JP2008299109A - Conductive roller, its manufacturing method, electrophotographic device and process cartridge - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a conductive roller capable of reducing the occurrence of an image defect even though a layer for controlling electric characteristic is not provided on the outer periphery of a conductive elastic layer containing conductive particles when using the conductive roller while making it abut on a body to be electrified, and an electrophotographic device and a process cartridge using the conductive roller. <P>SOLUTION: The conductive roller containing the conductive particles is set so that voltage dependency at the end of the roller will be smaller than that in the center part of the roller. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a conductive roller such as a developing roller, a charging roller, and a transfer roller used in an electrophotographic apparatus, an electrophotographic apparatus and a process cartridge using the conductive roller, and a method for manufacturing the conductive roller.

  Conventionally, many methods are known as electrophotographic methods.

As a general example,
A potential is applied to a charged object using a photosensitive (photoconductive) substance (charging process),
An electrical latent image is formed by partially exposing the object to be charged (exposure process),
Next, the latent image is made visible with toner (development process), and the toner image is transferred to a transfer material such as paper (transfer process).
Then, fix the toner image on the transfer material with heat, pressure, etc. (fixing process)
There is a method for obtaining an image.

  In addition, an additional process such as removing toner particles remaining on the charged body without being transferred onto the transfer material from the charged body by various means (cleaning process) may be added.

  Among these processes, a conductive roller having an elastic layer is generally used as a member used in the charging process, the developing process, and the transfer process. By rotating in a roller shape, image defects due to local accumulation of toner, external additives, paper powder, and other powders are less likely to occur. In addition, since the contact energization site with the member to be charged changes, there is an effect that an increase in electrical resistance is suppressed.

  When such a conductive roller is used in contact with a member to be charged, image defects due to contact traces and pinhole leakage described later have occurred.

  First, the contact trace will be described. When the conductive roller is used after being brought into contact with the member to be charged and left unused for a long period of time, the contact portion of the conductive roller has become an image defect as a contact mark on the image.

  The cause of the image failure can be considered in various ways. One of the causes is that the electrical resistance of the contact portion changes irreversibly by changing the dispersion state of the conductive agent contained in the conductive elastic layer. Is mentioned. When the electrical resistance of the abutting portion changes, the electrical resistance differs between the abutting portion and the non-abutting portion, so that a difference occurs in the discharge amount and the uniformity of the image is impaired.

  As a countermeasure, Patent Document 1 proposes that a semiconductive polymer composition is provided on the outer periphery of the conductive elastic layer to suppress variation in electric resistance and to impart uniform conductivity to the conductive roller. Yes.

  Next, image defects due to pinhole leak will be described. An image defect when using a conductive roller in contact with a member to be charged is that an excessive current flows through a defective portion of the member to be charged (referred to as pinhole leak in the present invention). .

  Hereinafter, the cause of the pinhole leak will be described in detail. In some cases, the object to be charged has a minute recess (pinhole) of millimeter or less that does not normally cause an image defect. When an excessive current flows in this part, the electric charge flows to the periphery of the dent, resulting in an image defect of several millimeters that is many times larger than the size of the dent. In a severe case, the electric charge flows to both ends in the axial direction of the member to be charged and a horizontal line appears on the image. This pinhole leak is more likely to occur because an excessive current flows as the electrical resistance of the conductive roller is lower. When the electrical resistance is high, even if a pinhole of the same size exists, an image defect does not occur.

  In order to solve this pinhole leak problem, a resin layer having a higher resistance than the conductive elastic layer is provided on the surface of the conductive elastic layer as a protective layer. If the protective layer has a higher electrical resistance, pinhole leakage is less likely to occur, but if it is too high, the charging ability will be reduced, causing image defects such as uneven image density and streaks due to abnormal discharge. Therefore, the conductivity of the protective layer is controlled to a medium resistance, and conductive particles are added to the protective layer. If there is an agglomerate in the added conductive particles, it becomes an image defect, so that uniform dispersion is preferably obtained.

As such an invention, Patent Document 2 proposes a protective layer in which a porous fluororesin is a main component and the porous particles are filled with conductive particles.
Japanese Patent Laid-Open No. 02-199163 Japanese Patent Laid-Open No. 2005-266312

  However, in the proposals described in Patent Documents 1 and 2, after the formation of the conductive elastic layer, it is necessary to form a semiconductive polymer composition on the outer periphery, a protective layer to which conductive particles are added, and the like. Was complicated.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a conductive roller that can reduce image defects that occur when the conductive roller is used in contact with a member to be charged by a simpler manufacturing process, and an electrophotographic apparatus and process using the same. It is to provide a cartridge.

The present invention relates to a conductive roller having a conductive elastic layer containing at least conductive particles on a conductive support.
When the conductive elastic layer is divided into eight in the roller axial direction (in the present invention, the region where the conductive elastic layer is charged is divided into eight),
The arithmetic average of the electric resistances at both ends is the electric resistance Re at the end, and the arithmetic average of the two central points is the electric resistance Rc at the center.
When the applied voltage is 50 V and 500 V, the electrical resistance of the end and the electrical resistance of the center are Re (50 V), Rc (50 V), Re (500 V), Rc (500 V),
When the electric resistance of the entire axial direction when the applied voltage is 200 V is R (200 V),
0.1 <log [Re (50V) / Re (500V)] / log [Rc (50V) / Rc (500V)] ≦ 0.9 and 1.0 ≦ log (Re (50V) / Re (500V)) ≦ 2.2 and 1.7 ≦ log (Rc (50 V) / Rc (500 V))
Furthermore, a conductive roller characterized by satisfying 10 ⁴ Ω ≦ R (200 V) ≦ 10 ⁶ Ω is provided.

  The present invention also provides an electrophotographic apparatus and a process cartridge using the conductive roller.

  Furthermore, this invention provides the manufacturing method of the said electroconductive roller.

  By making the voltage dependency at both ends of the conductive roller smaller than the voltage dependency at the center, the occurrence of image defects can be reduced when the conductive roller is used in contact with the member to be charged. .

  Moreover, since it is not necessary to provide the layer for controlling an electrical property in the outer periphery of a conductive elastic layer, the conductive roller of this invention can be obtained with a manufacturing process simpler than the prior art.

  Hereinafter, embodiments of the present invention will be described in detail.

In the conductive roller having a conductive elastic layer containing at least conductive particles,
Electrical resistance Re at the end of the conductive elastic layer,
Electric resistance Rc at the center,
Axial length of electrical resistance R (200V)
The following conditions have been found, and the present inventors have found that a conductive roller capable of reducing image defects due to the occurrence of contact marks and pinhole leakage can be provided.

The conditions for reducing the occurrence of contact marks are 0.1 <log [Re (50V) / Re (500V)] / log [Rc (50V) / Rc (500V)] ≦ 0.9 and 1.0 ≦ log. (Re (50V) / Re (500V)) ≦ 2.2 and R (200V) ≦ 10 ⁶ Ω.

Conditions for reducing image defects due to pinhole leakage are 1.7 ≦ log (Rc (50 V) / Rc (500 V)) and 10 ⁴ Ω ≦ R (200 V).

  To illustrate the structure and form of the conductive roller of the present invention, as shown in FIG. 1, the conductive elastic layer 12 is formed on the outer periphery of the conductive support 11, and surface treatment 13 is applied to the outermost surface. An example of such a conductive roller can be given.

  As the conductive support, a cylinder made of a metal material such as iron, copper, stainless steel, aluminum, and nickel can be used. Furthermore, plating treatment may be performed on these metal surfaces for the purpose of imparting rust prevention and scratch resistance as long as good conductivity is not lost. Moreover, you may apply | coat the adhesive agent of thickness 1 micrometer or more and 20 micrometers or less for the purpose of adhesion | attachment with a conductive elastic layer in the range which does not lose good electroconductivity.

  The conductive elastic layer can be formed of rubber, thermoplastic elastomer, or the like conventionally used as a conductive elastic layer of a conductive roller.

As rubber,
A rubber composition containing polyurethane rubber, silicone rubber, butadiene rubber, isoprene rubber, chloroprene rubber, styrene-butadiene rubber, ethylene-propylene rubber, polynorbornene rubber, styrene-butadiene-styrene rubber, epichlorohydrin rubber or the like is preferably used.

  The type of the thermoplastic elastomer is not particularly limited, and a thermoplastic elastomer composition containing one or more types of thermoplastic elastomers selected from general-purpose styrene elastomers and olefin elastomers is preferably used. it can.

  In practicing the present invention, it is necessary that the compression set of the conductive elastic layer is small in order to reduce the dent of the contact portion that causes the contact mark. Compared to thermoplastic elastomer compositions, crosslinked rubber compositions generally have a lower compression set. Therefore, a crosslinked rubber composition is preferred as the thermoplastic elastomer.

The conductive elastic layer corresponding to the present invention needs to have an electric resistance of 10 ⁴ to 10 ⁶ Ω by a measurement method described later. In order to form such a conductive elastic layer, a conductive elastomer such as rubber or thermoplastic elastomer is used. The conductive mechanism of the conductive elastomer is roughly classified into an ion conductive mechanism and an electronic conductive mechanism.

The conductive elastomer of the ion conduction mechanism is
In general, a polar elastomer represented by epichlorohydrin rubber, chloroprene rubber, acrylonitrile-butadiene rubber and an ion conductive agent that is ionized in the polar elastomer and has high ion mobility. However, the conductive elastomer of the ion conduction mechanism is highly dependent on the environment of the electrical resistance, and due to the mechanical problem that the conductivity develops due to the migration of ions, it causes bleed bloom that causes contact marks. Cheap.

  On the other hand, conductive elastomers based on an electronic conduction mechanism are generally composites in which carbon black, carbon fiber, graphite, fine metal powder, metal oxide, and the like are dispersed as conductive particles in the elastomer. The conductive elastomer of the electronic conduction mechanism has advantages such as less electrical resistance dependency on temperature and humidity, less bleed and bloom, and lower cost compared to the conductive elastomer of the ion conduction mechanism.

  Since the conductive roller of the present invention needs to reduce the appearance of the contact portion appearing as an image defect even if the conductive roller is in contact with the member to be charged and left unused for a long period of time, there is little bleed and bloom. Conductive elastomers with electronic conduction mechanisms are preferred.

  Furthermore, in the present invention, desired electrical characteristics are obtained by utilizing the fact that the conductive elastomer by the electronic conductive mechanism is a dispersed composite material. It is known that the physical properties of a conductive elastomer based on an electronic conductive mechanism vary greatly depending not only on the filling amount of conductive particles but also on the dispersion state. The dispersion state of the conductive particles in the conductive elastic layer changes depending on mechanical energy such as shearing or heating applied during processing or heat energy, and the electric resistance changes at this time. This change in electrical resistance is interpreted to be due to the following two mechanisms.

  The first is a mechanism in which the agglomeration (mainly agglomerate) of the conductive particles is loosened, the conductive path is broken, and the electrical resistance is increased.

  Second, when heat or the like is applied, the reaction rate at which the conductive particles agglomerate increases, and the aggregation of the conductive particles proceeds. This is a mechanism in which the conductive particles are aggregated to form a conductive path and the electric resistance is lowered.

  Further, when the conductive elastomer containing the conductive particles passes through the flow path of the extruder or the injection molding machine, the conductive particles are unevenly distributed. In an extruder, an injection molding machine, or the like, the flow velocity distribution in the pipe that becomes the flow path of the conductive elastomer is the slowest near the pipe wall. At this time, a material having a low molecular weight approaches the tube wall, and a material having a high molecular weight and conductive particles move away from the tube wall. Therefore, the concentration distribution of the conductive particles is generated in the conductive elastomer, and the electric resistance is lowered in the dark portion and the electric resistance is increased in the thin portion.

  Utilizing these phenomena, the present invention can be achieved by controlling the concentration distribution of the conductive particles in the radial direction of the conductive roller and the dispersion state of the conductive particles in the axial direction.

As the conductive particles used in the present invention,
Conductive carbon such as ketjen black EC, acetylene black;
Carbon for rubber such as SAF, ISAF, HAF, FEF, GPF, SRF, FT, MT;
Oxidized color (ink) carbon, pyrolytic carbon, natural graphite, artificial graphite;
Examples thereof include metals such as tin oxide, titanium oxide, zinc oxide, copper and silver, and metal oxides.

  The filling amount of these conductive particles can be appropriately selected depending on the types of raw rubber, conductive particles, and other compounding agents so that the conductive elastic layer has a desired electric resistance. For example, it can be 0.5 to 100 parts by mass, preferably 2 to 50 parts by mass with respect to 100 parts by mass of the polymer.

These rubber elastic layer compositions are generally used as a rubber compounding agent as long as the properties of the conductive roller of the present invention, such as low compression set, low bleeding, and semiconductivity, are not lost. ,
Processing aids, crosslinking agents, crosslinking accelerators, crosslinking accelerators, crosslinking retarders, fillers, dispersants, foaming agents, lubricants, anti-aging agents, antiozonants, antioxidants, conductive agents, etc. are added as appropriate can do.

  Examples of the kneading method of these raw rubber and compounding agent include a method using a closed kneader such as a Banbury mixer, an intermix or a pressure kneader, or a method using an open kneader such as an open roll. can do.

  As a method for molding the unvulcanized rubber composition thus formed, extrusion molding in which the elastic layer roller is molded by extruding the unvulcanized rubber composition integrally with the conductive support is preferable.

  Here, FIG. 2 shows a schematic diagram of the extruder 2 used in the present invention. The extruder includes a crosshead 21. The crosshead can insert the conductive support 23 fed by the conductive support feed roller 22 from a direction perpendicular to the extrusion screw 24, and can simultaneously extrude the cylindrical kneaded material simultaneously with the conductive support. . After the cylindrical unvulcanized rubber composition was molded around the conductive support, the end was cut and removed 25 to obtain an 8.7 mm cylindrical unvulcanized rubber roller 26.

  FIG. 3 is a schematic diagram showing a radial cross section of the unvulcanized rubber roller. Thus, when the cross section is seen, the abundance of the conductive particles has a distribution, and the concentration of the conductive particles is thin in the vicinity of the conductive support and in the vicinity of the surface. This is presumed to be a phenomenon caused by the flow velocity distribution of the kneaded material in the extruder.

  Normally, the flow velocity of fluid traveling in a certain pipe is the slowest near the pipe wall. At this time, a material having a low molecular weight approaches the tube wall, and a material having a high molecular weight and conductive particles move away from the tube wall. Therefore, the concentration distribution of the conductive particles is generated. This concentration distribution can be controlled by changing the conductive particles and viscosity characteristics of the kneaded product.

  This concentration distribution is also closely related to the voltage dependence of the electrical resistance of the conductive elastic layer. When the concentration distribution is small, the distance between the conductive particles is uniform in the radial direction, and in this case, the voltage dependency of the electrical resistance is small. On the other hand, when the concentration distribution is large, the distance between the conductive particles becomes long near the conductive support or near the surface, and close at the center, so that the voltage dependency of the electrical resistance becomes large.

  As a result of examination, it has been clarified that pinhole leakage is less likely to occur as the voltage dependency of the electrical resistance increases.

  The reason for this is that when the voltage dependency is large, the concentration distribution of the conductive particles increases in the radial direction, and the volume resistance increases at the portion where the concentration is low. For this reason, it is presumed that excessive charges are prevented from flowing into the pinholes on the member to be charged in the same manner as when the protective layer is provided.

In the present invention, the electrical resistance of the entire length of the conductive roller in the axial direction is 10 ⁴ Ω or more, and the voltage dependency log (Rc (50 V) / Rc (500 V)) at the center of the roller is 1.7 or more, more preferably By increasing the resistance to 2.2 or higher, pinhole leakage can be reduced.

  From the viewpoint of reducing pinhole leakage, it is preferable that the voltage dependency at the center of the roller is large. However, from the viewpoint of charging ability, the voltage dependency is too large, that is, if the electrical resistance near the surface is too large, This is not preferable because the performance decreases. Therefore, the voltage dependency of the roller center is preferably log (Rc (50V) / Rc (500V)) ≦ 5.0, and log (Rc (50V) / Rc (500V)) ≦ 3.0. More preferably.

  Examples of the vulcanization method for the unvulcanized rubber roller include mold vulcanization, vulcanization can vulcanization, continuous vulcanization, far / near infrared vulcanization, and induction heating vulcanization.

  In order to obtain a desired roller shape and roller surface roughness after vulcanization, it is preferable to grind with a grindstone.

  Generally, a grinding method called a traverse method is used as a method of grinding a roller-shaped elastic layer. This system grinds a roller by moving a short grindstone according to the roller. On the other hand, there is a grinding method called a wide grinding method. This method is a method in which roller grinding can be performed in a short time by literally using a grindstone having a wide width, that is, a grindstone having a width wider than the roller length. In consideration of work efficiency and the like, it can be said that the wide grinding method is more preferable.

  A configuration which is a wide grinding cylindrical grinder will be described with reference to FIG. The headstock unit 401 includes a collet chuck 403, a main bearing 402 that supports the collet chuck, a pulley that transmits power to the main shaft, a belt 404, and a work rotation motor 405 that drives and rotates the pulley. The tailstock unit 406 includes a tailstock slide section (not shown) and a forward / backward movement of the tailstock unit, each of which includes a centerstock shaft center 408, a centering bearing portion 407, and a linear guide for moving the tailstock unit forward and backward. It is comprised by the cylinder 409 which is a drive part. Moreover, it is comprised from the diamond dresser 410 attached to the tailstock slide part in the position orthogonal to the rotating shaft of a grinding wheel.

  The swivel table 411 is mounted with a headstock unit 401 via a headstock and a tailstock unit 406 via a tailstock. A main bearing 402, which is a part of the main spindle unit 401, is attached to the main spindle and holds a main spindle that can be driven and rotated. Further, a core press bearing portion 407 that is disposed to face the main bearing portion 402 and is a part of the core press base unit is attached to the core press stand and holds a core press shaft (not shown) that can be driven to rotate. Further, the center axis of the core pressing shaft is matched with the center axis of the main shaft.

  The conductive support end portion 402a of the unground vulcanized rubber roller 412 is held by the collet chuck 403, and the other conductive support end portion 412b is moved by the core pushing shaft center 408 moving forward to the vulcanized rubber roller 412 side. Press contact is maintained. The unground vulcanized rubber roller 412 held in pressure contact is configured to drive and rotate the unground vulcanized rubber roller 412 via the pulley, the belt 404 and the main bearing portion 402 when the work rotation motor 405 is driven.

  Further, a diamond dresser 410 is attached to the core press bearing portion 407 of the core press base unit 406 so as to face the grinding surface of the grinding wheel 413.

  Next, the cutting configuration of the grinding wheel 413 to the vulcanized rubber roller 412 will be described. The grinding wheel base 415 is placed on the receiving base 414 in a direction orthogonal to the center line of the main shaft or the center line of the centering shaft via a linear guide. It is arranged so that it can move forward and backward. The grindstone table 415 is connected to the receiving table 414 by a ball screw (not shown), and moves forward and backward in the B direction by driving from a cutting motor 416 directly connected to the ball screw. Further, the receiving table 414 is fixed on the thrust moving table 417, and the thrust moving table 417 can move back and forth in a direction C orthogonal to the moving direction B of the grindstone table 415 via a linear guide 418 on a base body (not shown). Are arranged as follows. The thrust moving base 417 moves forward and backward in the C direction by driving from a directly connected thrust moving motor 419 via a ball screw (not shown).

  The grinding wheel 413 having a reverse crown shape can be driven and rotated by a grinding wheel motor 422 via a grinding wheel bearing 420, a belt 421, and a pulley. The grinding wheel 413, the grinding wheel bearing portion 420, and the grinding wheel motor 422 are mounted on a grinding wheel base 415.

  The rotational center of the grinding wheel 413 of the grinding wheel base 415 is arranged in parallel to the rotational center of the vulcanized rubber roller 412 held in pressure contact with the collet chuck 403 and the core pushing shaft center 408. The rotation center of the grinding wheel 413 and the rotation center of the vulcanized rubber roller 412 are configured to be movable in a direction perpendicular to the rotation center while being kept parallel.

  With this configuration, a desired cutting of the grinding wheel 413 to the vulcanized rubber roller 412 can be set, and the vulcanized rubber roller 412 can be used as a wide grinding cylindrical grinder capable of appropriately determining the outer diameter shape and surface property.

  Further, the grinding surface of the grinding wheel 413 is dressed by giving a desired cut while the diamond dresser 410 is translated in the thrust direction with respect to the rotational axis of the grinding wheel 413 with respect to the grinding wheel 413 that is driven to rotate. Can do.

  By the way, for a conductive roller having a roller shape, a method in which the conductive support portions at both ends thereof are rotatably supported and brought into contact with the charged body to rotate and follow the driven body has become common. ing. When the conductive roller is driven by this method, there is an advantage that the roller is inexpensive because it is not necessary to attach a force driving part such as a gear to the roller. At this time, in order to ensure uniform adhesion with the member to be charged, it is preferable to form the conductive elastic layer in a so-called crown shape by grinding so that the central portion is thickest and narrows toward both ends.

  In the case of a cylindrical shape whose thickness does not change in the axial direction, when both ends of the roller are supported and brought into contact with the cylindrical body to be charged, the pressing force at the central portion is small, and the both end portions are large. Therefore, density unevenness occurs in images corresponding to the center and both ends. The crown shape is formed to reduce this.

  The shape of the wide grinding wheel used in the present invention is shown in FIG. If the shape of this grinding wheel is transferred to the conductive elastic layer as it is, the contact pressure at both ends of the conductive elastic layer will be weakened when it comes into contact with the object to be charged. It may disappear. However, in the present invention, the feed speed of the grinding wheel, that is, the grinding speed of the conductive elastic layer is increased to a certain level or more, and the vulcanized rubber roller including the conductive support is ground while being bent in the direction opposite to the grinding wheel. As a result, the shape of the conductive elastic layer is obtained by combining the shape of the grindstone and the shape of the vulcanized rubber roller.

  At this time, both ends have a larger curvature than the central portion of the grindstone, and the central portion of the vulcanized rubber roller bends, so that the mechanical energy received by the conductive elastic layer from the grindstone increases toward both ends. At this time, both ends receiving a lot of mechanical energy are more dispersed and the voltage dependence of the electrical resistance becomes smaller than that of the central portion. Further, during grinding, the higher the hardness of the conductive elastic layer, the better because the vulcanized rubber roller including the conductive support is more easily bent. Further, when the hardness is high, there is an effect that a roller having a good outer diameter difference deflection accuracy can be obtained.

  However, if the roller is too hard, a sufficient nip between the charging roller and the photoreceptor cannot be secured, and charging failure may occur. As a result of examining the indexes representing the hardness and the ease of bending of the vulcanized rubber roller, it was found that the breaking stress in the tensile test (JIS K6251-1993) shows a good correlation.

  Therefore, the optimum hardness of the conductive elastic layer is preferably 8 MPa or more and 24 MPa or less, and more preferably 12 MPa or more and 18 MPa or less as a breaking stress in a tensile test.

  Factors affecting the way the vulcanized rubber roller bends in the grinding machine include the outer diameter of the grinding wheel, the size of the abrasive used in the grinding wheel, the bubble rate of the grinding wheel, the rotational speed and direction of the grinding wheel and conductive roller, and grinding There are the rigidity and chucking force of the chuck part of the conductive support attached to the machine.

  Factors that affect the bending method as the material of the vulcanized rubber roller include the material of the conductive support.

  In addition, carbon black with a larger DBP oil absorption tends to develop a structure of conductive particles, and even if the conductive elastic layer is ground under the same grinding conditions, the voltage dependence of the central portion and the end portion is increased. It is easy to make a difference. That is, the voltage dependency of the end portion tends to be reduced by grinding the conductive elastic layer. Conversely, the voltage dependence of electrical resistance tends to increase as the carbon black with a larger DBP oil absorption. This is presumably because the larger the DBP oil absorption, the easier the concentration distribution in the radial direction by molding such as extrusion. Therefore, the DBP oil absorption is preferably in the range of 40 ml / 100 g to 300 ml / 100 g, more preferably in the range of 80 ml / 100 g to 150 ml / 100 g. The DBP oil absorption value shown here is a value measured according to JIS K6217: 1997.

  As described above, pinhole leakage is achieved by reducing the concentration of conductive particles in the vicinity of the surface of the conductive elastic layer during extrusion and molding the conductive elastic layer that has a large voltage dependency on electrical resistance and electrical resistance. Can be reduced.

  However, if the voltage dependency at both ends of the conductive elastic layer is large (that is, the dispersion of the conductive particles is not so advanced), a contact mark is generated. In order to reduce the occurrence of the contact mark, the conductive elastic layer is ground to give mechanical energy to the conductive particles contained in the conductive elastic layer, thereby concentrating the conductive particles at the end of the roller. To disperse. In this way, the voltage dependency of the roller end can be reduced.

  Note that the cause of the contact mark may be a bleed from the conductive roller or a dent in the contact part. However, as a result of the investigation, it was clarified that bleed is hardly seen and it is not the main cause of the occurrence of contact marks. Further, the depth of the dent of the contact mark is very small as 2 to 6 μm, and it was revealed that the correlation between the depth of the dent and the generation of the contact mark is low. On the other hand, it was found that the electrical resistance of the contact portion was high, and it was found that the higher the electrical resistance of the contact portion, the worse the degree of image failure.

  Further, the contact mark occurs mainly at the end portion of the image. This is considered to be caused by a large change in electrical resistance due to a strong contact pressure at the end. Therefore, an attempt was made to increase the curvature of the crown shape to weaken the contact pressure at the end, but the image density at the end decreased, and the uniformity of the image density at the end and the center was lost. . Therefore, the contact pressure cannot be reduced by the crown shape.

  In order to measure the electrical resistance of the contact trace of the roller end, the electric resistance of 200V at the end in the axial direction of the roller in the divided resistance measurement described later is measured, and the result of graphing the electrical resistance waveform in the roller circumferential direction is as follows. FIG. It can be seen that the contact portion has a high resistance.

The difference between the average value and the maximum value of the electric resistance waveform is the peak height log (Re _{maximum value} (200 V) / Re _{average value} (200 V)), and the voltage dependence log (Re FIG. 6 is a plot of the relationship with (50 V) / Re (500 V)). Thus, the voltage dependency of the end portion and the peak height are well correlated.

  From this, it can be seen that the dispersion of the conductive particles during grinding is less advanced as the voltage dependency at the end is larger, and the dispersion of the conductive particles is advanced as the voltage dependency at the end is smaller. Is inferred.

  In the present invention, 0.1 <log [Re (50V) / Re (500V)] / log [Rc (50V) / Rc (500V)] ≦ 0.9 and 1.0 ≦ log (Re (50V) /Re(500V))≦2.2 is preferable.

  First, the reason why log [Re (50V) / Re (500V)] / log [Rc (50V) / Rc (500V)] ≦ 0.1 is not preferable is that this state is obtained by a realistic production method. This is because it is difficult. In addition, even if it is achieved, the electrical resistance is greatly different between the end portion and the center portion, so that unevenness in image density occurs at the end portion and the center portion, and the image quality is impaired.

  Next, the reason why 0.9 <log [Re (50V) / Re (500V)] / log [Rc (50V) / Rc (500V)] is not preferable is that the dispersion of the conductive particles at the end is sufficient. This is probably because contact marks are likely to occur.

  Furthermore, when 2.2 <log (Re (50 V) / Re (500 V)), the voltage dependency at the end is too high, that is, the electrical resistance at the end is too large, resulting in insufficient charging. Scars occur.

  From such a viewpoint, it is more preferable to set the range of 0.6 <log [Re (50V) / Re (500V)] / log [Rc (50V) / Rc (500V)] ≦ 0.8. Moreover, it is more preferable to set it as the range of 1.2 <= log (Re (50V) / Re (500V)) <= 1.8.

≪Calculation method of curvature ratio between full length and half length≫
In the present invention, the term “curvature” refers to the curvature of a perfect circle, and the value of 1 / r is defined as the curvature, where r is the radius of a perfect circle passing through certain three points.

Measure the diameter of the three grinding wheels whose distances between the axial ends of the grinding wheel surface are 0/4, 2/4, and 4/4, and the curvature of the perfect circle passing through these three points is k _A ,
The diameters of the three grinding wheels whose distances between the axial ends of the grinding wheel grinding surface are 1/4, 2/4, and 3/4 are measured, and the curvature of the perfect circle passing through the three points is k _B and when,
The value of k _A / k _B is defined as the curvature ratio between the full length and half length of the grindstone.

When the curvature ratio k _A / k _{B of the} grindstone is less than 1.2, the effect of reducing the voltage dependence at both ends of the conductive elastic layer is small, which is not preferable. When the curvature ratio k _A / k _B is greater than 70.0, the conductive elastic layers at both ends of the conductive elastic layer become thin, and discharge occurs between the cored bar and the rotating drum type electrophotographic photosensitive member. This is not preferable because it may be

From such a viewpoint, the curvature ratio k _A / k _B of the grindstone is preferably 1.2 or more and 70.0 or less, and more preferably 5.0 or more and 20.0 or less.

The diameters of the three conductive elastic layers at which the distance between both ends of the charged region in the axial direction of the conductive elastic layer is 0/4, 2/4, and 4/4 are measured, and the true value passing through the three points is measured. the curvature of the circle and K _a,
Measure the diameter of the conductive elastic layer at three points where the distance between the axial ends of the conductive elastic layer is 1/4, 2/4 and 3/4, and the curvature of the perfect circle passing through the three points when is referred to as _{K B,}
The value of K _A / K _B is defined as the curvature ratio between the full length and half length of the conductive elastic layer.

Curvature ratio of the conductive elastic layer K _{A /} K _B is a conductive roller when brought into contact with the member to be charged, the contact pressure at both ends of the conductive elastic layer is not too strong, the range not too weak good.

If the curvature ratio K _A / K _B is less than 0.8, the contact pressure is too weak, and it is considered that it is difficult to appropriately charge both ends of the conductive elastic layer. Further, if the curvature ratio K _A / K _B is greater than 1.2, the contact pressure is too strong, and it is assumed that bleeding from the conductive roller and dent of the contact portion are likely to occur. All of these cause contact marks. As a result of examination, it was found that the shape of the conductive elastic layer is better as it is closer to a perfect circular arc.

Thus the curvature ratio _K A / _{K B} of the conductive elastic layer is preferably from 0.8 to 1.2, further preferably 0.9 to 1.1.

  Examples of the method for forming a coating film on the surface of the conductive elastic layer include dipping coating, spray coating, ring coating (disclosed in JP-A-2005-321749), brush coating, and the like. However, it is not limited to these. The coating solution is preferably one that does not affect the voltage dependency in the axial direction of the conductive elastic layer or the electrical resistance. Therefore, it is preferable that fine particles such as carbon black, metal, metal oxide and the like generally used for conductivity control are not added to the coating film of the conductive roller.

  Moreover, the lower the viscosity of the coating solution, the smaller the coating film thickness and the smaller the contribution to electrical characteristics, which is preferable. Therefore, it is preferable to reduce the viscosity of the coating liquid by appropriately diluting with a solvent. At this time, the viscosity of the coating solution is more preferably 2.0 mPa · s or less as measured by a B-type viscometer.

  Moreover, it is preferable that it is 1.00 micrometer or less and 0.01 micrometer or more by the film thickness after adjusting a coating quantity and volatilizing a solvent.

  As the binder system of the coating liquid, a coating liquid such as silicone, fluorine, urethane, acrylic, urethane-modified acrylic, and silicone-modified urethane is used.

  As the coating solution as described above, an organic-inorganic hybrid sol containing an epoxy group and a cationically polymerizable catalyst is preferably used. In this coating solution, the cationically polymerizable catalyst is activated by ultraviolet rays, and the epoxy groups contained in the coating film are opened and crosslinked. The organic-inorganic hybrid gel film thus formed has flexibility to follow the deformation of the conductive elastic layer and has good wear resistance even if it is a very thin film. Therefore, even if a thin film having a thickness of 1 μm or less is formed on the conductive elastic layer, it has practical durability and can maintain the electrical characteristics of the conductive elastic layer.

  The organic-inorganic hybrid sol is a sol state of an organic-inorganic hybrid material produced by a so-called sol-gel method, and condenses a mixture of hydrolyzable silane compounds including at least an hydrolyzable silane compound having an epoxy group by hydrolysis. Can be obtained at A cationically polymerizable catalyst is added to the organic-inorganic hybrid sol, and the epoxy group is cleaved by irradiation with ultraviolet rays to be crosslinked to form an organic-inorganic hybrid gel.

  The coated film is preferably crosslinked by heat, ultraviolet light, electron beam, or the like from the viewpoint of wear resistance as a conductive roller and low adhesion of dirt. In particular, when the above organic-inorganic hybrid sol is used, it is preferable to irradiate ultraviolet rays. By irradiating with ultraviolet rays, the outermost surface of the conductive elastic layer is simultaneously modified to reduce bleed and dirt.

  A high-power low-pressure mercury lamp, an electrodeless low-pressure mercury lamp, an excimer lamp, a high-pressure mercury lamp, a metal halide lamp, or the like is used for ultraviolet irradiation.

  Among these, the material of the high-output low-pressure mercury lamp and electrodeless low-pressure mercury lamp that is most suitable for the present invention is, for example, quartz glass, which has a titanium oxide film or a silica film formed on the inner and outer surfaces of the quartz glass. Some contain titanium or silica. With this material, wavelengths below 200 nm are cut.

  Further, it is preferable to use these lamps because the intensity of ultraviolet rays typified by a wavelength of 254 nm is 60% or more of the total wavelength intensity.

  The excimer lamp has a peak at a short wavelength of 172 nm and has few other peaks. When an excimer lamp is used, ultraviolet light having a wavelength of 172 nm absorbs oxygen and generates ozone, so that the surface of the conductive roller is subjected to ozone treatment and is extremely oxidized. As a result, the contact angle of the roller surface with water tends to decrease, which is not preferable.

  Further, the high-pressure mercury lamp and the metal halide lamp are ultraviolet rays having a relatively long wavelength represented by a wavelength of 365 nm. When a high-pressure mercury lamp or a metal halide lamp is used, the influence of heat on the roller is increased, and the rubber may be deteriorated.

In addition, since the efficiency of ultraviolet rays is poor due to ultraviolet rays having a relatively long wavelength, the irradiation time becomes long, which is not preferable. The degree of surface modification by ultraviolet rays can be adjusted by the integrated light quantity. The cumulative amount of ultraviolet light is defined below.
UV integrated light quantity (mJ / cm ² ) = UV intensity (mW / cm ² ) × irradiation time (sec)
What is necessary is just to select suitably the integrated light quantity of an ultraviolet-ray according to the effect of surface modification. The adjustment can be performed by any of irradiation time, lamp output, and distance between the lamp and the roller, and may be determined so as to obtain a desired integrated light amount.

  FIG. 7 shows an example in which the conductive roller of the present invention is applied to an electrophotographic apparatus. Reference numeral 71 denotes a rotating drum type electrophotographic photosensitive member (charged member) as an image carrier. The charged body 71 is driven to rotate at a predetermined peripheral speed (process speed) in a clockwise direction indicated by an arrow in the drawing. As the member to be charged 71, for example, a known member to be charged having at least a roll-like conductive support and a photosensitive layer containing an inorganic photosensitive material or an organic photosensitive material on the support may be adopted.

  Reference numeral 72 denotes a charging roller to which the conductive roller of the present invention is applied. As the charging device, known means other than the charging roller can be used. The charging means is constituted by the charging roller 72 and a charging bias application power source S1 for applying a charging bias to the charging roller 72. The charging roller 72 is brought into contact with the charged body 71 with a predetermined pressing force, and is driven to rotate in the forward direction with respect to the rotation of the charged body 71 in this example. A predetermined DC voltage (in this example, −1200 V) is applied to the charging roller 72 from the charging bias application power source S1, so that the surface of the charged body 71 has a predetermined polarity potential (in this example, a dark portion). Is uniformly charged (DC charging). In addition to this DC charging, known charging methods such as AC / DC superimposed charging and injection charging can be used.

  Reference numeral 73 denotes exposure means. A known means can be used for the exposure means 73. For example, a laser beam scanner or the like can be preferably exemplified.

  When the exposure unit 73 performs image exposure corresponding to target image information on the surface to be charged 71 of the object to be charged 71, the potential of the exposed bright portion of the charged surface (in this example, the bright portion potential is −350 V). The electrostatic latent image is formed on the charged body 71 by being selectively lowered (attenuated).

  Reference numeral 74 denotes reversal developing means. As the developing unit 74, a known unit can be used. For example, the developing means 74 in the present example is disposed in the opening of the developing container, and controls the toner carrying body 74a that carries and conveys the toner, the stirring member 74b that stirs the toner, and the toner carrying amount of the toner carrying body 74a. And a toner regulating member 74c. The developing means 74 is a toner (negative toner, in this example, charged with a developing bias of −350 V) charged in the exposed bright portion of the electrostatic latent image on the surface of the charged body 71 with the same polarity as the charged polarity of the charged body 71. ) Is selectively attached to visualize the electrostatic latent image as a toner image. There is no particular limitation on the development method, and all existing methods can be used. As existing methods, for example, there are a jumping development method, a contact development method, a magnetic brush method, and the like. Especially in an image forming apparatus that outputs a color image, a contact development method is used for the purpose of improving toner scattering properties. The developing roller is preferable. The conductive roller of the present invention can be suitably used for this developing roller.

  Reference numeral 75 denotes a transfer roller using the conductive roller of the present invention as transfer means. The transfer roller 75 is brought into contact with the member to be charged 71 with a predetermined pressing force to form a transfer nip portion. The peripheral speed of the transfer roller 75 is approximately the same as the rotation peripheral speed of the member to be charged 71 in the forward direction with the rotation of the member to be charged 71. Rotate with. Further, a transfer voltage having a polarity opposite to the charging characteristics of the toner is applied from the transfer bias application power source S2. The transfer material P is fed to the transfer nip portion from a paper feed mechanism portion (not shown) at a predetermined timing. The back surface of the transfer material P is charged to a polarity opposite to the charging polarity of the toner by the transfer roller 75 to which a transfer voltage is applied. Accordingly, the toner image on the surface of the charged body 71 is electrostatically transferred to the surface side of the transfer material P in the transfer nip portion. The conductive roller of the present invention can be suitably used for this transfer roller.

  The transfer material P that has received the transfer of the toner image at the transfer nip part is separated from the surface of the charged body, introduced into a toner image fixing unit (not shown), and fixed as a toner image and output as an image formed product. In the case of the double-sided image forming mode or the multiple image forming mode, the image formed product is introduced into a recirculation conveyance mechanism (not shown) and reintroduced into the transfer nip portion.

  Residues on the member to be charged 71 such as transfer residual toner are collected from the member to be charged by a cleaning means 76 such as a blade type.

  Further, from the viewpoint of image defects, there are preferably 77 pre-exposure means if necessary. In the case where the staying charge remains on the charged body 71, it is better to remove the staying charge on the charged body 71 by the pre-exposure device 77 before the primary charging by the charging member 72.

  Main body of electrophotographic apparatus such as a copying machine or a laser beam printer, in which a process cartridge in which a plurality of the above-mentioned objects to be charged, charging member, developing member, cleaning member, toner, toner container, waste toner container, etc. are combined together However, it may be configured so as to be detachable. By using a process cartridge, it is possible to replace the members that are severely deteriorated at once, and to replenish the toner and collect the waste toner without scattering the toner.

  EXAMPLES Hereinafter, although an Example and a comparative example are shown and this invention is demonstrated concretely, this invention is not limited to the following. In the following, unless otherwise specified, commercially available high-purity products were used unless otherwise specified.

[Conductive elastic layer 1]
100 parts by mass of NBR (trade name “N230SL”: manufactured by JSR Co., Ltd.) as the main rubber of the conductive elastic layer
Carbon black as a conductive particle (trade name “Toka Black # 7360SB”: Tokai Carbon, DBP oil absorption 87 ml / 100 g) 52 parts by mass,
1 part by weight of zinc stearate,
5 parts by mass of zinc oxide,
20 parts by mass of calcium carbonate (trade name “Nanox # 30”: manufactured by Maruo Calcium Co., Ltd.)
Liquid epoxidized polybutadiene (trade name “Adekaizer BF-1000”: manufactured by Asahi Denka Kogyo Co., Ltd.) 10 parts by mass was kneaded with a pressure kneader for 15 minutes. further,
1 part by mass of dibenzothiazolyl disulfide (trade name “Noxeller DM-P”: manufactured by Ouchi Shinsei Chemical Co., Ltd.)
3 parts by mass of tetrabenzylthiuram disulfide (trade name “Noxeller TBzTD” manufactured by Ouchi Shinsei Chemical Co., Ltd.)
As a vulcanizing agent, 0.8 part by mass of sulfur was added and kneaded with an open roll for 15 minutes.

  Next, a thermosetting adhesive (trade name “Metaloc N-33”) is attached to the central portion 231 mm in the axial direction of the cylindrical surface of a cylindrical conductive support (steel surface industrial nickel plating) having a diameter of 6 mm and a length of 256 mm: Toyo Chemical Co., Ltd.) was applied. Next, this was dried at 150 ° C. for 10 minutes to make the adhesive semi-cured.

  The kneaded product and the conductive support were extruded together with the conductive support and the cylindrical kneaded product together with an extruder equipped with a crosshead and a conductive support feeding device to obtain an unvulcanized rubber roller. The conductive elastic layer is left at the central portion of 232 mm in the axial direction, both ends thereof are cut and removed, the unvulcanized rubber roller is placed in a hot air oven and heated at 160 ° C. for 30 minutes, and a cylindrical 8.7 mm in diameter is added. A vulcanized rubber roller was obtained.

  This vulcanized rubber roller was ground with the wide grinding machine described above using a grinding wheel having the shape shown in FIG. 8 (1A) under the following grinding conditions (Table 1) until the center outer shape was 8.5 mm. The wide grinding machine used is a trade name “Rubber roll dedicated CNC grinder LEO-600F-F4L-BME” manufactured by Mizuguchi Seisakusho. Moreover, the used grindstone is the brand name "grinding grindstone GC-120-B-VRG-PM" made by Noritake Company Limited.

  The grinding amount is 0.1 mm because the vulcanized rubber roller having a diameter of 8.7 mm is ground to 8.5 mm. A thickness of this level is preferable because the high resistance portion on the surface due to the concentration distribution of the conductive particles generated by extrusion molding is scraped off and the low resistance portion is not exposed. Moreover, since the amount of grinding is small, it can grind in a short time, and since production efficiency is also high, it is preferable.

When the diameter in the axial direction of the conductive elastic layer 1a after grinding was measured, it was as shown in FIG. 8 (1a). The conductive elastic layer has an axial length of 232 mm, but the measurement was performed at 230 mm excluding 1 mm from both ends. In addition, the calculated value of a perfect circular arc is also shown. When the curvature ratio between the full length and half length of the grindstone used for the production of the conductive elastic layer 1a and the conductive elastic layer 1a is calculated by the method described later, the curvature ratio of the grindstone is k _A / k _B = 5.6, The curvature ratio of the elastic elastic layer 1 was K _A / K _B = 1.0. In this way, grinding is performed with a grindstone whose curvature increases as it goes to both ends of the grindstone as shown in FIG. 8 (1A), but the conductive elastic layer after grinding has a shape close to a perfect circular arc. It was.

Further, a conductive elastic layer is used except that instead of the grindstone having the shape of FIG. 8 (1A), the grindstone of the shape of FIG. 8 (1B) in which the curvature ratio of the grindstone is k _A / k _B = 1.2 is used. What was produced by the method similar to 1a was set as the electroconductive elastic layer 1b. The shape of the conductive elastic layer was as shown in FIG. 8 (1b), and the curvature ratio was K _A / K _B = 0.8.

[Conductive elastic layer 2]
_A grindstone having the shape of FIG. 9 (2A) in which the curvature ratio of the grindstone is k _A / k _B = 1.0 is used instead of the grindstone having the shape of FIG. 8 (1A) obtained by grinding the conductive elastic layer 1. The roller grinding speed of 20 mm / min was set to 0.2 mm / min. Except for these, the conductive elastic layer 2a was prepared by the same method as the conductive elastic layer 1a. The shape of the conductive elastic layer was as shown in FIG. 9 (2a), and the curvature ratio was K _A / K _B = 1.1.

Further, the conductive elastic layer 1a is used except that instead of the grindstone having the shape of FIG. 8 (1A), the grindstone of FIG. 9 (2B) in which the curvature ratio of the grindstone is k _A / k _B = 1.0 is used. A conductive elastic layer 2b was prepared by the same method as described above. The shape of the conductive elastic layer was as shown in FIG. 9 (2b), and the curvature ratio was K _A / K _B = 0.7.

[Conductive elastic layer 3]
Carbon black (trade name “# 1000B”: manufactured by Mitsubishi Chemical Corporation, DBP) instead of 52 parts by mass of carbon black (trade name “Talker Black # 7360SB”: manufactured by Tokai Carbon) as conductive particles in the conductive elastic layer Oil absorption 49 ml / 100 g) 45 parts by mass was used. Other than that, the conductive elastic layer 3 was prepared by the same method as the conductive elastic layer 1a. The curvature ratio of the conductive elastic layer 3 was K _A / K _B = 1.1.

[Conductive elastic layer 4]
Carbon black (trade name “Asahi # 35”: manufactured by Asahi Carbon Co., Ltd.) instead of 52 parts by mass of carbon black (trade name “Toka Black # 7360SB”: manufactured by Tokai Carbon) as the conductive particles in the conductive elastic layer, DBP oil absorption 50 ml / 100 g) 100 parts by mass was used. Other than that, the conductive elastic layer 4 was prepared by the same method as the conductive elastic layer 1a. The curvature ratio of the conductive elastic layer 4 was K _A / K _B = 0.9.

[Conductive elastic layer 5]
Carbon black, which is conductive particles in the conductive elastic layer (trade name “Toka Black # 7360SB”: manufactured by Tokai Carbon Co., Ltd.) In the same manner as the conductive elastic layer 1a, except that 52 parts by mass is reduced to 49 parts by mass. The produced one was used as the conductive elastic layer 5. The curvature ratio of the conductive elastic layer 5 was K _A / K _B = 1.0.

[Conductive elastic layer 6]
Carbon black, which is conductive particles in the conductive elastic layer (trade name “Toka Black # 7360SB”: manufactured by Tokai Carbon Co., Ltd.) In the same manner as the conductive elastic layer 1a, except that 52 parts by mass is increased to 56 parts by mass. The produced one was used as the conductive elastic layer 6. The curvature ratio of the conductive elastic layer 6 was K _A / K _B = 1.0.

[Coating solution]
Glycidoxypropyltriethoxysilane (GPTS) 27.84 g (0.1 mol),
17.83 g (0.1 mol) of methyltriethoxysilane (MTES),
Tridecafluoro-1,1,2,2-tetrahydrooctyltriethoxysilane (FTS, carbon number 6 of perfluoroalkyl group) 7.68 g (0.0151 mol (equivalent to 7 mol% with respect to the total amount of hydrolyzable silane compound)) ),
17.43 g of water and 37.88 g of ethanol
After mixing, the mixture was stirred at room temperature and then heated to reflux for 24 hours to obtain an organic-inorganic hybrid sol.

  By adding this condensate to a 2-butanol / ethanol mixed solvent, an organic-inorganic hybrid sol-containing alcohol solution having a solid content of 7% by mass was prepared. Further, 0.35 g of an aromatic sulfonium salt (trade name: Adekaoptomer SP-150, manufactured by Asahi Denka Kogyo Co., Ltd.) as a photocationic polymerization initiator is contained in 100 g of this 7% by mass solution, containing an organic-inorganic hybrid sol. Added to the alcohol solution. Next, a solution obtained by adding an aromatic sulfonium salt to a 7% by mass solution diluted with a mixed solvent of 2-butanol / ethanol so that the solid content becomes 0.5% by mass was used as a coating solution. When the viscosity of the coating solution was measured with a B-type viscosity type, it was 1.5 mPa · s or less.

[Example 1]
A coating solution was applied to the conductive elastic layer 1a by ring coating. Then, a conductive roller that is irradiated with ultraviolet rays uniformly while rotating the conductive elastic layer 1a so that the amount of ultraviolet rays is 8000 mJ / cm ² with a sensitivity of 254 nm sensor using a low-pressure mercury lamp is shown in Example 1. It was. A low-pressure mercury lamp manufactured by Harrison Toshiba Lighting Co., Ltd. was used for ultraviolet irradiation.

[Example 2]
A conductive roller was produced in the same manner as in Example 1 except that the conductive elastic layer 1b was used instead of the conductive elastic layer 1a in Example 1.

Example 3
A conductive roller was produced in the same manner as in Example 1 except that the conductive elastic layer 3 was used in place of the conductive elastic layer 1a in Example 1, and Example 3 was used.

Example 4
A conductive roller was produced in the same manner as in Example 1 except that the conductive elastic layer 4 was used in place of the conductive elastic layer 1a in Example 1.

Example 5
A conductive roller was prepared in the same manner as in Example 1 except that the kneading time in the pressure kneader in the conductive elastic layer 1a was reduced from 15 minutes to 5 minutes.

Example 6
A conductive roller was produced in the same manner as in Example 1 except that the kneading time in the pressure kneader in the conductive elastic layer 1a was extended from 15 minutes to 30 minutes.

[Comparative Example 1]
Comparative Example 1 was obtained by preparing a conductive roller in the same manner as in Example 1 except that the conductive elastic layer 2a was used instead of the conductive elastic layer 1a in Example 1.

[Comparative Example 2]
Comparative Example 2 was obtained by producing a conductive roller in the same manner as in Example 1 except that the conductive elastic layer 2b was used instead of the conductive elastic layer 1a in Example 1.

[Comparative Example 3]
Comparative Example 3 was obtained by producing a conductive roller in the same manner as in Example 1 except that the conductive elastic layer 5 was used instead of the conductive elastic layer 1a in Example 1.

[Comparative Example 4]
A conductive roller was produced in the same manner as in Example 1 except that the conductive elastic layer 6 was used instead of the conductive elastic layer 1a in Example 1 and the kneading time in the pressure kneader was extended from 15 minutes to 30 minutes. This was designated as Comparative Example 4.

  Film thickness measurement, split resistance measurement, resistance measurement, curvature ratio between full length and half length of grinding wheel and conductive elastic layer, contact trace test, drum of Examples 1-6 and Comparative Examples 1-4 A pinhole leak test was conducted. The measurement conditions for each evaluation item are described below.

≪Measurement conditions≫
<Measurement of coating layer thickness>
When the thickness of the coating film of the coating solution crosslinked by ultraviolet irradiation was measured with a transmission electron microscope (TEM), all of Examples 1 to 6 and Comparative Examples 1 to 4 were 0.1 μm or less. Usually, when the film thickness is about this level, the electrical characteristics of the conductive elastic layer are not greatly changed, and the effect as a protective film for preventing pinhole leakage is not exhibited. However, if a conductive elastic layer having electrical characteristics within the range of the present invention is used, the occurrence of pinhole leakage can be reduced.

<Measurement of split resistance>
Log [Re (50V) / Re (500V)] / log [Rc (50V) / Rc (500V)] and log (Re (50V) / Re () of Examples 1 to 6 and Comparative Examples 1 to 4 described above. 500V)) was measured and calculated by the following method. FIG. 10 shows a schematic diagram of a conductive roller and a divided resistance measuring instrument obtained by dividing the conductive elastic layer portion of the charging region into eight in the roller axial direction. The conductive roller 102 was put on eight independent φ24 stainless cylinders 101, and a load of 100 g was applied to each cylinder and brought into contact with each cylinder. The rotation speed of the cylinder was 30 rpm, and the conductive roller was driven to rotate. . Reference numeral 103 denotes a fixed resistor (1 kΩ), 104 denotes a recorder, and 105 denotes a bias application power source. The applied voltage was set to 50V and 500V to energize. The test environment was a temperature of 23 ° C. and a humidity of 50% RH. In this state, the electrical resistance was sampled at intervals of 200 Hz, and the average value for 2 seconds was measured as the electrical resistance at 8 locations in the roller axial direction.

  The arithmetic average of the electrical resistances at both ends of the electrical resistance at the eight points in the roller axis direction thus obtained is defined as the electrical resistance Re at the end, and the arithmetic average of the two central points is defined as the electrical resistance Rc at the central portion. The electrical resistance when the applied voltage is 50 V and 500 V is Re (50 V), Re (500 V), Rc (50 V), and Rc (500 V), respectively. Log [Re (50V) / Re (500V)] / log [Rc (50V) / Rc (500V)] and log (Re (50V) / Re (500V)) were calculated from the values.

<Resistance measurement>
The electric resistances of the conductive rollers of Examples 1 to 6 and Comparative Examples 1 to 4 were measured by the following method. FIG. 11 shows a schematic diagram of a resistance measuring device. A conductive roller 112 is placed on a φ24 stainless cylinder 111, a load of 500 g is applied to the conductive support on both ends thereof, the cylinder is rotated at 30 rpm, and the conductive roller is driven to rotate. It was. Reference numeral 113 denotes a fixed resistor (1 kΩ), 114 denotes a recorder, and 115 denotes a bias application power source. The applied voltage was set to 200V and energized. The test environment was a temperature of 23 ° C. and a humidity of 50% RH. In this state, the electric resistance was sampled at intervals of 200 Hz, and the average value for 2 seconds was measured as the electric resistance of the entire length in the axial direction of the roller.

≪Image evaluation≫
<Contact mark test>
The conductive rollers obtained in the above-described Examples 1 to 6 and Comparative Examples 1 to 4 are incorporated in a cartridge (trade name “Toner Cartridge 307” manufactured by Canon Inc.) as a charging roller, and the room temperature is 40 ° C. and the humidity is 95%. For 1 month in a constant temperature and humidity chamber. The cartridges in which Examples 1 to 6 and Comparative Examples 1 to 4 were incorporated were taken out of the thermostatic chamber, and the temperature was 23 ° C. and the humidity was 50% RH in LBP5000 (manufactured by Canon Inc.) as an electrophotographic apparatus. A halftone image was output under the environment of.

  In the halftone image, the circumferential period of the conductive roller, that is, whether or not an image defect having a different image density from the non-contact portion occurs in the contact portion. The evaluation was made in three stages: x when there was a contact mark, ◯ when the contact mark was reduced, and ◎ when there was almost no contact mark.

<Drum pinhole leak test>
A to-be-charged body of the cartridge has a diameter of 0.3 mm, and a pin hole up to the front of the undercoat layer is perpendicular to the surface of the to-be-charged body. The conductive roller obtained in 1 was incorporated as a charging roller. Then, a halftone image was output by an electrophotographic apparatus in an environment of a temperature of 23 ° C. and a humidity of 50% RH. At this time, it was determined that an image defect called pinhole leak occurred when the image density in the periphery of the object to be charged was significantly different from the position of the pinhole in the image output direction. The evaluation was made in three stages: “X” when there was pinhole leakage, “◯” when it was reduced, and “◎” when almost no pinhole leak was observed. The cartridge used is a product name “toner cartridge 307” manufactured by Canon Inc. The electrophotographic apparatus used is a trade name “LBP5000” manufactured by Canon Inc.

≪Evaluation results≫
[Example 1]
FIG. 12 shows the electrical resistance in the axial direction of the conductive roller of Example 1.

In Example 1, log [Re (50 V) / Re (500 V)] is 1.8, log [Rc (50 V) / Rc (500 V)] is 2.6, and log [Re (50 V) / Re (500 V)]. / Log [Rc (50V) / Rc (500V)] was 0.7. R (200 V) was 1 × 10 ⁵ Ω.
The conductive roller of Example 1 showed almost no image of contact traces and pinhole leaks.

[Example 2]
In Example 2, log [Re (50 V) / Re (500 V)] is 2.1, log [Rc (50 V) / Rc (500 V)] is 2.6, and log [Re (50 V) / Re (500 V)]. / Log [Rc (50V) / Rc (500V)] was 0.8. R (200 V) was 1 × 10 ⁵ Ω.
In the conductive roller of Example 2, the occurrence of contact marks was reduced. Further, almost no pinhole leak image defect was observed.

Example 3
In Example 3, log [Re (50 V) / Re (500 V)] is 1.6, log [Rc (50 V) / Rc (500 V)] is 2.0, and log [Re (50 V) / Re (500 V)]. / Log [Rc (50V) / Rc (500V)] was 0.8. R (200 V) was 3 × 10 ⁵ Ω.
In the conductive roller of Example 3, almost no contact mark was observed. Moreover, the image defect of pinhole leak was reduced.

Example 4
In Example 4, log [Re (50 V) / Re (500 V)] is 1.5, log [Rc (50 V) / Rc (500 V)] is 1.7, and log [Re (50 V) / Re (500 V)]. / Log [Rc (50V) / Rc (500V)] was 0.8. R (200 V) was 8 × 10 ⁵ Ω.
In the conductive roller of Example 4, the occurrence of contact marks was reduced, and the pinhole leak image defect was reduced.

Example 5
In Example 5, log [Re (50 V) / Re (500 V)] is 2.2, log [Rc (50 V) / Rc (500 V)] is 3.7, and log [Re (50 V) / Re (500 V)]. / Log [Rc (50V) / Rc (500V)] was 0.6. R (200 V) was 1 × 10 ⁴ Ω.
In the conductive roller of Example 5, the occurrence of contact marks was reduced. Further, almost no pinhole leak image defect was observed.

Example 6
In Example 6, log [Re (50 V) / Re (500 V)] is 1.2, log [Rc (50 V) / Rc (500 V)] is 1.7, and log [Re (50 V) / Re (500 V)]. / Log [Rc (50V) / Rc (500V)] was 0.7. R (200 V) was 1 × 10 ⁶ Ω.
In the conductive roller of Example 6, almost no generation of contact marks was observed. Moreover, the image defect of pinhole leak was reduced.

[Comparative Example 1]
The electrical resistance in the axial direction of the conductive roller of Comparative Example 1 is shown in FIG.

In Comparative Example 1, log [Re (50 V) / Re (500 V)] is 2.3, log [Rc (50 V) / Rc (500 V)] is 2.3, and log [Re (50 V) / Re (500 V)]. / Log [Rc (50V) / Rc (500V)] was 1.0. R (200 V) was 8 × 10 ⁴ Ω.
In the conductive roller of Comparative Example 1, generation of contact marks was observed. Further, almost no pinhole leak image defect was observed.

[Comparative Example 2]
The electrical resistance in the axial direction of the conductive roller of Comparative Example 2 is shown in FIG.

In Comparative Example 2, log [Re (50 V) / Re (500 V)] is 2.5, log [Rc (50 V) / Rc (500 V)] is 2.3, and log [Re (50 V) / Re (500 V)]. / Log [Rc (50V) / Rc (500V)] was 1.1. R (200 V) was 1 × 10 ⁵ Ω.
In the conductive roller of Comparative Example 2, generation of contact marks was observed. Further, almost no pinhole leak image defect was observed.

[Comparative Example 3]
In Comparative Example 3, log [Re (50 V) / Re (500 V)] is 1.7, log [Rc (50 V) / Rc (500 V)] is 2.4, and log [Re (50 V) / Re (500 V)]. / Log [Rc (50V) / Rc (500V)] was 0.7. R (200 V) was 4 × 10 ⁶ Ω.
In the conductive roller of Comparative Example 3, generation of contact marks was observed. Further, almost no pinhole leak image defect was observed.

[Comparative Example 4]
In Comparative Example 4, log [Re (50V) / Re (500V)] is 1.1, log [Rc (50V) / Rc (500V)] is 1.5, log [Re (50V) / Re (500V)] / Log [Rc (50V) / Rc (500V)] was 0.7. R (200 V) was 7 × 10 ⁴ Ω.
In the conductive roller of Comparative Example 4, almost no contact mark was observed. Moreover, the image defect of pinhole leak was seen.

  Table 2 summarizes the material compositions of Examples 1 to 6 and Comparative Examples 1 to 4, Table 3 summarizes the implementation conditions, and Table 4 summarizes the evaluation items.

It is the schematic which shows an example of the electroconductive roller of this invention. It is the schematic which shows an example of the extruder for manufacturing the electroconductive roller of this invention. It is a schematic diagram showing the distribution state of the electroconductive particle of the electroconductive elastic layer in the electroconductive roller of this invention. (1) is a schematic view showing an example of a grinding machine for producing the conductive roller of the present invention. (2) is a schematic view showing an example of the shape of the grinding wheel of the present invention. It is a graph which shows an example of the waveform of the roller peripheral direction of the electrical resistance in an edge part measured with the division resistance measuring device in the present invention. It is the graph which plotted the peak height log (Re _{maximum value} (200V) / Re _{average value} (200V)) and voltage dependence log (Re (50V) / Re (500V)) in this invention. It is the schematic which shows an example of the electrophotographic apparatus using the electroconductive roller of this invention. (1A) is a graph showing the shape of a grindstone for grinding the conductive elastic layer 1a (Example 1) in the present invention. (1B) is a graph showing the shape of a grindstone for grinding the conductive elastic layer 1b (Example 2) in the present invention. (1a) is a graph showing an example of the shape of the conductive elastic layer 1a (Example 1) in the present invention. (1b) is a graph showing an example of the shape of the conductive elastic layer 1b (Example 2) in the present invention. (2A) is a graph showing the shape of a grindstone for grinding the conductive elastic layer 2a (Comparative Example 1) in the present invention. (2B) is a graph showing the shape of a grindstone for grinding the conductive elastic layer 2b (Comparative Example 2) in the present invention. (2a) is a graph showing an example of the shape of the conductive elastic layer 2a (Comparative Example 1) in the present invention. (2b) is a graph showing an example of the shape of the conductive elastic layer 2b (Comparative Example 2) in the present invention. It is the schematic which shows an example of the division | segmentation resistance measuring device in this invention. It is the schematic which shows an example of the resistance measuring device in this invention. It is a graph which shows an example of the electrical resistance of the axial direction of Example 1 in this invention. It is a graph which shows an example of the electrical resistance of the axial direction of the comparative example 1 in this invention. It is a graph which shows an example of the electrical resistance of the axial direction of the comparative example 2 in this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Conductive support body 12 Conductive elastic layer 13 Surface treatment 21 Extruder crosshead 22 Conductive support body feed roller 23 Conductive support body 24 Extrusion screw 25 Cutting / removal treatment 26 Unvulcanized rubber roller 401 Main shaft base unit 403 Collet Chuck 406 Core holder unit 407 Core holder portion 408 Core holder shaft center 410 Diamond dresser 412 Vulcanized rubber roller 413 Grinding wheel 415 Grinding wheel table 416 Cutting motor 417 Thrust moving table 419 Thrust moving motor 422 Grinding wheel motor 71 Electrophotographic photosensitive drum Body (Subject to be charged)
72 Charging member (charging roller)
73 Exposure means 74 Development means 74a Toner carrier 74b Stirring member 74c Toner regulating member 75 Transfer means 76 Cleaning means 77 Pre-exposure means L Laser light S1, S2 Bias application power supply P Transfer material 101 Eight independent stainless steel cylinders 102 Conductive roller 103 Fixed resistor (1kΩ)
104 Recorder 105 Bias application power supply 111 Stainless steel cylinder 112 Conductive roller 113 Fixed resistor (1 kΩ)
114 Recorder 115 Bias applied power supply

Claims (13)

In a conductive roller having a conductive elastic layer containing at least conductive particles on a conductive support,
When the conductive elastic layer is divided into 8 with respect to the roller axial direction,
The arithmetic average of the electric resistances at both ends of the conductive roller is the electric resistance Re at the end, and the arithmetic average of the two central points is the electric resistance Rc at the central part.
When the applied voltage is 50 V and 500 V, the electrical resistance of the end and the electrical resistance of the center are Re (50 V), Rc (50 V), Re (500 V), Rc (500 V),
When the electric resistance of the entire axial direction when the applied voltage is 200 V is R (200 V),
A conductive roller characterized by satisfying the following formula (1), formula (2) and formula (3), and further satisfying formula (4).
0.1 <log [Re (50V) / Re (500V)] / log [Rc (50V) / Rc (500V)] ≦ 0.9 (1)
1.0 ≦ log (Re (50 V) / Re (500 V)) ≦ 2.2 (2)
1.7 ≦ log (Rc (50 V) / Rc (500 V)) (3)
10 ⁴ Ω ≦ R (200 V) ≦ 10 ⁶ Ω (4) The electric resistance Re of the end portion and the electric resistance Rc of the central portion are 0.6 ≦ log [Re (50V) / Re (500V)] / log [Rc (50V) / Rc (500V)] ≦ 0.8
And 1.2 ≦ log (Re (50 V) / Re (500 V)) ≦ 1.8
And 2.2 ≦ log (Rc (50 V) / Rc (500 V))
The conductive roller according to claim 1, wherein:   The conductive roller according to claim 1, wherein the conductive elastic layer is formed by extrusion molding. In a conductive roller having a conductive elastic layer containing conductive particles in a polymer on a conductive support,
4. The conductive roller according to claim 1, wherein a filling amount of the conductive particles is 0.5 parts by mass or more and 100 parts by mass or less with respect to 100 parts by mass of the polymer.   5. The conductive roller according to claim 4, wherein a filling amount of the conductive particles is 2 parts by mass or more and 50 parts by mass or less with respect to 100 parts by mass of the polymer.   6. The conductive roller according to claim 1, wherein the conductive particles are carbon black, and the DBP oil absorption amount of the carbon black is 40 ml / 100 g or more and 300 ml / 100 g or less.   The conductive roller according to claim 6, wherein the carbon black has a DBP oil absorption of 80 ml / 100 g or more and 150 ml / 100 g or less.   8. An electrophotographic apparatus having an electrophotographic photosensitive member, a charging unit, an exposure unit, a developing unit, and a transfer unit, wherein at least one of the charging unit, the developing unit, and the transfer unit is any one of claims 1 to 7. An electrophotographic apparatus characterized by using a conductive roller. In a process cartridge that is detachable from the electrophotographic apparatus main body, at least including the electrophotographic photosensitive member, the charging unit, and the developing unit.
A process cartridge comprising the conductive roller according to claim 1 as at least one of the charging unit and the developing unit. In a manufacturing method for manufacturing a conductive roller having a conductive elastic layer containing conductive particles on a conductive support by grinding with a cylindrical grindstone wider than the conductive elastic layer,
K _A is the curvature of a perfect circle passing through three points that are 0/4, 2/4, and 4/4 of the distance between both ends in the axial direction of the grinding wheel surface,
When the curvature of a perfect circle passing through three points that are 1/4, 2/4, and 3/4 of the distance between both ends of the grinding wheel grinding surface in the axial direction is k _B ,
The method for producing a conductive roller according to claim 1, wherein grinding is performed with a grindstone having a curvature ratio k _A / k _B of 1.2 to 70.0. The method for producing a conductive roller according to claim 10, wherein grinding is performed with a grindstone having a curvature ratio k _A / k _B of 5.0 to 20.0. A conductive roller manufactured by the method for manufacturing a conductive roller according to claim 10 or 11,
The 0/4 and 2/4 the curvature of a perfect circle passing through three points is the position of 4/4 of the axial length of the conductive elastic layer and K _A,
1/4 and 2/4 the curvature of a perfect circle passing through three points is the position of 3/4 of the distance between the axial ends of the conductive elastic layer when the K _B,
8. The conductive roller according to claim 1, wherein the conductive elastic layer is formed so that a curvature ratio K _A / K _B is 0.8 or more and 1.2 or less. A conductive roller manufactured by the method for manufacturing a conductive roller according to claim 10 or 11,
Conductive roller according to claim 12, characterized in that the curvature ratio K _{A /} K _B of the conductive elastic layer is formed so as to be 0.9 to 1.1.

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