JP4366167B2 - Charging member, process cartridge, and image forming apparatus - Google Patents

Description

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

  In the electrophotographic charging process, a contact charging method in which a charging member is brought into contact with or close to a photoreceptor and a voltage is applied to the charging member to charge the surface of the photoreceptor has been put into practical use. As a specific example of the charging member used in such a contact charging method, a conductive roller having a conductive support and a coating layer covering the periphery thereof can be cited.

It has been proposed to add various substances to the surface layer constituting the outermost surface of such a charging member in order to improve or stabilize the charging performance. For example, in Patent Document 1, the surface layer is made hydrophobic by containing particles surface-treated with a coupling agent, thereby reducing the resistance value by suppressing water adsorption on the surface of the conductive member under high temperature and high humidity. It is described that can be prevented.
JP 2003-107825 A

  By the way, in the contact charging method in which only the direct current voltage is applied to the charging roller to charge the electrophotographic photosensitive member, the inventors of the present invention tend to show the uneven shape on the surface of the charging roller in the electrophotographic image, and the image quality is low. The above problem can be solved by adding insulating particles surface-treated with silicone oil to the surface layer of the charging roller after treating with a silane coupling agent, in order to reduce the problem of high-quality electrophotographic images. The knowledge that it can form stably is acquired. However, as a result of further investigation, when the new electrophotographic photosensitive member was first used, image formation was performed after the contact state between the charging roller and the stopped electrophotographic photosensitive member continued for a predetermined time. However, it has been found that streaks may occur in the image. Although the occurrence of such streaks in the image is alleviated as the number of image outputs increases, it is a problem to be solved in providing an image forming apparatus that always provides a high-quality electrophotographic image stably. Got the recognition.

  Therefore, as a result of repeated studies on the above problems, the silicone oil used for the surface treatment of the inorganic fine particles adheres to the surface of the electrophotographic photosensitive member when the charging roller and the electrophotographic photosensitive member are in contact with each other. It was speculated that one of the causes was a partial change in sex. On the other hand, it has been found that there is the following problem when the surface treatment with the silicone oil of the insulating fine particles surface-treated with the silane coupling agent is not performed. That is, as one method for forming the surface layer, there is a method of applying a coating solution containing a component constituting the surface layer. A uniform surface layer may not be formed with the coating liquid containing insulating fine particles that are not subjected to surface treatment with the silicone oil. Even when a uniform surface layer is formed, when a part of the surface of the obtained charging roller is rubbed, uneven charging occurs due to the rubbing, resulting in unevenness in the electrophotographic image. There was a case.

  Therefore, as a result of further studies, the present inventors, as inorganic fine particles, inorganic fine particles surface-treated with a coupling agent, and inorganic fine particles surface-treated with a coupling agent and then surface-treated with silicone oil, The charging roller in which both are included in the surface layer does not cause streaks in the image formed after contact with the stopped photoconductor for several minutes, and the surface layer is coated or formed on the surface of the charging roller. The inventor obtained that charging unevenness caused by rubbing can be suppressed.

  An object of the present invention is to provide a charging member that stably provides a high-quality electrophotographic image.

  Another object of the present invention is to provide an image forming apparatus capable of stably forming a high-quality electrophotographic image, and a process cartridge usable for the image forming apparatus.

According to the present invention, there is provided a charging member for contact charging having a conductive support and a coating layer covering the periphery of the conductive support, the outermost surface of the charging member being constituted The conductive surface layer includes first particles and second particles, and the first and second particles are made of insulating inorganic fine particles having the same chemical composition, particle size, and surface area. in all SANYO different surface treatment has been performed, the first grains are those surface treated is made with a coupling agent in the base material, the particles of said second coupling agent to the base material after surface treatment with a charging member, characterized in der Rukoto those surface-treated with a silicone oil has been performed it is provided.

  In addition, according to the present invention, a process cartridge and an image forming apparatus provided with the charging member are provided.

  According to the present invention, even when the charging roller comes into contact with the electrophotographic photosensitive member in a stopped state in the initial use of the electrophotographic photosensitive member, no streak is formed on the image and the surface of the charging member is rubbed. In this case, uneven charging at the rubbing portion is alleviated, and a high-quality electrophotographic image can be obtained stably.

  In addition, according to the present invention, even when a low molecular compound is volatilized from another member that is close to the charging member in the process cartridge, charging unevenness due to the low molecular compound can be effectively reduced. .

  Embodiments of the present invention will be described below in detail with reference to the drawings.

  FIG. 1A is a schematic cross-sectional view of a charging roller which is an embodiment of the charging member according to the present invention. In the figure, reference numeral 1 denotes a conductive support, and its periphery is covered with a conductive elastic layer 2 as a coating layer and a surface layer 3 constituting the outermost surface of the charging roller. FIG. 1B is a cross-sectional view taken along the conductive support 1 of the charging roller of FIG. The surface layer 3 includes first particles obtained by subjecting the base material to surface treatment with a silane coupling agent, and surface treatment with a silane coupling agent on the same kind of base material as the base material, and then silicone oil or silicone varnish. And second particles surface-treated with.

The surface layer (i) for the first and second particles;
(I-1) base material;
Examples of the base material of the first and second particles include metal oxides, spherical carbon particles, silica fine particles, and composite oxides such as strontium titanate fine particles, calcium titanate fine particles, and silicon titanate fine particles. It is done. Among these, inorganic fine particles are preferable, insulating inorganic fine particles are particularly preferable, and titanium oxide is particularly preferable. In particular, metal oxide or double oxide insulating fine particles having a large relative dielectric constant are preferable. When inorganic fine particles having a large relative dielectric constant are used as a base material, it is effective for increasing the charging potential of the charging roller and uniformly charging the object to be charged.

  The base material of the first particles and the base material of the second particles are preferably of the same type. Here, the same kind of base material means that the chemical molecular composition, particle diameter, and surface area are almost equal. Specifically, the molecular composition represented by the general molecular formula and the composition of the element represented by the composition formula are generally within a variation of plus or minus 20%, more preferably within plus or minus 10%. It is preferable to be within the range. Regarding the particle size, it is preferable that the average particle size is approximately within 10 times, preferably within 2 times. Further, it is preferable that the surface area by the BET method or the like is approximately within 10 times, preferably within 2 times. If the physical properties as described above are different between the base material of the first particles and the base material of the second particles, the stability of the coating material for forming the surface layer may be impaired.

(I-2) surface treatment with a coupling agent;
As the coupling agent (a central element such as silicon, titanium, aluminum and zirconium is not particularly selected), an alkoxysilane coupling agent and a fluoroalkylalkoxysilane coupling agent are particularly preferable.

  Examples of coupling agents include silane coupling agents and titanate coupling agents. Examples of the silane coupling agent include isobutylsilane, hexamethyldisilazane, trimethylsilane, trimethylchlorosilane, trimethylethoxysilane, dimethyldichlorosilane, methyltrichlorosilane, allyldimethylchlorosilane, allylphenyldichlorosilane, and benzyldimethyl. Chlorosilane, bromomethyldimethylchlorosilane, α-chloroethyltrichlorosilane, β-chloroethyltrichlorosilane, chloromethyldimethylchlorosilane, triorganosilylmercaptan, trimethylsilylmercaptan, triorganosilylacrylate, vinyldimethylacetoxysilamen, dimethyldi Ethoxysilane, dimethyldimethoxysilane, diphenyldiethoxysilane, hexamethyldisiloxane, 1,3-divinyl Rutetramethyldisiloxane, 1,3-diphenyltetramethyldisiloxane, and 2-12 siloxane units per molecule, each containing a hydroxyl group bonded to each silicon atom in the terminal unit Dimethylpolysiloxane.

  As the hydrolyzing group of the coupling agent, for example, an alkoxy group such as a methoxy group, an ethoxy group, a propoxy group and a butoxy group having a relatively high hydrophilicity is used. In addition, an acryloxy group, a methacryloxy group, modified products thereof, halogen, and the like are also used. In addition, the hydrophobic group may be bonded via a carboxylic acid ester, alkoxy, sulfonic acid ester, or phosphoric acid ester, or directly in the bonding form with the central element. Furthermore, functional groups such as ether bonds, epoxy groups and amino groups may be included in the structure of the hydrophobic group. By treating with the coupling agent, it is possible to suppress the adsorption of moisture to the surface of the fine particles, and to obtain a surface layer material with smaller environmental fluctuations.

  As a method for hydrophobizing the fine particles, for example, in the case of a silane coupling agent, there are two methods, a dry method and a wet method.

(A) Dry method A silane coupling agent is sprayed or blown in a vapor state while thoroughly stirring the conductive agent. Add heat treatment if necessary. More specifically, it is preferable to use a dry method in which a silane coupling agent is allowed to react with fine particles in the form of cloud in the presence of water vapor. In the treatment with the silane coupling agent, the silane coupling agent is treated in the presence of water vapor, so that the water vapor acts as a catalyst, and the reaction of the silane coupling agent can be enhanced, thereby enabling uniform surface treatment. . The presence of water vapor during the treatment of the silane coupling agent is preferable in order to cause a favorable reaction between the silane coupling agent and the base material.

(B) Wet method A conductive agent is dispersed in a solvent, and a silane coupling agent is also diluted with water or an organic solvent and added while stirring vigorously in a slurry state. This method is preferable for uniform treatment. Furthermore, there are the following three methods as specific methods for the silane pretreatment of the conductive agent surface.

(B-1) Aqueous solution method About 0.1 to 0.5% of silane is injected and dissolved in water having a constant pH or water-solvent with sufficient stirring, followed by hydrolysis. After the filler is immersed in this solution, it is filtered or squeezed to remove water to some extent, and then sufficiently dried at 120 to 130 ° C.

(B-2) Organic solvent method Silane is dissolved in an organic solvent (alcohol, benzene, halogenated hydrocarbon) containing a small amount of water and a hydrolysis solvent (hydrochloric acid, acetic acid). After the filler is immersed in this solution, it is filtered or squeezed, the solvent is removed, and it is sufficiently dried at 120 to 130 ° C.

(B-3) Spraying method An aqueous solution of silane or a solvent solution is sprayed while vigorously stirring the filler. Then, it is sufficiently dried at 120 to 130 ° C.

  In this invention, it is good to add and process a silane coupling agent in 5-60 mass parts with respect to 100 mass parts of fine particle raw materials, More preferably, in the range of 10-50 mass parts. When the amount is less than 5 parts by mass, the surface treatment is not sufficient, and precipitation tends to occur, and the stability of the coating liquid for coating the surface layer is deteriorated. It may be difficult.

(I-3) Surface treatment with silicone oil;
As a silicone oil, what is represented by the following general formula (I) is preferable.

  In the above general formula (I), R is an alkyl group having 1 to 3 carbon atoms, R ′ is a silicone oil-modified group such as alkyl, halogen-modified alkyl, phenyl, and modified phenyl, and R ″ is 1 to 1 carbon atoms. It is an alkyl or alkoxy group of 3. m and n represent m ≧ 0, n ≧ 0, and m + n> 0.

  Specific examples of the general formula (I) include dimethyl silicone oil, alkyl-modified silicone oil, α-methylstyrene-modified silicone oil, chlorophenyl silicone oil, and fluorine-modified silicone oil.

  In the present invention, as the silicone oil, a modified silicone oil having a structure represented by the following general formula (II) can also be used.

In the general formula (II), R ₁ and R ₆ represent a hydrogen atom, an alkyl group, an aryl group or an alkoxy group, R ₂ represents an alkylene group or a phenylene group, and R ₃ represents a nitrogen-containing heterocycle in the structure. R ₄ and R _{5 each} represent a hydrogen atom, an alkyl group or an aryl group, and R ₂ may not be present. However, the above alkyl group, aryl group, alkylene group, and phenylene group may have an amine, or may have a halogen as a substituent as long as the chargeability is not impaired. m is a number of 1 or more, and n and k are positive numbers including 0. However, n + k is a positive number of 1 or more.

  The most preferred structure among the above structures is one in which the number of nitrogen atoms in the side chain containing a nitrogen atom is 1 or 2. An example of the structure of an unsaturated heterocyclic ring having nitrogen is given below.

  An example of the structure is given below as a saturated heterocyclic ring having nitrogen.

  However, the present invention is not limited to the above compound examples, but those having a 5-membered or 6-membered heterocyclic ring are preferred. Examples of the derivative include a derivative in which a hydrocarbon group, a halogen group, an amino group, a vinyl group, a mercapto group, a methacryl group, a glycidoxy group, or a ureido group is introduced into the above compound group. These may be used alone or in combination of two or more.

(I-4) Surface treatment with silicone varnish Examples of the silicone varnish used in the present invention include methyl silicone varnish and phenylmethyl silicone varnish. In particular, in the present invention, methyl silicone varnish is used. Is preferred. Methyl silicone varnish is a polymer composed of T ³¹ units, D ³¹ units and M ³¹ units represented by the following structure, and is a three-dimensional polymer containing a large amount of T ³¹ units.

  Specifically, the methyl silicone varnish or the phenyl methyl silicone varnish is a substance having a chemical structure represented by the following structural formula (III).

式中、Ｒ^３１は、メチル基又はフェニル基を示す。

In the formula, R ³¹ represents a methyl group or a phenyl group.

In the above silicone varnish, the T ³¹ unit is particularly an effective unit for imparting a good thermosetting property to a three-dimensional network structure. It is preferable to use a silicone varnish containing the T ³¹ unit in a range of 10 to 90 mol%, particularly 30 to 80 mol%.

  Such a silicone varnish has a hydroxyl group at the end or side chain of the molecular chain, and is cured by a dehydration condensation reaction of the hydroxyl group. Examples of the curing accelerator that can be used to accelerate the curing reaction include fatty acid salts such as zinc, lead, cobalt, and tin; and amines such as triethanolamine and butylamine. Of these, amines can be preferably used.

In order to make the silicone varnish as described above into an amino-modified silicone varnish, a part of methyl group or phenyl group present in the T ³¹ unit, D ³¹ unit and M ³¹ unit is substituted with a group having an amino group. do it. Examples of the group having an amino group include those represented by the following structural formulas, but are not limited thereto.

  As a surface treatment method of the base material with these silicone oils or silicone varnishes, for example, fine particles and silicone oil or silicone varnish are mixed using a mixer; and silicone oil or silicone varnish is sprayed into fine powder The method of spraying using is mentioned.

  As a treatment form for producing the second fine particles used in the present invention, it is preferable to perform treatment by combining both a silane coupling agent and silicone oil or silicone varnish. As a preferable treatment form, first, treatment with a silane coupling treatment agent and then treatment with silicone oil or silicone varnish can be mentioned. Among these, the form of treating with silicone oil after treating with isobutylsilane is particularly preferred.

Examples of the surface treatment method of the insulating base material with silicone oil and / or silicone varnish include a method of directly mixing fine particles and silicone oil not diluted with a solvent using a mixer such as a Henschel mixer; A method of spraying silicone oil that has not been diluted with a solvent onto the fine particles may be mentioned. In this case, the silicone oil and / or the silicone varnish is more preferable because it can achieve a more uniform treatment if it is heated to a temperature of 50 to 200 ° C. to lower the viscosity. As described above, in the present invention, since the silicone oil and / or silicone varnish is used for the surface treatment without being diluted with a solvent, it is preferable to use one having a kinematic viscosity at 25 ° C. of 500 mm ² / s or less.

  Therefore, in order to obtain the surface-treated fine particles used in the present invention, the fine particles are treated with a silane coupling agent, sprayed with silicone oil or silicone varnish, and then heat-treated at a temperature of 200 ° C. or higher. Are preferably used. According to the method of spraying the silicone oil or the silicone varnish after the treatment with the silane coupling agent during the treatment of the fine particles, and then heating at a high temperature of 200 ° C. or higher, the silicone oil or the silicone varnish is uniformly and strongly applied to the fine particle surface. It becomes possible to adhere to.

  Silicone oil or silicone varnish is used in an amount of 2 to 40 parts by weight, more preferably 5 to 35 parts by weight, based on 100 parts by weight of the base material or coupling-treated base material. Within this range, even when the charging member is left in a severe high-temperature and high-humidity environment, surface treatment components such as silicone oil and silicone varnish are prevented from seeping out onto the surface of the charging member. be able to. In addition, a high quality surface layer can be applied and formed, and the problem of rubbing memory can be alleviated.

  As the particle diameter of the particles used in the present invention, the number average particle diameter (length average) is preferably 1.0 μm or less, and more preferably 0.001 μm to 0.5 μm. By setting the number average particle diameter of the fine particles within this range, the problem of sedimentation in the paint is less likely to occur, and uniform surface treatment can be achieved.

  An electron microscope is used for the measurement of the particle diameter. The shooting magnification is 100,000 times, but if difficult, the image is enlarged to 100,000 times after shooting at a low magnification. Measure the primary particle size on the photo. At this time, the major axis and the minor axis are measured, and the average value is defined as the particle size. This is measured for 100 samples, and the 50% value is taken as the average particle size.

(I-5) ratio of the first particles to the second particles;
As a blending ratio of the first particles and the second particles subjected to different surface treatments using the same base material, the blending ratio of the first particles to the second particles is 1: 1 to 1000: 1. More preferably, it is 10: 1 to 100: 1. By including in the surface layer at such a ratio, the charging member that can suppress the occurrence of image unevenness due to contact with the photoreceptor and the coating unevenness when the surface layer is applied and has a stable charging ability. It can be.

(Ii) a binder;
As the binder for the surface layer, a resin such as a thermosetting resin or a thermoplastic resin is used.

  As the binder for the surface layer of the present invention, a urethane resin obtained by crosslinking a lactone-modified acrylic polyol with isophorone diisocyanate and hexamethylene diisocyanate is particularly preferably used.

  When hexamethylene diisocyanate is used alone as the isocyanate that crosslinks the polyol on the surface layer, the surface layer is flexible and the surface after the application of the roller is uniformly finished. There is a possibility that uncured components (for example, ionic conductive agent and plasticizer) in the base layer cannot be sufficiently prevented from oozing out to the roller surface. The presence of such a leachable substance may contaminate the photoreceptor.

  On the other hand, when isophorone diisocyanate is used alone as the isocyanate that crosslinks the polyol of the surface layer, the surface layer has a great effect of preventing the exudation of the exuding substance from the base layer, but the surface layer becomes too hard to cause heat shrinkage of the base layer rubber. There is an adverse effect that it cannot follow, wrinkles occur on the surface of the completed roller, and the desired roller cannot be obtained in terms of the surface roughness and shape of the roller.

  The surface layer of the roller of the present invention provides a surface layer resin having good properties that combines the exuding substance blocking property of isophorone diisocyanate and the flexibility of hexamethylene diisocyanate, and the exuding material from the ionic base layer is provided on the roller surface. Thus, it is possible to obtain a charging roller having a good surface shape while preventing it from seeping out.

  That is, the resin used for the surface layer in the present invention is such that lactone-modified acrylic polyol, isophorone diisocyanate, and hexamethylene diisocyanate are blended and cured, so that isophorone diisocyanate and hexamethylene diisocyanate react randomly with lactone-modified acrylic polyol. Thus, a crosslinked structure is formed.

  The isocyanate used in the present invention is more preferably an isocyanurate type trimer. The rigid trimer of the molecule serves as a cross-linking point, the surface layer can be cross-linked more closely, and the exudation substance from the ionic base layer is more effectively prevented from exuding on the roller surface. Can do.

  The isocyanate used in the present invention is more preferably a blocked isocyanate in which an isocyanate group is blocked with a blocking agent. The reason for this is that the isocyanate group is easy to react, and if the surface coating is left at room temperature for a long time, the reaction gradually proceeds and the characteristics of the coating may change. On the other hand, the blocked isocyanate has an advantage that the active isocyanate group is blocked and does not react up to the dissociation temperature of the blocking agent, so that the paint can be easily handled. Examples of the blocking agent for masking include phenols such as phenol and cresol, lactams of ε-caprolactam, and oximes such as methyl ethyl ketoxime. In the present invention, oximes having a relatively low dissociation temperature are used. preferable.

  1 illustrates a trimer of a lactone-modified acrylic polyol and a blocked isocyanate constituting a surface layer resin used in the present invention.

  On the other hand, the OH value of the lactone-modified acrylic polyol is preferably about 80 KOHmg / g. When the OH value is small, it is difficult to crosslink with an isocyanate, whereby the resin becomes too soft and easily sticks to the photoreceptor. If the OH group is too large, the coating film becomes too hard and easily cracks.

  The lactone-modified acrylic polyol used in the present invention is a copolymer of styrene and acrylic with a molecular chain skeleton, and has an appropriate hardness and non-contaminating property. In addition, the modified lactone group having a hydroxyl group at the terminal serves as a number of cross-linking points, and it is possible to cross-link closely with an isocyanate, thereby preventing the unvulcanized component from exuding from the base layer. Examples of such lactone-modified acrylic polyol include Plaxel DC2009 (manufactured by Daicel Chemical Industries, Ltd.).

  The glass transition temperature Tg of the resin used for the surface layer is a viscoelasticity measurement method, and the peak temperature is preferably 45 ° C. or higher, and particularly preferably 50 ° C. or higher. When the temperature is lower than 45 ° C., it is not preferable because it may be adhered to the photoconductor when left in contact with the photoconductor for a long period of time, or the surface of the charging roller is easily contaminated with toner. .

  The measuring method of the glass transition temperature Tg in the present invention is as follows. First, a surface layer sample for measurement is peeled off from the roller state and cut into a strip of about 5 mm × 40 mm. 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.

  Although not particularly limited, too high Tg is not preferable because the flexibility of the resin is lost and the coating film is easily broken. Tg is adjusted by the ratio or amount of isocyanate to be crosslinked.

  The blending ratio of the lactone-modified acrylic polyol resin and the isocyanate is the ratio of the number of NCO groups (A) in the isocyanate in the blended paint to the number of OH groups (B) in the lactone-modified acrylic polyol resin, NCO The / OH ratio = A / B is preferably 0.1 to 2.0, and particularly preferably adjusted to be in the range of 0.3 to 1.5.

  By cross-linking the lactone-modified acrylic polyol with isocyanate, it prevents the low-molecular component from oozing out from the conductive elastic base layer, and the surface layer on which the charging roller itself is not easily contaminated with toner and does not contaminate the photoreceptor. Can be formed.

  It is also preferable to mix various conductive agents and leveling agents into the resin coating that forms the surface layer. Examples of the leveling agent include silicone oil.

(Iii) a conductive agent;
Examples of the conductive agent used for the surface layer include metal powders and fibers such as aluminum, palladium, iron, copper, and silver, carbon black, metal powder, metal oxides such as titanium oxide, tin oxide, and zinc oxide, and copper sulfide. Electrolytic treatment, spray coating, metal compounds such as zinc sulfide, tin oxide, antimony oxide, indium oxide, molybdenum oxide, zinc, aluminum, gold, silver, copper, chromium, cobalt, iron, lead, platinum, rhodium, Examples thereof include powders adhered to the surface by mixed shaking, carbon powders such as acetylene black, ketjen black, PAN-based carbon, and pitch-based carbon.

  In the present invention, conductive tin oxide is particularly preferably used as the conductive agent. The reason is that conductive tin oxide has a relatively large volume resistivity of the conductive agent itself, and the difference from the volume resistivity of the resin in which the conductive agent is dispersed is small compared to other conductive agents. When dispersed and used as a surface layer material of medium resistance, a slight difference in the distribution of the conductive agent hardly causes a difference in the resistance of the surface layer material, and it is possible to suppress variation due to the position of the resistance relatively small. It is because it is suitable as a conductive agent for the surface layer material.

  Examples of the conductive tin oxide include oxygen-deficient tin oxide, fluorine-doped tin oxide, phosphorus-doped tin oxide, tungsten-doped tin oxide, antimony-doped tin oxide, and indium-doped tin oxide.

The amount of these conductive agents added to the surface layer resin is such that the volume resistivity of the surface layer resin is a low temperature and low humidity environment (L / L: 15 ° C./10% RH), a normal temperature and normal humidity environment (N / N: 23 ° C. / 55% RH) and a high-temperature and high-humidity environment (H / H: 30 ° C./80% RH) so that the medium resistance region (volume resistivity is 1 × 10 ⁶ to 1 × 10 ¹⁵ Ω · cm).

  When the volume resistivity of the surface layer is smaller than this, when used as a charging roller, when there is a pinhole in the photoconductor, an excessive current flows through the pinhole and leaks, and the leaked trace appears in the image. Therefore, it is not preferable. On the other hand, if the volume resistivity is too large, no current flows through the charging roller, and the photosensitive member cannot be charged to a predetermined potential, so that the image does not have the desired density. Further, even if the potential is charged to a certain level, it is not preferable because the charging becomes non-uniform and appears on the image.

  For the volume resistance of the surface layer, the surface layer is peeled off from the roller state and cut into a strip of about 5 mm × 5 mm. Metal is vapor-deposited on both sides to produce an electrode and a guard electrode, and a voltage of 200V is applied using a microammeter (ADVANTEST R8340A ULTRA HIGH RESISTANCE METER Co., Ltd., Advantest) to measure the current after 30 seconds. And calculated from the film thickness and the electrode area.

  As a compounding quantity of electroconductive tin oxide, 10-80 mass% is preferable with respect to the surface layer after coating, Most preferably, it is 20-60 mass%. The primary particle size of the conductive tin oxide is preferably 0.1 μm or less by observation with a differential scanning electron microscope. Disperse by a known method until the secondary particles become small in the surface coating. The secondary particle size is a value of volume average particle size MEDIAN measured by a centrifugal sedimentation type particle size distribution meter (CAPA700: manufactured by Horiba Seisakusho), preferably 1.0 μm or less, and particularly preferably 0.5 μm or less. If the secondary particle diameter is large, the variation due to the position of the resistance of the surface layer material becomes large, which causes uneven charging.

  The surface of the conductive tin oxide used in the present invention is preferably subjected to the surface treatment described in the section of the surface treatment of fine particles. Specifically, the surface treatment is preferably performed with a silane coupling agent, particularly a silane coupling agent containing a compound having a branched chain alkyl group in the molecule such as isobutylsilane. The charging member having such a configuration extremely effectively suppresses deterioration in charging ability or unevenness even when the charging member is incorporated in a process cartridge and left in a high temperature and high humidity condition for a long time. be able to.

(Iv) Resin fine particles The surface layer of the charging member of the present invention preferably contains resin fine particles for roughening the surface of the charging roller. More preferably, the resin fine particles are cross-linked fine particles. If it is not cross-linked, it is not preferred because it may dissolve when used as a coating for surface coating. The monomer for forming the crosslinked polymer fine particles is not particularly limited, but vinyl monomers are preferably used from the viewpoint of ease of polymerization.

  Examples of the vinyl monomer used in the present invention include acrylic acid esters such as methyl acrylate, butyl acrylate and 2-ethylhexyl acrylate, and methacrylates such as methyl methacrylate, butyl methacrylate and hexyl methacrylate, Examples thereof include aromatic vinyl monomers such as styrene, p-methylstyrene, and α-methylstyrene, vinyl acetate, and acrylonitrile.

  In order to form polymer particles in which the resin particles are crosslinked, in the present invention, a crosslinkable vinyl monomer having two or more vinyl groups in the molecule is used in addition to the above vinyl monomer. Examples of such a crosslinkable vinyl monomer include ethylene glycol diacrylate, ethylene glycol dimethacrylate, trimethylolpropane triacrylate, trimethylolpropane trimethacrylate, and the like. The addition amount of these crosslinkable vinyl monomers is preferably 0.5 to 30 parts by mass with respect to the non-crosslinkable vinyl monomer.

  These crosslinked polymer fine particles are polymerized by seed emulsion polymerization, dispersion polymerization, suspension polymerization, etc., but are preferably polymerized by suspension polymerization because there is little residue of a low molecular surfactant or the like. . The polymerization initiator is not particularly limited, and examples thereof include peroxide catalysts such as benzoyl peroxide and lauroyl peroxide, and azo catalysts such as azobisisobutyronitrile.

  It is more preferable that the crosslinked polymer fine particles used in the present invention have a more nearly spherical shape.

  Specifically, the average circularity is preferably 0.95 or more. By precisely controlling the particle shape of the polymer fine particles so that the average circularity is 0.95 or more, the surface roughness of the charging roller becomes uniform, and the charging characteristics are more uniform even when used at different process speeds. Can be obtained.

  Furthermore, the circularity standard deviation is more preferably less than 0.040. By precisely controlling the particle shape of the polymer fine particles so that the standard deviation of the circularity is less than 0.04, the ratio of the resin fine particles far away from the true sphere is reduced, suddenly on the surface of the charging roller. The probability that the protrusions of the resin particles are generated and disturb the charging is suppressed, the surface roughness of the charging roller becomes more uniform, and even charging characteristics can be obtained even when used at different process speeds.

  The circularity in the present invention is used as a simple method for quantitatively expressing the particle shape. In the present invention, the particle shape is measured using a flow particle image analyzer FPIA-1000 manufactured by Toa Medical Electronics. The circularity is obtained by the following formula. Furthermore, as shown by the following equation, a value obtained by dividing the total roundness of all the measured particles by the total number of particles is defined as the average circularity.

  Here, the “particle projected area” is the area of the binarized resin particle image, and the “peripheral length of the particle projected image” is the length of the contour line obtained by connecting the edge points of the resin particle image. Define.

  In addition, “FPIA-1000”, which is a measuring apparatus used in the present invention, calculates the circularity of each particle, and then calculates the average circularity and the circularity standard deviation. Degrees of 0.400 to 1.000 at intervals of 0.010, 0.400 or more and less than 0.410, 0.410 or more and less than 0.420 ... 0.990 or more and less than 1.000 and 1.000 A calculation method is used in which the average circularity and the circularity standard deviation are calculated using the center value and frequency of the division points.

  Error between each value of average circularity and circularity standard deviation calculated by this calculation method and each value of average circularity and circularity standard deviation calculated by the above-described calculation formula that directly uses the circularity of each particle. Is very small and substantially negligible. Therefore, in the present invention, the circular shape of each particle described above is used for the reason of handling data such as a short calculation time and a simplified calculation formula. This calculation method is partially modified by using the concept of a calculation formula that directly uses the degree.

  The circularity in the present invention is an index indicating the degree of unevenness of particles, and is 1.000 when the particles are completely spherical, and the circularity becomes smaller as the surface shape becomes more complicated.

  As a specific measurement method, 10 ml of ion-exchanged water from which impure solids and the like are previously removed is prepared in a container, and a surfactant, preferably an alkylbenzene sulfonate, is added as a dispersant therein, and then further measurement is performed. Add 0.02 g of sample and disperse uniformly. As a means for dispersion, an ultrasonic disperser “UH-50 type” (manufactured by SMT Co., Ltd.) equipped with a titanium alloy chip of φ5 mm as a vibrator is used. To do. In that case, it cools suitably so that the temperature of this dispersion may not be 40 degreeC or more.

  For the measurement of the shape of the resin particles, the flow type particle image measuring apparatus is used, and the concentration of the dispersion is readjusted so that the resin particle concentration at the time of measurement is 3000 to 10,000 particles / μl. measure.

  The average particle size of the resin particles is preferably 100 μm or less, more preferably 0.5 to 50 μm, and still more preferably 1 to 25 μm. Moreover, it is preferable that there are substantially no resin particles having a particle size of 3 times or more the mass average particle size. If the particle size is too large, the charging roller surface becomes too rough and charging becomes uneven. On the other hand, if it is too small, the effect of stabilizing charging in the region of low process speed by adding resin particles does not appear.

  Below, the specific example of the particle size measurement of the resin particle in this invention is shown.

  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 a measurement sample is added thereto. The electrolytic solution in which the sample is suspended is dispersed for 1 to 3 minutes using an ultrasonic disperser, and 0.3 μm based on the volume using an aperture that is appropriately matched to the resin particle size such as 17 μm or 100 μm by a Coulter counter multisizer. The particle size distribution of ˜40 μm is measured. The number average particle size and mass average particle size measured under these conditions are obtained by computer processing, and the cumulative ratio of the weight average particle size more than the triple diameter cumulative distribution is calculated from the volume-based particle size distribution. Find the cumulative value of.

  The addition amount of the resin particles is preferably 1 to 80% by mass as a mass ratio in the surface layer after coating. If the amount is too small, the effect of stabilizing the charging by adding resin particles cannot be obtained. If the amount is too large, it is difficult to control the viscosity of the surface coating material, and it is difficult to uniformly apply the coating.

Conductive Support The conductive support 1 in FIG. 1 is a cylinder having a nickel plating with a thickness of 5 μm on the surface of a carbon steel alloy, for example. In addition to the materials constituting the conductive support, for example, metals such as iron, aluminum, titanium, copper and nickel, alloys such as stainless steel, duralumin, brass and bronze containing these metals, and carbon black and carbon fibers are also included. It is also possible to use a known material that is rigid and shows conductivity, such as a composite material hardened with plastic. Moreover, as a shape, it can also be set as the cylindrical shape which made the center part the cavity other than column shape.

Conductive Elastic Base Layer The conductive elastic base layer 2 is formed so as to cover the outer periphery of the conductive support 1. The conductive elastic base layer 2 is made of a conductive elastic body. The conductive elastic body is formed by mixing a conductive agent and a polymer elastic body. The conductive agent contains at least an ionic conductive agent. As the polymer elastic body, epichlorohydrin rubber is particularly preferably used. Epichlorohydrin rubber has some conductivity in the rubber itself, can exhibit good conductivity even with a small amount of conductive agent added, and can also reduce variations in electrical resistance depending on the environment and position. Therefore, it is suitably used as a polymer elastic body.

  Epichlorohydrin rubber is a ring-opening polymer of a cyclic ether centered on epichlorohydrin. Examples of main monomers constituting the rubber include epichlorohydrin, ethylene oxide, and acryl glycidyl ether.

  Examples of the epichlorohydrin rubber that is a polymer include epichlorohydrin homopolymer, epichlorohydrin-ethylene oxide copolymer, epichlorohydrin-allyl glycidyl ether copolymer, epichlorohydrin-ethylene oxide-allyl glycidyl ether terpolymer, and the like. Of these, epichlorohydrin-ethylene oxide-allyl glycidyl ether terpolymer is particularly preferably used since it exhibits stable conductivity in a 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.

  The polymer elastic body is mainly composed of epichlorohydrin rubber, but may contain other general rubbers as necessary.

  Examples of other general rubbers include EPM (ethylene / propylene rubber), EPDM (ethylene / propylene rubber), norbornene rubber, NBR (nitrile rubber), chloroprene rubber, natural rubber, isoprene rubber, butadiene rubber, styrene- Examples thereof include butadiene block, chlorosulfonated polyethylene, urethane rubber, styrene block copolymers such as SBS (styrene / butadiene / styrene / block copolymer), SEBS (styrene / ethylene butylene / styrene / block copolymer), and silicone rubber.

  When it contains said general rubber, it is preferable that the content is 1-50 mass% with respect to the polymer elastic body whole quantity.

  As the conductive agent, it is necessary to contain an ionic conductive agent for the purpose of reducing unevenness in electrical resistivity of the conductive elastic base layer. By uniformly dispersing the ionic conductive agent in the polymer elastic body and making the electronic resistivity of the conductive elastic body uniform, uniform charging can be obtained even when the charging roller is used with only DC voltage applied. be able to.

The ion conductive agent, for example, perchlorate such as LiClO ₄ and NaClO _4, include quaternary ammonium salts and the like can be used in combination singly or two or more kinds. Among ionic conductive agents, quaternary ammonium perchlorate is particularly preferably used because of its resistance to environmental changes.

  In addition to the ionic conductive agent, an electronic conductive conductive agent can be added within a range that does not cause unevenness in the electrical resistance of the conductive elastic body. The electroconductive conductive agent can be used in a range in which the electrical conductivity of the electronic conductive agent is smaller than the electrical conductivity of the ionic conductive agent. That is, the electron conductive conductive agent has a volume resistivity in the case of adding and adding an electron conductive conductive agent to the volume resistivity in the case where only the ionic conductive agent is added to the polymer elastic body. It can be used at a blending ratio of 2 or more. Examples of the electron conductive conductive agent include metal powders and fibers such as aluminum, palladium, iron, copper, and silver, carbon black, metal powders, metal oxides such as titanium oxide, tin oxide, and zinc oxide, Metal oxide powder such as copper sulfide and zinc sulfide, or the surface of appropriate particles tin oxide, antimony oxide, indium oxide, molybdenum oxide, zinc, aluminum, gold, silver, copper, chromium, cobalt, iron, lead, platinum, Examples of the powder include rhodium powder deposited by electrolytic treatment, spray coating, and mixed shaking, acetylene black, ketjen black, PAN (polyacrylonitrile) carbon, pitch carbon, and the like. These can be used alone or in combination of two or more.

In the present invention, the blending amount of these conductive agents is such that the volume resistivity of the conductive elastic body is a low temperature and low humidity environment (L / L: 15 ° C./10% RH), a normal temperature and normal humidity environment (N / N: 23 ° C. / 55% RH), in a high-temperature and high-humidity environment (H / H: 30 ° C./80% RH), the amount is such that the middle resistance region (volume resistivity is 1 × 10 ⁴ to 1 × 10 ⁷ Ω · cm). preferable.

  The volume resistance of the conductive elastic body was molded into a sheet having a thickness of 1 mm, and then metal and metal were vapor-deposited on both sides to produce an electrode and a guard electrode. ADVANTEST R8340A ULTRA HIGH RESISTANCE METER Co., Ltd. Advantest A voltage of 200 V is applied using a product, a current after 30 seconds is measured, and the current is calculated from the film thickness and the electrode area.

  If the volume resistivity of the conductive elastic body is smaller than this, if there is a pinhole in the photoconductor that is the image carrier, a large current will be concentrated in the pinhole, making the hole larger. There is a risk that a current may not flow in a place other than the hole and a black band may appear on a high-definition halftone image, and a portion with insufficient charging potential may appear. On the contrary, if the volume resistivity is too large, the applied voltage drops in the conductive elastic layer, and the required discharge current cannot be obtained and the photoreceptor cannot be uniformly charged to a desired potential. is there.

  Other additives such as plasticizers, fillers, vulcanizing agents, vulcanization accelerators, anti-aging agents, scorch preventing agents, dispersants and mold release agents are added to the conductive elastic body as necessary. It is also preferable.

  Examples of the method for forming the conductive elastic body include known methods such as extrusion molding, injection molding, and compression molding by mixing the raw materials for the conductive elastic body. The conductive elastic base layer may be produced by directly forming a conductive elastic body on the conductive support, or by covering the conductive support with a conductive elastic body formed into a tube shape. Also good. Note that the surface may be polished and the shape may be adjusted after the production of the conductive elastic base layer.

  The shape of the conductive elastic base layer is such that the diameter of the central portion of the conductive elastic base layer roller is the end so that the contact nip width between the completed charging roller and the photoreceptor is as uniform as possible in the longitudinal distribution of the roller. It is preferable that the crown shape is larger than the diameter. In addition, since the contact nip width of the completed roller becomes uniform, it is preferable that the conductive elastic base layer roller has a small runout.

  As shown in FIG. 2, the measured value of run-out is obtained by rotating a conductive elastic base layer roller about a conductive substrate as a rotation axis, and a non-contact laser length measuring device perpendicular to the rotation axis (in the present invention, Keyence Corporation). The difference between the maximum value and the minimum value of the radius of the conductive elastic base layer measured by LS-5000) is obtained as a value. The difference between the maximum value and the minimum value of the radius is obtained at a pitch of 1 cm in the axial direction of the conductive elastic base layer, and the maximum value among these values is set as the deflection value of the conductive elastic base layer roller.

  Similarly, the diameter of the roller is the maximum of the diameter of the conductive elastic base layer measured by a non-contact laser length measuring device perpendicularly to the rotational axis by rotating the conductive elastic base layer roller around the conductive base. The average of the value and the minimum value.

  The difference between the diameter of the central portion in the axial direction of the conductive elastic base layer roller and the average of the two values of the diameter of the central portion 10 mm from both ends of the elastic body is obtained as the value of the crown amount.

  A preferable value of the deflection of the conductive elastic base layer roller is 0.7% or less, more preferably 0.5% or less of the diameter of the central portion of the roller. Since the diameter of the roller of the present invention is preferably about 9 mm, the deflection value is specifically preferably 63 μm or less, more preferably 45 μm or less.

  The value of the crown amount is determined so that the nip width of the completed roller is uniform, but preferably 0.1 to 5.0% of the roller diameter, specifically 12 to 600 μm.

  The Asker C hardness of the conductive elastic body is preferably 85 ° or less, and more preferably 80 ° or less. When the Asker C hardness exceeds 85 °, the nip width between the charging member and the photosensitive member is reduced, the contact force between the charging member and the photosensitive member is concentrated in a narrow area, and the contact pressure is increased. As a result, adverse effects such as charging becoming unstable or developer or the like being easily attached to the surface of the photosensitive member or the charging member become remarkable.

  The “Asker C hardness” is the hardness of the charging member measured using an Asker C spring rubber hardness tester (manufactured by Kobunshi Keiki Co., Ltd.) in accordance with Japan Rubber Association standard SRIS0101, and is at normal temperature and humidity. A value measured 30 seconds after the hardness meter is brought into contact with a charging member left in an environment of (23 ° C./55% RH) for 12 hours or more with a force of 10 N.

  In order to reduce Asker C hardness, a plasticizer is blended in the conductive elastic body. The amount is preferably 1 part by mass or more, more preferably 3 parts by mass or more. As the plasticizer, for example, an ester-based polymer plasticizer such as a copolymer of sebacic acid and propylene glycol can be used. Such ester plasticizers are close in polarity to epichlorohydrin rubber, can be blended in a relatively large amount, and have an advantage that the hardness of the base layer can be controlled small. The molecular weight of the polymer plasticizer is preferably 2000 or more, more preferably 4000 or more. If the molecular weight is less than 2000, the plasticizer may ooze out on the surface of the roller and contaminate the photoreceptor.

  The conductive elastic base layer is bonded to the conductive support through an adhesive as necessary. In this case, the adhesive is preferably conductive. In order to make it conductive, the adhesive may have a known conductive agent.

  Examples of the binder of the adhesive include resins such as a thermosetting resin and a thermoplastic resin, and known adhesives such as urethane, acrylic, polyester, polyether, and epoxy can be used.

The conductive agent, for example, perchlorate such as LiClO ₄ and NaClO _4, the ion conductive agent such as quaternary ammonium salts, aluminum, palladium, iron, copper, metal-based powder and fibers such as silver, carbon black , Metal oxide such as metal powder, titanium oxide, tin oxide, zinc oxide, metal compound powder such as copper sulfide, zinc sulfide, or the surface of appropriate particles of tin oxide, antimony oxide, indium oxide, molybdenum oxide, zinc, Aluminum, gold, silver, copper, chromium, cobalt, iron, lead, platinum, rhodium, electrolytic powder, powder applied by spray coating, mixed shaking, acetylene black, ketjen black, PAN (polyacrylonitrile) There are carbon powders such as carbon and pitch-based carbon. These can be used alone or in combination of two or more.

-Surface layer After the conductive elastic base layer is completed, a surface layer 3 that covers the outermost surface of the charging roller is provided.

  As a method for forming the surface layer, the materials constituting the surface layer of the above (i) to (iv) are prepared by a known method using a conventionally known dispersing device using beads such as a sand mill, a paint shaker, a dyno mill, and a pearl mill. The obtained resin coating for forming the surface layer is dispersed and applied on the surface of the charging member, in the present invention, on the conductive elastic base layer by dip coating.

  The film thickness of the surface layer is preferably 5 to 100 μm, more preferably 10 to 50 μm. When the thickness of the surface layer is larger than 100 μm, the uniformity of charging is impaired, and fine white stripes are generated in the axial direction of the image upper roller, which is not preferable. The film thickness can be measured by cutting the roller cross section with a sharp blade and observing it with an optical microscope or an electron microscope.

  In the present invention, a cross-sectional photograph of 2000 times is taken with a microscope, film thicknesses at five locations are measured randomly in one screen, and the film thickness at one location is calculated by averaging the lengths. This measurement was carried out for a total of 6 points of 3 points in the axial direction and 2 points in the circumferential direction of the same roller, and averaged to obtain the total average film thickness.

  To adjust the surface layer thickness, the solid content of the surface layer paint and the coating pull-up speed are controlled. When the solid content of the resin in the surface coating is increased, the film thickness of the surface layer is increased, and when the solid content is decreased, the film thickness is also decreased. In the surface coating composition of the present invention, the solid content of the resin with respect to the volatile solvent is adjusted to 10 to 40%. Further, when the coating pulling speed is increased, the film thickness is increased, and when the coating pulling speed is decreased, the film thickness is decreased. Adjust to.

  As the surface roughness of the charging member of the present invention, preferably the ten-point average roughness Rz according to JIS B0601-1994 is 0.5 μm to 40 μm, Ra is 0.1 μm to 5 μm, more preferably the ten-point average roughness. Rz is from 1 μm to 30 μm, and Ra is from 0.4 μm to 3 μm. When the surface roughness of the charging member is within the above range, it becomes difficult to appear in the output image as charging unevenness, and both the stabilization of charging at a slow process speed and suppression of charging unevenness are high by adding resin particles. You can be satisfied with the level.

  As a measuring method of average roughness (Ra, Rz), based on the surface roughness of JIS B0601, surf coder SE3400 manufactured by Kosaka Laboratories was used to measure a total of 6 points, 3 in the axial direction and 2 in the circumferential direction. , Take the average value. In the present invention, the contact needle is 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.

  In order to obtain a charging member having a surface roughness in the above range, the surface roughness of the base layer, the film thickness of the surface layer, the average particle diameter of the resin particles, and the addition amount are adjusted. The ten-point average roughness of the base layer is 20 μm or less, more preferably 15 μm or less in terms of Rz.

Further, as shown in FIGS. 6A and 6B, the charging member of the present invention has a circular cylindrical shape having the same curvature as that of the photosensitive member under the same stress as that in the use state when used in the image forming apparatus. While abutting against the metal 32 and rotating the columnar metal at the same rotational speed as in the state of use (in the present invention, a force of 5 N is applied to both ends of the support 1 to contact the metal cylinder with a diameter of 30 mm. The electric resistance of the charging member when a DC voltage of −250 V (rotated at a peripheral speed of 45 mm / s of the metal cylinder) is applied is 1 × 10 ⁶ Ω in a high temperature and high humidity environment of 30 ° C./80% RH. Thus, it is preferably 1 × 10 ⁸ Ω or less in a low temperature and low humidity environment of 15 ° C./10%. More preferably, it is 2 × 10 ⁶ Ω or more in a high temperature and high humidity environment of 30 ° C./80% RH, and it is preferably 6 × 10 ⁷ Ω or less in a low temperature and low humidity environment of 15 ° C./10%.

  By setting the resistance value in a low-temperature and low-humidity environment within the above range, fine horizontal white lines on the halftone image due to charging unevenness hardly occur. Further, by setting the resistance in a high temperature and high humidity environment within the above range, even if there is a pinhole in the photoconductor, the applied current does not leak, and the uneven density of charging does not appear on the halftone image.

In order to set the electric resistance within the above range, the volume resistivity of the conductive elastic base layer of the charging member is 1 × 10 ⁴ to 1 × 10 ⁷ Ω · cm, and the volume resistivity of the surface layer is 1 × 10 ⁸ to 1 What is necessary is just to adjust so that it may be x10 < ¹⁵ > (omega | ohm) * cm and the film thickness of a surface layer may be 10-50 micrometers.

<2> Image Forming Apparatus FIG. 3 is a schematic cross-sectional view of an image forming apparatus using a charging roller 6 which is an embodiment of a charging member according to the present invention. The photosensitive drum 5 as an image carrier is primarily charged by the charging roller 6 while rotating in the direction of the arrow, and then exposed to exposure 11 by the exposure means to form an electrostatic latent image. The toner in a thin layer on the developing roller 4 as developing means is charged by the toner charging roller 29 and then brought into contact with the surface of the photosensitive drum 5 to develop the electrostatic latent image and visualize the toner image. Is formed.

  The developed toner image is transferred from the photosensitive drum 5 to the print medium 7 as the transfer target member in the developing portion between the transfer roller 8 as the transfer member and the photosensitive drum 5, and then heated and fixed in the fixing portion 9. It is fixed by pressure and becomes a permanent image. The latent image remaining on the photosensitive drum is exposed by the pre-charging exposure device 11, and the potential of the photosensitive drum returns to the ground potential. The untransferred toner that has not been transferred is collected by the cleaning blade 10.

  Voltages are respectively applied to the developing roller 4, the toner charging roller 29, the charging roller 6, and the transfer roller 8 from power sources 18, 19, 20, and 22 of the image forming apparatus.

  Here, a DC voltage is applied from the power source 20 to the charging roller 6 which is the charging member of the present invention. By using a DC voltage as the applied voltage, there is an advantage that the cost of the power supply can be kept low. In addition, there is an advantage that no charging noise is generated when an AC voltage is applied.

  The absolute value of the DC voltage to be applied is preferably the sum of the discharge start voltage of air and the primary charging potential of the surface of the member to be charged (photosensitive member surface). Usually, the discharge start voltage of air is about 600 to 700 V, and the primary charging potential of the photoreceptor surface is about 300 to 800 V. Therefore, the specific primary charging voltage is preferably 900 to 1500 V.

  In the case of a full-color image forming apparatus, as shown in FIG. 4, the photosensitive drums 5a to 5d, the image rollers, the transfer rollers 8a to 8d, the charging rollers 6a to d, the toner charging rollers 29a to 29d, and the elastic regulation blades 30a to 30d. d, exposures 11a to 11d, toner containers 31a to 31d and the like may be prepared for each of four colors and arranged in series.

<3> Charging method The present invention provides a charging method for charging an object to be charged by applying a DC voltage to a charging member.

<4> Process Cartridge As shown in FIG. 5, the process cartridge according to the present invention transfers toner to a photosensitive member 5 that is an image carrier and an electrostatic latent image formed on the image carrier. Developing means including a developing roller 4 for visualizing and forming a toner image; and cleaning means including a cleaning blade 10 for removing toner remaining on the image carrier after the toner image is transferred to the transfer member. One or two or more selected are supported by the casing integrally with the charging member 6 according to the present invention, and are configured to be detachable from the main body of the image forming apparatus.

  Before the electrophotographic process cartridge is used, it is preferable to avoid contact between the developing roller 4 and the toner by the toner seal 27.

  The present invention will be described below with reference to examples, but the present invention is not limited to the examples.

(Example 1)
<Production of charging roller>
(1) Preparation of Conductive Elastic Base Layer Epichlorohydrin rubber (trade name: Epichromer CG102, manufactured by Daiso Corporation) 100 parts by mass, calcium carbonate 30 parts by mass as a filler, zinc stearate 1 part by mass as a lubricant, polishing Colored grade carbon (trade name: SEAST SO, manufactured by Tokai Carbon Co., Ltd.) 4 parts by mass, zinc oxide 5 parts by mass, and a plasticizer, sebacic acid and propylene glycol copolymer (molecular weight 8000) 5 parts by weight, 2 parts by weight of perchloric acid quaternary ammonium salt of the following formula, and 1 part by weight of 2-mercaptobenzimidazole as an antioxidant are mixed for 20 minutes with an open roll, and further DM as a vulcanization accelerator. (2-benzothiazolyl disulfide) 1 part by mass, TS (tetramethylthiuram monosulfide) as a vulcanization accelerator Aid) 0.5 parts by mass and 1.2 parts by mass of sulfur as a vulcanizing agent were added, and the mixture was further kneaded with an open roll for 15 minutes.

  This was extruded into a cylindrical shape with an outer diameter of 13 mm and an inner diameter of 5.5 mm using a rubber extruder, cut into a length of 250 mm, and primary in 40 ° C. water vapor at 160 ° C. for 40 minutes. Vulcanized to obtain a primary vulcanized tube of conductive elastic base layer rubber.

  Next, a thermosetting adhesive of metal and rubber (trade name: product name: 231 mm in the axial central portion 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. Metallock U-20) was applied, dried at 80 ° C. for 30 minutes, and then dried at 120 ° C. for 1 hour. This conductive support was inserted into the conductive elastic base layer rubber primary vulcanization tube, then subjected to secondary vulcanization and curing of the adhesive in an electric oven at 160 ° C. for 2 hours to form an unpolished layer. Obtained.

  After cutting off both ends of the rubber part of this unpolished layer and setting the length of the rubber part to 231 mm, the rubber part is polished with a rotating grindstone to form a crown shape with an end diameter of 8.40 mm and a central part diameter of 8.50 mm. A charging roller having a conductive elastic base layer having a surface ten-point average roughness Rz of 6 μm and a deflection of 25 μm was obtained.

When the charging roller having the conductive elastic base layer was measured after the charging roller having the conductive elastic base layer was left in an N / N (normal temperature and normal humidity: 23 ° C./55% RH) environment for 24 hours or more, the resistance of the charging roller having the conductive elastic base layer was measured. It was 3.0 × 10 ⁵ Ω. The Asker C hardness of the rubber part was 74 °.

(2) Preparation of surface layer coating liquid 50 parts by mass of conductive tin oxide powder (trade name: SN-100P, manufactured by Ishihara Sangyo Co., Ltd.), 500 parts by mass of 1% isopropyl alcohol solution of isobutylsilane and average particle diameter Add 300 parts by weight of 0.8 mm glass beads, disperse with a paint shaker for 70 hours, filter the dispersion through a 500 mesh screen, and then warm the solution in a 100 ° C. water bath while stirring with a Nauta mixer. Alcohol was blown off and dried, and a silane coupling agent was applied to the surface to obtain a surface-treated conductive tin oxide powder.

  100 parts by mass of insulating rutile-type titanium oxide fine particles (primary particle size 0.02 μm) were surface-treated with 10 parts by mass of isobutylsilane by a wet method. This surface-treated titanium oxide corresponding to the first particles in the present invention is referred to as titanium oxide A.

An amount corresponding to 100 parts by mass of the base mass of titanium oxide A was surface-treated with 10 parts by mass of dimethyl silicone oil having a kinematic viscosity of 100 mm ² / s at 25 ° C. The surface-treated titanium oxide corresponding to the second particles in the present invention is referred to as titanium oxide B.

  288 parts by mass of lactone-modified acrylic polyol (trade name: Plaxel DC2016, manufactured by Daicel Chemical Industries, Ltd.) was dissolved in 972 parts by mass of MIBK (methyl isobutyl ketone) to obtain a solution having a solid content of 14% by mass. 48 parts by mass of the surface-treated conductive tin oxide powder, 6.5 parts by mass of titanium oxide A, 0.3 parts by mass of titanium oxide B, silicone oil (trade name: 0.04 parts by mass of SH-28PA, manufactured by Toray Dow Corning Silicone Co., Ltd., 17 parts by mass of crosslinked polymethyl methacrylate (trade name: MBX-5, manufactured by Sekisui Plastics Co., Ltd.) having an average particle size of 5 μm Was formulated.

  30 liters of the above blended solution was put into a stainless steel cylindrical container having a diameter of 30 cm, and the stirring blade was rotated at 300 rpm and stirred for 30 minutes. 30 liters of this dispersion was circulated in a horizontal bead mill with an internal volume of 2 liters filled with 80% 0.8 mm glass beads and dispersed. It was dispersed for 20 hours while rotating at a peripheral speed of 4 mm / s, a circulation rate of 2 liters / minute, and a temperature of the outer wall of the mill of 22 ° C. Block type isocyanurate type trimer of isophorone diisocyanate (trade name: Bestanat B1370, manufactured by Degussa Huls) and isocyanurate type trimer of hexamethylene diisocyanate with respect to 370 parts by mass of this dispersion (Product name: Duranate TPA-B80E, manufactured by Asahi Kasei Kogyo Co., Ltd.) was mixed at a ratio of 12.9 parts by mass, stirred for 1 hour with a ball mill, and finally filtered with a 200 mesh net to obtain a surface coating material. The viscosity of the paint was 7.8 mPa · s under an environment of 23 ° C.

  This coating liquid was put into a coating tank for dip coating, and slowly circulated for 12 hours. When the liquid was stabilized, the coating was applied to the base layer. The surface coating was applied by dip coating to 300 mm / min. It applied to the surface of the said electroconductive elastic body base layer at the speed | rate. After air-drying for 15 minutes, the axis direction during roller application is reversed and coating is continued. Inversion was applied in the same manner as the first coating. After air-drying again for 30 minutes, it was dried in an oven at 80 ° C. for 30 minutes, and then dried in an oven at 160 ° C. for 60 minutes.

  A surface layer having a uniform film thickness of 18 μm was formed on the obtained charging roller over the entire image area of the roller. The completed roller was used as the charging roller of Example 1.

<Evaluation of charging roller>
-Evaluation of coating property 100 charging rollers of Example 1 were continuously applied, and the coating finish was observed. All 100 pieces had a good surface finish without unevenness.

Image Evaluation The electrophotographic laser printer used in this test is an A4 vertical output machine, the output speed of the recording medium is 100 mm / sec and 30 mm / sec, and the image resolution is 600 dpi.

  The photoreceptor is a reversal development type photosensitive drum in which an aluminum cylinder is coated with an OPC layer having a film thickness of 16 μm, and the outermost layer is a charge transport layer using a modified polyarylate resin as a binder resin.

  The toner is made by polymerizing a random copolymer of styrene and butyl acrylate containing a charge control agent and a pigment mainly with wax, further polymerizing a thin polyester layer on the surface, and externally adding silica fine particles, etc., glass transition temperature 63 ° C., mass This is a polymerized toner having an average particle size of 6.5 μm.

  For primary charging, a DC voltage of −1150 V was applied to the charging roller. The surface potential of the photoreceptor was -650V. The surface potential of the photosensitive member when irradiated with a laser with such intensity that a solid image having the maximum density was output was -150V.

  Next, the charging roller according to the present embodiment is incorporated in the image forming apparatus, and the initial image is obtained in an environment of normal temperature and humidity (23 ° C./55% RH) within 2 minutes after contacting the new photoconductor. Was output. When a halftone image (image when irradiated with laser light whose output was reduced so that the photoreceptor surface potential was −400 V) was output as an initial image, a uniform and good image was obtained.

Similarly, the charging roller according to the present embodiment is incorporated into the image forming apparatus, 30 minutes after being brought into contact with a new photoconductor, and halftone in a normal temperature and humidity environment (23 ° C./55% RH). The image was output as an image after contact for 30 minutes, and the presence or absence of occurrence of horizontal streaks on the image due to contact was examined. Again, a uniform and good image was obtained. The contact portion did not appear as a streak in the image at all. Furthermore, in the image forming apparatus which has output the image after 30 minutes, with the charging roller of this embodiment being incorporated, it is continuously 2 dots wide in an environment of normal temperature and humidity (23 ° C./55% RH). The horizontal lines with intervals of 98 dots were repeatedly drawn, and 50 images were output. When 50 halftone images were output again as an image after output, a uniform and good image was obtained. The above results are summarized in Table 2 below (Examples 2 to 4).
The charging rollers of Examples 2 to 4 were obtained in the same manner as in Example 1 except that the blending amounts of the first particles and the second particles were changed as shown in Table 1 below. As for coating properties, 100 coatings were applied for all the formulations, but all had a good surface finish without unevenness. The initial images were all good. When the blending amount of the second particles was increased, a slight contact mark was observed in the image after contact for 30 minutes, but the image was at a level that was not noticed practically. The image after 50 sheets were output with no contact traces at all.

(Example 5)
A charging roller of Example 5 was obtained in the same manner as Example 1 except that the blending amount of the first particles was reduced to 2 parts. As for coating properties, 100 coatings were made, but all had a good surface finish without unevenness.

  Although the initial image was slightly blurred due to uneven charging potential, it was an image at a level that was not noticed in practice. In the image after 30 minutes of contact, no contact mark was found. The image after 50 sheets were output with no contact traces at all.

(Example 6)
A charging roller of Example 6 was obtained in the same manner as Example 1 except that the blending amount of the second particles was reduced to 0.1 part. As for coating properties, 100 coatings were made, but all had a good surface finish without unevenness.

  The initial image was good. In the image after contact for 30 minutes, no contact mark was observed. The image after 50 sheets were output with no contact traces at all.

(Example 7)
A charging roller of Example 7 was obtained in the same manner as Example 1 except that the blending amount of the first particles was reduced to 1 part. As for coating properties, 100 coatings were made, but all had a good surface finish without unevenness.

  Due to uneven charging potential, fog was initially observed on the image, but the image was at an acceptable level for practical use. In the image after 30 minutes of contact, no contact mark was found. The image after 50 sheets were output with no contact traces at all.

(Example 8)
A charging roller of Example 8 was obtained in the same manner as in Example 1 except that the blending amount of the second particles was reduced to 0.05 part. Regarding the coating property, even though 100 coatings were applied, slight coating unevenness was confirmed by visual observation, but it was at a level of no problem in practical use. All the other rollers had a good surface finish with no unevenness.

  For image evaluation, a roller with a slight unevenness in coating was used. Due to the unevenness of the charged potential, the initial image was faint on the image, but the image was at a level that was not noticed in practice. In the image after contact for 30 minutes, no contact mark was observed. The image after 50 sheets were output with no contact traces at all.

Example 9
A charging roller of Example 9 was obtained in the same manner as in Example 1 except that the surface-treated oil of the second particles was changed to amino silicone oil. As for coating properties, 100 coatings were made, but all had a good surface finish without unevenness. A good image was output in any of the initial image, the image after 30 minutes contact, and the image after 50 sheets were output.

(Example 10)
A charging roller of Example 10 was obtained in the same manner as in Example 1 except that the surface treatment coupling agent for both the first and second fine particles was changed to trifluoropropylsilane. There was no problem with all 100 coating properties. A good image was output in any of the initial image, the image after 30 minutes contact, and the image after 50 sheets were output.

Example 11
A charging roller of Example 11 was obtained in the same manner as in Example 1 except that the surface treatment coupling agent for the first particles was changed to trifluoropropylsilane. There was no problem with all 100 coating properties.

  Due to the unevenness of the charged potential, the initial image was faint on the image, but the image was at a level that was not noticed in practice. In the image after 30 minutes of contact, no contact mark was found. The image after 50 sheets were output with no contact traces at all.

Example 12
A charging roller of Example 12 was obtained in the same manner as in Example 1 except that the kinematic viscosity of the surface-treated oil of the second particles was changed to 20 m · s. There was no problem with all 100 coating properties. A good image was output in any of the initial image, the image after 30 minutes contact, and the image after 50 sheets were output.

(Example 13)
A charging roller of Example 13 was obtained in the same manner as in Example 1 except that the average particle diameter of the base titanium oxide of the first particles and the second particles was changed to 0.1 μm. There was no problem with all 100 coating properties. A good image was output in any of the initial image, the image after 30 minutes contact, and the image after 50 sheets were output.

(Example 14)
A charging roller of Example 14 was obtained in the same manner as Example 1, except that the amount of the base titanium oxide coupling agent treated with the first particles and the second particles was changed to 20 parts. There was no problem with all 100 coating properties. A good image was output in any of the initial image, the image after 30 minutes contact, and the image after 50 sheets were output.

(Example 15)
A charging roller of Example 15 was obtained in the same manner as in Example 1 except that the amount of the coupling agent treated with the base titanium oxide of the first particles and the second particles was changed to 5 parts. There was no problem with all 100 coating properties. Due to the unevenness of the charged potential, the initial image was faint on the image, but the image was at a level that was not noticed in practice. In the image after 30 minutes of contact, no contact mark was found. The image after 50 sheets were output with no contact traces at all.

(Example 16)
A charging roller of Example 16 was obtained in the same manner as in Example 1 except that the first particles and the second base titanium oxide were changed to silica having substantially the same average particle diameter. There was no problem with all 100 coating properties. A good image was output in any of the initial image, the image after 30 minutes contact, and the image after 50 sheets were output.

(Comparative Example 1)
As the surface coating material, the second particles were not blended, but only the first particles were blended in the same amount as in Example 1 except that the first particles and the second particles in Example 1 were combined. A surface coating was prepared, and a charging roller was produced in the same manner as in Example 1. As a result, out of 100 coatings, 15 had portions where the coating solution repelled and the base layer was exposed. Of the other rollers, 32 looked good in appearance, but the remaining 53 showed clear coating unevenness.

(Comparative Example 2)
0.03 part of silicone oil was added to the surface layer paint of Comparative Example 1. The silicone oil is a silicone oil obtained by surface-treating the second particles of Example 1, and the amount blended in the roller of Comparative Example 2 is the same as the amount blended in the surface layer of the roller of Example 1. I did it. As a result, there was no problem with all 100 coating properties.

  The initial image was satisfactory with no unevenness or streaks. However, when looking at the image after 30 minutes of contact, the occurrence of horizontal streaks was observed. Subsequently, when the image after the endurance of 50 sheets was output, the streaks caused by the contact disappeared and a good image was shown.

(Comparative Example 3)
The base of the first particles was the same as in Example 1, but only the base of the second particles was changed to silica to obtain a charging roller of Comparative Example 3.

  Among 100 coatings, 6 had a part where the coating solution repelled and the base layer was exposed. Of the other rollers, 24 looked good in appearance, but the remaining 70 showed clear coating unevenness.

(Comparative Example 4)
As the surface layer paint, the first particles were not blended, but only the second particles were blended in the same amount as in Example 1 except that the first particles and the second particles in Example 1 were combined. A surface coating was prepared, and a charging roller was produced in the same manner as in Example 1. As a result, there was no problem with all 100 coating properties.

  The initial image was satisfactory with no unevenness or streaks. However, when looking at the image after 30 minutes of contact, the occurrence of horizontal streaks was observed. Subsequently, when the image after the endurance of 50 sheets was output, the streaks caused by the contact disappeared and a good image was shown.

  Tables 1 and 2 collectively show the composition of the above examples and comparative examples and the results of image output.

＜初期画像＞
◎：非常に良好で全くムラの無い画像
○：わずかにムラが見られるが、実用上は気が付かないレベルの画像
△：ムラが見られるが、実用上は容認できる程度の画像
×：ムラが激しい画像
＜３０分間停止後当接スジ画像＞
◎：全くスジが発生しない画像
○：わずかにスジが見られるが、実用上は気が付かないレベルの画像
×：スジが激しい画像
＜５０枚画像出力後の当接スジ画像＞
◎：全くスジが発生しない画像
×：スジが激しい画像
＜塗工性＞
◎：１００本塗工して全て全く問題が無い。
○：１００本塗工して、実用上問題ないレベルの塗工ムラが数本にある。
×：１００本塗工した中に、塗工液をはじいて、基層が剥き出しになった部分が出来たローラがある。

<Initial image>
◎: Very good image with no unevenness ○: Image with slight unevenness but not noticeable for practical use Δ: Image with unevenness but acceptable for practical use ×: Intense unevenness Image <Contact streak image after 30 minutes of stoppage>
◎: Image with no streak at all ○: Image with slight streak but not noticeable in practical use ×: Image with severe streak <Contact streak image after 50 images are output>
A: Image with no streak at all ×: Image with severe streak <Coating property>
(Double-circle): There is no problem at all by coating 100 pieces.
◯: There are several coating unevennesses at a level where there is no practical problem with 100 coatings.
X: There is a roller in which 100 parts are coated and a part of the base layer is exposed by repelling the coating solution.

(A) It is sectional drawing of the direction orthogonal to the electroconductive support body of the charging roller which concerns on this invention, (b) It is sectional drawing of the direction in alignment with the electroconductive support body of the charging roller which concerns on this invention. (A) It is a schematic perspective view of the measuring apparatus of the deflection | deviation of the electroconductive elastic body base layer roller which comprises a charging roller, (b) It is a schematic sectional drawing of (a). 1 is a schematic cross-sectional view of an aspect of an image forming apparatus according to the present invention. It is a schematic sectional drawing of the other aspect of the image forming apparatus which concerns on this invention. It is a schematic sectional drawing of the process cartridge which concerns on this invention. It is a schematic explanatory drawing of the measuring method of the surface roughness of the charging member which concerns on this invention.

Claims (8)

A charging member for contact charging , having a conductive support and a coating layer covering the periphery of the conductive support, the conductive constituting the outermost surface of the charging member The surface layer comprises a first particle and a second particle;
First and second particles state, and are not chemical composition, surface treatment different base material particle size and surface area are made of the same insulating inorganic fine particles is made,
The first particles are those obtained by subjecting the base material to a surface treatment with a coupling agent,
Particles of the second, after surface treatment with a coupling agent in the base material, a charging member, characterized in der Rukoto what surface treatment is made by the silicone oil. The charging member according to claim 1, wherein the base material is titanium oxide or silica . The coupling agent, charging member according to claim 1 or 2, wherein at least either selected from a silane coupling agent and a titanate coupling agent. The charging member according to claim 1, wherein the surface layer further contains conductive particles. The charging member according to claim 4 , wherein the conductive particles are surface-treated with a silane coupling agent. The charging member according to claim 5 , wherein the silane coupling agent contains isobutylsilane. An electrophotographic photosensitive member, a charging member disposed in touching contact with the electrophotographic photosensitive member, and held together, and in the process cartridge is detachably attached to the image forming apparatus, the charging member, according to claim 1 7. A process cartridge, which is the charging member according to any one of items 6 to 6 . An electrophotographic photosensitive member, disposed come in contact to the electrophotographic photosensitive member, a charging member allowed to charge the electrophotographic photosensitive member surface, exposure to form an electrostatic latent image on the charged surface of the electrophotographic photosensitive member In the image forming apparatus, comprising: a developing unit configured to develop a toner image by developing the electrostatic latent image; and a unit configured to transfer the toner image to a transfer target. Item 7. An image forming apparatus comprising the charging member according to any one of Items 1 to 6 .

Images