JP5173247B2 - Charging member, process cartridge, and electrophotographic apparatus - Google Patents

Description

  The present invention relates to a charging member, a process cartridge using the charging member, and an electrophotographic apparatus.

  In an electrophotographic apparatus using an electrophotographic system such as a copying machine, a laser beam printer, a facsimile machine, or a printing machine, the surface of the photosensitive member is uniformly charged, and a latent image is formed on the surface by exposure means. At this time, as a primary charging method for charging the surface of the photoreceptor, a contact charging method is frequently used because low ozone and low power can be achieved. Among them, a roller charging system that uses a conductive elastic roller as a charging member, presses and contacts the photosensitive member, and generates a discharge by applying a voltage to the photosensitive member to charge the photosensitive member is a point of charge stability. And is widely used.

  As a contact charging method, there is a DC charging method in which charging is performed by applying a direct current voltage (DC voltage) obtained by adding a required photoreceptor surface potential Vd to a discharge start voltage to a charging member. Specifically, the direct current voltage (DC voltage) applied to the charging member is about 550 V when the charging roller is brought into pressure contact with an OPC (Organic Photo Conductor) photosensitive member. This is a voltage (DC voltage) obtained by adding the body surface potential Vd. In addition, in order to improve potential fluctuation due to the environment and long-term use, an alternating current component (AC component) having a peak-to-peak voltage more than twice the discharge start voltage to a DC voltage corresponding to the required photoreceptor surface potential Vd. There is an AC charging method in which charging is performed by applying a voltage superimposed on the charging member.

  Compared with the AC charging method, the DC charging method generally has a small amount of power consumption and is inexpensive, and has an advantage that the apparatus is small and can save space. However, compared with the AC charging method, the DC charging method has a narrow discharge area and does not have the effect of equalizing the AC discharge current, so that streak-like charging failure due to minute resistance value unevenness of the charging member is likely to occur. There are challenges.

  In order to deal with such a problem in the DC charging method, a method (Patent Document 1) has been proposed in which organic fine particles are included in the surface layer of the charging member to form unevenness (patent document 1).

  However, in the charging member described in Patent Document 1, an external additive or the like contained in the developer adheres through the surface of the photosensitive member with time, and may accumulate on the concave portion, resulting in a decrease in charging ability. . Furthermore, in recent years, due to the demand for higher image quality in the electrophotographic apparatus market, the toner has become smaller in particle size and the proportion of fine particle toner has increased. Various external additives are contained, and therefore the degree of contamination of the charging member tends to increase.

In addition, due to the demand for longer life of the electrophotographic apparatus, in the unit including the charging member and the photosensitive member, the amount of deposits on the charging member increases as the number of image formation increases, and image defects that did not occur conventionally May also occur in the latter half of the endurance life. Particularly in a low-humidity environment, the charging ability is likely to decrease due to the deposits on the charging member recesses. For this reason, unevenness on the surface for improving streak-like charging failure may hinder the effect, and image quality may deteriorate.
JP 2003-316112 A

  An object of the present invention is to provide uniform charging of an object to be charged, in particular, even in a low humidity environment, over a long period of time, and to achieve high image quality, color, long life, and miniaturization. An object of the present invention is to provide a charging member suitable for a photographic apparatus, particularly a DC charging system. Furthermore, even if a developer containing finely divided toner and various external additives is used in order to improve image quality, color, long life, and miniaturization, it is possible to suppress image defects due to poor charging of the charged body. The object is to provide a photographic apparatus and a process cartridge used therefor. In particular, it is an object to provide an electrophotographic apparatus suitable for a DC charging system capable of suppressing image defects due to defective charging even in a low humidity environment, and a process cartridge used therefor.

  The present inventors have studied in order to achieve stable charging of an object to be charged by a DC charging method. First, an investigation was made on the charged state of a photoreceptor to be charged based on observation of the discharge state between the charging member and the photoreceptor.

  When a charging member in which carbon black is contained in a binder resin and resin particles are contained in a conductive surface layer to form convex portions on the surface is used, the upstream side and the downstream side of the nip portion with the photoreceptor In addition to the discharge, it was confirmed that a discharge occurred in the nip portion (FIG. 9). However, when a conductive charging member having a smooth surface not containing resin particles is used, discharge occurs only on the upstream side and downstream side of the nip portion with the photoconductor (FIG. 8), and no discharge is observed in the nip portion. It was.

  When a charging member having a convex portion is used, in addition to the discharge between the photosensitive member and the charging member on the upstream and downstream sides of the nip portion, the reason why discharge occurs in the nip portion is It was considered that a minute gap was formed between the body. When a charging member having a convex portion is used, if the charging of the photosensitive member is uneven due to the discharge on the upstream side of the nip portion, it is evenly leveled by the discharge in the minute gap of the nip portion, and there is no convex portion. Compared to the case where a charged body was used, it was considered that the photoreceptor could be charged more uniformly.

  In addition, in charging members having convex portions on the surface, streaky charging failure occurs in the latter half of the endurance life. External additives or the like adhere to the concave portions and the surface of the conductive charging member is covered so that electrons due to discharge are generated. It was thought that the charging ability was lowered without reaching the surface of the photoreceptor (FIG. 10).

  Therefore, even when the surface of the concave portion of the conductive surface layer is covered with an external additive, etc., by making the convex portion conductive, discharge is generated between the slope of the convex portion and the photoreceptor. The knowledge that it can be made (FIG. 1) was acquired. This is the case where the convex portions are made conductive by the conductive resin particles, and the discharge can be maintained between the inclined surface and the photosensitive member, and an external additive or the like adheres to the concave portion of the charging member in the latter half of the durability life. However, it has been found that the occurrence of streak-like image defects caused by charging defects can be suppressed.

  In addition, there are not only streak-like images but also spot-like images and uneven images as charging failure images due to contamination of the charging member. By using a charging member with conductive projections, the occurrence of these image failures is suppressed. Gained the knowledge of being. Based on these findings, the present invention has been completed.

  That is, a charging member for contact charging having a conductive substrate and a conductive surface layer, the surface layer including a binder resin and resin particles dispersed in the binder resin, and the resin particles on the surface The surface roughness Rzjis on the surface is 3 μm or more and 20 μm or less, the resin particles have an average particle diameter of 1 μm or more and 30 μm or less, contain an ionomer resin, and are conductive. It is related with the charging member characterized by having.

  The present invention also relates to a process cartridge comprising the above charging member and a member to be charged and detachably integrated with the main body of the electrophotographic apparatus.

  The present invention also relates to an electrophotographic apparatus comprising the charging member, an object to be charged, an exposure unit, a developing unit, and a transfer unit.

  According to the charging member of the present invention, uniform charging of an object to be charged, in particular, uniform charging can be performed over a long period even in a low humidity environment. For this reason, it can be used for a DC charging method in which demands for unevenness in electrical resistance are severe, and it is possible to achieve low power consumption and space saving by downsizing the apparatus. Furthermore, it is suitable for high-quality, color, long-life, and miniaturized electrophotographic devices that use developer containing finely divided toner and various external additives. Is excellent in durability. For example, uniform charging can be stably performed even for a high-definition image such as a halftone image of 600 dpi.

  In addition, the electrophotographic process cartridge and the electrophotographic apparatus of the present invention can achieve high image quality, color, long life, miniaturization, and low power consumption, and these excellent features can be achieved particularly in a low humidity environment. An effect is obtained.

  The charging member of the present invention is a charging member for contact charging having a conductive substrate and a conductive surface layer having a convex portion derived from the resin particles formed on a binder resin in which resin particles are dispersed. is there. Further, the resin particles contain an ionomer resin that imparts conductivity to the resin particles, the average particle diameter is 1 μm or more and 30 μm or less, and the surface roughness Rzjis on the surface is 3 μm or more and 20 μm or less. To do.

[Conductive substrate]
The conductive substrate in the charging member of the present invention preferably has a conductive support and a conductive elastic layer formed thereon.

  The conductive support supports a conductive elastic layer, a surface layer, and the like provided thereon, and has a strength that can sufficiently withstand a load caused by contact with a charged body. Examples of the shape include a columnar shape and a cylindrical shape. Materials for the conductive support include metals such as iron, aluminum, titanium, copper and nickel; carbon steel, stainless steel, duralumin, brass and bronze alloys containing these metals; carbon black and carbon fibers are hardened with plastic And a rigid resin material. For these conductive supports, those subjected to plating such as nickel plating or oxidation treatment can be used as rust prevention measures. Examples of the thickness of the plating include 0.1 to 30 μm.

  The conductive elastic layer is provided to give the charging member the elasticity required in the apparatus used in order to ensure contact with the charged body without damaging the charged body. The conductive elastic layer may be either a solid or a foam, and may be a single layer or two or more layers.

  The conductive elastic layer is mainly formed of a conductive agent and a polymer elastic body. Specific examples of the polymer elastic body include the following. Thermoplastic elastomer of epichlorohydrin rubber, NBR (nitrile rubber), chloroprene rubber, urethane rubber, silicone rubber, SBS (styrene / butadiene / styrene / block copolymer), SEBS (styrene / ethylene butylene / styrene / block copolymer). Among these, epichlorohydrin rubber, in particular, has the conductivity of the middle resistance region, and the elastic layer can have a desired conductivity even when the amount of the conductive agent added is reduced, resulting in variations in electrical resistance. Can be reduced, which is preferable.

  Specific examples of the epichlorohydrin rubber include the following. Epichlorohydrin homopolymer, epichlorohydrin-ethylene oxide copolymer, epichlorohydrin-allyl glycidyl ether copolymer, epichlorohydrin-ethylene oxide-allyl glycidyl ether terpolymer. Of these, epichlorohydrin-ethylene oxide-allyl glycidyl ether terpolymer is preferred because it exhibits stable conductivity in the medium resistance region. The epichlorohydrin-ethylene oxide-allyl glycidyl ether terpolymer can control conductivity and workability by arbitrarily adjusting the degree of polymerization and composition ratio. As the polymer elastic body, those containing epichlorohydrin rubber as a main component and containing other general rubber as required are preferable.

  Examples of general rubber used for the elastic polymer having the epichlorohydrin rubber as a main component include the following. EPM (ethylene propylene rubber), EPDM (ethylene propylene rubber), NBR (nitrile rubber), chloroprene rubber, natural rubber, isoprene rubber, butadiene rubber, styrene-butadiene rubber, urethane rubber, silicone rubber. Thermoplastic elastomers of SBS (styrene / butadiene / styrene block copolymer) and SEBS (styrene / ethylene butylene / styrene block copolymer). The content of these general rubbers is preferably 1 to 50% by mass with respect to the total amount of the polymer elastic body.

  Examples of the conductive agent contained in the conductive elastic layer include an ionic conductive agent and an electronic conductive agent, but it is preferable to use an ionic conductive agent. An ionic conductive agent can be uniformly dispersed in a polymer elastic body, can form a conductive elastic layer having a uniform electrical resistivity, and can evenly charge an object to be charged even in DC charging. Is possible.

  Examples of the ionic conductive agent include the following. Inorganic ionic substances such as lithium perchlorate, sodium perchlorate, and calcium perchlorate. Cationic surfactants of lauryl trimethyl ammonium chloride, stearyl trimethyl ammonium chloride, octadecyl trimethyl ammonium chloride, dodecyl trimethyl ammonium chloride, hexadecyl trimethyl ammonium chloride, trioctyl propyl ammonium bromide, modified aliphatic dimethyl ethyl ammonium etosulphate. Zwitterionic surfactants of lauryl betaine, stearyl betaine, and dimethylalkyl lauryl betaine. Tetraethylammonium perchlorate, tetrabutylammonium perchlorate, quaternary ammonium salt of trimethyloctadecylammonium perchlorate; organic acid lithium salt of lithium trifluoromethanesulfonate. These can be used alone or in combination of two or more. Of these, perchloric acid quaternary ammonium salts can be particularly preferably used because of their resistance to environmental changes.

  Examples of the electronic conductive agent include the following. Metal powders and fibers of aluminum, palladium, iron, copper, silver; metal oxides of titanium oxide, tin oxide, and zinc oxide. Appropriate surface treatment of tin oxide, antimony oxide, indium oxide, molybdenum oxide, zinc, aluminum, gold, silver, copper, chromium, cobalt, iron, lead, platinum, or rhodium, electrolytic coating, or mixing Powder attached by shaking. Carbon powder of furnace black, thermal black, acetylene black, ketjen black, PAN (polyacrylonitrile) carbon and pitch carbon.

  As said furnace black, the following can be mentioned, for example. SAF-HS, SAF, ISAF-HS, ISAF, ISAF-LS, I-ISAF-HS, HAF-HS, HAF, HAF-LS, T-HS, T-NS, MAF, FEF, GPF, SRF-HS- HM, SRF-LM, ECF, FEF-HS. Moreover, as thermal black, FT and MT can be mentioned, for example.

  These ionic conductive agents and electronic conductive agents can be used alone or in combination of two or more.

As the blending amount of the conductive agent to be blended in the conductive elastic layer, the volume resistivity of the conductive elastic body is such that the volume resistivity of the middle resistance region is 1 × 10 ⁴ to 1 × 10 ⁸ Ω in any environment. -It is preferable to select so that it may become cm. Low temperature and low humidity environment (environment 1: 15 ° C / 10% RH), normal temperature and normal humidity environment (environment 2: 23 ° C / 50% RH), high temperature and high humidity environment (environment 3: 30 ° C / 80% RH) Is mentioned. If the volume resistivity of the conductive elastic layer is 1 × 10 ⁴ Ω · cm or more, even if there is a pinhole in the charged body, the applied voltage drop due to the concentration of discharge in the pinhole is suppressed, It is possible to suppress the occurrence of image defects that occur as a band on a fine halftone image. Moreover, it can suppress making a pinhole larger. When the volume resistivity of the conductive elastic layer is 1 × 10 ⁸ Ω · cm or less, it is possible to avoid applying a high voltage to obtain a desired charging potential.

  As the volume resistivity, a value measured by the following measurement method can be adopted. A metal is vapor-deposited on both surfaces of a sample formed into a sheet having a thickness of 1 mm using a conductive elastic layer raw material to produce an electrode and a guard electrode. A voltage of 200 V is applied using a microammeter (ADVANTEST R8340A ULTRA HIGH RESISTANCE METER (manufactured by Advantest)), and the current after 30 seconds is measured. The volume resistivity is calculated from the film thickness and the electrode area.

  If necessary, a plasticizer, a filler, a vulcanizing agent, a vulcanization accelerator, an anti-aging agent, a scorch preventing agent, a dispersant, and a release agent may be added to the conductive elastic layer. .

  As the shape of the conductive elastic layer, when the charging member is in the shape of a roller, in order to ensure uniform adhesion between the charging member and the object to be charged, the central portion is thick and has a thin crown shape toward both ends. preferable. In roller-shaped charging members, the crown shape generally cancels the difference between the pressing force at the center and both ends because a predetermined pressing force is applied to both ends of the conductive support to bring it into contact with the object to be charged. Even if the straightness of the roller is not sufficient, uneven charging can be suppressed.

  As the crown amount of the conductive elastic layer, a range in which the nip width between the charging member and the charged body can be uniform at the center and both ends of the charging member can be selected and is 5.0% or less of the roller diameter. Is preferred. Specifically, in the case of a roller having a diameter of about 12 mm, 600 μm or less is preferable.

  Here, the crown amount is an amount that specifies the crown shape based on the difference in diameter between the center portion and both end portions. Specifically, for example, in the case of a roller of about 250 mm in the axial direction, the diameter D1 of the central portion in the axial direction of the roller and the average of the two values of the diameters D2 and D3 of the portion on the end side of 90 mm from the central portion in the axial direction The difference {D1− (D2 + D3) / 2} is taken as the value of the crown amount.

  The thickness of the conductive elastic layer can be set to 0.5 to 5.0 mm, for example. In the case of a roller-shaped charging member, in order to make the nip width at the time of rotation uniform, it is preferable that the difference in outer diameter of the conductive elastic layer is 0.5% or less of the diameter of the central portion of the roller. More preferably, it is 0.25% or less. For example, when the diameter of the roller is about 12 mm, the value of deflection is specifically preferably 60 μm or less, and more preferably 30 μm or less.

  For the runout of the roller on which the conductive elastic layer is formed, it is possible to adopt a measured value measured using a non-contact laser length measuring device (LS-5000: manufactured by Keyence Corporation) shown in the schematic configuration diagram of FIG. it can. Specifically, the conductive support on which the conductive elastic layer is formed is rotated as a rotation axis, the distance from the central axis to the surface of the conductive elastic layer is measured perpendicular to the rotation axis, and the maximum value during one rotation is obtained. The difference between the minimum values is obtained, and this measurement is performed at a pitch of 1 cm in the axial direction, and the maximum value is set as the shake value. Similarly, the diameter of the roller refers to the maximum value and the minimum value from the rotation axis to the roller surface measured by a non-contact laser measuring instrument perpendicularly to the rotation axis. It can be an average.

  The hardness of the conductive elastic layer is preferably 70 ° or less, more preferably 60 ° or less in terms of micro hardness (MD-1 type). If the micro hardness (MD-1 type) is 70 ° or less, the width of the nip portion between the charging member and the member to be charged is sufficient, and this causes uneven charging on the upstream side of the nip portion. Thus, the charged object can be stably charged. Further, it is possible to suppress the developer or the like from adhering to the surface of the member to be charged or the charging member.

  Examples of the method for adjusting the hardness of the conductive elastic layer include a method of imparting flexibility by including a plasticizer. The content of the plasticizer is preferably 1 part by mass to 30 parts by mass, and more preferably 3 parts by mass to 20 parts by mass. As the plasticizer, it is preferable to use a polymer type. The molecular weight of the polymer plasticizer is preferably 2000 or more, more preferably 4000 or more. When the molecular weight is 2000 or more, contamination of the member to be charged due to leaching of the plasticizer from the conductive elastic layer can be suppressed.

  Here, the micro hardness (MD-1 type) is the hardness of the charging member measured using an Asker micro rubber hardness meter MD-1 type (manufactured by Kobunshi Keiki Co., Ltd.). As the value of micro hardness (MD-1 type), the conductive elastic layer of the object to be measured is allowed to stand for 12 hours or more in an environment of normal temperature and normal humidity (23 ° C./55% RH). The measured value in the peak hold mode can be adopted.

  As a method for forming the conductive elastic layer, a polymer elastic body of the conductive elastic layer material, a conductive agent, and other compounding agents are mixed in a closed mixer, for example, extrusion molding, injection molding, or compression. It is preferable to mold by a molding method. Even if the conductive elastic layer is formed directly on the conductive support, the conductive elastic layer is formed by covering the conductive support with a tube or sheet formed in advance as a conductive elastic layer. May be. After the production of the conductive elastic layer, the surface can be polished to adjust the shape.

  When the conductive elastic layer is molded as a molded body, it may be bonded to the conductive support through an adhesive as necessary. The adhesive is preferably conductive, and the conductive agent is contained in a urethane-based, acrylic-based, polyester-based, polyether-based, or epoxy-based adhesive using a thermosetting resin or a thermoplastic resin as a binder. Things can be used. As the conductive agent, specifically, those similar to those exemplified as the conductive agent used for the conductive elastic layer can be used alone or in combination of two or more.

[Surface layer]
The surface layer in the charging member of the present invention is conductive, is formed of a binder resin in which resin particles are dispersed, and has a convex portion derived from the resin particles on the surface.

[Resin particles]
The resin particles contained in the surface layer form a convex portion on the surface of the surface layer, thereby forming a discharge space between the surface of the charged body and the nip portion of the surface of the surface layer. It is preferable that the resin particles are made of a polymer compound resin, which has appropriate flexibility and elasticity, and does not have the possibility of damaging the member to be charged as compared with the inorganic fine particles. The resin particles have conductivity in order to enable stable charging even when the surface layer other than the convex portions is covered with the deposit.

  An ionomer resin is used as a conductive substance that imparts conductivity to the resin particles. Ionomer resins that are stable with respect to temperature and humidity can impart stable conductivity to the resin particles even with respect to changes in external factors. It is preferable because charging can be realized.

  Such an ionomer resin has a structure in which a polymer having a small amount of hydrophilic ionic groups (salts such as carboxylic acid and sulfonic acid) in a hydrophobic main chain of the polymer is crosslinked with metal ions. Specifically, an ethylene-unsaturated carboxylic acid copolymer can be mentioned as a preferable one. Preferred examples of the ethylene-carboxylic acid copolymer include a copolymer of ethylene and an unsaturated carboxylic acid having 3 to 6 carbon atoms, such as acrylic acid, methacrylic acid, maleic acid, and fumaric acid. The chemical formulas of these unsaturated carboxylic acid units in the ethylene copolymer are shown below.

Examples of the ion source of the metal ions that are bonded to the carboxyl group of these ethylene-carboxylic acid copolymers to form a bridge include alkali metals, alkaline earth metals, and transition metals. Specific examples of the ion source include sodium, potassium, rubidium, cesium, zinc, lithium, magnesium, manganese, calcium, and cobalt. Among these, an alkali metal is preferable as the ion source in order to make the resin particles have a suitable conductivity, for example, a volume resistivity of 1.0 × 10 ⁶ Ω · cm to 1.0 × 10 ¹⁰ Ω · cm. More preferably, they are potassium, rubidium, and cesium. The chemical formula of potassium ionomer of ethylene-acrylic acid is shown below.

  Such an ionomer resin is easily and uniformly mixed with the resin constituting the resin particles, and it is presumed that the resin particles can be imparted with conductivity in the middle resistance region, and stable uniform discharge can be realized. These ionomer resins are preferable because they are stable against changes in temperature and humidity, and the resin particles containing them have stable conductivity.

  The resin particles can be formed of only an ionomer resin, but other resins and additives may be mixed. Examples of the additive further include a conductive agent such as polyoxyethylene glycol, polyoxyalkylene glycol, and aliphatic polyhydric alcohol in order to impart conductivity.

The volume resistivity of the resin particles is preferably 1.0 × 10 ⁶ Ω · cm or more and 1.0 × 10 ¹⁰ Ω · cm or less. More preferably, it is 1.0 × 10 ⁷ Ω · cm or more and 1.0 × 10 ⁹ Ω · cm. If the volume resistivity is 1.0 × 10 ⁶ Ω · cm or more, the charged body can be stably charged. For example, at high temperature and high humidity and normal temperature and normal humidity, it is possible to suppress the occurrence of streak-like images and pinhole leak images due to overdischarge in some low resistance portions of the resin particles. When the volume resistivity is 1.0 × 10 ¹⁰ Ω · cm or less, discharge can be promoted, and for example, generation of a poorly charged image due to dirt on the surface of the charging member can be suppressed.

Here, the measured value by the following measuring methods can be employ | adopted for the volume resistivity of the resin particle. First, an appropriate amount of resin particles is put into a resistance measuring device manufactured by Mitsubishi Chemical Corporation and compressed by applying a pressure of 10.1 MPa (102 kgf / cm ² ) as a measurement target sample. A microammeter (trade name: ADVANTEST R8340A ULTRA HIGH RESISTANCE METER, manufactured by Advantest Co., Ltd.) is connected to this device, a voltage of 200 V is applied, and a current after 30 seconds is measured. And it calculates from the thickness of a sample, and an electrode area, and calculates | requires volume resistivity.

  The resin particles have an average particle size of 1 μm to 30 μm, preferably 3 μm to 15 μm. When the particle diameter of the resin particles is 30 μm or less, the charged body can be uniformly charged, and adhesion of toner and external additives to the concave portions of the surface layer can be suppressed. In addition, when the thickness is 1 μm or more, it is possible to form a convex portion that secures a gap that can generate a discharge at the nip portion between the charging member and the member to be charged, and to uniformly charge the member to be charged. .

  As the average particle diameter of the resin particles, a value measured by the following measuring method can be adopted. Measure using a Coulter Counter Multisizer using the powder of resin particles used. Specifically, 0.1 to 5 ml of a surfactant (alkylbenzene sulfonate) is added to 100 to 150 ml of the electrolyte solution, and 2 to 20 mg of measurement resin particles are added thereto. The electrolyte solution in which the resin particles are suspended is dispersed with an ultrasonic disperser for 1 to 3 minutes, and an aperture adjusted to an appropriate resin particle size of 17 μm or 100 μm with a Coulter counter multisizer is used, based on the volume. A particle size distribution of 3 to 64 μm is measured. From the measured particle size distribution, the mass average particle size is determined by computer processing.

  Moreover, the particle diameter of the resin particle contained can also be calculated | required by observing the cross section of a surface layer with a microscope etc. Specifically, the surface layer of the charging member is sliced thinly with a razor or the like so that the cross section can be observed. For example, as shown in FIGS. 3A and 3B, a total of nine cross-sections are taken with an electron microscope at three locations in the axial direction and three locations in the circumferential direction of the roller-shaped charging member. FIG. 3C shows a schematic diagram of a cut section. Except for the particles that have been secondary-aggregated on the image, only 100 primary particles were observed with a transmission electron microscope (TEM), the equivalent circle diameter was calculated from the projected area, the volume average particle diameter was obtained, and the average was calculated. It can be a particle size.

  As content in the surface layer of the said resin particle, 1 to 80 mass% is preferable. When the resin particles are contained in an amount of 1% by mass or more, stable charging can be performed. If the resin particles are 80% by mass or less, adjustment of the viscosity at the time of molding the surface layer becomes easy.

  As a method for producing resin particles in the present invention, a known method can be used, and it is not particularly limited. The resin composition can be prepared by mechanical pulverization or freeze pulverization. Preferably, it is freeze pulverization.

[Binder resin]
As the binder resin constituting the surface layer, a thermosetting resin or a thermoplastic resin can be used. Specific examples include urethane resins, fluorine resins, silicone resins, acrylic resins, and polyamide resins.

  Among these, in particular, a urethane resin obtained by crosslinking a lactone-modified acrylic polyol with an isocyanate is preferably used. By cross-linking the lactone-modified acrylic polyol with an isocyanate, the low molecular weight component from the conductive elastic layer is suppressed and contamination of the charged body is suppressed, and the toner and external additives attached to the surface of the charged body are suppressed. Contamination of the charging member itself with an agent or the like can be suppressed.

  As the isocyanate, an isocyanurate-type trimer serves as a cross-linking point and can form a denser cross-link in the surface layer, so that a low molecular weight component from the conductive elastic layer oozes out to the surface of the charging member. Since it can suppress, it is preferable. Moreover, it is preferable that it is the block isocyanate in which the isocyanate group was blocked by the blocking agent. The reason for this is that the isocyanate group is likely to react, and if the coating material for the surface layer is left at room temperature for a long time, the reaction gradually proceeds and the properties of the coating material may change. . On the other hand, in the blocked isocyanate, active isocyanate groups are blocked, and the reaction does not proceed below the dissociation temperature of the blocking agent. Examples of the blocking agent for masking include phenols, cresol phenols, ε-caprolactam lactams, and methylethylketoxime oximes. Of these, oximes having a relatively low dissociation temperature are preferred.

  As the lactone-modified acrylic polyol, it is preferable that the molecular chain skeleton is a copolymer of styrene and acrylic because appropriate hardness and non-contamination are imparted to the surface layer. In addition, it is preferable to have a modified lactone group having a hydroxyl group at the terminal because it enables formation of a large number of cross-linking points and enables close crosslinking with isocyanate. In the surface layer having crosslinks in the nectar, it is possible to suppress the exudation of low molecular components from the lower layer such as the conductive elastic layer.

  Such a lactone-modified acrylic polyol preferably has an OH value of about 80 KOHmg / g. Since the lactone-modified acrylic polyol has such an OH value, the surface layer becomes flexible due to insufficient crosslinking, the tendency of the charging member to stick to the photoreceptor is suppressed, and the surface layer becomes hard due to excessive crosslinking. Further, it is possible to suppress the occurrence of cracks due to a decrease in impact resistance.

  The blending ratio of the lactone-modified acrylic polyol resin and the isocyanate is the ratio of the number of NCO groups in the isocyanate (A) to the number of OH groups in the lactone-modified acrylic polyol resin (B), NCO / OH ratio (A / B ) Is preferably 0.1 to 2.0. More preferably, it is the range of 0.3-1.5.

  In the binder resin, various additives may be contained in a range that does not impair the function of the constituent of the surface layer, if necessary. Examples of such additives include leveling agents such as silicone oil.

[Conductivity]
Since the surface layer has conductivity, a voltage can be applied to generate a discharge between charged bodies. The volume resistivity of the surface layer is preferably 1.0 × 10 ⁶ Ω · cm or more and 1.0 × 10 ¹⁵ Ω · cm or less in the middle and high resistance regions in the above environments 1 to 3, respectively. If the volume resistivity of the surface layer is 1.0 × 10 ⁶ Ω · cm or more, the concentration of discharge in the pinhole existing in the object to be charged is suppressed and the applied voltage is reduced, and the pinhole is located. It is possible to suppress the occurrence of streaky charging failure over the entire longitudinal direction of the member to be charged. If the volume resistivity of the surface layer is 1.0 × 10 ¹⁵ Ω · cm or less, it is easy to energize the charging member, whereby the object to be charged can be charged to a predetermined potential, and an image with a desired density can be obtained. The generation of ghost images and the like can be suppressed.

  The volume resistivity of the surface layer is the same as in the case of measuring the volume resistivity of the conductive elastic layer on the front and back of the surface layer sample cut into a strip of about 5 mm × 5 mm from the surface of the charging member. It can be a measured value formed and measured. Or it can be set as the measured value which measured the coating film formed by apply | coating the coating material for surface layer shaping | molding on the aluminum sheet as a sample, vapor-depositing a metal on this, and forming an electrode. The measurement can be performed under the same conditions as in the case of the conductive elastic layer.

  In order to impart the conductivity to the surface layer, conductive fine particles can be used, and it is preferable that the conductive fine particles are not easily affected by external factors such as the environment. Specific examples of the conductive fine particles include those similar to the ion conductive agent and the electronic conductive agent specifically exemplified in the conductive elastic layer.

  The primary particle diameter of the conductive fine particles is preferably 1.0 μm or less, more preferably 0.1 μm or less, as observed with a differential scanning electron microscope. Particularly, it is more preferably 0.01 μm or more and 0.9 μm or less. The secondary particle diameter of the conductive fine particles is preferably a volume average particle diameter MEDIAN of 1.0 μm or less, more preferably 0.9 μm or less, as measured by a centrifugal sedimentation particle size distribution meter (CAPA700: manufactured by Horiba Seisakusho). Particularly preferably, it is 0.5 μm or less. If the secondary particle diameter is 1.0 μm or less, variation in electric resistance of the surface layer can be suppressed, and charging without uneven charging can be performed. In order to bring the secondary particle diameter of the conductive fine particles into the above range, a known method such as stirring and dispersing in a coating material for forming a surface layer can be used.

  Moreover, in order to make content in the surface layer of a electrically conductive agent into the said volume resistivity, the addition amount is adjusted.

  The conductive fine particles can be used by treating the surface with a coupling agent in order to suppress the adsorption of moisture to the surface and reduce the influence of environmental fluctuations. Examples of the coupling agent used for the surface treatment include compounds having a hydrolyzable group and a hydrophobic group in the same molecule, and these groups are bonded to a central element such as silicon, aluminum, titanium or zirconium. be able to. Examples of the hydrolyzable group include a methoxy group, an ethoxy group, a propoxy group or a butoxy group, an alkoxy group having a relatively high hydrophilicity, an acryloxy group, a methacryloxy group, a modified group thereof, or a halogen atom. be able to. Moreover, as a hydrophobic group, what is necessary is just to contain the alkyl group in which 6 or more carbon atoms are connected in a straight chain. Examples of the bonding form of these alkyl groups with the central element include a direct bond via a carboxylic acid ester, alkoxy, sulfonic acid ester or phosphoric acid ester. These hydrophobic groups may contain a functional group such as an ether bond, an epoxy group or an amino group. As the coupling agent, a silane coupling agent having high reactivity is preferable.

  Specific examples of such silane coupling agents include the following. Hexamethyldisilazane, trimethylsilane, trimethylchlorosilane, trimethylethoxysilane, dimethyldichlorosilane, methyltrichlorosilane, allyldimethylchlorosilane, allylphenyldichlorosilane, trifluoropropyltrimethoxysilane and hexyltrimethoxysilane.

  In addition to the above, the surface layer may contain insulating inorganic particles in order to enable more stable charging. As such inorganic particles, silica and titanium oxide are preferable. The primary particle diameter of silica or titanium oxide is preferably fine particles having a size of 0.5 μm or less. Silica or titanium oxide may be subjected to surface treatment. The surface treatment can include a chemical reaction or a treatment with an organic silicon compound that physically adsorbs, and specific examples of preferred methods include the following methods.

  A method of treating dry silica fine powder produced by vapor phase oxidation of a silicon halogen compound with a silane coupling agent.

  A method of treating with an organosilicon compound.

  A method of treating with an organosilicon compound after treating with a silane coupling agent or simultaneously with treating with a silane coupling agent.

  Specific examples of the silane coupling agent used for the surface treatment include the following. Hexamethyldisilazane, trimethylsilane, trimethylchlorosilane, trimethylethoxysilane, dimethyldichlorosilane, methyltrichlorosilane, allyldimethylchlorosilane, allylphenyldichlorosilane, benzyldimethylchlorosilane, bromomethyldimethylchlorosilane, α-chloro Ethyltrichlorosilane, β-chloroethyltrichlorosilane, chloromethyldimethylchlorosilane, triorganosilane mercaptan, trimethylsilyl mercaptan, triorganosilyl acrylate, vinyldimethylacetoxysilane, dimethylethoxysilane, dimethyldimethoxysilane, diphenyldiethoxysilane, hexamethyl Disiloxane, 1,3-divinyltetramethyldisiloxane, 1,3-diphenyltetramethyldisiloxane Siloxane.

  Examples of the organosilicon compound used for the surface treatment include silicone oil, and those having a viscosity at 25 ° C. of about 30 to 1,000 centistokes are preferable. For example, it is preferable to use dimethyl silicone oil, methylphenyl silicone oil, α-methylstyrene modified silicone oil, chlorophenyl silicone oil or fluorine modified silicone oil.

  Examples of the surface treatment method using such silicone oil include the following methods.

  A method in which silica fine powder treated with a silane coupling agent and silicone oil are directly mixed using a mixer such as a Henschel mixer.

  A method of injecting silicone oil into the base silica derivative.

  A method in which silicone oil is dissolved or dispersed in a suitable solvent and then mixed with the base silica fine powder to remove the solvent.

  As content in the surface layer of the said inorganic particle, 0.1-30 mass% is preferable. When the content of the inorganic particles is 0.1% by mass or more, stable charging can be performed, and when the content is 30% by mass or less, viscosity adjustment at the time of forming the surface layer can be easily performed.

[Characteristics of surface layer]
The glass transition temperature Tg of the surface layer is a viscoelasticity measuring method, and the peak temperature is preferably 45 ° C. or higher, and particularly preferably 50 ° C. or higher. When the temperature is 45 ° C. or higher, it is possible to suppress sticking to the member to be charged when left in contact with the member to be charged for a long period of time, and to suppress adhesion of toner or the like. The glass transition temperature Tg is preferably in a range that has an appropriate flexibility capable of suppressing the occurrence of cracks in the surface layer. The glass transition temperature Tg is adjusted to adjust the compounding ratio of the monomers constituting the binder resin. The blending ratio can be adjusted to achieve a desired temperature range.

  As the glass transition temperature Tg, a value measured by the following measuring method can be adopted. The surface layer is peeled off from the charging member to make a sample, or the coating film prepared by using the coating material for forming the surface layer on the PET resin sheet or fluorine resin sheet is peeled off from the sheet to make a sample of about 5 mm × 40 mm. A strip cut out is used for measurement. As a measuring device, a dynamic viscoelasticity measuring device RSA-II (manufactured by Rheometrics Scientific F.E.) is used, and a film tension fixture is used as a jig. The measurement was performed at a measurement frequency of 6.28 rad / sec and a temperature increase rate of 5 ° C./min. In an auto tension mode with an initial strain of 0.07 to 0.25%. The temperature dispersion of the loss tangent tan δ is measured, and the peak temperature is defined as Tg.

  The film thickness of the surface layer is preferably ½ to 10 times, more preferably 1 to 5 times the average particle diameter of the resin particles. If the film thickness of the surface layer is at least 1/2 times the particle diameter of the resin particles, the loss of the resin particles due to contact with the object to be charged or rubbing can be suppressed. For example, the amount of resin particles embedded in the surface layer can be reduced, and convex portions derived from the resin particles can be efficiently formed on the surface.

  As the film thickness, a value obtained by cutting the charging member with a sharp blade at a position indicated by an arrow in FIGS. 3A and 3B and observing with an optical microscope or an electron microscope can be adopted.

[Production method of surface layer]
Examples of the method for forming the surface layer include the following methods. Disperse resin particles, binder resin material, and other materials constituting the surface layer using a dispersing device using a sand mill, paint shaker, dyno mill, pearl mill beads, and mix with a medium as necessary to form a surface layer Create a paint for molding. The obtained surface layer molding paint can be formed by coating, drying and curing by dipping, spray coating, roll coating or ring coating.

  In order to create a surface layer having a predetermined thickness, it is possible to prepare by adjusting the solid content concentration of the resin of the surface layer-forming coating material, or in the case of dip coating, the pulling rate. When the solid content concentration of the resin in the surface layer molding paint is increased, the film thickness of the surface layer can be increased, and when the solid content concentration is decreased, the film thickness can be decreased. In order to create the surface layer having the above thickness, specifically, it is preferable to adjust the solid content of the resin with respect to the volatile dispersion medium to 10 to 40%.

  In addition, when the lifting speed from the immersed paint is increased, the film thickness increases, and when the speed is decreased, the film thickness decreases. Is preferably adjusted to 20 to 5000 mm / min.

[Charging member for contact charging]
[Surface roughness]
In the charging member of the present invention, the surface has a surface roughness Rzjis of 3 μm or more and 20 μm or less. The surface roughness is 10-point average roughness according to JIS B0601-2001, and more preferably 5 μm or more and 15 μm or less. By having such a surface roughness, it is possible to form a fine gap that can generate a good discharge between the surfaces at the nip portion with the member to be charged. When the surface roughness Rzjis is 3 μm or more, discharge can be generated, and streaky charging failure can be suppressed. Moreover, if it is 20 micrometers or less, it can suppress that a toner, an external additive, etc. adhere to the charging member surface, and can suppress performing nonuniform charging.

  As a method for forming a surface having a surface roughness in the above range on the charging member of the present invention, it is contained in the lower layer of the surface layer, for example, the surface roughness of the conductive elastic layer, the film thickness of the surface layer, or the surface layer. The method of adjusting the average particle diameter and addition amount of a resin particle can be mentioned.

  Of these surface roughness forming methods, the method of reducing the surface roughness of the lower layer and adjusting the surface roughness with the average particle diameter and the addition amount of the resin particles in the surface layer is the nip portion with the object to be charged. In order to form a discharge space, it is preferable. The method of adjusting the surface roughness of the lower layer tends to have a smaller effect of suppressing streaky charging defects than the method of adjusting the surface roughness with the resin particles in the surface layer. This is probably because the lower conductive elastic layer is more flexible than the surface layer, so that it compresses and deforms due to the pressing force against the member to be charged, and a sufficient gap cannot be formed. For this reason, the conductive elastic layer under the surface layer has a ten-point average roughness of Rzjis of preferably 10 μm or less, more preferably 5 μm or less.

  The average roughness (Rzjis) is determined by the method according to the surface roughness of JIS B0601-2001 using the Kosaka Laboratory Surfcoder SE3400, as shown in FIGS. Then, measurement is performed for each of a total of six points in two places in the circumferential direction. An average value of the measured values can be adopted. As measurement conditions, the contact needle may be a diamond having a tip radius of 2 μm, a measurement speed of 0.5 mm / s, a cutoff λc of 0.8 mm, a reference length of 0.8 mm, and an evaluation length of 8.0 mm.

[Electric resistance value]
The electrical resistance of the charging member of the present invention is 1 × 10 ⁴ Ω or more in a high temperature and high humidity environment of 30 ° C./80% RH, and 1 × 10 ^{8 in} a low temperature and low humidity environment of 15 ° C./10%. It is preferable that it is below Ω. If the electrical resistance in the low temperature and low humidity environment is 1 × 10 ⁸ Ω or less, it is preferable because the object to be charged can be charged to a predetermined potential and the generation of ghost images can be suppressed. Also, if the electrical resistance in a high temperature and high humidity environment is 1 × 10 ⁴ Ω or more, even if there is a pinhole in the object to be charged, a voltage drop of the applied voltage does not occur, and a horizontal band-like image defect on the image Is preferable. In order to make such an electric resistance within the above range, for example, the volume resistivity of the conductive elastic layer is adjusted to 1 × 10 ⁴ to 1 × 10 ⁸ Ω · cm, and the volume resistivity of the surface layer is adjusted. Examples include adjusting 1 × 10 ⁶ to 1 × 10 ¹⁵ Ω · cm and adjusting the film thickness to 1 to 100 μm.

  The measured value measured by the following method can be adopted as the electrical resistance. First, as shown in FIG. 4A, a conductive support 1 of a charging roller as a charging member is formed into a cylindrical shape having the same curvature as that of a photosensitive member as a member to be charged by bearings 33a and 33b under load. The charging roller is brought into contact with the metal 32 so as to be parallel. Next, as shown in FIG. 4 (b), the cylindrical metal 32 is rotated by a motor, and a DC voltage of −200 V is applied from the stabilizing power source 34 while the charging roller is driven and rotated while being in contact with the cylindrical metal. Apply. At this time, the current flowing through the charging roller is measured by an ammeter 35, and the resistance of the charging roller is calculated. Specifically, a method of measuring by rotating each metal cylinder at a peripheral speed of 45 mm / sec by applying a force of 5 N to both ends of the conductive support, contacting a metal cylinder with a diameter of 30 mm, and the like. .

  As an example of the charging member of the present invention, a roller-shaped member shown in FIG. 5A is a sectional view in the axial direction, and FIG. 5B is a sectional view in the direction perpendicular to the axial direction. The charging member for contact charging includes the conductive support 1 constituting the conductive base and the outer periphery thereof. A conductive elastic layer 2 provided on the surface, and a surface layer 3 provided so as to cover the outer periphery of the conductive elastic layer 2. The conductive support is a cylinder having a nickel plating with a thickness of 5 μm on the surface of a carbon steel alloy. The conductive elastic layer 2 is made of a conductive elastic body, and is formed of the surface layer 3 resin particles and a binder resin.

[Electrophotographic equipment]
The electrophotographic apparatus of the present invention comprises the above charging member, a member to be charged, an exposure unit, a developing unit, and a transfer unit, and only a DC voltage is applied to the charging member, It is preferable that it is charged.

  An example of the electrophotographic apparatus of the present invention is shown in FIG. Such an electrophotographic apparatus mainly includes a photosensitive member 4 as a member to be charged, and a developer container 6 a that stores the charging roller 5 as the charging member, the exposure unit, the developing roller 6, and the toner T around the photosensitive member 4. And a developing roller (transfer means) 8 are provided. Further, a cleaning blade 10 and a fixing unit 9 for fixing an image on the recording material are provided.

  In such an electrophotographic apparatus, a DC voltage is applied from a DC power source 19 to the charging roller. The absolute value of the DC voltage applied to the charging roller is preferably a voltage obtained by adding an air discharge start voltage to the primary charging voltage for charging the surface of the photoreceptor. Usually, the discharge start voltage of air is about 500 to 700 V, the primary charging voltage on the surface of the photoreceptor is about 300 to 800 V, and the applied voltage of the charging roller is preferably 800 to 1500 V. The photosensitive member is rotated in the direction of the arrow in contact with the charging roller to which such a voltage is applied. The photoreceptor is primarily charged by a charging roller.

  Next, exposure 11 is exposed to the surface of the photoconductor from the exposure means to form an electrostatic latent image on the surface of the photoconductor. On the other hand, a voltage lower than that of the electrostatic latent image is supplied from the power source 18 to the developing roller, the developing roller is rotated, and the toner adheres to the developing roller. The toner on the developing roller is conveyed while being formed in a thin layer by the elastic regulating blade 13, and moves onto the electrostatic latent image to develop it by contacting the surface of the photoreceptor. The developed toner image on the photoconductor is printed from the photoconductor by applying a transfer voltage higher than that of the electrostatic latent image from the power source 20 through the transfer roller from the back surface of the print medium 7 such as paper. Transferred onto the medium 7. Thereafter, the toner image on the print medium is fixed by heat and pressure in the fixing unit, becomes a permanent image, and the print medium is discharged out of the apparatus. After the toner image is transferred, the photosensitive member is exposed by the pre-charge exposure device 12, the remaining latent image is erased, the potential returns to the ground potential, and the toner remaining on the photosensitive member without being transferred is exposed to the cleaning blade. Removed and recovered from the body.

  Although only one developing unit is shown in the drawing, a developing unit may be provided for each toner of black, cyan, magenta, and yellow, and these may be arranged in series to form a color image forming apparatus. it can.

  In such an electrophotographic apparatus, by using only a DC voltage as a primary charging voltage to which a charging roller is applied, it is possible to reduce power consumption and reduce costs. Further, no charging noise is generated when an AC voltage is applied. Even when the charging roller is applied only by a DC voltage, the surface of the photoreceptor can be stably charged by stable discharge, and the occurrence of image defects due to charging failure is suppressed. In addition, even when the surface of the charging roller is covered with deposits in the latter half of the endurance life, the photoconductor is uniformly charged by the discharge from the slope of the convex portion of the surface of the charging roller, thereby suppressing the occurrence of image defects. Thus, the life of the device can be extended.

[Process cartridge]
A process cartridge according to the present invention includes the charging member and a member to be charged, and is detachably integrated with the main body of the electrophotographic apparatus.

  The process cartridge of the present invention may be any cartridge provided with the charging member and the member to be charged. In addition, one or more selected from developing means, cleaning means, and the like provided in the electrophotographic apparatus may be integrated with the charging member and configured to be detachable from the main body of the electrophotographic apparatus. .

  An example of the process cartridge of the present invention is shown in FIG. In the process cartridge shown in FIG. 7, the photosensitive member 4, the charging roller 5, the developing roller 6, and the cleaning blade 10 are integrally supported and configured to be detachable from the main body of the electrophotographic apparatus. Further, a toner seal 30 is provided at the opening of the developer container so as to avoid contact between the developing roller and the toner before the process cartridge is mounted on the electrophotographic apparatus.

  The charging member, process cartridge, and electrophotographic apparatus of the present invention will be specifically described below in detail, but the technical scope of the present invention is not limited to these.

[Production of resin particles]
[Resin particles 1]
12.5 kg of ethylene-acrylic acid copolymer (acrylic acid content 3 mmol / g), 23.5 kg of xylene, and 28 kg of isobutyl alcohol were prepared. An ethylene-acrylic acid copolymer, xylene and isobutyl alcohol prepared in a 250 L reaction vessel were added, and a solution obtained by dissolving 1.6 kg of potassium hydroxide in 5 L of methanol was added to the reaction vessel under stirring. The mixture was heated to 110 ° C. with stirring and reacted for 6 hours. After cooling to room temperature and allowing to stand, the supernatant was extracted. Subsequently, after further adding 50 L of acetone and stirring again for 30 minutes, the supernatant was taken out and dried under reduced pressure at 50 ° C. The obtained resin was pelletized with a twin screw extruder at 210 ° C. to obtain pellets.

The obtained pellets were pulverized with an atomizer pulverizer by cooling the pellet-like resin below the embrittlement temperature (−150 ° C.) using liquid nitrogen. Thereafter, classification was performed to obtain resin particles (1) having an average particle size of 8.1 μm. The volume resistivity of the resin particles (1) was 1.5 × 10 ⁸ Ω · cm. The crosslinked structure of the resin is shown below.

[Resin particles 2]
Other than using ethylene-methyl methacrylate copolymer (MMA content 2 mmol / g) instead of ethylene-acrylic acid copolymer (acrylic acid content 3 mmol / g), the amount of potassium hydroxide used was 1.25 Kg. Produced pellets in the same manner as the resin particles (1). The obtained pellets were crushed in the same manner as the resin particles (1) and then classified to obtain resin particles (2) having an average particle size of 8.3 μm. The volume resistivity of the resin particles (2) was 2.7 × 10 ⁷ Ω · cm. The crosslinked structure of the resin is shown below.

[Resin particles 3]
Pellets were produced in the same manner as the resin particles (1) except that 5.4 kg of cesium carbonate was used instead of 1.6 kg of potassium hydroxide. The obtained pellets were pulverized in the same manner as the resin particles (1) and then classified to obtain resin particles (3) having an average particle diameter of 7.9 μm. The volume resistivity of the resin particles (3) was 6.0 × 10 ⁵ Ω · cm. The crosslinked structure of the resin is shown below.

[Resin particles 4]
Resin particles (4) having an average particle diameter of 1.3 μm were obtained in the same manner as the resin particles (1) except that the particles were classified so as to have an average particle diameter of 1.5 μm. The volume resistivity of the resin particles (4) was 2.1 × 10 ⁸ Ω · cm.

[Resin particles 5]
Resin particles (5) having an average particle diameter of 20.5 μm were obtained in the same manner as the resin particles (1) except that the particles were classified so as to have an average particle diameter of 20 μm. The volume resistivity of the resin particles (5) was 1.9 × 10 ⁸ Ω · cm.

[Resin particles 6]
Resin particles (6) having an average particle diameter of 29.8 μm were obtained in the same manner as the resin particles (1) except that the particles were classified so as to have an average particle diameter of 30 μm. The volume resistivity of the resin particles (4) was 2.3 × 10 ⁸ Ω · cm.

[Resin particles 7]
3 Kg of the resin obtained in Example 1 and 2 Kg of ionomer 1601 (trade name: Mitsui DuPont Polychemical, Na ionomer) were melt-mixed with a Banbury mixer, and pellets were obtained with an under extruder. The obtained pellets were pulverized in the same manner as the resin particles (1) and then classified to obtain resin particles (7) having an average particle diameter of 7.9 μm. The volume resistivity of the resin particles (7) was 7.2 × 10 ¹⁰ Ω · cm.

[Resin particles 8]
Resin particles (8) having an average particle diameter of 0.4 μm were obtained in the same manner as the resin particles (1) except that the particles were classified so as to have an average particle diameter of 0.5 μm. The volume resistivity of the resin particles (8) was 7.7 × 10 ⁷ Ω · cm.

[Resin particles 9]
Resin particles (9) having an average particle diameter of 35.2 μm were obtained in the same manner as the resin particles (1) except that the particles were classified so as to have an average particle diameter of 35 μm. The volume resistivity of the resin particles (9) was 7.7 × 10 ⁷ Ω · cm.

[Example 1]
[Production of charging member]
[Preparation of conductive elastic layer]
The following materials were kneaded with a closed mixer for 10 minutes.
Epichlorohydrin rubber (Epichlorohydrin-ethylene oxide-allyl glycidyl ether terpolymer) 100 parts by mass Calcium carbonate (filler) 50 parts by mass Zinc stearate (lubricant) 1 part by mass Carbon black (FEF) (for improving polishing properties) Reinforcing material) 5 parts by weight zinc oxide 5 parts by weight Sebacic acid and propylene glycol copolymer (molecular weight 8000) (plasticizer) 5 parts by weight 2-mercaptobenzimidazole (anti-aging agent) 1 part by weight quaternary ammonium perchlorate Salt (following formula) 2 parts by mass

  Furthermore, 1 part by mass of DM (2-benzothiazolyl disulfide) as a vulcanization accelerator, 0.5 part by mass of TS (tetramethylthiuram monosulfide) as a vulcanization accelerator, 1 mass of sulfur as a vulcanization agent Then, the mixture was further kneaded with an open roll for 5 minutes.

  The obtained kneaded product was extruded into a cylindrical shape having an outer diameter of 13.5 mm and an inner diameter of 5.5 mm using an extruder, cut into a length of 250 mm, and a temperature of 160 ° C. was used using a steam vulcanizer. Primary vulcanization was performed in water vapor for 40 minutes to obtain a conductive elastic layer rubber primary vulcanization tube.

  Next, a thermosetting adhesive of metal and rubber is applied to the central portion 231 mm in the axial direction of the cylindrical surface of a cylindrical conductive support (made of steel, surface is nickel-plated) having a diameter of 6 mm and a length of 256 mm, Dry at 80 ° C. for 10 minutes. The conductive support was inserted into the conductive elastic layer rubber primary vulcanization tube, and then heat-treated at 150 ° C. for 1 hour in an electric oven to obtain an unpolished layer roller.

  Cut off both ends of the rubber part of this unpolished layer roller and make the length of the rubber part 232 mm, then polish the rubber part with a rotating grindstone, 90 mm on both sides from the center part, the diameter is 12.00 mm, the center part is A crown shape with a diameter of 12.15 mm was formed to obtain a conductive elastic roller. The ten-point average roughness Rzjis of the surface of the conductive elastic roller was 4.2 μm, and the runout was 22 μm.

[Production of surface layer]
Methyl isobutyl ketone was added to the caprolactone-modified acrylic polyol solution to adjust the solid content to 17% by mass. The following was added to 588.2 parts by mass of this mixed solution with respect to 100 parts by mass of the solid content to prepare a mixed solution.

Carbon black (HAF) 15 parts by mass Acicular rutile-type titanium oxide fine particles 30 parts by mass Modified dimethyl silicone oil 0.08 parts by mass 7: 3 of each butanone oxime block of hexamethylene diisocyanate (HDI) and isophorone diisocyanate (IPDI) blend
80.14 parts by mass The acicular rutile-type titanium oxide fine particles are surface-treated with hexamethylene disilazane and dimethyl silicone, and have an average particle diameter of 0.015 μm and length: width = 3: 1. The mixture of block HDI and block IPDI was added so that “NCO / OH = 1.0”.

  In a 450 mL glass bottle, 210 g of the mixed solution and 200 g of glass beads having an average particle diameter of 0.8 mm as a medium were mixed and dispersed for 24 hours using a paint shaker disperser. After dispersion, 5.44 parts by mass of resin particles (1) (equivalent to 20 parts by weight with respect to 100 parts by weight of acrylic polyol) was added, and then dispersed for 30 minutes to obtain a coating material for forming a surface layer.

  This surface layer-forming coating material was dipped on the conductive substrate once, air-dried at room temperature for 30 minutes or more, then dried in a hot air circulating dryer set at 90 ° C. for 1 hour, and then set at 160 ° C. It dried for 1 hour with the hot air circulation dryer, and formed the surface layer on the electroconductive base | substrate. The dipping coating dipping time is 9 seconds, the dipping coating lifting speed is adjusted so that the initial speed is 20 mm / s, and the final speed is 2 mm / s. Between 20 mm / s and 2 mm / s is linear with respect to time. The speed was changed.

  Thus, a charging roller having a surface layer on a conductive substrate was produced, and ten-point average roughness (Rzjis) was measured by the method described above. The results are shown in Table 1. The film thickness of the obtained surface layer was 15 μm.

[Image formation]
[Promoting dirt adhesion]
A charging roller is attached to the process cartridge, and 50 single-color solid images are output continuously in a normal temperature and humidity environment (25 ° C., 50% RH) with a color laser jet 3800 (manufactured by Canon Inc.). I passed one sheet. This operation was repeated 6 times, and a total of 300 single-color solid images were output. By this operation, toner and external additives were forcibly adhered to the surface of the charging roller.

[Charging evaluation]
Using a dirt adhesion charging roller, image formation was performed as shown below, and charging was evaluated.

  The electrophotographic laser printer used is a machine for A4 vertical output, the output speed of the recording medium is 200 mm / sec and 100 mm / sec, and the image resolution is 600 dpi. Using the charging roller forcibly adhered with dirt as described above, a DC voltage of −1100 V was applied to the charging roller. An endurance test was performed on a plurality of continuous images at a process speed of 150 mm / sec. Initially, after 3,000 images were output, a halftone image (an image that draws a horizontal line with a width of 1 dot and a spacing of 2 dots in the direction perpendicular to the rotation direction of the photosensitive member) was output for image checking after 6000 images were output. The image check output images at two process speeds. This image output is obtained in a low temperature and low humidity environment (environment 1: 15 ° C./10% RH), a normal temperature and normal humidity environment (environment 2: 23 ° C./50% RH), and a high temperature high humidity environment (environment 3: 30 ° C./80, respectively). % RH).

  The obtained image was visually evaluated for fine streak-like density unevenness (lateral streak) caused by charging unevenness. Rank A where the horizontal streak did not occur at all, Rank B for the level where the slight streak occurred, Rank C for the level where the horizontal streak occurred slightly but not conspicuous, and Level C where the horizontal streak is slightly conspicuous Rank D and a level E where the horizontal stripes are very conspicuous were designated as rank E. The results are shown in Table 2. The image check after 3000 and 6000 images were put out was performed immediately after the 3000 and 6000 images were put out (last image check) and 12 hours later (one image check in the morning).

[Resistance measurement]
The resistance of the charging roller was calculated by measuring the current flowing through the charging roller with an ammeter 35 when a DC voltage of −200 V was applied from the stabilized power supply 34 using the electrical resistance value measuring apparatus shown in FIG. The measurement is performed by applying a force of 5 N to both ends of the shaft, contacting a metal cylinder having a diameter of 30 mm, rotating the metal cylinder at a peripheral speed of 45 mm / sec, and N / N (normal temperature and normal humidity: 23 ° C./55). % RH) The charging roller was left in the environment for 24 hours or more. The electric resistance was 2.2 × 10 ⁵ Ω.

[Example 2]
A charging roller was prepared in the same manner as in Example 1 except that the resin particles (1) were replaced with the resin particles (2), and the surface roughness, film thickness, and electrical resistance were measured, and charging evaluation was performed. Tables 1 and 2 show the results of surface roughness and charging evaluation, respectively. The film thickness of the surface layer was 14 μm, and the electric resistance was 1.9 × 10 ⁵ Ω.

[Example 3]
A charging roller was prepared in the same manner as in Example 1 except that the resin particles (1) were replaced with the resin particles (3), and the surface roughness, film thickness, and electrical resistance were measured, and charging evaluation was performed. Tables 1 and 2 show the results of surface roughness and charging evaluation, respectively. The film thickness of the surface layer was 16 μm, and the electric resistance was 1.5 × 10 ⁵ Ω.

[Example 4]
A charging roller was prepared in the same manner as in Example 1 except that the resin particles (1) were replaced with the resin particles (4), and the surface roughness, film thickness, and electrical resistance were measured, and charging evaluation was performed. In the preparation of the surface layer, the dipping pull-up speed and the paint concentration were adjusted so that the film thickness was 5 μm. Tables 1 and 2 show the results of surface roughness and charging evaluation, respectively. The film thickness of the surface layer was 5.1 μm, and the electric resistance was 3.2 × 10 ⁵ Ω.

[Example 5]
A charging roller was prepared in the same manner as in Example 1 except that the resin particles (1) were replaced with the resin particles (5), and the surface roughness, film thickness, and electrical resistance were measured, and the charging evaluation was performed. In the preparation of the surface layer, the dipping pull-up speed and the paint concentration were adjusted so that the film thickness was 28 μm. Tables 1 and 2 show the results of surface roughness and charging evaluation, respectively. The film thickness of the surface layer was 27.5 μm, and the electric resistance was 3.7 × 10 ⁵ Ω.

[Example 6]
A charging roller was prepared in the same manner as in Example 1 except that the resin particles (1) were replaced with the resin particles (6), and the surface roughness, film thickness, and electrical resistance were measured, and charging evaluation was performed. In the preparation of the surface layer, the dipping pull-up speed and the paint concentration were adjusted so that the film thickness was 75 μm. Tables 1 and 2 show the results of surface roughness and charging evaluation, respectively. The film thickness of the surface layer was 74.5 μm, and the electric resistance was 5.7 × 10 ⁵ Ω.

[Example 7]
A charging roller was prepared in the same manner as in Example 1 except that the resin particles (1) were replaced with the resin particles (7), and the surface roughness, film thickness, and electrical resistance were measured, and charging evaluation was performed. Tables 1 and 2 show the results of surface roughness and charging evaluation, respectively. The film thickness of the surface layer was 14.8 μm, and the electric resistance was 8.7 × 10 ⁵ Ω.

[Comparative Example 1]
A charging roller was prepared in the same manner as in Example 1 except that no resin particles were added, and surface roughness and charging evaluation were performed. Tables 1 and 2 show the results of surface roughness and charging evaluation, respectively. Horizontal streaks were poorly charged from the beginning, and the level of horizontal streak-like image unevenness deteriorated as the number of durable sheets increased.

[Comparative Example 2]
A charging roller was prepared in the same manner as in Example 1 except that the resin particles (1) were replaced with the resin particles (8), and the surface roughness, film thickness, and electrical resistance were measured, and charging evaluation was performed. In the preparation of the surface layer, the dipping pull-up speed and the paint concentration were adjusted so that the film thickness was 5 μm. Tables 1 and 2 show the results of surface roughness and charging evaluation, respectively. The film thickness of the surface layer was 5.2 μm, and the electric resistance was 5.1 × 10 ⁵ Ω.

[Comparative Example 3]
A charging roller was prepared in the same manner as in Example 1 except that the resin particle (1) was replaced with the resin particle (9), and the surface roughness, film thickness, and electrical resistance were measured, and charging evaluation was performed. In the preparation of the surface layer, the dipping pull-up speed and the paint concentration were adjusted so that the film thickness was 45 μm. Tables 1 and 2 show the results of surface roughness and charging evaluation, respectively. The surface layer had a thickness of 48 μm and an electrical resistance of 7.7 × 10 ⁵ Ω.

  From the results, it was found that the charging member of the present invention can perform stable charging.

It is explanatory drawing which shows the discharge in the nip part by the charging member of this invention. It is the schematic which shows the non-contact laser length measuring device which measures the diameter of the charging member of this invention, and an outer diameter fluctuation | variation. It is explanatory drawing which shows the measuring method of the surface roughness of the charging member of this invention, or the film thickness of a surface layer. It is explanatory drawing which shows the measuring method of the electrical resistance value of the charging member of this invention. It is a schematic sectional drawing which shows an example of the charging member of this invention. It is a schematic block diagram which shows an example of the electrophotographic apparatus of this invention. It is a schematic block diagram which shows an example of the process cartridge of this invention. It is explanatory drawing which shows the discharge in the upstream and downstream of the nip part by the conventional charging member. It is explanatory drawing which shows the discharge in the nip part by the conventional charging member. It is explanatory drawing which shows the discharge in the nip part by the conventional charging member.

Explanation of symbols

1 Conductive support (conductive substrate)
2 Conductive elastic layer (conductive base)
3 Surface layer 4 Photoconductor (charged body)
5 Charging roller (charging member)
6 Development roller (development means)
8 Transfer roller (transfer means)
11 Exposure

Claims (9)

A charging member for contact charging having a conductive substrate and a conductive surface layer;
The surface layer includes a binder resin and resin particles dispersed in the binder resin, has a convex portion derived from the resin particle on the surface, and a surface roughness Rzjis on the surface is 3 μm or more and 20 μm or less. ,
A charging member, wherein the resin particles have an average particle diameter of 1 μm or more and 30 μm or less, contain an ionomer resin, and have conductivity. The charging member according to claim 1, wherein the resin particles have a volume resistivity of 1.0 × 10 ⁶ Ω · cm to 1.0 × 10 ¹⁰ Ω · cm.   The charging member according to claim 1, wherein the resin particles include an ethylene-unsaturated carboxylic acid copolymer using an alkali metal as an ion source.   The charging member according to claim 3, wherein the ion source is at least one selected from potassium, rubidium, and cesium.   The charging member according to claim 1, wherein the surface layer contains conductive fine particles having a primary particle diameter of 0.01 μm or more and 0.9 μm or less.   The charging member according to claim 1, wherein the surface layer is formed by a coating method.   7. A process cartridge comprising the charging member according to claim 1 and a member to be charged, and detachably integrated with an electrophotographic apparatus main body.   An electrophotographic apparatus comprising: the charging member according to claim 1; a member to be charged; an exposure unit; a development unit; and a transfer unit.   9. The electrophotographic apparatus according to claim 8, wherein only the direct current voltage is applied to the charging member to charge the member to be charged.