JP2005338168A - Charging member, image forming apparatus and process cartridge - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a charging member which performs stable charging for a long time even when it is used at different processing speed with good charging characteristic, for example, even in the case of outputting a high-definition image such as a halftone image of 600dpi especially by a DC charging method. <P>SOLUTION: The charging member is constituted of a conductive supporting body, a conductive elastic body layer provided on the conductive supporting body, and further a surface layer provided on the outer circumference of the conductive elastic body layer. When the resistance and the electrostatic capacity of the conductive elastic body layer are respectively defined as R1 and C1, and further the resistance and the electrostatic capacity of the surface layer are respectively defined as R2 and C2, they satisfy C2/C1≥6.3×(R2/R1)<SP>0.6</SP>in the charging member. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a charging member, an image forming apparatus using the charging member, and a process cartridge. More specifically, the present invention relates to a charging member for applying a voltage to charge the surface of an electrophotographic photosensitive member, which is an object to be charged, to a predetermined potential, an image forming apparatus using the charging member, and a process cartridge.

  A contact charging method has been put to practical use as a primary charging method for an electrophotographic image forming apparatus. This is because a conductive elastic layer is provided on the outer periphery of a conductive support (core metal) and a resistance roller is provided on the outer periphery of the conductive elastic layer to apply a voltage to the core. In this method, the surface of the photosensitive member is charged by causing a small discharge in the vicinity of the contact nip between the charging roller and the photosensitive member.

  As a method that has become widespread in practice, an AC + DC charging method in which a voltage obtained by superimposing an AC voltage on a DC voltage is applied. In this case, the AC voltage that is superimposed to obtain charging uniformity is the same as that at the time of DC voltage application. A voltage having a peak-to-peak voltage Vpp that is at least twice the charging start voltage is used.

  This AC + DC charging method is a method in which stable charging can be performed by applying an AC voltage. However, as compared with a DC charging method in which only a DC voltage is applied to a charging member by using an AC voltage source, an image is obtained. The cost of the forming apparatus is increased.

  Here, the DC charging method is generally lower in cost than the AC charging method, but has a problem. That is, since there is no AC current uniformity effect unlike AC + DC charging, the charging uniformity is inferior to that of the AC + DC charging method. In addition, since there is no uniform effect, there is a problem that the toner or its external additive adheres to the surface of the charging roller, and the electric resistance of the charging roller itself is not uniform in the image.

  In addition, when the electrophotographic apparatus is driven at two or more different process speeds to output an image due to the thickness of the print medium, the DC charging method is better than the AC charging method. There is also a problem that the range of the process speed that exhibits excellent charging characteristics is narrow. In other words, depending on the heat capacity of the print media, if you want to slow down the process speed and increase the time to pass through the fixing part for print media with thick media, or if you want to print on a transparency sheet, The DC charging method is used in situations such as when it is necessary to lengthen the time passing through the fixing portion in order to sufficiently melt and mix the toner in the fixing portion in order to suppress light scattering as much as possible and obtain an image with good light transmission. There is a problem that it is more difficult to perform good charging as compared with the AC charging method. In particular, in the DC charging method, when halftone images are output at different process speeds in a low temperature and low humidity environment (15 ° C./10% RH), charging uniformity becomes a problem.

Here, in the conductive roller having the resistance adjusting layer on the outer peripheral surface of the conductive elastic layer, when the electric resistance of each layer is R1 and R2, R1 is 10 ⁶ to 10 ⁸ Ω, and R2 A conductive roller that satisfies / R1 ≧ 10 has been proposed (see, for example, Patent Document 1).

  In addition, a conductive roller has been proposed in which the ratio of resistance between the intermediate layer and the coating film is 1: 0.1 to 1:10 (see, for example, Patent Document 2).

  However, if the resistance ratio of the conductive elastic layer and the outer peripheral surface layer is controlled within the above range, when a halftone image is output at different process speeds in a low-temperature and low-humidity environment, black In some cases, image defects may occur due to defective charging, and charging uniformity may not be satisfied.

  In addition, in order to suppress image defects due to adhesion of toner or its external additives to the surface of the charging roller, a proposal has been made to suppress it by uniformly covering the entire surface of the charging roller with a toner (for example, patents). Reference 3).

  However, even when such a charging member is used, it is difficult to hold a nearly spherical toner on the surface of the charging member, and the sliding friction with the photosensitive member, in particular, the higher the process speed, the more the toner on the charging member. In some cases, the portion is fused and eventually the portion causes discharge failure, overcharging, and the like, and the charging uniformity may not be satisfied.

  Similarly, in order to suppress image defects due to adhesion of toner or its external additives to the surface of the charging roller, it has been proposed to suppress it by attaching inorganic powder to the entire surface of the charging roller (for example, , See Patent Document 4).

However, even if such a charging member is used, charging will not be possible unless the adhesion between the charging member surface and the inorganic powder, or the resistance and capacitance of the charging member to which the powder is adhered, satisfy the optimum conditions for the process speed. Uniformity may not be satisfied.
JP 2002-139911 A JP-A-10-177290 JP 09-179375 A JP 11-311890 A

  The problem to be solved is stable even for a long time even when used at different process speeds due to good charging characteristics even when a high-definition image such as a halftone image of 600 dpi is output by the DC charging method. An object of the present invention is to provide a charging member that can perform charging.

  Another object of the present invention is to provide an image forming apparatus and a process cartridge using the charging member.

According to the present invention, the charging member is composed of a conductive support, a conductive elastic layer provided on the conductive support, and a surface layer provided on the outer periphery thereof. When the resistance and capacitance of the elastic elastic layer are R1 and C1, respectively, and the resistance and capacitance of the surface layer are R2 and C2, respectively,
C2 / C1 ≧ 6.3 × (R2 / R1) ^0.6
A charging member is provided.
According to the present invention, the charging member comprises a conductive support, a conductive elastic layer provided on the conductive support, and a surface layer provided on the outer periphery thereof, The surface layer is made of a directly insulating layered compound formed in advance, and the particle size when the average particle size of the directly insulating layered compound is 5 to 50 μm and the cumulative number% is 10% in the particle size distribution is D ( 10) When the particle diameter at 50% is D (50) and the particle diameter at 90% is D (90), D represented by the following formula satisfies D> 1.6. A characteristic charging member is provided.

                    D = (D (90) -D (10)) / D (50)

  Further, according to the present invention, an image carrier, a charging unit for charging the image carrier to a predetermined potential, an exposure unit for forming an electrostatic latent image on a charging surface of the image carrier, In the image forming apparatus, the charging unit includes: a developing unit that transfers the toner to the electrostatic latent image formed on the surface and visualizes the toner to form a toner image; and a transfer unit that transfers the toner image to a transfer member. There is provided an image forming apparatus comprising the charging member and charging the image carrier by applying only a DC voltage to the charging member.

  In addition, according to the present invention, there is provided a process cartridge that integrally supports the image carrier and the charging member and is detachable from the main body of the image forming apparatus.

  As described above, according to the present invention, a charging member capable of performing stable charging for a long period of time even when using a DC charging method or at different process speeds, an image forming apparatus having the charging member, and a process cartridge having the charging member. Can be provided.

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

The inventors of the present invention have a structure of a DC charging member, a conductive support, a conductive elastic layer provided on the conductive support, and a surface layer provided in advance on the conductive elastic layer. When the resistance and capacitance of the conductive elastic layer are R1 and C1, respectively, and the resistance and capacitance of the surface layer are R2 and C2, respectively, C2 / C1 ≧ 6.3 × ( R2 / R1) By using a charging member characterized by ^0.6, it is possible to provide a charging member that can be stably charged for a long time even when used at different process speeds in a low temperature and low humidity environment. As a result, the present invention has been achieved.

Here, in a roller configuration in which C2 / C1 <6.3 × (R2 / R1) ^0.6 , when used at different process speeds, for example, the output speed of the recording medium is 100 mm / sec and 30 mm / sec. Two types of image resolution of 600 dpi halftone image is output, 100 mm / sec output image is inferior in charging uniformity and many black streaks occur, but 30 mm / sec has very good charging uniformity. Or conversely very good charging uniformity at 100 mm / sec, but incompatible states such as a large number of similar black streaks appearing in the output image of 30 mm / sec, resulting in an image defect It becomes.

  Although the cause of this is not known in detail, the black streaks are generated on the image because the charging ability is insufficient in that portion. For this reason, it is sufficiently predicted that the electrostatic capacity of the conductive elastic layer and the surface layer is important in order to supply a stable charging performance independent of the process speed, that is, a stable discharge charge amount. At this time, it is considered that good image characteristics can be obtained if the capacitance ratio satisfies a certain condition corresponding to the resistance ratio between the conductive elastic layer and the surface layer.

  As a structure and form of the charging member of the present invention, FIG. 2 is a schematic diagram showing an example of a cross section of a charging roller which is the charging member of the present invention. The charging roller in the figure has a conductive elastic layer 12 on the outer periphery of a conductive support (shaft) 11, and an insulating layered compound 13 is directly provided as a surface layer on the outside of the conductive elastic layer 12 in advance. Have.

  The conductive elastic body layer 12 can be formed of a solid body such as rubber or thermoplastic elastomer that has been conventionally used as an elastic body layer of a charging member. Specifically, rubbers using base rubbers such as polyurethane, silicone rubber, butadiene rubber, isoprene rubber, chloroprene rubber, styrene-butadiene rubber, ethylene-propylene rubber, polynorbornene rubber, styrene-butadiene-styrene rubber, and epichlorohydrin rubber. The composition or thermoplastic elastomer is not particularly limited, and one or more thermoplastic elastomers selected from general-purpose styrene elastomers and olefin elastomers can be suitably used.

  Examples of commercially available styrene elastomers include “Lavalon” manufactured by Mitsubishi Chemical Corporation, “Septon Compound” manufactured by Kuraray Co., Ltd., and the like. Commercially available olefin elastomers include, for example, “Thermorun” manufactured by Mitsubishi Chemical Corporation, “Miralastomer” manufactured by Mitsui Petrochemical Co., Ltd., “Sumitomo TPE” manufactured by Sumitomo Chemical Co., Ltd., and advanced elastomers. It can be obtained from the market as "Santplane" manufactured by Systems.

Predetermined conductivity can be imparted to the conductive elastic layer 12 by adding a conductive agent. The conductive agent is not particularly limited, and lauryltrimethylammonium, stearyltrimethylammonium, octadodecyltrimethylammonium, dodecyltrimethylammonium, hexadecyltrimethylammonium, and modified fatty acid / dimethylethylammonium perchlorate, chlorate, borofluoride. Cationic surfactants such as quaternary ammonium salts such as hydrohalides, ethosulphate salts, benzyl bromides and benzyl chlorides, aliphatic sulfonates, higher alcohol sulfates, Anionic surfactants such as higher alcohol ethylene oxide addition sulfate ester salts, higher alcohol phosphate ester salts and higher alcohol ethylene oxide addition phosphate ester salts, zwitterionic surfactants such as various betaines, higher Le Call ethylene oxide, antistatic agents such as nonionic antistatic agents such as polyethylene glycol fatty acid esters and polyhydric alcohol fatty acid _{esters, LiCF 3 SO 3, NaClO 4} , LiAsF 6, LiBF 4, NaSCN, KSCN and Li, such as NaCl ^+, Na ⁺ and ^{K +,} etc. periodic table group 1 metal salt or quaternary ammonium salt electrolytes such as of, also, Ca _{(ClO 4) 2} and the like ^{Ca 2+} and periodic table second ^{Ba 2+,} etc. Group metal salts and these antistatic agents have at least one group having an active hydrogen that reacts with an isocyanate such as a hydroxyl group, a carboxyl group, and a primary or secondary amine group. Furthermore, they and complexes of polyhydric alcohols such as 1,4-butanediol, ethylene glycol, polyethylene glycol, propylene glycol and polyethylene glycol and derivatives thereof, or monools such as ethylene glycol monomethyl ether and ethylene glycol monoethyl ether Ionic conductive agent such as a complex with, or conductive carbon such as ketjen black EC and acetylene black, Super Ablation Furnace (SAF super abrasion resistance), Intermediate Super Ablation Furnace (ISAF quasi-super abrasion resistance), High Ablation Furnace (HAF high wear resistance), Fast Extruding Furnace (FEF good extrudability), Genera l Carbon for rubber such as Purchase Furnace (GPF versatility), Semi Reinforcing Furnace (SRF medium reinforcement), Fine Thermal (FT fine particle thermal decomposition) and Medium Thermal (MT medium particle thermal decomposition), etc. Ink) carbon, pyrolytic carbon, natural graphite, artificial graphite, tin oxide, titanium oxide, zinc oxide, nickel, copper, silver and germanium and other metal and metal oxides, or conductive polymers such as polyaniline, polypyrrole and polyacetylene Etc.

The blending amount of these conductive agents is appropriately selected according to the type of the composition, and the electric resistance of the conductive elastic layer 12 is preferably 10 ² to 10 ⁸ Ω, more preferably 10 ³ to 10 ⁶ Ω. Adjusted to

  In addition, the materials used for the conductive elastic layer include inorganic fillers such as silica (white carbon), calcium carbonate, magnesium carbonate, clay, talc, zeolite, alumina, barium sulfate, aluminum sulfate, etc., sulfur, peroxides, crosslinks A crosslinking agent such as an auxiliary agent, a crosslinking accelerator, a crosslinking acceleration assistant, and a crosslinking retarder may be appropriately added.

  In the present invention, the hardness of the conductive elastic layer is preferably 70 degrees or more in Asker C, and particularly preferably 73 degrees or more. If the hardness is less than 70 degrees, the amount of deformation at the time of contact with the member to be charged increases, so that the amount of permanent deformation at the contact portion tends to increase.

  The direct insulating layered compound 13 is a silicate mineral mainly composed of clay, a tetrahedral sheet having a two-dimensional connection of the Si—O tetrahedral crystal structure, Al—O, Mg—O, etc. It is preferable to have an octahedral sheet structure having an octahedral net-like connection and to have a composite layer called a 1: 1 layer or a 2: 1 layer by combining these two sheets. Moreover, by making the shape into a layer, it is possible to improve the adhesion with the conductive elastic layer and to reduce the drop-out during use.

  Of these, kaolinite, kaolinite, dickite, nacrite, halosite, auditeite, which has a 1: 1 layer structure as a natural direct insulating layered compound, and talc as a 2: 1 layer structure. -Pyrophyllite talc, willemsite, kellolite, pimelite, pyrophyllite, ferripyroferrite; smectite saponite, hectorite, soconite, stevensite, swinholderite, montmorillonite, beidellite, nontronite, Borconicite; vermiculite trioctahedral vermiculite, dioctahedral vermiculite; biotite biotite, phlogopite, iron mica, East Knight, siderophilite tetraferri iron mica, sericite, polyricinite , Baiyun , Celadonite, iron ceradonite, iron alumino ceradonite, alumino ceradonite, alumino mica, soda mica; brittle mica clintonite, bite mica, ananda stone, pearl mica; chlorite, clinoclear, chamosite, Penantite, nimite, bailicroa, dombasite, kukeite, suedoite; mixed layer minerals such as cholensite, hydrobiotite, arietite, krucareite, rectolite, tosdite, dodrite, lnjanite, salioite. The mica group is particularly preferable.

  Synthetic mica and synthetic smectite are also effective as synthetic direct insulating layered compounds. Synthetic mica is particularly preferable.

  The reason why these mica compounds are particularly good is considered to be a compound having a relatively large electrostatic capacity.

  The directly insulating layered compound is preferably surface-treated. As the surface treatment means, various known methods (for example, plasma treatment, surface polymerization, coating, treatment with acid or alkali) can be used as physical and chemical surface treatment, but coupling agent treatment can be used as a simple means. The silane coupling agent treatment is particularly preferable.

  The coupling agent used is a compound which has a hydrolyzable group and a long-chain alkyl hydrophobic group in the same molecule and is bonded to a central element such as silicon, aluminum, titanium or zirconium. As the water-repellent group, a structure in which 4 or more carbon atoms, preferably 6 or more, and more preferably linearly connected is suitable. However, when the number exceeds 30, it tends to be difficult to dissolve in a solvent in general. In order to obtain a uniform coating state, additional means such as heating may be required.

  In addition, in the coupling | bonding form with a central element, you may couple | bond together via carboxylate ester, alkoxy, sulfonate ester, phosphate ester, or directly. Further, the structure may contain a functional group such as an ether bond, an epoxy group or an amino group. As the hydrolytic group, for example, an alkoxy group such as a methoxy group, an ethoxy group, a propoxy group, or a butoxy group having relatively high hydrophilicity is used. In addition, an acryloxy group, a methacryloxy group, a halogen derivative thereof, and the like can also be used.

  At this time, if the amount of the coupling agent is 0.0001% by mass or more and 1.0% by mass or less with respect to 100 parts by mass of the powder, and the reaction rate of the coupling agent is 80% or more, it is even better. In addition, in order to measure the abundance of the coupling agent, there is a method in which a weight loss by heating is obtained using a thermobalance and this value is used as the abundance. In addition, as a method for measuring the reaction rate of the coupling agent, for example, a method of immersing in a solvent 100 times the amount of the treated powder, and quantifying the coupling agent component in the solvent by chromatography, or remaining on the powder surface Means for quantifying the coupling agent component by a method such as ESCA, CHN, TGA, and the like are possible.

  The average particle size of the directly insulating layered compound is preferably 5 to 50 μm. 10-25 micrometers is especially preferable. If the average particle size is smaller than 5 μm, a predetermined capacitance ratio cannot be obtained, charging uniformity corresponding to different process speeds is not satisfied, and if it is larger than 50 μm, adhesion to the conductive elastic layer is poor. It is easy to cause uneven adhesion, and the charging uniformity is also deteriorated at this portion.

  Further, in the particle size distribution of the directly insulating layered compound, the particle size when the cumulative number% is 10% is D (10), the particle size when 50% is D (50), and the particle size when 90% is When D (90) and D = (D (90) −D (10)) / D (50), it is preferable that D> 1.6. More preferably, D> 1.7. If D <1.6, the coefficient of dynamic friction increases as shown in FIG. 3, so that the deposited directly insulating layered compound is more easily removed by sliding with the photoreceptor when the process speed is changed. Therefore, the charging uniformity at that portion is inferior.

  The average particle size and particle size distribution D of the directly insulating layered compound were measured using the following apparatus. A Coulter Counter Multisizer II type (manufactured by Coulter Inc.) is used as the measuring device, and an interface (manufactured by Nikka) and a CX-1 personal computer (manufactured by Canon) that output the number distribution and volume distribution are connected. Alternatively, a 1% NaCl aqueous solution is prepared using primary sodium chloride. As a measuring method, 0.1 to 5 ml of a surfactant, preferably alkylbenzenesulfonate is added as a dispersant to 100 to 150 ml of the electrolytic aqueous solution, and 2 to 20 mg of a measurement sample is further added. The electrolytic solution in which the sample is suspended is subjected to dispersion treatment with an ultrasonic disperser for about 1 to 3 minutes, and is measured by using a 100 μm aperture as an aperture by the Coulter Counter Multisizer II type. The particle size distribution was calculated from the cumulative number% data obtained here.

FIG. 4 shows an example (outline) of a method for measuring the static friction coefficient and the dynamic friction coefficient in the present invention. This measurement method is a method suitable for the case where the measurement object has a roller shape, and is a method that conforms to Euler's belt method. According to this method, the measurement object contacts the charging member at a predetermined angle (θ). In the belt (thickness 20 μm, width 30 mm, length 180 mm), one end is connected to a measurement unit (load meter) and the other end is connected to a weight W. When the charging member is rotated at a predetermined direction and speed in this state, the friction coefficient (μ) is as follows when the force measured by the measuring unit is F (g) and the weight of the weight is W (g): Is obtained by the following formula;
μ = (1 / θ) ln (F / W)

  An example of a chart obtained by this measurement method is shown in FIG. Here, since the value immediately after rotating the charging member is the force necessary to start the rotation, and the subsequent value is the force necessary to continue the rotation, the rotation start point (ie, t = 0 second time) can be referred to as a static friction force, and a force at an arbitrary time of 0 <t (seconds) ≦ 10 can be referred to as a dynamic friction force at an arbitrary time. The value was taken as the dynamic friction force.

The adhesion amount of the directly insulating layered compound on the conductive elastic layer is preferably 0.1 to 2.0 mg / cm ² . When the amount is less than 0.1 mg and when the amount is more than 2.0 mg, in both cases, adhesion unevenness occurs, resulting in poor charging uniformity.

  The method for forming the directly insulating layered compound 13 is not particularly limited, but a coating material in which the directly insulating layered compound is adhered by rubbing or dispersed in a solvent is prepared, and this coating material is dipped. A method of coating by spraying or forming a coating film is preferably used. In this case, when the insulating layered compound is directly formed into a plurality of layers, dipping or spraying may be repeated using a coating material for forming each layer.

  In the present invention, in order to increase adhesion between the conductive elastic body layer 12 and the surface layer 13, a treatment with a coupling agent is performed, or energy rays (ultraviolet rays, electron beams) are used. Processing can also be provided.

  FIG. 6 shows an example in which a process cartridge using the charging member of the present invention is applied to an electrophotographic apparatus. Reference numeral 21 denotes a rotating drum type electrophotographic photosensitive member (photosensitive member) as an image bearing member. The photosensitive member 21 is rotationally driven at a predetermined peripheral speed (process speed) in a clockwise direction indicated by an arrow in the drawing. As the photoreceptor 21, for example, a known photoreceptor 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 employed. The photoconductor 21 may further include a charge injection layer for charging the surface of the photoconductor to a predetermined polarity and potential.

  Reference numeral 22 denotes a charging roller (conductive roller) as a charging member. A charging unit is configured by the charging roller 22 and a charging bias application power source S1 that applies a charging bias to the charging roller 22. The charging roller 22 is brought into contact with the photoconductor 21 with a predetermined pressing force, and is driven to rotate in the forward direction with respect to the rotation of the photoconductor 21 in this example. A predetermined DC voltage (in this example, −1200 V) is applied to the charging roller 22 from the charging bias application power source S1 (DC charging method), whereby the surface of the photoconductor 21 has a predetermined polarity potential ( In this example, it is uniformly charged to a dark portion potential of −600 V).

  Reference numeral 23 denotes exposure means. A known means can be used as the exposure means 23. For example, a laser beam scanner or the like can be preferably exemplified. L is exposure light.

  The exposure unit 23 performs image exposure corresponding to target image information on the charged surface of the photosensitive member 21, thereby exposing the exposed bright portion of the photosensitive member charging surface (in this example, the bright portion potential is −350 V). Is lowered (attenuated) selectively, and an electrostatic latent image is formed on the photoreceptor 21.

  Reference numeral 24 denotes reversal developing means. As the developing unit 24, a known unit can be used. For example, the developing unit 24 in this example is provided in a toner container 24 a that is disposed in an opening of a developing container that stores toner and carries and transports toner. The agitating member 24b for agitating the toner that has been used, and the toner regulating member 24c for regulating the toner carrying amount (toner layer thickness) of the toner carrying member 24a. The developing unit 24 selectively attaches toner (negative toner) charged to the same polarity as the charged polarity of the photosensitive member 21 to the exposed bright portion of the electrostatic latent image on the surface of the photosensitive member 21 to form the electrostatic latent image. It is visualized as a toner image (in this example, the developing bias is −350 V). 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. Is preferable.

  Reference numeral 25 denotes a transfer roller as transfer means. As the transfer roller 25, known means can be used. For example, a transfer roller formed by coating an elastic resin layer having a medium resistance on a conductive support such as metal can be exemplified. The transfer roller 25 is brought into contact with the photoconductor 21 with a predetermined pressing force, and rotates in the forward direction with the rotation speed of the photoconductor 21 at substantially the same peripheral speed as the rotation speed of the photoconductor 21. 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 at a predetermined timing from a sheet feeding mechanism (not shown) to the contact portion between the photosensitive member 21 and the transfer roller, and the back surface of the transfer material P is charged with toner by the transfer roller 25 to which a transfer voltage is applied. The toner image on the surface of the photoconductor 21 is electrostatically transferred to the surface of the transfer material P at the contact portion between the photoconductor 21 and the transfer roller.

  The transfer material P that has received the transfer of the toner image is separated from the surface of the photosensitive member, 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, this image formed product is introduced into a recirculation conveyance mechanism (not shown) and reintroduced into the transfer unit.

  Residues on the photosensitive member 21 such as transfer residual toner are collected from the photosensitive member by a cleaning means 26 such as a blade type.

  In the case where residual charge remains on the photosensitive member 21, it is better to remove the residual charge on the photosensitive member 21 by a pre-exposure device (not shown) after the transfer and before the primary charging by the charging member 22. .

  The process cartridge of the present invention is configured to support at least the charging member 22 and the photosensitive member 21 and be detachable from the main body of the electrophotographic apparatus. The charging member 22, the photosensitive member 21, the developing unit 24, and the cleaning unit 26 are integrally supported to form a process cartridge.

  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.

[Example 1]
(Formation of conductive elastic layer-1)
100 parts by mass of epichlorohydrin rubber (trade name “Epichromer CG102”: manufactured by Daiso Corporation), 5 parts by mass of MT carbon (trade name “HTC # 20”: manufactured by Nisshin Carbon Co., Ltd.), zinc oxide 5 1 part by mass and 1 part by mass of stearic acid are kneaded with an open roll for 30 minutes, and further 1 part by mass of a vulcanization accelerator (DM: di-2-benzothiazolyl disulfide) and a vulcanization accelerator (TS: tetramethylthiuram mono). 0.5 parts by weight of sulfide) and 1.2 parts by weight of sulfur as a vulcanizing agent were added, and the mixture was further kneaded with an open roll for 15 minutes.

  The obtained kneaded product was extruded into a cylindrical shape having an outer diameter of 10 mm and an inner diameter of 5.5 mm with a rubber extruder, cut into a length of 250 mm, and primary vulcanized with steam at 160 ° C. for 45 minutes in a vulcanizing can, A conductive elastic layer primary vulcanization tube was obtained.

  Next, a thermosetting adhesive (trade name: metal and rubber) 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. Metallock U-20) was applied, dried at 80 ° C. for 30 minutes, and further dried at 120 ° C. for 1 hour. This support was inserted into the conductive elastic base layer primary vulcanization tube, and then subjected to secondary vulcanization and adhesive curing at 160 ° C. for 1 hour using an electric oven to obtain an unpolished product. . After cutting both ends of the rubber part of this unpolished product to make the length of the rubber part 231 mm, the rubber part is polished with a rotating grindstone, and the crown shape with an end diameter of 8.2 mm and a central part of 8.5 mm is used. A 10-point average roughness (Rz) of 4.5 μm and a deflection of 20 μm were obtained.

  The ten-point average roughness (Rz) of the charging member was measured according to JIS B6101.

  The measurement of the deflection of the charging member was performed using a high precision laser measuring machine LSM-430v manufactured by Mitutoyo Corporation. The outer diameter is measured by the measuring device, and the difference between the maximum outer diameter value and the minimum outer diameter value is defined as the outer diameter difference fluctuation. It was calculated as the diameter difference runout.

  The hardness was 74 degrees (Asker C).

Mica-1 (trade name “NCR-300”, manufactured by Yamaguchi Mica Kogyo Co., Ltd.) as a directly insulating layered compound is uniformly placed on a Sylbon paper using a medicine sword, and the conductive elastic layer is formed thereon. Was attached to the surface while rolling, and the excess adhering part was adhered while squeezing with another sylbon paper to obtain a charging member. The adhesion amount at this time was 0.30 mg / cm ² .

Measurement of the average particle size and particle size distribution of mica-1 as the directly insulating layered compound is performed as follows. Using a Coulter Counter Multisizer II type (manufactured by Beckman Coulter Co., Ltd.) as the measuring device, an interface (manufactured by Nikka Ki Bios Co., Ltd.) for outputting the number distribution and volume distribution and a CX-1 personal computer (Canon Co., Ltd.) )), And a 1% NaCl aqueous solution is prepared using a special grade or first grade sodium chloride as the electrolyte. 0.1 to 5 ml of a surfactant, preferably alkyl benzene sulfonate, is added as a dispersant to 100 to 150 ml of the electrolytic aqueous solution, and 2 to 20 mg of a measurement sample is further added. The electrolyte solution in which the sample is suspended is dispersed for about 1 to 3 minutes with an ultrasonic disperser, and the volume of the insulating layered compound is directly increased by using a 100 μm aperture as an aperture by the multisizer type II of the Coulter counter. The number distribution is measured to calculate the volume distribution and the number distribution. Then, the volume-based weight average particle diameter obtained from the volume distribution was obtained. At this time, the average particle diameter of mica-1 was 18.360 μm. In addition, the particle size distribution D is assigned to the following equation using the particle diameter at the time of D (10%), D (50%), D (90%),
D = (D (90) -D (10)) / D (50)
The particle size distribution was determined. At this time, the particle size distribution D of mica-1 was 1.91.

  Furthermore, regarding the dielectric characteristics of the charging member, the charging member is left in an environment of L / L (low temperature and low humidity: 15 ° C., 10% RH) for 24 hours, and the cylindrical electrode (metal roller) 31 shown in FIG. (Used together with a 1296 type dielectric constant measurement interface and 1260 type impedance analyzer manufactured by Solartron, UK) Using a dielectric constant measuring device composed of S3 and the like, the measurement was performed at an applied voltage of 3 V and a measurement frequency of 0.1 Hz to 1 MHz.

At this time, an impedance characteristic as shown in FIG. 8 is obtained. As shown in FIG. 9, the resistance of the conductive elastic layer when the charging member is an equivalent circuit in parallel with RC at the conductive elastic layer / surface layer / interface. The analysis was performed with the electrostatic capacity being R1 and C1, and the resistance and electrostatic capacity of the surface layer being R2 and C2. From the analysis results, R1 is 8.51 × 10 ⁵ Ω, R2 is 9.21 × 10 ⁵ Ω, C1 is 5.02 × 10 ⁻¹⁰ F, C2 is 6.39 × 10 ⁻⁸ F, and R2 / R1 = 1.082 and C2 / C1 = 127.414.

(Evaluation of charging member)
Using the charging member obtained as described above, image evaluation was performed as follows.

  The electrophotographic laser printer used in this test is a reverse development type A4 vertical output machine equipped with a process cartridge having a charging member and a photosensitive member integrally. The output speed of the recording medium is 100 mm / sec, 30 mm. / Sec and the image resolution is 600 dpi.

  The photoreceptor is a photosensitive drum in which an organic photoreceptor layer (OPC layer) having a film thickness of 15 μm is coated on an aluminum cylinder, and the outermost layer is a charge transport layer using a modified polycarbonate as a binder resin. The toner was obtained by polymerizing a random copolymer of styrene and butyl acrylate containing a charge control agent, a pigment and the like centering on wax, and further polymerizing a thin polyester layer on the surface to externally add silica fine particles. This toner is a polymerized toner having a glass transition temperature of 63 ° C. and a volume average particle diameter of 6 μm.

  All image evaluations were performed in a low-temperature and low-humidity environment (L / L: 15 ° C., 10% RH), and A4 halftone (image that draws a horizontal line with a width of 1 dot and an interval of 2 dots in the direction perpendicular to the rotation direction of the photoconductor). The image was output at an initial output speed of 100 mm / sec and 30 mm / sec and after endurance of 6000 sheets, and the charging uniformity was visually observed. A case where no uneven charging occurred was indicated by ◎, a case where a little occurred at the edge of the image was indicated by ○, a case where intermediate occurrence occurred was indicated by Δ, and a case where unevenness was extremely large was indicated by ×.

  The charging member of Example 1 showed no uneven charging even after the endurance of 6000 sheets in the L / L environment.

[Example 2]
(Formation of conductive elastic layer-2)
Epichlorohydrin rubber (trade name “Epichromer CG105”: manufactured by Daiso Corporation) 75 parts by mass, NBR (trade name “N230S”: manufactured by JSR Corporation) 25 parts by mass, MT carbon (trade name “HTC # 20”) as a filler ": Nippon Nikka Carbon Co., Ltd.) 35 parts by mass, 5 parts by mass of zinc oxide and 1 part by mass of stearic acid were kneaded with an open roll for 30 minutes, and further a vulcanization accelerator (DM: di-2-benzothiazolyl disulfide). 1 part by mass, 2.5 parts by mass of a vulcanization accelerator (TBT: tetrabutylthiuram disulfide) and 0.8 parts by mass of sulfur as a vulcanizing agent were added, and the mixture was further kneaded with an open roll for 15 minutes.

  The obtained kneaded material was obtained by the same molding method as in Example 1 to obtain a conductive elastic layer having a 10-point average roughness (Rz) of 5.1 μm and a deflection of 17 μm.

  The hardness was 71 degrees (Asker C).

As a directly insulating layered compound, mica-2 (trade name “NCC-180”: manufactured by Yamaguchi Mica Industry Co., Ltd.) was attached in the same manner as in Example 1 to obtain a charging member. The adhesion amount at this time was 0.15 mg / cm ² .

  Mica-2 had an average particle size of 9.566 μm and a particle size distribution D of 1.71.

As a result of analysis from the impedance characteristics, R1 is 3.11 × 10 ⁶ Ω, R2 is 2.54 × 10 ⁶ Ω, C1 is 1.61 × 10 ⁻¹⁰ F, and C2 is 1.68 × 10 ⁻⁸ F. , R2 / R1 = 0.819, C2 / C1 = 104.35.

  In the charging member of Example 2, the charging unevenness did not occur at all even after the endurance of 6000 sheets in the L / L environment.

[Example 3]
The same conductive elastic layer as in Example 1 was used.

As a directly insulating layered compound, mica-3 (trade name “Silane cup-treated NCC-322”: manufactured by Yamaguchi Mica Kogyo Co., Ltd.) was attached in the same manner as in Example 1 to obtain a charging member. The adhesion amount at this time was 0.30 mg / cm ² .

  Mica-3 had an average particle diameter of 17.19 μm and a particle size distribution D of D = 1.65.

As a result of analysis from the impedance characteristics, R1 is 4.80 × 10 ⁵ Ω, R2 is 1.63 × 10 ⁶ Ω, C1 is 2.50 × 10 ⁻¹⁰ F, and C2 is 7.04 × 10 ⁻⁹ F. , R2 / R1 = 3.388 and C2 / C1 = 28.138.

  In the charging member of Example 3, the charging unevenness did not occur at all even after the endurance of 6000 sheets in the L / L environment.

[Example 4]
The same conductive elastic layer as in Example 2 was used.

Mica-4 (trade name “MK-300”: manufactured by Coop Chemical Co., Ltd.) was directly attached as an insulating layered compound in the same manner as in Example 1 to obtain a charging member. The adhesion amount at this time was 0.22 mg / cm ² .

  Mica-4 had an average particle size of 15.58 μm and a particle size distribution D of D = 1.82.

As a result of analysis from the impedance characteristics, R1 is 2.94 × 10 ⁶ Ω, R2 is 3.15 × 10 ⁶ Ω, C1 is 1.40 × 10 ⁻¹⁰ F, and C2 is 2.48 × 10 ⁻⁹ F. , R2 / R1 = 1.068 and C2 / C1 = 17.642.

  The charging member of Example 4 had no charging unevenness even after the endurance of 6000 sheets at an initial output speed of 100 mm / sec in an L / L environment. At an output speed of 30 mm / sec, charging unevenness slightly occurred at the edge of the image after the endurance of 6000 sheets.

[Example 5]
The same conductive elastic layer as in Example 1 was used.

As a directly insulating layered compound, montmorillonite (trade name “Esven NX” manufactured by Hojun Co., Ltd.) was attached in the same manner as in Example 1 to obtain a charging member. The adhesion amount at this time was 0.20 mg / cm ² .

  The average particle size of montmorillonite was 40.50 μm, and the particle size distribution D was D = 1.61.

As a result of analysis from the impedance characteristics, R1 is 4.74 × 10 ⁵ Ω, R2 is 4.70 × 10 ⁶ Ω, C1 is 3.77 × 10 ⁻¹⁰ F, and C2 is 2.36 × 10 ⁻⁸ F. , R2 / R1 = 9.909 and C2 / C1 = 62.649.
In the charging member of Example 4, in the L / L environment, the output speed was 100 mm / sec and 30 mm / sec.

[Comparative Example 1]
The same conductive elastic layer as in Example 2 was used.

As a directly insulating layered compound, mica-5 (trade name “MK-100” manufactured by Co-op Chemical Co., Ltd.) was attached in the same manner as in Example 1 to obtain a charging member. The adhesion amount at this time was 0.05 mg / cm ² .

  Mica-5 had an average particle size of 4.230 μm and a particle size distribution D of D = 1.41.

As a result of analysis from the impedance characteristics, R1 is 1.44 × 10 ⁶ Ω, R2 is 3.35 × 10 ⁷ Ω, C1 is 5.29 × 10 ⁻¹⁰ F, and C2 is 1.62 × 10 ⁻⁹ F. , R2 / R1 = 23.92 and C2 / C1 = 3.055.

  In the charging member of Comparative Example 1, the initial charging uniformity at the output speed of 30 mm / sec in the L / L environment was such that slight charging unevenness was observed at the image edge, but at 100 mm / sec, the black streak was Many occurred. After the endurance of 6000 sheets, the output speed was 30 mm / sec, and charging unevenness occurred in the center of the image. At 100 mm / sec, black streaks due to numerous charging unevenness occurred on the front of the image.

[Comparative Example 2]
The same conductive elastic layer as in Example 1 was used.

As a directly insulating layered compound, mica-6 (trade name “A-61” manufactured by Yamaguchi Mica Kogyo) was attached in the same manner as in Example 1 to obtain a charging member. The adhesion amount at this time was 2.50 mg / cm ² .

  The average particle size of mica-6 was 51.10 μm, and the particle size distribution D was D = 1.31.

As a result of analysis from the impedance characteristics, R1 is 2.40 × 10 ⁵ Ω, R2 is 1.03 × 10 ⁸ Ω, C1 is 4.59 × 10 ⁻¹⁰ F, and C2 is 2.37 × 10 ⁻⁹ F. , R2 / R1 = 429.951 and C2 / C1 = 5.177.

  The charging member of Comparative Example 2 had many black streaks in the initial charging uniformity at an output speed of 100 mm / sec in an L / L environment, and charging unevenness was observed at the center of the image at 30 mm / sec. After the endurance of 6000 sheets, the output speed was 100 mm / sec and 30 mm / sec, and black streaks due to a large number of uneven charging occurred on the front surface of the image.

[Comparative Example 3]
The same conductive elastic layer as in Example 1 was used.

Surface-treated silica (trade name “RX-200”: manufactured by Nippon Aerosil Co., Ltd.) was attached as a directly insulating compound by the same method as in Example 1 to obtain a charging member. The adhesion amount at this time was 0.20 mg / cm ² .

  The surface-treated silica had an average particle size of 0.012 μm and a particle size distribution D of D = 1.51.

As a result of analysis from the impedance characteristics, R1 is 3.15 × 10 ⁵ Ω, R2 is 5.41 × 10 ⁶ Ω, C1 is 3.01 × 10 ⁻¹⁰ F, and C2 is 2.60 × 10 ⁻⁹ F. , R2 / R1 = 17.144 and C2 / C1 = 8.633.

  In the charging member of Comparative Example 3, in the L / L environment, the output speed was 100 mm / sec and 30 mm / sec, and the initial charging uniformity had many white spots due to overcharging due to uneven adhesion. Even after the endurance of 6000 sheets, the output speed was 100 mm / sec and 30 mm / sec, and many white spots remained on the entire image.

[Comparative Example 4]
The same conductive elastic layer as in Example 1 was used.

As a directly insulating compound, surface-treated titanium oxide (trade name “T-805”: manufactured by Nippon Aerosil Co., Ltd.) was attached in the same manner as in Example 1 to obtain a charging member. The adhesion amount at this time was 0.30 mg / cm ² .

  The average particle diameter of the surface-treated titanium oxide was 0.021 μm, and the particle size distribution D was D = 1.46.

As a result of analysis from the impedance characteristics, R1 is 5.00 × 10 ⁵ , R2 is 1.46 × 10 ⁷ , C1 is 4.67 × 10 ⁻¹⁰ , C2 is 1.16 × 10 ⁻⁸ , and R2 / R1 = 29.140, C2 / C1 = 24.911.

  In the charging member of Comparative Example 4, in the L / L environment, the initial charging uniformity at an output speed of 100 mm / sec was such that slight charging unevenness was observed at the edge of the image. Many occurred. Further, in the image at an output speed of 100 mm / sec after the endurance of 6000 sheets, a little black streak occurred at the center of the image, but at 30 mm / sec, black streaks due to a large number of charging unevenness occurred on the front surface of the image.

[Comparative Example 5]
The same conductive elastic layer as in Example 1 was used.

Graphite (trade name “CMX” manufactured by Nippon Graphite Industries Co., Ltd.) was attached as a conductive layered compound in the same manner as in Example 1 to obtain a charging member. The adhesion amount at this time was 0.25 mg / cm ² .

  The average particle size of graphite was 40.00 μm, and the particle size distribution D was D = 1.52.

As a result of analysis from the impedance characteristics, R1 is 2.96 × 10 ⁴ , R2 is 1.70 × 10 ² , C1 is 2.98 × 10 ⁻⁹ , C2 is 1.85 ⁻ × 10 ¹⁰ , and R2 / R1 = 0.006 and C2 / C1 = 0.062.

  In the charging member of Comparative Example 5, the initial charging uniformity at the output speed of 100 mm / sec in the L / L environment was such that slight charging unevenness was observed at the image edge, but at 30 mm / sec, the black streak was Many occurred. Further, in the image at an output speed of 100 mm / sec after the endurance of 6000 sheets, a little black streak occurred at the center of the image, but at 30 mm / sec, black streaks due to a large number of charging unevenness occurred on the front surface of the image.

  FIG. 1 shows the relationship between the resistance ratio of the conductive elastic layer and the surface layer of the charging members of Examples 1 to 5 and Comparative Examples 1 to 5 and the capacitance ratio.

It is a figure which shows the relationship between the resistance ratio of an electroconductive elastic-body layer of the charging member of this invention, and a surface layer, and a capacitance ratio. It is the schematic which shows an example of the cross section of the charging roller which is a charging member of this invention. It is a figure which shows the particle size distribution dependence of the dynamic friction coefficient of the direct insulation layered compound of this invention. It is the outline of the static friction coefficient measuring device of the charging member of the present invention. It is the outline of the chart obtained with the dynamic friction coefficient measuring device of the charging member of the present invention. 1 is a schematic diagram illustrating an example of an image forming apparatus (electrophotographic apparatus) according to the present invention. It is the schematic which shows the charging roller impedance measuring apparatus which is a charging member of this invention. It is the outline of the characteristic view obtained by the impedance measurement of the charging member of the present invention. It is the schematic which shows RC equivalent circuit model of the charging member of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Conductive support body 12 Conductive elastic body layer 13 Surface layer 21 Image carrier (electrophotographic photoreceptor)
22 Charging member (charging roller)
23 exposure means 24 developing means 24a toner carrier 24b stirring portion 24c toner regulating member 25 transfer means 26 cleaning means
31 Cylindrical electrode (metal roller)
32 Fixed resistor 33 Recorder (recorder)
L Laser light S1, S2 Bias applied power source S3 Dielectric constant measurement system P Transfer material

Claims (8)

The charging member is composed of a conductive support, a conductive elastic layer provided on the conductive support, and a surface layer provided on the outer periphery thereof, and the resistance of the conductive elastic layer , When the capacitance is R1 and C1, respectively, and the resistance and capacitance of the surface layer are R2 and C2, respectively,
C2 / C1 ≧ 6.3 × (R2 / R1) ^0.6
A charging member. The charging member is composed of a conductive support, a conductive elastic layer provided on the conductive support, and a surface layer provided on the outer periphery thereof. It is composed of an insulating layered compound, and the average particle size of the directly insulating layered compound is 5 to 50 μm, and the particle size distribution when the cumulative number% is 10% is D (10), 50% A charging member characterized in that D represented by the following formula satisfies D> 1.6 when the particle size is D (50) and the particle size at 90% is D (90).
D = (D (90) -D (10)) / D (50)   The charging member according to claim 2, wherein the directly insulating layered compound is a silicate mineral mainly composed of clay.   The silicate mineral is composed of any one of kaolin group, talc-pyroferrite group, smectite group, vermiculite group, mica group, brittle mica group, chlorite group, and a mixture thereof. Charging member.   The charging member according to claim 3, wherein the silicate mineral is surface-treated with a coupling agent. The charging member according to any one of claims 3 to 5 weight attached to the conductive elastic body on該珪salt minerals, characterized in that a 0.1 to 2.0 mg / cm ^2.   An image bearing member, the charging member according to claim 1 for charging the image bearing member to a predetermined potential, an exposure unit for forming an electrostatic latent image on a charging surface of the image bearing member, and the image An image forming apparatus comprising: a developing unit that transfers toner to a latent image formed on a carrier for visualization, and forms a toner image; and a transfer unit that transfers the toner image to a transfer member. An image forming apparatus, wherein the charging means includes the charging member, and the image bearing member is charged by applying only a DC voltage to the charging member.   A process cartridge which integrally supports the image carrier and the charging member according to any one of claims 1 to 6 and is detachable from a main body of the image forming apparatus.

Images