JP2007292298A - Method for producing charging member - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method capable of secularly stably producing a conductive member which can output a satisfactory image free from image defect even in application to an electronic photographic device adapted to limit the voltage to be applied to a charging member to only DC voltage. <P>SOLUTION: As a conductive coating layer to be provided on a conductive support, a layer having conductive particles dispersed therein is formed, and stirring treatment of a layer forming mixture in the formation is performed by low-share multipass operation with high flow rate. A bead mill which can continuously perform the process for dispersing the conductive particles even in a dispersing machine and perform multipass circulation stirring treatment(circulating operation with high flow rate) with a low dispersion share is used. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for manufacturing a charging member for charging a latent image holding member such as a photosensitive member used in an electrostatic latent image process in a copying machine, a printer, and the like, and more particularly, a charging method including a step of dispersing conductive particles in a mixture. The present invention relates to a method for manufacturing a member.

  An image forming apparatus employing an electrophotographic system, that is, an electrophotographic apparatus, generally includes an electrophotographic photosensitive member, a charging unit, an exposure unit, a developing unit, and a transfer unit.

  Further, as this charging means, a voltage (a voltage of only DC voltage or a voltage obtained by superimposing an AC voltage on a DC voltage) is applied to a charging member that is in contact with or close to the surface of the electrophotographic photosensitive member. Many systems that charge the surface of the photoreceptor are used.

  When a voltage in which an AC voltage is superimposed on a DC voltage is used as the voltage applied to the charging member, an AC power supply is required, leading to an increase in size and cost of the electrophotographic apparatus, and an increase in power consumption. . Furthermore, since the durability of the charging member and the electrophotographic photosensitive member is reduced due to a large amount of ozone generated due to the use of an AC power source, from these viewpoints, the voltage applied to the charging member is a DC voltage only. It is preferable.

  Furthermore, a contact-type charging method is preferably used from the viewpoint of stable charging, generation of ozone, or low cost.

  When the voltage applied to the charging member is a DC voltage only, the charged potential on the surface of the charged object is likely to be uneven, and minute streak-like image defects are likely to occur, and the charging uniformity. May be difficult to obtain. In addition, when the charging member is deteriorated due to continuous use, there is a problem that the resistance of the charging member is likely to increase (charge up), and the charged potential of the charged object surface is reduced accordingly. Further, in the image forming apparatus using the contact-type charging method, when the charging member is contaminated (development of the developer surface, etc.), there is a problem that image density unevenness is caused by the charging failure due to the contamination. . In particular, in the charging method in which only the DC voltage is applied to the charging member, the influence of contamination on the charging member tends to appear as an image defect compared to the charging method in which a voltage obtained by superimposing the AC voltage on the DC voltage is applied.

  With respect to this problem, for the purpose of obtaining uniformity of charging, a technique of obtaining uniformity of resistance by using conductive particles is disclosed (for example, Patent Document 1).

  However, particles having a small particle size have a large surface energy, so that the particles have a strong cohesive force and often form secondary aggregates such as a structure structure. For this reason, it is not easy to uniformly disperse the conductive particles having a small particle diameter in the conductive member, and micro resistance unevenness is likely to occur, and it may be difficult to obtain resistance uniformity.

  On the other hand, technologies for increasing the dispersion share and efficiency by increasing the number of dispersers and processes in the dispersion process and obtaining high dispersibility are disclosed (for example, Patent Documents 2 and 3).

Japanese Patent Laid-Open No. 06-250494 JP 2003-207966 A JP 09-146342 A

  However, if dispersion processing is performed with a strong share so as to obtain high dispersibility, when the dispersion process is completed, the dispersion is suddenly released from the share, and reaggregation may occur repulsively. In such a case, there is a problem that the dispersed state of the conductive particles becomes unstable and the stability is poor.

  Also, in the manufacturing process of the coating layer of the charging member, if the dispersion process is performed under general conditions using a dispersing device such as a bead mill or a sand mill in the liquid paint, the particle size of the pigment etc. in the liquid paint The distribution is inevitably wide. When such a liquid paint is applied as a coating layer of the charging member, generation of a pigment having a relatively coarse particle diameter due to aggregation is a problem in terms of charging characteristics. When a pigment having a coarse particle size is present in the charging member, unevenness in resistance value is generated in the layer where the resistance is high and low, that is, in resistance value, when viewed microscopically. The unevenness of the resistance value causes a deviation of the conductive path in the charging member.

  Therefore, in an electrophotographic apparatus using a charging member having such a constituent layer, when a predetermined potential is placed on a photoreceptor to be charged, minute charging unevenness tends to occur in the potential on the photoreceptor. This may cause image defects such as spots on the image. This is particularly noticeable in the halftone image area. This phenomenon tends to appear when the applied voltage is only a DC voltage. This is probably because there is no “run-in effect” due to an oscillating electric field such as an alternating voltage.

  An object of the present invention is to provide a method for producing a charging member having good dispersibility of conductive particles and ensuring uniformity of resistance as a charging member for charging a contacted object by applying a DC voltage. Is to provide. Another object of the present invention is to have a conductive coating layer that has good dispersibility of conductive particles, does not cause microscopic resistance unevenness, and has uniform resistance, and is free from charging defects and image defects. It is an object of the present invention to provide a method for manufacturing a charging member for direct current application that has improved generation and uniform resistance over a long period of time.

The method for producing a charging member according to the present invention includes a method for producing a charging member having an elastic layer on a conductive support and at least a conductive coating layer containing conductive particles.
A step of preparing a mixture containing at least the layer forming material of the conductive coating layer and conductive particles, a dispersion step of stirring the mixture to disperse the conductive particles in the mixture, and the dispersion step. A coating step of applying the dispersion liquid on the elastic body layer, and a drying step of drying after the coating to form the conductive coating layer.
The method for producing a charging member is characterized in that the dispersing step is a bead mill circulating stirring unit having the following conditions.
πr ³ gv ² <20
L <6x
L <xy / 50
r: radius of bead (mm)
g: Bead density (g / cm ³ )
v: Disk peripheral speed (m / s)
L: Preparation amount (ml)
x: Processing speed (ml / min)
y: Dispersion time (min)

  According to the present invention, even if the charging member has a conductive coating layer in which conductive particles are dispersed as a surface layer, the particle size distribution of the particles can be dispersed very sharply and uniformly. Resistance uniformity does not occur and resistance uniformity is obtained. Therefore, as a contact charging member of an electrophotographic apparatus, a contact that is unlikely to cause a charging failure, can output a good image without image defects, and can maintain the uniformity of resistance over a long period of time. A charging member can be provided.

The present invention provides a method for producing a charging member having an elastic layer on a conductive support and having at least a conductive coating layer containing conductive particles.
A step of preparing a mixture containing at least the layer forming material of the conductive coating layer and conductive particles, a dispersion step of stirring the mixture to disperse the conductive particles in the mixture, and the dispersion step. A coating step of applying the dispersion liquid on the elastic body layer, and a drying step of drying after the coating to form the conductive coating layer.
The method for producing a charging member is characterized in that the dispersing step is a bead mill circulating stirring unit having the following conditions.
πr ³ gv ² <20
L <6x
L <xy / 50
r: radius of bead (mm)
g: Bead density (g / cm ³ )
v: Disk peripheral speed (m / s)
L: Preparation amount (ml)
x: Processing speed (ml / min)
y: Dispersion time (min)

  An example of the structure of the charging member manufactured using the manufacturing method of the present invention is shown in FIGS. The charging member shown in FIG. 2 has a roller shape, and includes a conductive support 2a and an elastic layer 2b integrally formed on the outer periphery thereof as a coating layer. FIG. 3 shows another configuration of the charging member (the coating layer has a multilayer configuration). As shown in FIG. 3, the charging member may be a two-layered coating layer composed of an elastic layer 2b and a surface layer (outermost layer) 2c. In addition, the elastic layer 2b, the resistance layer 2d and the surface layer 2c, and the second resistance layer 2e are provided between the resistance layer 2d and the surface layer 2c, and four or more layers are provided on the conductive support 2a. It is good also as a structure formed in.

  As the conductive support 2a, a round bar made of a metal material such as iron, copper, stainless steel, aluminum and nickel can be used. Furthermore, these metal surfaces may be plated for the purpose of providing rust prevention and scratch resistance, but it is necessary not to impair the conductivity.

  In the charging roller having the above configuration, the elastic layer 2b has appropriate conductivity and elasticity to supply power to the electrophotographic photosensitive member as a member to be charged and to ensure good uniform adhesion to the electrophotographic photosensitive member. is there. In order to ensure uniform adhesion between the charging roller and the electrophotographic photosensitive member, it is preferable to form the elastic layer 2b in a so-called crown shape by polishing so that the central portion is thickest and narrows toward both ends. In the structure of a general electrophotographic apparatus, the charging roller 2 applies a predetermined pressing force to both ends of the support 2a and is in contact with the electrophotographic photosensitive member. The part is getting bigger. For this reason, there is no problem if the straightness of the charging roller is sufficient, but if it is not sufficient, density unevenness may occur in the images corresponding to the center and both ends. The crown shape is formed to prevent this.

The conductivity of the elastic layer 2b is a conductive agent having an electron conduction mechanism selected from carbon black, graphite and a conductive metal oxide in an elastic material such as rubber, and ions such as alkali metal salts and quaternary ammonium salts. It is preferable to adjust to less than 10 ¹⁰ Ωcm by appropriately adding a conductive agent having a conduction mechanism.

  Specific elastic materials as a layer forming material for forming the elastic layer 2b include, for example, natural rubber, ethylene propylene rubber (EPDM), styrene butadiene rubber (SBR), silicone rubber, urethane rubber, epichlorohydrin rubber, isoprene. Synthetic rubbers such as rubber (IR), butadiene rubber (BR), nitrile butadiene rubber (NBR), and chloroprene rubber (CR), as well as polyamide resins, polyurethane resins, and silicone resins are also included.

In a charging member that applies a DC voltage only to charge the object to be charged, in order to achieve charging uniformity, particularly a moderate resistance polar rubber (for example, epichlorohydrin rubber, NBR, CR, urethane rubber, etc.) It is preferable to use polyurethane resin as an elastic material. These polar rubbers and polyurethane resins are considered to have a slight conductivity due to moisture and impurities in the rubber and resin as carriers, and these conduction mechanisms are considered to be ionic conduction. However, an elastic layer is prepared without adding a conductive agent to these polar rubbers and polyurethane resins, and the obtained charging member has a high resistance value of 10 ¹⁰ Ωcm or more in a low temperature and low humidity environment (L / L). Therefore, a high voltage must be applied to the charging member.

Therefore, it is preferable to adjust the conductive member having the above-described electronic conductive mechanism and the conductive agent having the ionic conductive mechanism by appropriately adding so that the resistance value of the charging member is less than 10 ¹⁰ Ωcm in the L / L environment. However, the conductive agent having an ionic conduction mechanism has a small effect of lowering the resistance value, and particularly in the L / L environment. Therefore, the resistance adjustment may be performed by supplementarily adding a conductive agent having an electronic conductive mechanism in addition to the addition of a conductive agent having an ionic conductive mechanism.

  The elastic layer 2b may be a foam obtained by foaming these elastic materials.

  The thickness of the elastic layer is preferably 0.5 to 20 mm, particularly 1 to 10 mm.

  The surface layer 2c constitutes the surface of the charging member, and is not preferable in a material configuration that contaminates the photoconductor because it contacts the photoconductor that is the object to be charged. Moreover, it can be said that the thing with surface releasability is preferable. Therefore, it can be said that it is preferable to use a resin as the layer forming material (binding material) for forming the surface layer.

  As the binder resin material for the surface layer 2c, fluorine resin, polyamide resin, acrylic resin, polyurethane resin, silicone resin, butyral resin, styrene-ethylene-butylene-olefin copolymer (SEBC), and olefin-ethylene-butylene-olefin It is preferable to use a copolymer (CEBC) or the like. When the surface layer 2c is formed by the coating layer forming step according to the production method of the present invention, a fluororesin, an acrylic resin, a silicone resin, and the like are particularly preferable.

  For the purpose of reducing the static friction coefficient to these binder resins, solid lubricants such as graphite, mica, molybdenum disulfide and fluororesin powder, or fluorosurfactants, wax, silicone oil, etc. may be added. Good.

  Various conductive particles are appropriately used for the surface layer 2c. Examples of the conductive particles include metal oxide-based conductive particles, metal-based conductive particles, carbon black, and carbon-based conductive particles. In the present invention, in order to obtain a desired electric resistance, Two or more kinds of the various conductive particles may be used in combination.

  Examples of the metal oxide conductive particles include zinc oxide, tin oxide, indium oxide, titanium oxide (such as titanium dioxide and titanium monoxide), iron oxide, and aluminum oxide. Some of the metal oxide-based conductive particles show sufficient conductivity by themselves, but some of them do not. In order to make the conductivity of the particles sufficient, a dopant may be added to these particles. In general, it is considered that surplus electrons are generated due to the presence of metal oxide lattice defects and show conductivity, and formation of lattice defects is promoted by addition of a dopant, and sufficient conductivity can be obtained. For example, aluminum is used as a dopant for zinc oxide, antimony is used as a dopant for tin oxide, and tin is used as a dopant for indium oxide. Moreover, when obtaining the electroconductivity of titanium oxide, what coated electroconductive tin oxide on titanium oxide etc. can be mentioned. Furthermore, the thing which coat | covered the layer containing carbon black on the surface of the base | substrate which consists of metal oxides, such as a silica, etc. are mentioned.

  Examples of the metal conductive particles include silver, copper, nickel, and zinc.

  Examples of carbon black include acetylene black, furnace black, and channel black.

  Examples of the carbon conductive particles include graphite, carbon fiber, activated carbon, charcoal and the like.

  The average particle size of the conductive particles is preferably less than 1.0 μm. If the average particle size exceeds 1.0 μm, pinhole leakage may occur if pinholes exist on the photosensitive drum. When the specific gravity of the conductive particles is heavy, if the average particle diameter exceeds 1.0 μm, the conductive particles are likely to settle in the coating solution, and the dispersion stability of the coating solution may be deteriorated.

  The specific gravity of the conductive particles is preferably 0.8 to 8.0, particularly 1.0 to 7.0.

  These particles may be subjected to surface treatment, modification, introduction of functional groups, coating, and the like.

  Moreover, in the manufacturing method of the charging member of this invention, as a result of our earnest examination, it discovered that there existed the following new trends.

It is preferable that the hydroxyl value (mgKOH / g) α of the resin, which is the main component of the layer forming material, and the acidity (pH) β of the conductive particles satisfy the following formula range.
12 <α / β <30

  In the method for manufacturing a charging member of the present invention, when the value of α / β is 30 or more, the progress of dispersion rapidly proceeds, and it tends to be difficult to accurately obtain a desired resistance value as a charging roller. Further, since the dispersion has progressed rapidly, the temporal stability tends to deteriorate.

  On the contrary, in the method for manufacturing a charging member of the present invention, when the value of α / β is 12 or less, the speed of dispersion is very slow, and it is very long until a desired resistance value as a charging roller is obtained. Time is required and productivity is reduced.

  Furthermore, the hydroxyl value (mgKOH / g) α of the resin as the main component of the layer forming material is preferably in the range of 75 to 85, and the acidity (pH) β of the conductive particles is pH 3 to A range of 6 is preferable.

The resistance value of the surface layer is preferably 10 ^{4 to} 10 ¹⁵ Ωcm. The thickness is preferably 1 to 500 μm. In particular, the thickness is preferably 1 to 50 μm. The thickness of the resistance layer is also preferably the same as that of the surface layer.

  The surface coating layer, the elastic coating layer, and the resistance layer may be formed by, for example, adhering or coating a sheet-shaped or tube-shaped layer formed in advance to a predetermined film thickness, or electrostatic spraying. The coating may be performed by a coating method such as coating or dipping. Moreover, after forming a layer roughly by extrusion molding, the method of adjusting the shape of a layer by grinding | polishing etc. may be used, and the method of hardening and shaping | molding material to a predetermined shape within a type | mold may be used. That is, when a sheet-like or tube-like layer is formed in advance and this layer is coated on a conductive support to form a coating layer, the conductive layer is formed from a mixture containing conductive particles in a dispersed state. And the step of making the conductive layer a coating layer on the conductive support are performed as separate steps. When the conductive coating layer is provided directly on the conductive support as in the coating method, these steps are performed as one step.

  When a layer is formed by a coating method, the solvent used in the coating solution is a solvent that can dissolve or disperse a layer forming material, for example, a binding material or other materials necessary for forming a coating layer. Good. For example, alcohols such as methanol, ethanol and isopropanol, ketones such as acetone, methyl ethyl ketone and cyclohexanone, amides such as N, N-dimethylformamide and N, N-dimethylacetamide, sulfoxides such as dimethyl sulfoxide, , Ethers such as tetrahydrofuran, dioxane, ethylene glycol monomethyl ether, esters such as methyl acetate and ethyl acetate, aliphatic halogenated hydrocarbons such as chloroform, ethylene chloride, dichloroethylene, carbon tetrachloride, trichloroethylene, Aromatic compounds such as benzene, toluene, xylene, ligroin, chlorobenzene, dichlorobenzene and the like can be mentioned.

  As a method of dispersing the conductive particles in a desired dispersion degree in the mixture containing the conductive particles and the layer forming material, the mixture is supplied to a ribbon blender, a Nauter mixer, a Henschel mixer, a super mixer, etc. Existing methods such as stirring and mixing, or stirring and mixing with a Banbury mixer, a pressure kneader, or the like can be used. For the layer formation by the coating method, a solvent, a layer forming material and conductive particles are mixed, and the conductive liquid is mixed into the coating liquid using a conventionally known solution dispersing means such as a ball mill, a sand mill, a paint shaker, a dyno mill and a pearl mill. Disperse the particles. The coating layer in which the conductive particles obtained in this manner are coated in a dispersed state on a predetermined position of the conductive support and subjected to a drying treatment to improve the dispersibility of the conductive particles. Can be formed. In the present invention, among these dispersers, a bead mill capable of continuously performing a step of dispersing conductive particles, having a low dispersion share, and capable of a multi-pass circulation stirring process (circulation operation at a large flow rate). It is characterized by using. FIG. 5 is a conceptual diagram of the disperser in the present invention. Moreover, the conceptual diagram of this disperser is an example and is not limited to this.

  As described above, as the layer forming material to be included in the mixture, materials selected from various rubbers and resins are used in the formation of the conductive elastic layer (2b). Various additives for controlling properties and the like can be further added. In the formation of the surface layer (2c), a binder material, preferably a binder resin, is a layer forming material. In this case as well, various additives for controlling conductivity and the like are added as necessary. Can be added. Moreover, although a solvent can be added to a mixture as needed, a solvent is essential for formation by a coating method. What is necessary is just to select a composition required in order to obtain the electroconductive coating layer which has a desired function and characteristic as a composition of a mixture. In that case, the ratio of the binder material to the conductive particles is preferably binder resin: conductive particles = 1: 0.2 to 1: 2.5, and the content of the conductive material in the coating liquid Is preferably 1 to 20%, and the content of the binder resin in the coating solution is preferably 5 to 40%.

  Regarding the content of the solvent, it is added so that the viscosity of the coating solution is 1 to 100 mPa · s, more preferably 5 to 50 mPa · s, and the content is preferably 10 to 90% by mass, particularly 30 to 80%. It is preferable that it is mass%.

In the production method of the present invention,
πr ³ gv ² <20
L <6x
L <xy / 50
r: radius of bead (mm)
g: Bead density (g / cm ³ )
v: Disk peripheral speed (m / s)
L: Preparation amount (ml)
x: Processing speed (ml / min)
y: Dispersion time (min)
The mechanism by which the dispersibility of the conductive particles in the coating layer is improved by providing a bead mill circulation stirring process that satisfies all of the above has not been clarified. did it.

  The uniformity of charging of the member is largely due to the dispersibility of the conductive agent and functional particles used as the material constituting the charging member. When the dispersibility of the conductive agent is inferior, the uniformity of resistance is not sufficient, so that it is difficult to obtain the uniformity of charging. In addition, the conductive agent is likely to be deteriorated by energization. When conductive particles are used as the conductive agent in order to obtain uniformity of resistance, the cohesive force between the particles is strong, and in order to disperse the particles up to the vicinity of the primary particle size, It has been found necessary to break up the aggregates of strong particles. Moreover, it is thought that the dispersion | distribution state of electroconductive particle and the contact state of electroconductive particles are also affecting the deterioration by electricity supply. If the dispersibility of the conductive particles is improved, it is considered that the resistance does not increase even when the charging member is continuously used (continuous energization). However, if dispersion processing is performed with a strong share, when the dispersion process is completed, it is suddenly released from the share, so re-aggregation tends to occur repulsively, the dispersion state of the conductive particles becomes unstable, and stability is improved. It gets worse.

  In addition, when the dispersion process is performed by a circulation operation with a normal number of passes, the resistance value as the charging member is satisfied, but the particle size distribution of the conductive particles in the liquid paint is inevitably wide. Problem arises. Such a liquid paint is considered to be easily agglomerated and the like, and when such a liquid paint is applied as a coating layer of a charging member, resistance value unevenness and This will cause a point-like image defect.

Therefore, πr ³ gv ² <20 of the present invention.
L <6x
L <xy / 50
r: radius of bead (mm)
g: Bead density (g / cm ³ )
v: Disk peripheral speed (m / s)
L: Preparation amount (ml)
x: Processing speed (ml / min)
y: Dispersion time (min)
By performing a bead mill circulation stirring process that satisfies all of the above, energy applied to the conductive particles can be applied many times with a weak force. When the dispersion proceeds with a weak force, activation of the surface of the conductive particles (increase in surface energy) can be suppressed. This is effective for suppressing the occurrence of re-aggregation and the like, that is, stabilizing the paint. Furthermore, by increasing the number of passes, conductive particles having a sharp particle size distribution can be obtained. This is also effective for stabilizing the paint.

  The maximum peripheral speed of the disk when dispersing by the stirring type dispersing device is preferably 2 to 8 m / s, particularly 4 to 6 m / s. The bead diameter is preferably φ1.0 mm or less, particularly preferably φ0.8 mm or less. The specific gravity of the beads is not particularly limited, but is preferably 3 or less.

“Πr ³ gv ² <20” defines the amount of energy given by one bead, and when a condition such that πr ³ gv ² exceeds 20 is selected, the energy applied to the conductive particles becomes too large. , It tends to cause aggregation and the like.

  “L <6x” defines the paint processing speed, that is, it is necessary to secure a flow rate of 1/6 or more of the total paint amount per minute, that is, one pass or more in 6 minutes. That's what it means. If the residence time in the tank during the circulation stirring process becomes long, reagglomeration or the like easily occurs during that time, and the dispersion time becomes very long and the dispersion efficiency is remarkably lowered.

  “L <xy / 50” defines the relationship between the processing speed and the dispersion time with respect to the charged amount. That is, it is preferable that at least 50 passes or more is preferable. When the number of passes is 50 or less, the particle size distribution becomes wide, and aggregation or the like is likely to occur.

  Through various studies as described above, in the method for producing a conductive member containing conductive particles in the coating layer, in the step of dispersing the conductive particles in the coating layer, a low share at a large flow rate is obtained. By conducting the multipass circulation stirring process, it has been possible to produce a conductive member capable of maintaining the uniformity of resistance and the uniform dispersion state of conductive particles for a long period of time.

  Next, a description will be given based on a schematic configuration of an image forming apparatus using a contact charging member (charging roller) of the electrophotographic apparatus of the present invention.

(1) Image Forming Apparatus FIG. 1 is a schematic configuration diagram of an example of an image forming apparatus provided with a process cartridge of the present invention. The image forming apparatus of this example is a reversal developing method using transfer type electrophotography, and a developing and cleaning method (cleanerless). A rotary drum type electrophotographic photosensitive member 1 as an image carrier is disposed in the process cartridge 6 and is driven to rotate at a predetermined peripheral speed (process speed) in the direction of the arrow. Around the electrophotographic photosensitive member 1, first, a charging roller 2 as a charging unit is disposed in a state of being in contact with the electrophotographic photosensitive member 1 with a predetermined pressing force. In this example, the charging roller 2 is driven to rotate at the same speed as the electrophotographic photosensitive member 1. A predetermined DC voltage (in this case, -1180 V) is applied to the charging roller 2 from the charging bias application power source S1, so that the surface of the electrophotographic photosensitive member 1 has a predetermined polarity potential (dark part potential -400 V). ) Is uniformly charged by a contact charging method or a DC charging method.

  The exposure unit 3 is, for example, a laser beam scanner. The exposure unit 3 performs exposure L corresponding to target image information on the charging surface of the electrophotographic photosensitive member 1, so that the surface potential of the electrophotographic photosensitive member 1 is changed to the potential of the exposure bright portion (bright portion potential −120 V The electrostatic latent image is formed by selectively decreasing (attenuating). The toner (negative toner) charged with the same polarity as the charging polarity of the electrophotographic photosensitive member 1 (developing bias −350 V) is selectively applied to the exposed bright portion of the electrostatic latent image of the electrophotographic photosensitive member by the reversal developing unit 4. And the electrostatic latent image is visualized as a toner image. In the figure, 4a is a developing roller, 4b is a toner supply roller, and 4c is a toner layer thickness regulating member.

  The transfer roller 5 serving as a transfer unit is disposed in contact with the electrophotographic photosensitive member 1 with a predetermined pressing force to form a transfer portion, and the electrophotographic photosensitive member rotates in the forward direction with the rotation of the electrophotographic photosensitive member 1. It rotates at the same peripheral speed as the rotational peripheral speed of 1. Further, a transfer voltage having a polarity opposite to the charging polarity of the toner is applied from the transfer bias applying power source S2. The transfer material P is fed to the transfer portion from a paper feed mechanism portion (not shown) at a predetermined control timing. The back surface of the fed transfer material P is charged to a polarity opposite to the charging polarity of the toner by the transfer roller 5 to which a transfer voltage is applied, so that the toner image on the electrophotographic photosensitive member 1 is transferred to the transfer material at the transfer portion. Electrostatic transfer to P.

  The transfer material that has received the transfer of the toner image at the transfer portion is separated from the electrophotographic photosensitive member, introduced into a toner image fixing means (not shown), subjected to a toner image fixing process, and output as an image formed product. In the case of the double-sided image formation mode or the multiple image formation mode, this image formed product is introduced into a recirculation conveyance mechanism (not shown) and reintroduced into the transfer unit.

  Residues on the electrophotographic photosensitive member such as transfer residual toner are charged to the same polarity as the charging polarity of the electrophotographic photosensitive member by the charging roller 2. Then, the transfer residual toner reaches the developing means 4 through the exposure portion, and is electrically collected in the developing device by the back contrast, thereby achieving development and cleaning (cleanerless).

  In this example, the electrophotographic photosensitive member 1, the charging roller 2, and the developing means 4 are integrally supported, and the process cartridge 6 is detachable from the main body of the image forming apparatus. At this time, the developing means 4 may be a separate body.

  Furthermore, the electrophotographic apparatus to which the charging member obtained by the manufacturing method according to the present invention is applied is not limited to the configuration shown in FIG. Process cartridge different from the construction shown in the drawing having at least a charging member and an electrophotographic photosensitive member (such as a developing means using a main body side or a cleaning means between a toner image transfer region and a charging member) It can be set as the structure using. Furthermore, it is possible to employ a configuration in which each member necessary for the apparatus main body is arranged without using the process cartridge.

  When a DC voltage is applied to the charging member 2 of the apparatus shown in FIG. 1, a discharge occurs in a minute space between the charging member and the photosensitive member, and the surface of the photosensitive member 1 is charged. If the conductive member obtained by the production method of the present invention is used as the charging member 2, not only can the charging uniformity of the charging member be improved, but also the resistance change can be suppressed, so a very excellent image can be obtained. Obtainable. In particular, as shown in FIG. 1, a plurality of image forming apparatuses adopting a so-called developing and cleaning (cleanerless) system that does not have a developing and independent cleaning unit and collects toner remaining on the photosensitive member after transfer by the developing unit. It is extremely effective in enabling sheet printing.

  Hereinafter, the present invention will be described in more detail with reference to examples.

<Example 1>
A charging roller as a charging member of the present invention was produced in the following manner.
Epichlorohydrin rubber: 100 parts by mass Quaternary ammonium salt: 2 parts by mass Calcium carbonate: 90 parts by mass Zinc oxide: 5 parts by mass Fatty acid: 5 parts by mass After kneading the above materials for 10 minutes in a closed mixer adjusted to 60 ° C. Then, 15 parts by mass of an ether ester plasticizer was added to 100 parts by mass of epichlorohydrin rubber, and the mixture was further kneaded with a closed mixer cooled to 20 ° C. for 20 minutes to prepare a raw material compound. To this compound, 100 parts by mass of epichlorohydrin rubber as a raw rubber, 1 part by mass of sulfur as a vulcanizing agent, 1 part by mass of noxeller DM (dibenzothiazyl sulfide) as a vulcanization accelerator, and noxeller TS (tetramethylthiuram monosulfide) 0.5 parts by mass was added and kneaded for 10 minutes in a two-roll mill cooled to 20 ° C. The resulting compound is molded by an extruder so as to form a roller around a φ6 mm stainless steel support, heated and steam vulcanized, and then polished to an outer diameter of φ12 mm to obtain an elastic layer. It was. The roller length was 230 mm.

Subsequently, the following materials:
Acrylic polyol solution (manufactured by Daicel Chemical Industries, Ltd .: PLACEL DC2016): 100 parts by mass;
Isocyanate A (IPDI) (manufactured by Degussa: VESTANAT B1370): 27 parts by mass;
Isocyanate B (HDI) (Asahi Kasei Chemicals Corporation: DURANATE TPA-B80E): 17 parts by mass;
Conductive particles (CS-Bk100Y manufactured by Toda Kogyo Co., Ltd.): 13 parts by mass;
Modified dimethyl silicone oil (SH28PA manufactured by Toray Dow Corning Silicone): 0.3 parts by mass; and methyl isobutyl ketone: 300 parts by mass were stirred using a mixer to prepare a mixed solution. The acrylic polyol solution had a hydroxyl value (α) of 80.2 mgKOH / g, and the conductive particles had an acidity (β) of pH 3.9 (α / β = 20.6). Next, a bead mill disperser in which the mixed solution was filled with glass beads having an average particle diameter of φ0.8 mm (radius 0.4 mm, density 2.5 g / cm ³ ) at a filling rate of 80% with respect to the volume of the vessel. (Ashizawa Finetech Co., Ltd. Star Mill LMZ-2) was used to perform a circulation operation for 360 minutes (equivalent to 90 passes) at a disk peripheral speed of 4 m / s and a processing speed of 3000 ml / min (1/4 of the total paint amount). 12000 ml of dispersion solution was obtained. This dispersion solution was applied by a dipping method to form a surface layer having a film thickness of 15 μm to obtain a roller-shaped charging member.

  Table 1 shows a list of the distributed processing conditions, and Table 2 shows whether each satisfies the conditions of the present invention. Tables 1 and 2 collectively show examples and comparative examples described later.

“Evaluation of stability of dipping coating solution over time”
The viscosity of the coating solution for dipping produced by the above method was measured on the first day of production and 7 days after production. The viscosity was measured at 60 rpm with a No. 1 rotor using a Bismetron viscometer (VDA-L type) manufactured by Shibaura System. The results are shown in Table 3. After the production, the viscosity of the paint that is considered to have decreased dispersibility is large.

"Evaluation of image when only DC voltage is applied to charging roller"
The charging roller obtained above is attached to the electrophotographic image forming apparatus shown in FIG. 1, and a halftone image is output in an L / L environment (temperature 15 ° C./humidity 10%). Images were evaluated. The results are shown in Table 4. The applied voltage (DC voltage only) was adjusted so that the surface potential (dark portion potential) VD of the electrophotographic photosensitive member charged by the charging member was around −400V. A in the table indicates that the obtained image is very good, B is good, C indicates that the halftone image has a slight streak-like defect, and D indicates that the image defect of the streak is conspicuous.

  Further, before the image evaluation was started, the resistance of the charging roller was measured by the method shown in FIG. The results are shown in Table 4. In the figure, 2 is a conductive member, 11 is a cylindrical electrode made of stainless steel, 12 is a resistor, and 13 is a recorder. The pressing force between them is the same as that of the image forming apparatus used, and the resistance value when -200 V is applied from the external power source S3 is measured. In addition, as an evaluation of the uniformity of resistance, the ratio of the measured maximum resistance value to the minimum value was defined as resistance unevenness. The results are shown in Table 4.

  The above evaluation was performed on each of the charging rollers prepared using the dipping coating liquid on the first day of production and 7 days after the production. When the evaluation after 7 days from the production was A or B, the produced charging roller was good, and for C and D, the image result was not good.

<Example 2>
Example 1 except that the conductive particle dispersion treatment was carried out for 360 minutes (equivalent to 60 passes) at a disk peripheral speed of 6 m / s and a treatment speed of 2000 ml / min (1/6 of the total coating amount). Similarly, a charging member was produced. The charging roller was evaluated in the same manner as in Example 1, and the results are shown in Tables 3 and 4.

<Example 3>
A charging member was produced in the same manner as in Example 1 except that the dispersion treatment was performed using conductive particles having an acidity (β) of pH 5.4. The charging roller was evaluated in the same manner as in Example 1, and the results are shown in Tables 3 and 4. Α / β is 14.9.

<Example 4>
A charging member was produced in the same manner as in Example 2 except that conductive particles having an acidity (β) of pH 2.5 were used and the dispersion treatment was performed at a disk peripheral speed of 4 m / s. The charging roller was evaluated in the same manner as in Example 1, and the results are shown in Tables 3 and 4. Α / β is 32.1.

<Example 5>
A charging member was produced in the same manner as in Example 1 except that conductive particles having an acidity (β) of pH 6.9 were used and the dispersion treatment was performed at a disk peripheral speed of 6 m / s. The charging roller was evaluated in the same manner as in Example 1, and the results are shown in Tables 3 and 4. Α / β is 11.6.

<Comparative Example 1>
A charging member was produced in the same manner as in Example 1 except that the conductive particles were dispersed at a disk peripheral speed of 8 m / s. The charging roller was evaluated in the same manner as in Example 1, and the results are shown in Tables 3 and 4.

<Comparative example 2>
A charging member was prepared in the same manner as in Example 1 except that the conductive particles were dispersed for 1080 minutes (equivalent to 90 passes) at a processing speed of 1000 ml / min (1/12 of the total coating amount). did. The charging roller was evaluated in the same manner as in Example 1, and the results are shown in Tables 3 and 4.

<Comparative Example 3>
A charging member was produced in the same manner as in Example 1 except that the conductive particles were dispersed in 160 minutes (equivalent to 40 passes). The charging roller was evaluated in the same manner as in Example 1, and the results are shown in Tables 3 and 4.

<Comparative example 4>
Example 1 except that the conductive particles were dispersed for 1080 minutes (equivalent to 90 passes) at a disk peripheral speed of 8 m / s and a processing speed of 1000 ml / min (1/12 of the total coating amount). Similarly, a charging member was produced. The charging roller was evaluated in the same manner as in Example 1, and the results are shown in Tables 3 and 4.

<Comparative Example 5>
A charging member was produced in the same manner as in Example 1, except that the conductive particles were dispersed in a circulation operation of 480 minutes (equivalent to 40 passes) at a treatment speed of 1000 ml / min (1/12 of the total coating amount). did. The charging roller was evaluated in the same manner as in Example 1, and the results are shown in Tables 3 and 4.

<Comparative Example 6>
A charging member was produced in the same manner as in Example 1, except that the conductive particles were dispersed in a circulation operation for 160 minutes (equivalent to 40 passes) at a disk peripheral speed of 8 m / s. The charging roller was evaluated in the same manner as in Example 1, and the results are shown in Tables 3 and 4.

<Comparative Example 7>
Example 1 is the same as Example 1 except that the dispersion treatment of the conductive particles was performed in a circulation operation of 480 minutes (equivalent to 40 passes) at a disk peripheral speed of 8 m / s and a processing speed of 1000 ml / min (1/12 of the total coating amount) Similarly, a charging member was produced. The charging roller was evaluated in the same manner as in Example 1, and the results are shown in Tables 3 and 4.

<Comparative Example 8>
Conductive particle dispersion treatment was performed in the same manner as in Example 1, except that glass beads having an average particle diameter of φ1.5 mm (radius 0.75 mm and density 2.5 g / cm ³ ) were used as media. A charging member was produced. The charging roller was evaluated in the same manner as in Example 1, and the results are shown in Tables 3 and 4.

<Comparative Example 9>
Conductive particle dispersion treatment was performed in the same manner as in Example 1 except that zirconia beads having an average particle diameter of φ0.8 mm (radius 0.4 mm, density 6.0 g / cm ³ ) were used as media. A charging member was produced. The charging roller was evaluated in the same manner as in Example 1, and the results are shown in Tables 3 and 4.

<Comparative Example 10>
The conductive particles were dispersed in the same manner as in Example 1 except that zirconia beads having an average particle diameter of φ1.5 mm (radius 0.75 mm, density 6.0 g / cm ³ ) were used as media. A charging member was produced. The charging roller was evaluated in the same manner as in Example 1, and the results are shown in Tables 3 and 4.

1 is a schematic configuration diagram of an image forming apparatus of the present invention. It is the schematic of a charging roller. It is the schematic of the charging roller which shows another Example. It is the schematic of the resistance measuring apparatus of a charging member. It is the schematic of the disperser which can be used by this invention.

Explanation of symbols

1 Image carrier (electrophotographic photoreceptor)
2 Charging member (charging roller)
3 Image exposure means 4 Development means 5 Transfer means (transfer roller)
6 Cleaning means S1, S2, S3 Bias application power supply P Transfer material 11 Cylindrical electrode (metal roller)
12 Fixed resistor 13 Recorder 51 Disk 52 Rotating shaft 53 Circulating tank 54 Piping 55 Stirring processing unit 56 Circulating pump

Claims (4)

In a method for producing a charging member having an elastic layer on a conductive support and having at least a conductive coating layer containing conductive particles,
A step of preparing a mixture containing at least the layer forming material of the conductive coating layer and conductive particles, a dispersion step of stirring the mixture to disperse the conductive particles in the mixture, and the dispersion step. A coating step of applying the dispersion liquid on the elastic body layer, and a drying step of drying after the coating to form the conductive coating layer.
The method for producing a charging member, wherein the dispersing step is a bead mill circulating stirring means having the following formula conditions.
πr ³ gv ² <20
L <6x
L <xy / 50
r: radius of bead (mm)
g: Bead density (g / cm ³ )
v: Disk peripheral speed (m / s)
L: Preparation amount (ml)
x: Processing speed (ml / min)
y: Dispersion time (min) The hydroxyl value (mgKOH / g) α of a resin, which is a main component of the layer forming material of the conductive coating layer, and the acidity (pH) β of the conductive particles satisfy the following formula range. Item 2. A method for producing a charging member according to Item 1.
12 <α / β <30   The method for producing a charging member according to claim 1, wherein the conductive coating layer has a multilayer structure, and the conductive particles contained in the outermost layer of the conductive coating layer are carbon black.   The method for producing a charging member according to claim 1, wherein the dispersion obtained in the dispersion step has a viscosity of 1 to 100 mPa · s.

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