface of the silica-based filler according to a conventional method. The compounding amount of the silica-based filler is preferably 40 to 100 parts by mass, more preferably 45 to 70 parts by mass, with respect to 100 parts by mass of the vinyl group-containing silicone raw rubber, and 50 to 60 parts by mass. Part is particularly preferred. A silica type filler can be used individually by 1 type or in mixture of 2 or more types.

  Suitable examples of the addition reaction crosslinking agent include known organohydrogenpolysiloxanes as addition reaction type crosslinking agents having two or more SiH groups (SiH bonds) in one molecule. An addition reaction crosslinking agent can be used individually by 1 type or in mixture of 2 or more types. The compounding amount of the addition reaction crosslinking agent is preferably 0.01 to 20 parts by mass with respect to 100 parts by mass in total of the vinyl group-containing silicone raw rubber and the silica filler.

  The addition reaction catalyst may be any catalyst that is usually used for the addition reaction of silicone raw rubber, and examples thereof include simple metals of 9th group or 10th group and compounds thereof. The amount of addition reaction catalyst affects the hardness of the non-foamed conductive elastic layer, and is 0.40 to 0.7 mass relative to a total of 100 mass parts of the vinyl group-containing silicone raw rubber and the silica-based filler. When it is a part, the Asker F hardness and the hardness ratio of the non-foamed conductive elasticity 3 can be adjusted within the above range. An addition reaction catalyst can be used individually by 1 type or in mixture of 2 or more types.

  As the reaction control agent, a known reaction control agent can be used without particular limitation, and examples thereof include methylvinylcyclotetrasiloxane, acetylene alcohols, siloxane-modified acetylene alcohol, and hydroperoxide. The compounding amount of the reaction control agent is preferably 0.1 to 2 parts by mass with respect to a total of 100 parts by mass of the vinyl group-containing silicone raw rubber and the silica filler. The reaction control agents can be used alone or in combination of two or more.

  The conductivity imparting agent is as described above, and can be used alone or in combination of two or more. The blending amount of the conductivity-imparting agent is preferably 5 to 50 parts by mass with respect to 100 parts by mass in total of the vinyl group-containing silicone raw rubber and the silica filler.

  The organic peroxide cross-linking agent can be used to cross-link vinyl group-containing silicone raw rubber alone, but when used as an auxiliary cross-linking agent for addition reaction cross-linking agents, the physical properties of silicone rubber, such as strength and strain, are improved. To do. Examples of the organic peroxide crosslinking agent include benzoyl peroxide, bis-2,4-dichlorobenzoyl peroxide, dicumyl peroxide, di-t-butyl peroxide, and 2,5-dimethyl-2,5-bis. (T-butylperoxy) hexane and the like. The compounding amount of the organic peroxide crosslinking agent may be 0.3 to 10 parts by mass with respect to 100 parts by mass in total of the vinyl group-containing silicone raw rubber and the silica-based filler. An organic peroxide crosslinking agent can be used individually by 1 type or in mixture of 2 or more types.

  The heat resistance improver may be a compound that improves the heat resistance of the foamed elastic layer 3 other than the conductivity imparting agent, and examples thereof include iron oxide (also referred to as bengara), cerium oxide, and cerium hydroxide. . These can be used individually by 1 type or in mixture of 2 or more types.

  As the silicone rubber composition containing the vinyl group-containing silicone raw rubber, the silica filler, and the various additives, for example, trade names “KE series” and “KEG series” manufactured by Shin-Etsu Chemical Co., Ltd. can be easily used. It can be obtained.

  The rubber composition is, for example, several minutes to several hours, preferably 5 until it is uniformly mixed using a rubber kneader such as a two-roll, three-roll, roll mill, Banbury mixer, dough mixer (kneader) or the like. It can be obtained by kneading at room temperature or under heating for 1 minute or more.

The foamed conductive elastic layer 4 is disposed on the outer peripheral surface 8 of the central portion 6 so as to be sandwiched between the annular flanges 5. The foamed conductive elastic layer 4 has a hollow portion (also referred to as a cell; not shown in FIG. 1) that opens to the inside and / or the outer surface thereof. The cells of the foamed conductive elastic layer 4 are formed in a hollow region produced by foaming or decomposition of a foaming agent or gas contained in a rubber composition described later that forms the foamed conductive elastic layer 4, and in the foamed rubber composition. It refers to a hollow region derived from the contained hollow filler or the like. This cell has an independent cell that is in an independent state that does not contact or communicate with other cells, and a continuous cell that contacts or communicates with other cells in the vicinity. This continuous cell preferably forms a three-dimensional communication path in the foamed conductive elastic layer 4. The shape of each cell is not particularly limited, and may be, for example, a substantially spherical shape, an ellipsoidal shape, an indefinite shape, or a tubular shape in which a plurality of cells communicate with each other. The average cell diameter of the cells is preferably 50 to 400 μm. The average cell diameter is an opening in each cell existing in the observation field by observing an area of about 20 mm ² with an electron microscope or the like on the surface of the foamed conductive elastic layer 4 or a cut surface when cut on an arbitrary surface. Is determined as an average length obtained by arithmetically averaging the measured maximum length.

  The foamed conductive elastic layer 4 secures a predetermined nip width when mounted on the image forming apparatus, and has an effect of transporting or removing toner depending on the application. It preferably has a hardness of 40 or more and an Asker C hardness of 50 or less. Specifically, the foamed conductive elastic layer 4 has a hardness included in the range of 40 to 80 in Asker F hardness or in the range of 10 to 50 in Asker C hardness. The hardness of the foamed conductive elastic layer 4 is preferably 45 to 70 for Asker F hardness and 25 to 45 for Asker C hardness depending on the application. Asker C hardness (1.0 kg load) can be measured according to JIS K6253. In addition, the Asker F hardness is measured by, for example, using a “Asker rubber hardness meter F type” manufactured by Kobunshi Keiki Co., Ltd. on the curved outer surface of the conductive roller 1, that is, on the outer peripheral surface of the foamed conductive elastic layer 4. This value is obtained by reading the scale at the moment when the central portion is pressed and the reference surface contacts the outer surface of the conductive roller 1. The hardness of the foamed conductive elastic layer 4 is a value obtained by arithmetically averaging measured values obtained by measuring a plurality of locations.

The foamed conductive elastic layer 4 preferably has an electric resistance value (100 V) of 1 × 10 ⁵ to 1 × 10 ⁹ Ω, and particularly preferably 1 × 10 ⁶ to 1 × 10 ⁸ Ω. When the electrical resistance value of the foamed conductive elastic layer 4 is within the above range, an effect of reducing the influence on the foamed elastic layer when energized for a long time is obtained by a synergistic effect with the non-foamed conductive elastic layer. The electrical resistance value of the foamed conductive elastic layer 4 can be measured using, for example, an electrical resistance meter (trade name: ULTRA HIGH RESISTANCE METER R8340A, manufactured by Advantest Corporation) in an environment of a temperature of 20 ° C. and a relative humidity of 50%. Specifically, the conductive roller 1 is placed horizontally, a gold-plated plate having a length on which the entire foamed conductive elastic layer 4 of the conductive roller 1 can be placed, and a load of 500 g is applied to the conductive roller. 1 in a state of being supported on both ends of the shaft body 2 in 1 (total load 1000 g), applying DC 100V between the shaft body 2 and the electrode, reading the value of the electric resistance meter after 1 second, Measured according to the method of obtaining the electrical resistance value. The electric resistance value of the foamed conductive elastic layer 4 can be adjusted by the carbon black content and the like.

  As shown in FIG. 1, the foamed conductive elastic layer 4 has a constant outer radius in the axial direction and an outer radius larger than the outer radius of the annular flange 5, and protrudes from the annular flange 5. Yes. The outer radius of the foamed conductive elastic layer 3 only needs to be larger than the outer radius of the annular flange 5, and preferably has a thickness that protrudes 0.25 mm or more from the annular flange 5. When the outer radius and thickness of the foamed conductive elastic layer 3 are within the above ranges, the effect of reducing the deformation of the foamed conductive elastic layer can be obtained.

  The foamed conductive elastic layer 4 contains rubber, a conductivity imparting agent, and various additives as required. The rubber, conductivity imparting agent and various additives are as described above.

  The foamed rubber composition for forming the foamed conductive elastic layer 4 may be a composition containing rubber, a conductivity-imparting agent, a foaming agent, and various additives as required, and the non-foamed conductive elastic layer 3 is formed. As a suitable example, a foamed rubber composition obtained by adding a foaming agent to the rubber composition can be used.

  The foaming agent may be a foaming agent conventionally used for foamed rubber, and examples thereof include the inorganic foaming agent and the organic foaming agent. In the present invention, the foaming agent is preferably an organic foaming agent because the foamed elastic layer 3 can be easily formed. Specifically, for example, azodicarboxylic acid amide, azobis-isobutyro An azo compound such as nitrile is preferably used. In particular, dimethyl-1,1'-azobis (1-cyclohexanecarboxylate) can be preferably used. The blending amount of the foaming agent is, for example, 0.1 to 10 parts by mass, particularly 0.5 to 8 parts by mass with respect to a total of 100 parts by mass of the vinyl group-containing silicone raw rubber and the silica filler. Is good. A foaming agent can be used individually by 1 type or in mixture of 2 or more types.

  As shown in FIG. 2E, a conductive roller 1 as another example of the conductive roller according to the present invention includes a shaft body 2 and a non-foamed conductive elasticity disposed on the outer peripheral surface of the shaft body 2. A layer 3 and a foamed conductive elastic layer 4 disposed on the outer peripheral surface of the non-foamed conductive elastic layer 3 are provided. This conductive roller 1 is basically the same as the conductive roller 1 shown in FIG. 2D except that the form of the foamed conductive elastic layer 4 is different.

  The foamed conductive elastic layer 4 shown in FIG. 2 (e) extends in the axial direction, and is preferably continuously connected to each of the central portion 4a having a constant outer radius and the end portions of the central portion 4a. And an annular taper portion 4b whose outer radius gradually decreases toward each end edge. Each of the annular tapered portions 4b has a truncated cone shape so that the outer radius decreases from the central portion 4a side toward each edge, and the maximum outer radius is the same as that of the central portion 4a. The radius is the same as the outer radius of the inner end face 7 of the annular flange 5. As described above, the annular tapered portion 4 b is continuous from the central portion 4 a of the foamed conductive elastic layer 4 to the annular flange 5 of the non-foamed conductive elastic layer 3.

  The conductive roller according to the present invention can be manufactured by forming a non-foamed conductive elastic layer on the outer peripheral surface of the shaft body and then forming a foamed conductive elastic layer on the outer peripheral surface of the non-foamed conductive elastic layer.

  The non-foamed conductive elastic layer is formed by placing the non-foamed rubber composition on the outer peripheral surface of the shaft and then vulcanizing it. For example, after forming a non-foamed elastic body having a constant outer radius, a method of cutting or grinding the central portion leaving both ends thereof, molding having a tubular cavity with annular recesses radially recessed at both ends Examples thereof include a method of molding using a mold, a method of adhering the annular end portion 13 to both end portions of the central portion 6 formed in advance.

  The foamed conductive elastic layer is formed by placing a foamed rubber composition or the like in the recess surrounded by the central portion 6 and the annular flange 5 of the non-foamed conductive elastic layer and then vulcanizing. If desired, the annular tapered portion 24 may be integrally formed with the central portion 23, and the end of the foamed elastic body having a constant outer radius can be formed by grinding or polishing.

  If desired, the foamed conductive elastic layer thus formed can be serrated.

  If desired, the conductive roller 1 is manufactured by forming a surface layer or the like on the outer peripheral surface of the foamed conductive elastic layer formed as described above.

  An example of the image forming apparatus according to the present invention will be described with reference to FIG.

  The image forming apparatus 30 according to the present invention includes a rotatable image carrier 31 on which an electrostatic latent image is formed, such as a photosensitive member, and a charging unit 32 disposed around the image carrier 31, for example, the conductive member of the present invention. A charging roller formed of a conductive roller, an exposure unit 33, a developing unit 40, a transfer unit 34, for example, a transfer roller and a cleaning unit 37 formed of a conductive roller of the present invention, and a fixing device 35 on the downstream side in the conveyance direction of the recording medium. And. The developing means 40 is formed basically in the same manner as the conventional developing means. Specifically, as shown in FIG. 2, the developer accommodating portion 41 and the developer 42 are supplied to the image carrier 31. A developer carrier 44, a developer supply unit 43 that supplies the developer 42 to the developer carrier 44, and a developer regulating member 45 that charges the developer 42 are provided.

  The fixing device is a heat fixing device having a low hardness fixing roller 53 having a Asker C hardness (load 1.0 kg) in the range of 20 to 35 and a low hardness pressure roller 56. That is, the fixing device 35 includes a fixing roller 53 formed of the conductive roller of the present invention and an endless belt disposed in the vicinity of the fixing roller 53 in a housing 50 having an opening 52 through which the recording medium 36 passes. The endless belt 55 wound around the support roller 54, the fixing roller 53 and the endless belt support roller 54, the pressure roller 56 that presses the fixing roller 53 via the endless belt 55, and the endless belt 55 are not in contact with each other. And a heating means 57 that heats the fixing roller 53 from the outside via the endless belt 55, so that the fixing roller 53 and the pressure roller 56 are in contact with or pressed against each other via the endless belt 55. It is a pressure heat fixing device that is rotatably supported.

  The endless belt support roller 54 may be a roller that is normally used in an image forming apparatus. For example, an elastic roller or the like is used. The endless belt 55 may be an endless belt made of, for example, a resin such as polyamide or polyamideimide, and the thickness and the like of the endless belt 55 can be appropriately adjusted to match the fixing device 35. The pressure roller 56 is in pressure contact with the fixing roller 53 via an endless belt 55 by an urging means (not shown) such as a spring. In the fixing device 35, the pressure roller according to the present invention is mounted as the pressure roller 56. The heating means 57 employs a radiant heating method using a halogen heater, a reflector, or the like, a direct contact heating method in which a heater or the like is directly contacted to heat, an induction heating method, or the like. The heating unit 57 is a member having substantially the same length as that of the fixing roller 53 in the axial direction, and may be disposed in any of the fixing devices 35, but is spaced from the surface of the fixing roller 53 by a certain distance. It is preferable that the fixing roller 53 be arranged substantially in parallel. In the induction heating method, a heating coil is used, and this heating coil is usually a ferromagnetic material such as ferrite, and is a typical shape used for a switching power source. It is formed into a mold or the like, and is formed by winding a conducting wire. By passing the recording medium 36 between the endless belt 55 and the pressure roller 56, the recording medium 36 is heated simultaneously with the pressurization, and the developer 42 (electrostatic latent image) transferred to the recording medium 36 is fixed. be able to.

  The image forming apparatus 30 according to the present invention operates as follows. First, in the image forming apparatus 30, the image carrier 31 is uniformly charged by the charging unit 32, and an electrostatic latent image is formed on the surface of the image carrier 31 by the exposure unit 33. Next, the developer 42 is supplied from the developing unit 40 to the image carrier 31 to develop the electrostatic latent image, and the developer image is conveyed between the image carrier 31 and the transfer unit 34 on the recording member 36. Is transcribed. The recording body 36 is conveyed to the fixing device 35 and the developer image is fixed on the recording body 36 as a permanent image. In this way, an image can be formed on the recording body 36.

  Since the pressure roller according to the present invention is employed as the pressure roller 56 in the fixing device 35 and the image forming apparatus 30 according to the present invention, the fixing device 35 and the image forming apparatus 30 are excellent in fixing property for fixing the developer on the recording medium and consume less power. .

  The image forming apparatus according to the present invention is not limited to the above-described embodiments, and various modifications can be made within a range in which the object of the present invention can be achieved.

  The image forming apparatus 30 is an electrophotographic image forming apparatus. However, in the present invention, the image forming apparatus is not limited to the electrophotographic system, and may be, for example, an electrostatic image forming apparatus. Good. Further, the image forming apparatus 30 is a monochrome image forming apparatus in which the developing unit 40 contains only a single color developer 42. However, in this invention, the image forming apparatus is not limited to a monochrome image forming apparatus. It may be an image forming apparatus. As the color image forming apparatus, for example, a four-cycle color image forming apparatus that sequentially repeats primary transfer of a developer image carried on an image carrier to an intermediate transfer body, and a plurality of image carriers provided with developing means for each color And a tandem type color image forming apparatus in which the toner is disposed in series on an intermediate transfer member or a transfer conveyance belt. The image forming apparatus 30 is an image forming apparatus such as a copying machine, a facsimile machine, or a printer.

  In the fixing device 35 and the image forming apparatus 30, the developer 42 is advantageously a one-component developer, but a two-component developer containing a toner and a carrier such as iron or nickel is also used. can do.

  When the conductive roller 1 is mounted on the image forming apparatus, the peripheral side surface of the bowl-shaped end portion 13 may come into contact with the image carrier. In this case, the developer leaks from both ends of the conductive roller 1. Can be prevented.

  The conductive roller, the fixing device, and the image forming apparatus according to the present invention are not limited to the above-described examples, and various modifications can be made within a range in which the object of the present invention can be achieved.

  In the conductive roller 1, the foamed conductive elastic layer 4 is directly disposed on the outer peripheral surface of the non-foamed conductive elastic layer 3. In this invention, the foamed conductive elastic layer is interposed via an adhesive layer or a primer layer. You may form in the outer peripheral surface of a non-foaming electroconductive elastic layer.

Example 1
The shaft body 2 (diameter 6 mm × length 250 mm, SUM22) subjected to electroless nickel plating was washed with toluene, and a primer “No. 101A / B” (manufactured by Shin-Etsu Chemical Co., Ltd .: trade name) was applied. . The primer-treated shaft body 2 was baked at a temperature of 150 ° C. for 30 minutes using a gear oven, and then cooled at room temperature for 30 minutes or more to form a primer layer.

  Next, a mixture of vinyl group-containing silicone raw rubber and silica-based filler (silicon rubber composition “KE-9410U” manufactured by Shin-Etsu Chemical Co., Ltd.), a mixture of vinyl group-containing silicone raw rubber and carbon black (Shin-Etsu Chemical Co., Ltd.) 100 parts by mass of a silicone rubber composition obtained by mixing a company-made silicone rubber composition “KE-3502U”) to have a predetermined resistance value, an addition reaction crosslinking agent “C-153A” (manufactured by Shin-Etsu Chemical Co., Ltd .: (Trade name) 2.0 parts by mass, an appropriate amount of platinum catalyst as an addition reaction catalyst, and a reaction control agent “R-153A” (manufactured by Shin-Etsu Chemical Co., Ltd .: trade name) 0.5 parts by mass Were sufficiently kneaded to prepare an addition reaction type non-foamed conductive silicone rubber composition.

Next, the shaft body 2 on which the primer layer is formed and the addition reaction type non-foaming conductive silicone rubber composition are integrally extracted with an extrusion molding machine, and the addition reaction type non-foaming conductivity is used using an infrared heating furnace (IR furnace). The silicone rubber composition was crosslinked by heating at 350 ° C. for 5 minutes. Thereafter, the addition reaction type non-foamed conductive silicone rubber composition after crosslinking was further heated at 200 ° C. for 4 hours using a gear oven, and left at room temperature for 1 hour or more. Then, it grind | pulverized so that an outer radius might be set to 6.9 mm with a cylindrical grinder, and then, it grind | polished so that an outer radius might be 3.75 mm leaving 5.0 mm of each both ends. In this way, the non-foamed conductive material having the central portion 6 having an outer radius of 3.75 mm and an axial length of 220 mm and the annular flange portions 5 having an outer diameter of 6.9 mm and an axial length of 5 mm at both ends thereof. The elastic layer 3 was integrally formed. The central portion has a thickness B of 0.75 mm. When the electrical resistance value and JIS A hardness of the non-foamed conductive elastic layer 11 formed integrally with the shaft body 2 thus produced were measured according to the above method, they were 7.41 × 10 ⁵ Ω and 45, respectively. there were.

Subsequently, the addition reaction type non-foamed conductive silicone rubber composition was mixed with 2.0 parts by mass of an organic foaming agent “azobis-isobutyronitrile” and the non-foamed addition reaction type foamed conductive silicone rubber composition was prepared. The region is surrounded by the outer peripheral surface 8 of the central portion 6 of the conductive elastic layer 3 and the inner end surface 7 of the annular flange portion 5 by using an extruder, and is heated at 250 ° C. for 10 minutes for crosslinking. It was. Thereafter, the addition reaction type foamed conductive silicone rubber composition after cross-linking was further heated at 200 ° C. for 7 hours using a gear oven, and left at room temperature for 1 hour or more. Thereafter, the outer radius was ground by 9 mm (projection amount from the annular flange 5 of 2.1 mm) with a cylindrical grinder to form the foamed conductive elastic layer 4 having an axial length of 220 mm, and the conductive roller 1 was manufactured. The electrical resistance value and Asker C hardness of the foamed conductive elastic layer 21 in the conductive roller 1 manufactured as described above were measured according to the above method, and were 1.02 × 10 ⁷ Ω and 15, respectively.

  The dimensional difference A between the outer radius of the annular flange 13 and the outer radius of the central portion 12 was 60% with respect to the thickness C of the foamed conductive elastic layer.

(Examples 2 to 8)
Table 1 shows the dimension difference A, the thickness B of the central portion, the difference C between the outer radius and the inner radius of the foamed conductive elastic layer, and the difference D between the outer radius of the foamed conductive elastic layer and the outer radius of the annular flange. A conductive roller was produced in the same manner as in Example 1 so that the indicated value was obtained. Table 1 shows the Asker C hardness of the foamed conductive elastic layer and the JIS A hardness and electrical resistance of the non-foamed conductive elastic layer in the various conductive rollers manufactured. Table 1 shows the measurement results of the electrical resistance value and hardness of the non-foamed conductive elastic layer 3 and the foamed conductive elastic layer 4 in the conductive roller of Example 2.

(Comparative Examples 1-2)
Table 1 shows the dimension difference A, the thickness B of the central portion, the difference C between the outer radius and the inner radius of the foamed conductive elastic layer, and the difference D between the outer radius of the foamed conductive elastic layer and the outer radius of the annular flange. A conductive roller was produced in the same manner as in Example 1 so that the indicated value was obtained. In addition, the comparative example 1 is an electroconductive roller in which the annular collar part is not formed. Table 1 shows the Asker C hardness of the foamed conductive elastic layer and the JIS A hardness and electrical resistance of the non-foamed conductive elastic layer in the various conductive rollers manufactured. Table 2 shows the measurement results of the electrical resistance value and hardness of the non-foamed conductive elastic layer 11 and the foamed conductive elastic layer 21 in the conductive roller of Comparative Example 2.

(Load-carrying durability test method and evaluation criteria)
It sets so that it can rotate with each two bearings to the shaft exposed part of the both ends of the created conductive roller. Next, bearings and gears are attached to both ends of a SUS303 shaft of φ40 length 240 mm (both ends 10 mm φ8), a drive belt is attached to the gear side, 50 rpm for 25 hours, 1000 V applied by an electric motor, total weight 2.5 kg load An adjusted test was conducted. The test results of Examples 1 to 7 are shown in Table 1, and the test results of Example 8 are shown in Table 2.

  It should be noted that the amount of decrease in Asker C hardness of the foamed conductive elastic layer after the load-carrying durability test was less than 3 and the change in resistance value was within 3 Logs, and “x” otherwise.

  As shown in Table 1, each conductive roller of the example has a small difference in electric resistance value, and the electric resistance value at the initial stage of manufacture is almost unchanged even after the durability test and is stable over time. It was also found that the difference in electrical resistance value between the central portion and the end portion is small and has a highly uniform electrical resistance value. Further, in each of the conductive rollers of the examples, the cell destruction at the end portion could not be substantially confirmed. Therefore, when each conductive roller of the embodiment is mounted on an image forming apparatus, the hardness and charging characteristics, the developer conveyance amount and the developer removal function hardly change over time, and the occurrence of filming is remarkably suppressed. it can.

  As shown in Table 2, all of the conductive rollers of the comparative examples are not stable because the electric resistance value is greatly lowered after the durability test, and the difference in electric resistance value between the central portion and the end portion is also large and uniform. It was found to have an electrical resistance value inferior to. Moreover, the cell destruction of the edge part has confirmed each conductive roller of the comparative example.

DESCRIPTION OF SYMBOLS 1 Elastic roller 2 Shaft body 3 Non-foaming electroconductive elastic layer 4 Foaming electroconductive elastic layer 5 Annular collar part 6 Center part 7 Inner end surface 8 Outer peripheral surface 9 Outer end surface 10 Outer peripheral surface 30 Image forming apparatus 31 Image carrier 32 Charging means 33 Exposure means 34 Transfer means 35 Fixing device 36 Transferred body 37 Cleaning means 40 Developing means 41 Developer storing section 42 Developer 43 Developer supplying means 44 Developer carrier 45 Developer regulating member 50 Housing 52 Opening 53 Fixing roller 54 Endless belt support roller 55 Endless belt 56 Pressure roller 57 Heating means

Claims (6)

  A non-foamed conductive elastic layer having a central portion disposed on the outer peripheral surface of the shaft body, and an annular flange formed so as to protrude in the radial direction at both ends in the axial direction of the central portion; And a foamed conductive elastic layer formed on the outer peripheral surface of the elastic elastic layer so as to cover the central portion with the annular flange, and having a larger outer diameter than the annular flange. roller.   The ratio of the dimensional difference A between the outer radius of the annular flange and the outer radius of the central portion to the thickness C of the foamed conductive elastic layer is 25% or more and 95% or less, and the central portion has a minimum thickness. The conductive roller according to claim 1, wherein B is 0.5 mm. The non-foamed conductive elastic layer contains carbon black and has an electric resistance value of 1 × 10 ⁴ to 1 × 10 ⁸ Ω.
The conductive roller according to claim 1, wherein the foamed conductive elastic layer contains carbon black and has an electric resistance value of 1 × 10 ⁵ to 1 × 10 ⁹ Ω.   The elastic roller according to any one of claims 1 to 3, wherein the foamed conductive elastic layer has an annular taper portion whose outer radius gradually decreases toward each edge at each of both ends thereof.   The non-foamed conductive elastic layer has a JIS A hardness of 20 to 70, and the foamed conductive elastic layer has an Asker F hardness of 40 or more and an Asker C hardness of 50 or less. Elastic roller as described in.   An image forming apparatus comprising the conductive roller according to claim 1 as at least one roller selected from the group consisting of a charging roller, a developing roller, a developer supply roller, and a cleaning roller.

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