JP2007178752A - Electrifying roll - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrifying roll capable of suppressing electric resistance fluctuation and exhibiting stable electric resistance characteristic. <P>SOLUTION: The electrifying roll is provided with: a shaft body 1; a conductive elastic body layer 2 formed on the outer circumference thereof; a resistance adjustment layer 3 formed on the outer circumference of the conductive elastic body layer 2; and a protective layer 4 formed on the outer circumference of the resistance adjustment layer 3, wherein the resistance adjustment layer 3 is formed of a semiconducting rubber composition indispensably composed of the following (A) to (C). (A) is a rubbery material, (B) is an electronically conductive particle in which silica is fixed on the surface of the particle and the outer circumference of the silica-fixed particle is coated with a silane coupling agent, and (C) is an insulating particle. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a charging roll used in an electrophotographic apparatus such as a copying machine, a printer, or a facsimile.

  In general, copying by an electrophotographic copying machine is performed by forming a document image as an electrostatic latent image on a photosensitive drum that rotates about its axis, forming a toner image by attaching toner to the image, and then transferring the toner image to a copy paper. It is done by transferring to. The electrostatic latent image is formed by charging the surface of the photosensitive drum in advance, projecting a document image onto the charged portion via the optical system, and canceling the charging of the portion exposed to light. As a method for charging the surface of the photosensitive drum prior to the formation of the electrostatic latent image, in recent years, a method (contact charging method) in which a charging roll is brought into direct contact with the surface of the photosensitive drum has been widely employed.

  As the charging roll used in the contact charging method, for example, an innermost layer made of a special foam containing a conductive agent, an intermediate layer, and an outermost layer are formed in this order on the outer periphery of the shaft body. Is known (see, for example, Patent Document 1).

Further, in the charging roll provided with the conductive elastic body layer, the resistance adjusting layer, and the protective layer on the outer periphery of the shaft body, the resistance adjusting layer is formed with (A) rubber material and (B) silica on the surface. Proposed is a semiconductive rubber composition containing fixed electronic conductive particles and (C) insulating particles as essential components (see, for example, Patent Document 2). It is described that better electrical resistance characteristics can be obtained when a silane coupling agent is added to the layer.
JP 2000-75600 A JP 2004-151498 A

  However, in the charging roll of the above-mentioned Patent Document 2, a composition in which the silane coupling agent is blended with the resistance adjustment layer can exhibit excellent electric resistance characteristics, but depending on the manufacturing conditions and processing history, the resistance of the resistance adjustment layer It has been found that the electrical resistance characteristics of the charging roll may become unstable due to large fluctuations, leading to image defects and the like. Therefore, it is strongly desired to provide a charging roll that suppresses such electrical resistance fluctuations and exhibits stable electrical resistance characteristics.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide a charging roll that suppresses fluctuations in electric resistance and exhibits stable electric resistance characteristics.

In order to achieve the above object, the present invention provides a shaft body, a conductive elastic layer formed on the outer periphery thereof, a resistance adjustment layer formed on the outer periphery of the conductive elastic layer, and the resistance adjustment layer. A charging roll provided with a protective layer formed on the outer periphery of the charging roller, wherein the resistance adjusting layer is formed of a semiconductive rubber composition having the following (A) to (C) as essential components: The roll is the first gist.
(A) Rubber material.
(B) Electronically conductive particles in which silica is fixed on the particle surface and the outer periphery thereof is coated with a silane coupling agent.
(C) Insulating particles.

  In addition, the present invention particularly includes a charging roll in which the electron conductive particles are at least one selected from the group consisting of carbon black, metal powder, conductive metal oxide, graphite, and carbon fiber. This is the second gist.

  Furthermore, the present invention has, as a third aspect, a charging roll in which the insulating particles (C) are coated with a silane coupling agent, and among them, particularly, A charging roll in which the silane coupling agent is tetrasulfide silane is a fourth gist.

  That is, the present inventors have made extensive studies focusing on the resistance adjustment layer material in order to solve the above-mentioned problems. As a result, the rubber material, the electronically conductive particles having silica fixed on the surface, and the semiconductive rubber composition containing the insulating particles as essential components are not simply blended with a silane coupling agent, When the outer periphery of the silica-fixed electronic conductive particles is coated with a silane coupling agent in advance, the rubber material as the matrix component and the silica on the surface of the electronic conductive particles are chemically reacted via the silane coupling agent. Since it is fixed by bonding, it has been found that the movement of the electronic conductive particles due to the processing history such as kneading and extrusion is restricted, and fluctuations in electric resistance are suppressed, and the present invention has been achieved.

  The charging roll of the present invention is formed on a shaft, a conductive elastic layer formed on the outer periphery thereof, a resistance adjusting layer formed on the outer periphery of the conductive elastic layer, and an outer periphery of the resistance adjusting layer. And the resistance adjusting layer is composed of a rubber material (A component), silica fixed electronic conductive particles (B component) whose outer periphery is coated with a silane coupling agent, and insulating particles (C component). )) As an essential component. For this reason, the rubber material that is the matrix component and the silica on the surface of the electronic conductive particles are firmly fixed by chemical bonding via a silane coupling agent coated on the silica, and processing such as kneading and extrusion The movement of the electronic conductive particles due to the history is limited. Therefore, in the past, the electroconductive particles inevitably moved and aggregated due to the processing history, resulting in variations in the electric resistance. On the other hand, the charging roll of the present invention suppresses fluctuations in electric resistance and has extremely high electric resistance characteristics. It will be stable. In addition, it is possible to prevent bleeding of the image due to pinhole leak, and a good image can be obtained.

  In addition, when at least one selected from the group consisting of carbon black, metal powder, conductive metal oxide, graphite, and carbon fiber is used as the electronic conductive particles used in the above (B), in particular, the electronic conductivity The particles have excellent dispersibility and conductivity.

  Moreover, when the particles coated with a silane coupling agent are used as the insulating particles (C), the electric resistance fluctuation is further suppressed, and the electric resistance characteristics are further stabilized.

  When tetrasulfide silane is used as the silane coupling agent, particularly, the rubber material and the silica-fixed electronic conductive particles can be firmly fixed, so that the electric resistance characteristics can be further stabilized.

  Next, the best mode for carrying out the present invention will be described. However, the present invention is not limited to this embodiment.

  FIG. 1 shows an embodiment of a charging roll according to the present invention. In this charging roll, a conductive elastic body layer 2 is formed along the outer peripheral surface of the shaft body 1, a resistance adjusting layer 3 is formed on the outer peripheral surface of the conductive elastic body layer 2, and the resistance adjusting layer 3 The protective layer 4 is formed on the outer peripheral surface.

  The shaft body 1 is not particularly limited, and for example, a metal core made of a metal solid body, a metal cylinder body hollowed out inside, or the like is used. Examples of the metal material include stainless steel, aluminum, and iron plated.

The material for the conductive elastic body layer 2 formed on the outer peripheral surface of the shaft body 1 is not particularly limited. For example, polynorbornene rubber, ethylene-propylene-diene rubber (EPDM), acrylonitrile-butadiene rubber ( NBR), hydrogenated acrylonitrile-butadiene rubber (H-NBR), styrene-butadiene rubber (SBR), butadiene rubber (BR), isoprene rubber (IR), natural rubber (NR), and the like. These are used together. Moreover, carbon black, graphite, potassium titanate, iron oxide, c-TiO ₂ , c-ZnO, c-SnO ₂ , ionic conductive agent (quaternary ammonium salt, borate, surfactant) A conventionally known conductive agent such as etc.) is appropriately added to the material. Further, if necessary, a foaming agent, a crosslinking agent, a crosslinking accelerator, oil, and the like may be added as appropriate.

The material for the conductive elastic layer 2 is appropriately prepared so that the volume resistivity of the conductive elastic layer 2 formed thereby is usually in the range of about 10 ¹ to 10 ⁶ Ω · cm. Is done.

As the material for the resistance adjusting layer 3 formed on the outer peripheral surface of the conductive elastic body layer 2, a special semiconductive rubber composition having the following components (A) to (C) as essential components is used.
(A) Rubber material.
(B) Electronically conductive particles in which silica is fixed on the particle surface and the outer periphery thereof is coated with a silane coupling agent.
(C) Insulating particles.

  First, the rubber material as the component (A) is not particularly limited, and examples thereof include acrylonitrile-butadiene rubber (NBR), epichlorohydrin rubber, acrylic rubber, and the like. These may be used alone or in combination of two or more. Used.

  Next, electronically conductive particles (treated electronically conductive particles) whose component (B) is silica fixed on the particle surface and whose outer periphery is coated with a silane coupling agent are treated with a predetermined treatment. Silica is fixed on the surface of the conductive particles, and the outer periphery thereof is coated with a silane coupling agent.

The electron conductive particles used for the component (B) are not particularly limited. For example, carbon black such as FEF, SRF, ketjen black, acetylene black, metal powder, C-TiO ₂ , C— Examples thereof include conductive metal oxides such as ZnO, graphite, and carbon fibers. And these are used individually or in combination of 2 or more types. These electronically conductive particles preferably have a volume resistance value of about 1 × 10 ¹ Ω · cm or less and an average particle diameter of about 120 μm or less.

  Examples of a method for fixing silica on the surface of the electron conductive particles include the following methods. That is, first, electronically conductive particles such as carbon black are dispersed in water, and a dispersing agent (for example, methanol, various surfactants) is added to obtain a uniform slurry. Next, this slurry is adjusted to pH 6 or more, preferably pH 10 to 11, and the sodium silicate is hydrolyzed while maintaining the temperature at 70 ° C. or more, preferably 85 to 95 ° C. to form amorphous silica on the surface of the electroconductive particles. To adhere or deposit. Thereby, it is possible to obtain electronically conductive particles in which silica is fixed on the particle surface.

  The amount of silica (Si) fixed in the silica fixed electron conductive particles is preferably set so that the content of silica with respect to the entire silica fixed electron conductive particles is in the range of 1 to 15% by weight. Preferably it is in the range of 3 to 10% by weight. That is, when the amount of silica is less than 1% by weight, the affinity with the rubber material as the matrix component tends to decrease in the state where the outer periphery is coated with a silane coupling agent, and conversely, 15% by weight. It is because the effect on electroconductivity tends to decrease when it exceeds.

  The average particle diameter of the silica fixed electronic conductive particles is preferably in the range of 0.01 to 0.8 μm, particularly preferably in the range of 0.02 to 0.5 μm. That is, if it is out of the above range, the dispersibility of the electron conductive particles may be deteriorated.

  And as a method of coating the outer periphery of the said silica fixed electron conductive particle with a silane coupling agent, the following method can be mention | raise | lifted, for example. That is, first, the silica-fixed electronic conductive particles, the silane coupling agent, and the low boiling point solvent (methyl ethyl ketone, methyl isobutyl ketone, acetone, etc.) are blended in an appropriate ratio and stirred with a Henschel mixer or the like. And the processed electronic conductive particle of (B) component can be obtained by drying in the state which made the silane coupling agent adhere uniformly to the outer periphery of a silica fixed electronic conductive particle.

  The silane coupling agent is not particularly limited, and mercaptan silane coupling agents such as γ-mercaptopropyltrimethoxysilane, polysulfide silane coupling agents such as tetrasulfide silane and disulfide silane, and the like. Are preferably used. And these are used individually or in combination of 2 or more types. Among these, tetrasulfide silane is particularly preferably used in terms of excellent binding to rubber materials, insulating particles, and silica.

  The coating amount of the silane coupling agent is preferably set to 3 to 8 parts with respect to 100 parts by weight of silica fixed electronic conductive particles (hereinafter abbreviated as “part”). That is, if the coating amount of the silane coupling agent is less than the above range, the effect of fixing the silica and the rubber material may be insufficient, and conversely, if it is more than the above range, the severe condition This is because excessive silane coupling agent may bleed on the surface when stored at a low temperature.

  And, the blending ratio of the component (B) is preferably set in the range of 30 to 100 parts with respect to 100 parts of the rubber material which is the component (A) in order to obtain desired semiconducting characteristics, and more Preferably it is the range of 40-70 parts.

In addition, the insulating particles as the component (C) have a volume resistance of about 1 × 10 ¹⁰ Ω · cm or more and an average particle diameter of about 0.01 to 40 μm. If it exists in, it will not specifically limit, For example, a silica, calcium carbonate, mica, clay etc. are mention | raise | lifted. And these are used individually or in combination of 2 or more types.

  And the compounding ratio of the said (C) component is set to the range of 10-100 parts with respect to 100 parts of said rubber materials of (A), in the resistance adjustment layer 3, an electronic conductive particle is disperse | distributed uniformly. It is preferable when doing, More preferably, it is the range of 30-70 parts.

  In addition, part or all of the insulating particles as the component (C) can be replaced with insulating particles coated with a silane coupling agent, as in the component (B). In that case, the type of silane coupling agent and the coating method are the same as in the case of component (B). However, the type of the silane coupling agent used for coating the insulating particles as the component (C) and the silane coupling agent used for the component (B) are not necessarily the same. Coating with a ring agent can be performed. Of course, it is preferable that both are coated at the same time in one step using the same silane coupling agent, since the treatment step becomes simple.

  In addition to the components (A) to (C) described above, the material for the resistance adjustment layer 3 includes various auxiliaries such as a vulcanizing agent, a vulcanization accelerator, an antistatic agent, zinc white, and stearic acid. You may mix | blend as needed.

  In order to impart conductivity, normal electronically conductive particles not treated with silica may be used in combination with the component (B).

The material for the resistance adjusting layer 3 obtained by kneading these components is in a semiconductive region where the volume resistivity of the resistance adjusting layer 3 formed thereby is approximately 10 ⁵ to 10 ¹¹ Ω · cm. It adjusts suitably so that it may become.

  Next, the material for the protective layer 4 formed on the outer peripheral surface of the resistance adjusting layer 3 is not particularly limited, and examples thereof include polyamide resins such as N-methoxymethylated nylon, fluororesins, and acrylic resins. , Urethane resin, silicone resin and the like, and are used alone or in combination of two or more. In order to impart conductivity, a conventionally known conductive agent such as carbon black is appropriately added to the material.

In addition, the said material for protective layers 4 is suitably prepared so that the volume resistivity of the electroconductive elastic body layer 2 formed by it may exist in the range of about 10 < ⁷ > -10 < ¹³ > (omega | ohm) * cm.

  The charging roll of the present invention can be produced, for example, as follows. That is, first, each component for the conductive elastic layer 2 is kneaded using a kneader such as a kneader or a roll to prepare a material for the conductive elastic layer 2. Moreover, after knead | mixing each component for the said resistance adjustment layer 3 with a Banbury mixer or a kneader, it knead | mixes using a roll, and prepares the material (compound) for resistance adjustment layers 3. Furthermore, the material for the protective layer 4 (coating liquid) is prepared by dissolving the material for the protective layer 4 in an organic solvent such as MEK and dispersing with a sand mill or the like.

  Next, an adhesive is applied to the outer peripheral surface of the shaft body 1, and the material for the conductive elastic body layer 2 and the material for the resistance adjustment layer 3 are coextruded on the surface using an extruder. Then, this is simultaneously cross-linked in the mold, and the conductive elastic layer 2 is formed on the outer peripheral surface of the shaft body 1, and the resistance adjusting layer 3 is formed on the outer peripheral surface of the conductive elastic layer 2. Create a roll. Further, the coating liquid as the material for the protective layer 4 is applied to the outer peripheral surface of the resistance adjusting layer 3 by a roll coating method, a spray coating method, a dipping method or the like, dried, and then heated and crosslinked under predetermined conditions. The protective layer 4 having a predetermined thickness is formed. In this way, a charging roll (see FIG. 1) having a three-layer structure in which the resistance adjusting layer 3 is formed on the outer peripheral surface of the conductive elastic layer 2 and the protective layer 4 is further formed on the outer peripheral surface is prepared. Can do.

  Moreover, you may produce the charging roll of this invention as follows. That is, first, the material for the conductive elastic body layer 2 is filled in the mold in which the shaft body 1 is set, and this is heated and crosslinked to form the conductive elastic body layer 2 on the outer peripheral surface of the shaft body 1 in advance. Next, a material for the resistance adjusting layer 3 (coating solution) dissolved in a solvent is applied to the surface of the conductive elastic body layer 2 by a roll coating method, a spray coating method, a dipping method, and the like, and dried. The resistance adjustment layer 3 is formed on the outer peripheral surface of the conductive elastic body layer 2 by performing heat crosslinking under conditions. Next, the coating liquid which is the material for the protective layer 4 is applied to the outer peripheral surface of the resistance adjusting layer 3 by a roll coating method, a spray coating method, a dipping method or the like, dried, and then heated and crosslinked under predetermined conditions. To form a protective layer 4 having a predetermined thickness. In this way, a charging roll (see FIG. 1) having a three-layer structure in which the resistance adjusting layer 3 is formed on the outer peripheral surface of the conductive elastic layer 2 and the protective layer 4 is further formed on the outer peripheral surface is prepared. You can also.

  In the charging roll of the present invention thus obtained, the resistance adjusting layer 3 is a rubber material (component A), silica fixed electronic conductive particles (component B) whose outer periphery is coated with a silane coupling agent, Since it is formed of a special semiconductive rubber composition containing insulating particles (component C) as essential components, the outer periphery is coated with a rubber material that is a matrix component and silica on the surface of electronic conductive particles. It is firmly fixed by chemical bonding via the silane coupling agent, and movement of the electronically conductive particles due to processing history such as kneading and extrusion is limited. Therefore, in the charging roll of the present invention, fluctuations in electric resistance are suppressed, and electric resistance characteristics are extremely stable. In addition, it is possible to prevent bleeding of the image due to pinhole leak, and a good image can be obtained.

  Incidentally, the reaction mechanism between the rubber material and silica when tetrasulfide silane is used as the silane coupling agent is schematically shown in FIG. First, FIG. 2A shows the chemical formula of silica fixed on the surface of the electronic conductive particles and the chemical formula of tetrasulfide silane which is a silane coupling agent. And the state which coated the silane coupling agent on the surface of a silica fixed electronic electroconductive particle is shown in FIG.2 (b). 5 is an electroconductive particle. In this state, it can be seen that the silica and the silane coupling agent are chemically bonded, and the respective electroconductive particles 5 are fixed via the silica and the silane coupling agent.

  FIG. 2 (c) shows a state where the rubber particles as the component (A) and the insulating particles as the component (C) are kneaded and vulcanized in this state. Thereby, it turns out that each electronic conductive particle 5 is fixed to the molecular chain of the rubber particle via silica and the silane coupling agent, and its movement is regulated.

  In the charging roll of the present invention, the thickness of each of the layers 2 to 4 is not particularly limited, but the thickness of the conductive elastic layer 2 is usually set within a range of 1 to 10 mm, preferably 2 to 2. The thickness of the resistance adjusting layer 3 is usually set in the range of 10 to 1000 μm, and preferably in the range of 20 to 700 μm. Moreover, it is preferable to set the thickness of the said protective layer 4 in the range of 1-50 micrometers, Most preferably, it exists in the range of 3-30 micrometers.

Further, as described above, the volume resistivity of the conductive elastic layer 2 is usually set in the range of 10 ¹ to 10 ⁶ Ω · cm, and the volume resistivity of the resistance adjustment layer 3 is Usually, it is set in the range of 10 ⁵ to 10 ¹¹ Ω · cm, and the volume resistivity of the protective layer 4 is usually set in the range of 10 ⁷ to 10 ¹³ Ω · cm.

  Note that the charging roll of the present invention is not limited to the three-layer structure shown in FIG. 1. For example, a softener migration preventing layer or an adhesive layer is interposed between the conductive elastic body layer 2 and the resistance adjusting layer 3. A layer structure of four or more layers may be provided by providing an agent layer or the like as necessary.

  Next, examples will be described together with comparative examples.

[Example 1]
[Preparation of conductive elastic layer material]
100 parts of EPDM (Mitsui Chemicals, EPT4045), 20 parts of carbon black (Ketjen Black EC), 5 parts of zinc oxide, 1 part of stearic acid, process oil (Diana Process PW380, manufactured by Idemitsu Petrochemical Co., Ltd.) 30 parts, 15 parts dinitrosopentamethylenetetramine (foaming agent), 1 part sulfur, 2 parts dibenzothiazole disulfide (crosslinking accelerator), and 1 part tetramethylthiuram monosulfide (crosslinking accelerator) Then, kneading was performed using a roll to prepare a conductive elastic layer material.

[Production of treated carbon black]
(1) Silica fixation on carbon black surface 500 parts of carbon black (manufactured by Mitsubishi Chemical Corporation, MA100) is weighed and wetted with 1000 parts of a mixed solution of methanol and water [methanol: water = 1: 9 (weight ratio)]. Further, 4000 parts of water was added and dispersed sufficiently with an attritor filled with steel balls until a uniform and viscous slurry was obtained. The slurry was then separated from the steel balls through a sieve and diluted to a volume corresponding to 10,000 parts of water. And after heating a slurry to 90 degreeC, pH was adjusted to 10.0 by the addition of sodium hydroxide solution. Next, the following two types of solutions (a) and (b) were prepared separately.
(A) A solution obtained by diluting 167 parts of No. 3 sodium silicate solution with water to a volume corresponding to 1000 parts of water.
(B) 1000 parts of a 2.50% sulfuric acid solution.

  Thereafter, 50 parts of the diluted sodium silicate solution of (i) was added within 30 seconds to the slurry whose pH was adjusted to 10.0, and the pH of the slurry was adjusted to 11.0. Stirring was continued for 10 minutes while maintaining this pH, and then 50 parts of the sulfuric acid solution (b) was added within 30 seconds to adjust the pH of the slurry to 8.5. This addition method was repeated 20 times, and the addition of both solutions (a) and (b) was completed. Stirring was further continued for 1 hour, and diluted sulfuric acid was added to adjust the pH to 6.5 to 7.0. The slurry was filtered, washed until there was no soluble salt, and dried to prepare silica-fixed carbon black (Si content: 10% by weight).

(2) Silica-fixed carbon black coated with silane coupling agent To 100 parts of the above silica-fixed carbon black, 6.48 parts of tetrasulfide silane (A-1289, manufactured by Nihon Unicar), low boiling point 40 parts of acetone as a solvent was blended, stirred with a Henschel mixer, and dried to obtain silica-fixed carbon black (treated carbon black) whose outer periphery was coated with tetrasulfide silane.

[Preparation of material for resistance adjustment layer]
100 parts of NBR (Nippon Zeon, Nipol DN3335), 45 parts of the above treated carbon black, 20 parts of silica (Nipsil ER, manufactured by Nippon Silica), 30 parts of mica (Lepco, Repcomica M-XF) Were kneaded using a kneader, and further kneaded using a roll to prepare a resistance adjusting layer material (compound).

(Preparation of protective layer material)
Fluorine-modified acrylate resin (Dainippon Ink Co., Ltd., Defensa TR230K) 50 parts, fluorinated olefin resin (Atfina Japan Co., Ltd., Kyner SL) 50 parts, conductive titanium oxide (Ishihara Techno Co., Ltd., Tyco ET- (300W) 100 parts were dissolved in 200 parts of MEK and dispersed using a sand mill to prepare a protective layer material.

[Preparation of charging roll]
A cored bar made of a metal shaft having a diameter of 6 mm is prepared, and an adhesive is applied to the outer peripheral surface. Then, the conductive elastic layer material and the resistance adjusting layer material are applied to the surface using an extruder. Co-extruded. Then, this is subjected to simultaneous crosslinking and foaming in a mold, and a conductive elastic layer (thickness 2.5 mm) is formed on the outer peripheral surface of the core metal. A resistance adjusting layer (thickness is formed on the outer peripheral surface of the conductive elastic layer). A roll having a thickness of 500 μm was produced. Subsequently, the protective layer material is applied to the outer peripheral surface of the resistance adjustment layer by a roll coating method, dried, and then heated and crosslinked at 150 ° C. for 60 minutes to form a protective layer (thickness 6 μm). As a result, an intended charging roll having a three-layer structure was obtained.

[Examples 2-6, Comparative Examples 1-3]
As shown in Tables 1 to 3 below, the resistance adjustment layer material was changed. Other than that was carried out similarly to the said Example 1, and obtained 5 types of Example goods and 3 types of comparative example goods.

  About each charging roll of the said Examples 1-6 and Comparative Examples 1-3, each characteristic was evaluated according to the following reference | standard. These results are also shown in Tables 1 to 3 below.

(Circumferential resistance variation)
The circumferential resistance variation was calculated by measuring roll electrical resistance by a metal roll electrode method using an apparatus as shown in FIG. That is, first, a charging roll 11 as a sample is brought into contact with a metal roll 10 made of stainless steel, and both ends of the charging roll 11 are pressed with a load of 500 g (4.9 N), respectively. A voltage of AC voltage: 300 Hz 500 Vpp, DC voltage: -200 V was applied. In this state, the charging roll 11 is rotated, the DC component of the electrical resistance in the charging roll 11 is measured, and the circumferential resistance variation (X) is calculated according to the following equation (1) based on the data. Calculated.

  In the above formula (1), Rmax is the maximum value of roll electrical resistance, Rmin is the minimum value of roll electrical resistance, and Ra is the average value of roll electrical resistance. The above X was evaluated as “◎” when 60% or less, “◯” when exceeding 60% and 70% or less, “Δ” when exceeding 70% and 80% or less, and “X” when exceeding 80%.

[Image bleeding]
Each charging roll was incorporated into a commercially available laser printer (Laser Jet 4L, manufactured by Nippon Hewlett-Packard Company). On the other hand, a pinhole having a diameter of 0.2 mm was provided on the surface of the photosensitive drum of the laser printer with a needle or the like. . Then, a white image was output under an environment of 15 ° C. × 10% RH, and an image formed by the pinhole on the photosensitive drum was evaluated. Then, the ratio of the blur diameter on the actually output image with respect to the pinhole was obtained, and the image blur was evaluated. That is, the above ratio is less than 1.4, ◎, 1.4 or more and less than 1.8, ◯, 1.8 or more and less than 2.2, △, 2.2 or more Was evaluated as x.

  From the above results, the example products have excellent dispersibility of the electronic conductive particles (silica fixed electronic conductive particles coated with the silane coupling agent) in the resistance adjustment layer, and have small variations in electrical resistance and bleeding. It can be seen that a good copy image with almost no image can be obtained. In particular, the product of Example 1 is a material for the resistance adjustment layer, the amount of silica fixed on the surface of the electron conductive particles, the amount of the silane coupling agent coated on the outer periphery, and the blending of the component (B) with the rubber material Since all the proportions are set appropriately, the rubber material and electronic conductive particles are firmly fixed via the silane coupling agent and silica, and the electric resistance characteristics are very stable. I understand. Moreover, since the product of Example 6 uses the silane coupling agent-coated particles as the component (C) as the insulating particles of the component (C), it can be seen that more stable electric resistance characteristics are exhibited. .

  On the other hand, it can be seen that the products of Comparative Examples 1 to 3 have poor dispersibility of the electronic conductive particles in the resistance adjustment layer and the variation in electric resistance compared to the product of Example, and the product characteristics are not so good. It is not stable. Further, some blurring of the copied image is seen, and it can be seen that the level required by the present invention has not been reached.

  In addition, about each of the resistance adjustment layer material of Example 1, and the resistance adjustment layer material of the comparative example 3, the resistance fluctuation by kneading time was measured in accordance with the following method. The result is shown in FIG.

[Fluctuation of resistance due to kneading time]
Three types of charging rolls were prepared for each of Example 1 and Comparative Example 3 by changing the roll kneading time at the time of adjusting the resistance adjusting layer material (compound) (7 minutes, 9 minutes, 11 minutes). Then, the resistance (Ω) of each charging roll was measured.

  From the results of FIG. 4, it can be seen that the resistance adjustment layer material used in Example 1 has little resistance variation even when the kneading time is extended, and the electrical resistance characteristics are stable regardless of the processing history.

  Further, 2500 charging rolls of Example 1 and Comparative Example 3 are mass-produced, and the degree of variation in DC current value (%) is shown in a frequency distribution graph as shown in FIG. 5 and FIG. . From these results, it can be seen that the charging roll of Example 1 has a narrow variation distribution width and is distributed in a region where the value is small, so that it is difficult for the quality of the product to vary even in mass production.

It is sectional drawing which shows an example of the charging roll of this invention. (A)-(c) is explanatory drawing which illustrates typically the characteristic of the structure in the resistance adjustment layer of this invention. It is explanatory drawing which shows the measuring method of the electrical resistance of a charging roll. It is a diagram which shows the relationship between the kneading time of a resistance adjustment layer material, and resistance variation. It is a frequency distribution graph which shows the dispersion | variation in the direct current value of Example 1 goods. It is a frequency distribution graph which shows the dispersion | variation in the direct current value of 3 comparative products.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Shaft body 2 Conductive elastic body layer 3 Resistance adjustment layer 4 Protective layer

Claims (4)

A shaft body, a conductive elastic layer formed on the outer periphery thereof, a resistance adjustment layer formed on the outer periphery of the conductive elastic layer, and a protective layer formed on the outer periphery of the resistance adjustment layer. A charging roll, wherein the resistance adjusting layer is formed of a semiconductive rubber composition having the following components (A) to (C) as essential components.
(A) Rubber material.
(B) Electronically conductive particles in which silica is fixed on the particle surface and the outer periphery thereof is coated with a silane coupling agent.
(C) Insulating particles.   2. The charging roll according to claim 1, wherein the electron conductive particles are at least one selected from the group consisting of carbon black, metal powder, conductive metal oxide, graphite, and carbon fiber.   The charging roll according to claim 1 or 2, wherein the insulating particles (C) are coated with a silane coupling agent.   The charging roll according to claim 1, wherein the silane coupling agent is tetrasulfide silane.

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