JP2009109858A - Charging roller, electrophotographic process cartridge, and electrophotographic equipment - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a charging roller which is inexpensive but excellent in electrostatic charging and adhesion-proofing and also excellent in the points of charged horizontal stripes, start stripes and cleaning failures. <P>SOLUTION: This charging roller has a conductive elastic layer 2 formed around a conductive shaft core, and two or more conductive coat layers 3 at least formed on the outer surface of the conductive elastic layer. When representing the film thickness of the outermost layer 3(o) of the conductive coat layers by (a) and the total film thickness of the inner layer 3(i) of the conductive coat layers by (b), expression 0.016≤a/b≤0.300 is satisfied, provided that 3 μm≤(a)≤50 μm and (b)≥150 μm. The outermost layer 3(o) contains particulates 11 whose average particle size is (a)/4 or larger and 3(a)/4 or smaller. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a charging roller mainly used in an electrophotographic apparatus such as a printer / copier. The present invention also relates to an electrophotographic process cartridge and an electrophotographic apparatus that include the charging roller.

  In an electrophotographic apparatus such as a printer or a copying machine, an image forming body such as a photosensitive drum is provided on the surface of which charge is held, and a part of the held charge is neutralized to remove the charge on the surface of the image forming body. An electrostatic latent image is formed. Development is performed by supplying charged toner onto the electrostatic latent image. The toner image on the image forming body thus obtained is transferred to paper and fixed, whereby the output of the image in the electrophotographic apparatus is completed.

  In recent years, a charge roller often plays a role of supplying charges to the image forming body. The charging roller is a component that charges the image forming body while rotating in contact with the image forming body. The charging roller is configured by forming a conductive elastic layer made of a conductive rubber composition or the like around a conductive shaft core, and a coating layer that plays a role of adjusting electric resistance on the outer periphery thereof. ing.

  The charging roller is manufactured by various manufacturing methods. The main ones are a tube coating type and a coating type, but a tube coating type charging roller is advantageous particularly from the viewpoint of sufficient mass productivity and ease of cost reduction. The advantage of this type of charging roller is that it is easily manufactured simply by coating a conductive tube as the coating layer on the outside of the conductive elastic layer formed around the conductive shaft core. . Furthermore, the tube coating type does not require a firing step after coating a coating as a coating layer on the outside of the conductive elastic layer as in the coating type, and it is not necessary to consider stability as much as the coating. In addition, once the conditions for the coating tube are determined, it is possible to stably produce a large number of tubes having the same characteristics, and thus the cost merit is very high.

  However, a certain degree of elasticity is indispensable in the tube coating type charging roller in terms of expanding the tube. Therefore, there is a problem that the hardness of the roller surface portion cannot be increased as in the case of a coating type charging roller unless special post-treatment is added. Accordingly, the tube-coating type charging roller is disadvantageous than the coating type in terms of adhesion resistance of toner and external additives. Since the tube is rich in elasticity unlike the coating film after baking, the toner, the external additive, and the like are easily attached, and the attached portion is likely to appear on the output image.

  If the adhesion resistance is insufficient, the following problems occur. For example, the toner and external additives that are sandwiched between the charging roller and the image forming body during a long stop remain adhered to the surface of the roller for a while, and the horizontal pitch of the roller on the image. Black streaks appear. This is referred to as a startup streak, but this start streak disappears as the image printing is repeated and does not appear in the image. Another problem is called defective cleaning, which is caused by the toner, external additives, etc. remaining on the image forming body that cannot be completely removed by the toner cleaning means, adhering to a specific portion of the surface of the charging roller in a ring shape. There is also a problem. With this cleaning failure, a large number of vertical stripes appearing thin and thin centering on the edge on the image. These defects do not improve the symptoms even after repeated image printing. Both are phenomena that occur when adhesion resistance is insufficient.

  As a countermeasure against this, a method of appropriately roughening the roller surface is often used. When the surface is roughened, a roller using a tube having high elasticity can suppress the linear adhesion of toner, external additives, and the like to the roller surface, which helps to eliminate starting stripes. The reason why the adhesion is suppressed is that the surface of the roller is roughened so that the portion where the roller comes into contact with the image forming body is reduced, so that the toner and external additives that are sandwiched between the two are slipped through. is there. Therefore, most of the toner and external additives are not subjected to stress due to the roughening of the roller surface, and the adhesion itself is reduced.

  However, when the surface is significantly roughened, another problem occurs. If the surface of the charging roller is too rough, the contact area between the image forming body and the charging roller is extremely reduced, so the pressure applied locally at the contact point increases, resulting in a cleaning defect that can be said to be a strong adhesion trace. It will get worse. Therefore, it is not possible to eliminate all the defects caused by the adhesion resistance only by this countermeasure.

  By the way, the surface roughening has another great effect. Charging performance can be improved by increasing the electric field density in a region that is thought to contribute to the discharge based on Paschen's law. This is very useful to supplement the charging performance, which is often lacking in tube-coated charging rollers.

  Conventional tube-covered charging rollers have a limit to the minimum film thickness of the tube that can be produced, and therefore the volume specific resistance of the tube-coated layer cannot be increased. If the volume resistivity is increased, the resistance of the entire surface layer of the charging roller becomes too high, and the current flowing through the charging roller itself becomes small. Furthermore, even if only a single tube is considered, the thickness becomes very high due to its thickness, so that the supplied charge is difficult to spread uniformly over the entire coating layer. As a result, a slight mixing failure at the time of forming the tube causes uneven resistance, and it tends to appear as a charging failure such as uneven density on the image as it is.

  In the above-described case, it is conceivable to reduce the overall resistance of the charging roller in order to increase the current flowing through the charging roller. However, even in this case, if the volume resistivity of the tube serving as the coating layer is not sufficiently large, the voltage applied to the surface layer of the charging roller is insufficient. It is easy to become. If the charging performance is insufficient, there may be a large amount of thin black streaks randomly extending to the left and right, called charging horizontal streaks, on the entire output image. The blackened portion on the screen indicates that charging was not sufficiently performed there. The roughening of the roller surface also contributes to a drastic improvement in the charging performance of such a roller.

  As described above, the tube coating type charging roller manufacturing method is more advantageous from the viewpoint of mass productivity and ease of cost reduction. On the other hand, if the emphasis is on the physical property design of the surface layer portion of the charging roller, The charging roller manufacturing method is more suitable. This is because in the coating type, secondary crosslinking can be performed to harden the roller surface, which is advantageous in terms of adhesion resistance. In addition, since the coating layer is formed by a paint, the coating method is excellent in that the coating layer can be made very thin. For this reason, a stable charging characteristic can be obtained by making this coating layer a high resistance layer, and quality merit such as enhancing the environmental stability of roller resistance can be provided (Patent Document 1). ).

  On the other hand, with the coating method, it is difficult to ensure the stability of the paint until it is used, and even if the surface layer of the charging roller is formed with the same prescription paint, the electric characteristics of the resulting charging roller are always the same. It may not always be. Even if the same paint is used continuously, the resistance changes gradually, so careful control of the paint quality is necessary. Further, considering the time required for secondary crosslinking and cooling, the coating type charging roller is inevitable in cost even though it is advantageous in terms of performance.

  In addition, the superiority with respect to adhesion resistance is no longer advantageous for recent low-melting toners in consideration of the environment, and further design efforts are required.

JP-A-5-224502

  In view of the above situation, the object of the present invention is to improve the constitution of the coating layer, and to provide a charging roller for electrophotography which is excellent in charging performance / adhesion resistance, and therefore excellent in charging lateral stripes, starting stripes and poor cleaning. There is only to be provided at a low price.

  As a result of diligent investigation, in order to solve these problems, it is desirable to make the outermost layer sufficiently thin and roughened, and to provide another coating layer on the inside to provide sufficient thickness. I understood.

Therefore, the charging roller according to the present invention is:
In a charging roller having a conductive elastic layer formed around a conductive shaft core and having at least two conductive coating layers outside the conductive elastic layer,
When the film thickness of the outermost layer of the conductive coating layer is a and the total film thickness of the inner layers in the conductive coating layer is b, the ratio is in the range of the following values, and the average particle diameter is in the outermost layer. Is characterized by containing fine particles having a / 4 to 3a / 4.
0.016 ≦ a / b ≦ 0.300
However, 3 μm ≦ a ≦ 50 μm and b ≧ 150 μm

Further, the charging roller has a surface roughness Rz _jis of the outermost layer of 6 μm or more and 24 μm or less.
Further, the total film thickness of the a and the b is in the range of the following values.
160 ≦ a + b ≦ 1000

  The fine particles are spherical organic fine particles.

  Furthermore, the spherical organic fine particles are made of polyurethane, polystyrene, polymethyl methacrylate, or silicone rubber.

  Further, the present invention is an electrophotographic process cartridge in which a charging roller having these characteristics is incorporated.

  Further, the electrophotographic apparatus is characterized in that the electrophotographic process cartridge is mounted on a main body and used.

  In addition, the electrophotographic apparatus has the electrophotographic charging roller having the above-described features directly incorporated in the main body.

  According to the configuration of the present invention, the outermost layer can be increased in resistance and hardness, and the roller surface can be roughened to ensure sufficient chargeability and adhesion resistance. Therefore, it is possible to provide a charging roller that does not cause charging lateral streaks, start-up streaks, and cleaning defects at relatively low cost.

The charging roller according to the present invention is
In a charging roller having a conductive elastic layer formed around a conductive shaft core and having at least two conductive coating layers outside the conductive elastic layer,
When the film thickness of the outermost layer of the conductive coating layer is a and the total film thickness of the inner layers in the conductive coating layer is b, the ratio is in the range of the following values, and the average particle diameter is in the outermost layer. Is characterized by containing fine particles having a / 4 to 3a / 4.
0.016 ≦ a / b ≦ 0.300
However, 3 μm ≦ a ≦ 50 μm and b ≧ 150 μm

  Hereinafter, a charging roller according to the present invention will be described with reference to the drawings, and a preferable method for producing a charging roller for carrying out the present invention will be described.

  The charging roller of the present invention has a cross section as shown in FIG. 1 and has a structure in which a conductive elastic body layer 2 is provided on the outer periphery of a conductive shaft core body 1. Furthermore, two or more coating layers 3 are provided on the outer periphery of the conductive elastic layer because of functional necessity. In this case, the coating layer is expected to have functions such as prevention of leakage of drum contaminants from the conductive elastic layer, prevention of set marks, securing of charging characteristics, and prevention of adhesion of paper powder and toner components.

(Conductive shaft core)
As the conductive shaft core of the charging roller, for example, a cylinder having a surface of carbon steel alloy with industrial nickel plating having a thickness of 3 μm can be used. In addition, as a material constituting the conductive shaft core, for example, a metal such as iron, aluminum, titanium, copper or nickel, or an alloy such as stainless steel, duralumin, brass or bronze containing these metals is used. You can also. In addition, the conductive shaft core is not a mere column, but may be a cylinder having a hollow central portion.

(Preparation of conductive elastic layer)
In manufacturing the charging roller in the present invention, first, the conductive elastic body layer 2 is formed on the outer periphery of the conductive shaft core body 1.

  For the conductive elastic layer, it is desirable to use a material capable of obtaining an appropriate low hardness and low compression set in order to keep the contact surface with the image forming member uniform, and this object can be achieved. Any type is acceptable. In general, the conductive elastic layer includes a rubber composition, a conductive filler, a plasticizer, a softening agent, an anti-aging agent, a heat-resistant agent, a filler, and the like.

  As the rubber composition used for the conductive elastic layer, the same rubber composition as used conventionally can be used. For example, natural rubber (NR), isoprene rubber (IR), styrene butadiene rubber (SBR), butadiene rubber (BR), (meth) acrylonitrile butadiene rubber, ethylene propylene rubber (EPM), ethylene propylene diene rubber (EPDM), butyl rubber (IIR), halogenated butyl rubber, silicone rubber, fluorine rubber, urethane rubber, ethylene vinyl acetate copolymer, ethylene- (meth) acrylate rubber, epichlorohydrin rubber, and the like.

  There is no restriction | limiting in particular in the molecular weight of the rubber | gum used for a conductive elastic body layer, It contains from low molecular weight (oligomer) to high molecular weight. Such rubber is commercially available.

As the conductive filler, for example, metal powder such as carbon black, graphite, aluminum, palladium, iron, copper or silver can be used. Alternatively, a metal oxide such as titanium oxide, tin oxide, or zinc oxide, or a metal sulfide powder such as copper sulfide or zinc sulfide may be used. Furthermore, the surface of suitable particles is electrolytically treated with tin oxide, antimony oxide, indium oxide, molybdenum oxide, zinc, aluminum, gold, silver, copper, chromium, cobalt, iron, lead, platinum or rhodium, spray coating, etc. Alternatively, powder adhered by mixing and shaking can also be used. Further, carbon powders such as acetylene black, “Ketjen black” (registered trademark), PAN-based carbon black, and pitch-based carbon black are also listed as candidates that can be used. Further examples include ionic conductive substances such as perchlorates such as LiClO ₄ and NaClO _{4 and} quaternary ammonium salts, and these can be used alone or in combination of two or more. Particularly preferred as the conductive filler is carbon black. By adding a small amount of carbon black, the volume resistivity of the conductive elastic layer can be reduced, and conductivity can be imparted without increasing the hardness of the rubber composition. Examples of carbon black brands include “Ketjen Black EC” (registered trademark), “Ketjen Black EC600JD” (registered trademark) (both manufactured by “Ketjen Black International”), and the like.

The blending amount of the conductive filler needs to be adjusted moderately, but it is preferable to determine the volume specific resistance of the conductive elastic layer so as to fall within a medium resistance region of about 10 ⁴ to 10 ⁷ Ω · cm. If the volume resistivity is less than 10 ⁴ Ω · cm, even if the outer layer of the conductive elastic layer has a high resistance without any problem with resistance, a small surface defect called a pinhole defect is formed on the surface of the image forming body. In some cases, most of the applied voltage is concentrated on the outer layer of the charging roller. For this reason, a large current flows through the charging roller and concentrates on the pinhole, which may make the hole larger. At that time, there is a possibility that a current may not flow to a place other than the hole, and a charging potential may be insufficient and a black band may appear on a high-definition halftone image. In extreme cases, the charging roller itself may be energized and destroyed. Conversely, if the volume resistivity of the conductive elastic layer is too large, the voltage drop in the conductive elastic layer is too large to obtain the discharge current required to uniformly charge the image forming body. There is. Furthermore, it may be difficult to control the electrical conductivity, for example, it may be difficult to adjust the electrical resistance and it may be difficult to uniformly disperse.

  As a plasticizer added to the conductive elastic layer, for example, polydimethylsiloxane oil, diphenylsilanediol, trimethylsilanol, phthalic acid derivative or adipic acid derivative can be used.

  As the softener added to the conductive elastic layer, for example, lubricating oil, process oil, coal tar, castor oil, or the like can be used.

  As an anti-aging agent added to the conductive elastic layer, for example, phenylenediamines, phosphates, quinolines, cresols, phenols or dithiocarbamate metal salts can be used.

  As a heat-resistant agent added to the conductive elastic layer, for example, iron oxide, cerium oxide, potassium hydroxide, iron naphthenate, or potassium naphthenate can be used.

  In addition, the rubber composition used for the conductive elastic layer has a conventionally known vulcanizing agent, vulcanization accelerator, reinforcing filler as long as it does not impair the characteristics of low hardness and low compression set. Various compounding agents and additives such as processing aids, foaming aids, and vulcanization aids can be further added as necessary. These blends may be added in the course of producing the elastic layer material, if necessary.

Other examples of the reinforcing filler added to the conductive elastic layer include ionic conductive materials such as KSCN, LiClO ₄ , NaClO ₄ or quaternary ammonium salts, fumed silica, wet silica, quartz fine powder, diatomaceous earth. , Carbon black, zinc oxide, basic magnesium carbonate, activated calcium carbonate, magnesium silicate, aluminum silicate, titanium dioxide, talc, mica powder, aluminum sulfate, calcium sulfate, barium sulfate, glass fiber, organic reinforcing agent or organic filler An agent etc. can be mentioned. The surface of these reinforcing fillers may be hydrophobized by treatment with an organosilicon compound such as polydiorganosiloxane.

  Examples of the method for forming the conductive elastic layer include known methods such as extrusion molding, injection molding, and compression molding. The conductive elastic layer may be directly formed on the conductive shaft core using a crosshead extruder, or the conductive elastic body formed into a tube shape may be coated on the conductive shaft core. . If necessary, the surface of the conductive elastic body may be polished after shaping to adjust the shape.

(Formation of coating layer)
On the outer periphery of the conductive elastic layer formed as described above, at least two coating layers are provided. The coating layer in the present invention may be formed by either a coating type or a tube coating type. Here, a single layer or a plurality of layers of seamless tubes are formed, and these are successively fitted onto the conductive elastic layer. The method of forming by this is shown below.

  The thickness of the coating layer is preferably 160 to 1000 μm as a whole, and particularly preferably 200 to 800 μm. If the thickness is too small, the image forming body may be contaminated by the low molecular weight component exuding in the base layer. If the thickness is too thick, the surface layer of the charging roller becomes hard, which may cause deterioration in fusing and set mark recovery. It is not preferable.

  If the desired surface properties are obtained, the coating layer may be two layers or three or more layers. When a plurality of functions such as prevention of drum attack and prevention of set deformation due to long-term adhesion to the image forming body are particularly suitably achieved, it may be easier to design three or more layers.

  The resin, elastomer or copolymer used for the tube serving as the coating layer may be any thermoplastic resin that can be extruded. For example, ethylene vinyl acetate, ethylene ethyl acrylate, ethylene methyl acrylate, polyester, chlorinated polyethylene, polyurethane, nylon 6, nylon 66, nylon 11, nylon 12, styrene ethylene butyl, ethylene butyl, 1,2-polybutadiene, chlorosulfone Polyethylene, ethylene propylene rubber (EPM), nitrile butadiene rubber, polysulfide rubber, chloroprene rubber, butadiene rubber, isoprene rubber, polynorbornene rubber, styrene-butadiene-styrene (SBS) or styrene-butadiene-styrene water additive ( SEBS) or the like can be used, and is not particularly limited.

  In addition, elastomers such as the above-mentioned resins and copolymers, or elastomers such as modified products, and saturated polyesters such as polyethylene, polypropylene, polyethylene terephthalate (PET), and polybutylene terephthalate (PBT), polyethers, polyamides, polycarbonates, polyacetals , Polyurethane, polyphenylene oxide, polytetrafluoroethylene, acrylonitrile butadiene styrene, polystyrene, high impact polystyrene (HIPS), acrylonitrile-butadiene-styrene resin (ABS), acrylonitrile-ethylene / propylene rubber-styrene resin (AES), acrylonitrile-acrylic Rubber-styrene resin such as styrene resin (AAS) or acrylic resin, polyvinyl chloride such as polyvinyl acetate Fat, vinylidene chloride resins such as polyvinylidene fluoride, or combinations thereof made of a copolymer of the resin material is preferable.

  Furthermore, a polymer alloy or a polymer blend comprising at least two kinds of polymers selected from the above rubber, thermoplastic elastomer or thermoplastic resin can also be used.

  The tube uses the above-mentioned various polymers, the following conductive fillers and spherical particles, and further, if necessary, a conductive polymer composition composed of other additives, an extrusion molding method, an injection molding method, a blow molding method, etc. Can be obtained by forming a film. Of the various molding methods described above, the extrusion molding method is particularly suitable.

  In particular, in order to obtain the film thickness uniformity of each layer of the tube to be formed and to obtain a more uniform dispersibility of the conductive material or the like, it is preferable to use a vertical tube extruder.

  When the tube is composed of two layers, the charging roller was completed by forming the two-layer tube at one time and finishing the outer fitting at a time from the viewpoint of simplification of the process and stability of the characteristic after the outer fitting. Better. For tube formation at this time, an extrusion method using a crosshead extruder as shown in FIG. 2 is particularly suitable. If the tube consists of three or more layers, the thin outermost layer and the inner layer adjacent to each other are integrally formed using a crosshead extruder, and the other thick layers are made into individual single-layer tubes and the outer fitting is repeated several times. May be. In this case as well, the characteristic is stabilized when it is integrally formed as much as possible.

  In FIG. 2, a die 4 used for molding is provided with inner and outer double annular extrusion channels 6 and 7 around a central through hole 5 for air introduction. At the time of molding, air is blown from the central through-hole 5, while the raw material composition constituting the inner layer of the coated tube is fed from the first extruder 8 to the extrusion channel 6, and the coating tube is fed from the second extruder 9 to the extrusion channel 7. Each of the raw material compositions constituting the outer layer is injected under pressure. The tube 3 obtained by superposing and extruding the inner layer 3 (i) and the outer layer 3 (o) is cooled by a water cooling ring 10 provided on the outer periphery of the tube 3 while the inside is inflated with air. (Timing pulley) 21 Subsequently, it is cut | disconnected sequentially by the cutting machine 23 to predetermined length, and a conductive elastic body layer is coat | covered by the next process as a coating tube for charging rollers.

  In FIG. 2, reference numeral 22 denotes an outlet part mold (nipple) in contact with the inner side of the tube, and reference numeral 24 denotes an outlet part mold (die) in contact with the outer surface side.

  As the fine particles added to the outermost coating layer, fine particles made of a resin having a predetermined average particle diameter can be used. The fine particles are preferably spherical organic fine particles (hereinafter abbreviated as spherical particles). Examples of the material include plastic pigments such as polymethyl methacrylate, silicone rubber, polyurethane, polystyrene, amino resin, and phenol resin. In particular, polymethyl methacrylate, polyurethane or silicone rubber is preferred.

  The average particle diameter of the spherical particles may be selected so that the thickness of the outermost layer of the conductive tube is a / 4 or more and 3a / 4 or less. The method for measuring the film thickness and the method for measuring the average particle diameter will be described later. By adding spherical particles having this average particle diameter to the thin outermost layer, the surface of the charging roller (the outermost coating layer) is added. Appropriate roughness can be imparted, stress applied to the drum scraping powder, toner, external additive, etc. can be reduced, making it difficult to adhere to the roller surface. Further, the electric field density in the corona discharge region according to Paschen's law can be positively increased to uniformly charge the image forming body.

Moreover, regarding the film thickness of a coating layer, it shape | molds so that the following relationships may be satisfy | filled.
0.016 ≦ a / b ≦ 0.300 (1st formula)
However, 3 μm ≦ a ≦ 50 μm and b ≧ 150 μm
(A: film thickness of outermost layer in coating layer, b: total film thickness of all coating layers other than outermost layer)

  That is, the film thickness a of the outermost layer must be sufficiently smaller than the total film thickness b of the other inner layers in the coating layer (first formula). In this way, the outermost layer can be made thin and have a high volume resistivity so as to have an electrostatically advantageous configuration, and the thinned outermost layer can be sufficiently supported from the inside. If there is no inner layer that supports the outermost thin film from the inside, the outermost thin film tends to undergo permanent deformation due to compression. When the outermost thin film, that is, the roller surface is deformed, the gap between the image forming body and the image forming body is reduced, and the effect of roughening is not sufficiently exhibited.

  In the case of a tube, it has been found that when the outermost layer is extruded with a thin film, the outermost layer becomes stronger due to the strong pressure during the molding. For this reason, the penetration of the toner and the external additive to the roller surface is suppressed, and a roller that is less likely to cause toner / external additive adhesion and poor cleaning as in the case of the thin film by coating is completed. In that sense, a / b is preferably as small as possible even within the range of the first equation.

  However, on the other hand, if a is very small, it is difficult to achieve the aforementioned roughening. Therefore, 0.020 ≦ a / b ≦ 0.250 is preferable. More preferably, 0.025 ≦ a / b ≦ 0.200. In addition, since the support from the inner layer in the coating layer required by the outermost layer is considered to be inversely proportional to the thickness a of the outermost layer, even if a / b is a large value as long as it falls within the above range, there is no problem. Absent.

  In particular, when a is a small value, an appropriate support is required for the outermost layer. In particular, at a lower limit of a and a thickness of a = 3 μm, 150 μm is required as the total film thickness b of the other inner layers in the coating layer. If b is too small, the thin outermost layer is deformed by compression together with the inner layer in the coating layer, and it becomes difficult to recover.

  Further, it is necessary that a ≦ 50 μm. If it is too thick, the volume resistivity of the outermost layer must be reduced to suppress the roller resistance, and sufficient charging performance cannot be obtained.

  However, if a <3 μm, no matter how much spherical particles having an average particle diameter of 3a / 4 or less are contained in the outermost layer, the roller surface cannot secure the necessary roughness for maintaining charging property and adhesion resistance. . Therefore, a needs to satisfy 3 μm ≦ a ≦ 50 μm.

  On the other hand, the total film thickness b of the inner layers in the coating layer must not be too thick. If it is too thick, the deformation of the roller is too small and the nip width of the contact portion with the image forming body becomes too small, and the toner / external additive is received between the top of the roughened roller surface and the image forming body. The pressure becomes too large, resulting in poor cleaning. Therefore, the lower limit and the upper limit of the inner layer in the coating layer must be appropriately managed according to the film thickness of the outermost layer.

  The film thickness of each coating layer can be measured as follows, for example. First, when measuring in order to manage the film thickness of each coating layer, in the case of a tube coating type, a tube with a part cut is prepared. In the case of a coating type, a roller obtained by cutting one surface portion out of the simultaneously coated rollers is prepared. Each of these has a shape as shown in FIG. 3 and is measured while observing with a scanning electron microscope. In this way, the thickness can be reliably measured even with an extremely thin film thickness. Here, FIG. 3 shows a case where there are two inner layers in the coating layer in contact with the outermost layer.

  As shown in FIG. 3, at least five measurement points are selected, and the data at each measurement point measured at a magnification of 300 to 500 times is averaged. This is performed for each of the outermost layer and the other inner layers of the coating layer, and the measured value of the outermost layer is a (12 in FIG. 3), and the measured value of the inner layer in the coating layer is b (13 in FIG. 3).

  About the average particle diameter of the said spherical particle, the thing of the diameter according to the objective can be selected from a commercially available spherical particle fundamentally. A Coulter counter is used for actual measurement and confirmation. This is an apparatus as shown in FIG. 4, and the particle size distribution of particles is obtained by the pore electrical resistance method (ESZ) called the Coulter principle. In this apparatus, an impedance change is measured at an aperture (pore) through which an electrolyte mixed with particles is applied with a voltage.

  When spherical particles pass through the aperture, the electrolyte solution in the aperture decreases at that moment, and this is detected as an instantaneous increase in impedance (particle pulse). The changed impedance is converted into the volume of the particle, and the equivalent sphere diameter (ESD) is obtained on the assumption that the particle is a perfect sphere. The particle size distribution of the particles thus mixed is obtained (FIG. 5), and the average particle size is calculated therefrom.

  If a plurality of particles pass through the aperture at the same time, the volume is counted as one in this method, so the diameter becomes larger. However, since the particle pulse at that time is different from the waveform when one particle passes, it is possible to separate the data as a plurality of particles having different diameters by an appropriate algorithm (FIG. 6). Thus, the average particle diameter when counting a plurality of volumes as one is referred to as a volume average particle diameter, and the average particle diameter when correction is performed so as to separate into a plurality of particles is referred to as a number average particle diameter. When the particle size is sufficiently large relative to the diameter of the aperture, it is good that the volume average is not subjected to complicated processing, but if the particle size is small, the volume average is greatly different from the actual condition. It is better to use.

  Known materials can be used as the conductive filler added to the coating layer, for example, carbon fine particles such as carbon black or graphite; metal fine particles such as nickel, silver, aluminum or copper; tin oxide, zinc oxide, titanium oxide, oxidation Conductive metal oxide fine particles mainly composed of aluminum or silica and doped with impurity ions having different valences; conductive fiber such as carbon fiber; metal fiber such as stainless steel fiber; carbon whisker or potassium titanate whisker Conductive whisker such as conductive potassium titanate whisker whose surface is conductively treated with metal oxide or carbon; or conductive polymer fine particles such as polyaniline or polypyrrole.

  Since the outermost layer is a thin film, a very high pressure is applied during molding, which tends to cause a shape defect. For this reason, it is desirable to add a wax to at least the outermost layer.

  Examples of waxes to be added include beeswax, spermaceti, shellac wax, other waxes derived from various animals, carnauba wax, wood wax, rice bran wax (rice wax), candelilla wax, other plant-derived wax, and petroleum-derived paraffin wax. , Microcrystalline wax, montan wax derived from minerals, ozokerite, ceresin and wax extracted from oil shell. Various synthetic waxes, oxidized waxes, compounded waxes, modified montan waxes, other processed / modified waxes, and the like can also be used. Various synthetic waxes are preferably used because they have a particularly well-defined molecular weight distribution. Examples include hydrocarbon synthetic waxes roughly classified into Fischer-Tropsch wax and polyethylene wax, fatty acid ester waxes such as coconut oil and beef tallow fatty acid, stearamide, diheptadecyl ketone, and hardened castor oil. Further, those subjected to fractionation by press sweating method, solvent method, use of vacuum distillation or fractional crystallization method are more preferable.

  The tube formed by the above various molding methods can be used as it is, but for example, for the purpose of obtaining superior durability and environmental resistance, the obtained tube is further crosslinked to form a conductive crosslinked polymer. You can also As the crosslinking method, a chemical crosslinking method in which a crosslinking agent such as sulfur, an organic peroxide, or an amine is added in advance according to the type of the polymer and a crosslinking bond is generated at a high temperature, or an electron beam or γ A radiation crosslinking method in which crosslinking is performed by irradiating radiation such as lines is effective. Among the above various crosslinking methods, the electron beam crosslinking method is preferable because there is no fear of contamination of the image forming body due to the migration of the crosslinking agent or its decomposition product. Further, the electron beam cross-linking method does not require a high temperature treatment and is preferable from the viewpoint of safety.

  The tube to be used may be either non-heat-shrinkable or heat-shrinkable, but a non-heat-shrinkable tube is used in the examples.

  In the case of a non-heat-shrinkable tube, the inner diameter of the tube needs to be less than or equal to the outer diameter of the elastic layer in order to ensure adhesion with the elastic layer. In this case, by inserting compressed air into the elastic layer having the conductive shaft core with the tube diameter enlarged, and releasing the air pressure, the outer fitting process is completed and the charging roller can be completed. it can. FIG. 7 shows a cross section of the coating layer of the charging roller in a coated state.

  Regarding the thin layer of the coating layer, it may be easier to produce the coating layer by coating rather than tube coating. The method for preparing the paint is described below.

  The material for forming the coating layer by coating is not particularly limited. For example, various polyamides, fluorine resins, hydrogenated styrene-butylene resins, urethane resins, silicone resins, polyester resins, phenol resins, imide resins Or an olefin resin etc. are mentioned. Among these, it is preferable to use a urethane resin. This is because the physical properties can be changed in a wide range by variously changing the structure and blending ratio of the polyol and diisocyanate.

  When an isocyanate for urethane resin is used as a material for forming the coating layer of the charging roller, a difunctional or trifunctional isocyanate and a modified isocyanate are usually used. Among these aromatic compounds, 1,5-naphthalene diisocyanate, 2,4- / 2,6-tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate, p-phenylene diisocyanate, m- / P-xylylene diisocyanate, which includes isophorone diisocyanate and 4,4'-dicyclohexylmethane diisocyanate for alicyclic groups, and 1,6-hexamethylene diisocyanate and lysine di for aliphatic groups. An isocyanate and 1,6,11-undecane triisocyanate are mentioned.

  Examples of the polyol for urethane resin include polyether, polyester, polybutadiene polyol, acrylic polyol, saponified ethylene-vinyl acetate copolymer having 2 to 3 functionalities and number average molecular weight of several hundred to several thousands. By adjusting the functionality and number average molecular weight of these isocyanates and polyols, desired physical properties such as elasticity can be imparted to the surface of the charging roller.

  The material constituting these coating layers should be dispersed using a conventionally known dispersing device such as a dispersing device using beads such as a sand mill, paint shaker, dyno mill, pearl mill, visco mill, or a dispersing device using a ball mill. Can do. The obtained coating for forming a coating layer can be applied to the surface of the conductive elastic layer, the surface of the tube before coating, or the surface of the roller after coating by spray coating, dipping, or the like. The thickness of the coating layer can correspond to about 5 to 500 μm, but 5 to 30 μm is particularly preferable because it is easy to apply uniformly.

  In order to use the coating layer by coating as described above as the outermost layer, the above-mentioned various spherical particles are blended in the course of dispersion.

  FIG. 8 shows a schematic configuration as an example of an electrophotographic apparatus in which the charging roller 1 ′ formed as described above is incorporated in the main body.

  In FIG. 8, reference numeral 31 denotes an image forming body, which is rotationally driven in the direction of the arrow at a predetermined peripheral speed. In the rotation process, the image forming body 31 is uniformly charged with a positive or negative predetermined potential on the peripheral surface thereof by the charging roller 1 ′, and then from image exposure means (not shown) such as slit exposure or laser beam scanning exposure. The image exposure light 33 is received. In this way, electrostatic latent images are sequentially formed on the peripheral surface of the image forming body 31.

  The formed electrostatic latent image is then developed with toner by the developing unit 34, and the developed toner image is transferred from the paper supply unit (not shown) between the image forming unit 31 and the transfer unit 36. The image is sequentially transferred by the transfer means 36 to the transfer material 37 fed in synchronization with the rotation.

  The transfer material 37 that has received the image transfer is separated from the surface of the image forming body, introduced into an image fixing means, and subjected to image fixing, thereby being printed out as a copy (copy).

  The surface of the image forming body 31 after the image transfer is cleaned by receiving the toner remaining after the transfer by the cleaning means 35, and is repeatedly used for image formation.

  Among the components such as the image forming body 31, the charging roller 1 ′, the developing unit 34, and the cleaning unit 35 described above, a plurality of components are integrally coupled as a process cartridge, and the process cartridge is configured as a copying machine or a laser beam. You may comprise so that attachment or detachment with respect to electrophotographic apparatus main bodies, such as a printer, is possible. For example, as shown in FIG. 9, the developing means 34 and the cleaning means 35 are integrally supported together with the image forming body 31 and the charging roller 1 'to form a cartridge, and the apparatus main body is used using guide means such as a rail 42 of the apparatus main body. It can be set as the process cartridge 41 which can be attached or detached.

  Further, when the electrophotographic apparatus is a copying machine or a printer, the image exposure light 33 is a reflected light or transmitted light from the original, or a signal read from the original by a sensor and converted into a signal. The light is emitted by scanning, driving the LED array, driving the liquid crystal shutter array, and the like.

  Hereinafter, the effects of the present invention will be clarified by showing examples and comparative examples, but the present invention is not limited to the following examples.

[Examples 2-7, 9-14, 16-21, Comparative Examples 2-7, 9-14, 16-21]
(Conductive shaft core)
An iron rod having a diameter of 6 mm obtained by iron extrusion was cut to a length of 258 mm, and then subjected to chemical nickel plating having a thickness of about 3 μm.

(Formation of conductive elastic layer)
Ethylene-propylene-diene rubber (EPDM) 100 parts by mass, zinc oxide 5 parts by mass, stearic acid 1 part by mass, conductive carbon black 11 parts by mass, paraffin oil 50 parts by mass, vulcanization accelerator 2-mercaptobenzothiazole ( MBT) 2 parts by mass, vulcanization accelerator dipentamethylene thiuram tetrasulfide (DPTT) 1 part by mass, vulcanization accelerator zinc dibutyldithiocarbamate (ZDBC) 1 part by mass, sulfur 1 part by mass, blowing agent ADCA 8 parts by mass, urea An unvulcanized rubber composition was prepared by kneading 3 parts by mass of a foaming aid. The conductive shaft core was prepared by applying an adhesive.

  Next, the rubber composition was extruded into a hose shape using a crosshead extruder, and at the same time, a conductive shaft core was inserted into the extrusion center to be integrated into a roll shape. Subsequently, after removing excess rubber at both ends of the roll, heating, vulcanization and foaming reaction were performed in a continuous furnace, and then cooling and curing were performed to obtain a raw material roller having an outer diameter of 8.5 mm. The hose end of this raw material roller was cut to a length of 224 mm to obtain a conductive shaft core having a conductive elastic layer formed thereon.

  Further, the surface of the conductive elastic layer was polished by a polishing machine. If the shape of the roller is seen in a cross section passing through the shaft core body of the roller, the surface is finished so as to draw an arc by polishing. Looking at the same cross-section, if the outer diameter of the end face which is the opposite ends of the roller is called the end diameter 51 and the outer diameter of the thickest central part is called the central diameter 52, the central diameter 52 at this time is 7.95 mm, The end diameter 51 is set to 7.75 mm. This shape is shown in FIG.

Here, when the resistance is measured by bringing the conductive elastic layer into contact with a metal drum having a diameter of 30 mm and supporting it at both ends of the conductive shaft core body, the volume specific resistance when 50 V is applied is about 10 ⁴ Ω. -It was cm.

(Formation of coating layer)
As the coating layer, a coating layer composed of an inner layer and an outer layer was formed, and spherical organic fine particles were added to the outer layer. As the spherical organic fine particles, polyurethane fine particles, polymethyl methacrylate (PMMA) fine particles, and silicone rubber fine particles were used individually for each roller. “Art Pearl” (trade name) manufactured by Negami Kogyo Co., Ltd. was used as the polyurethane fine particles. As polymethyl methacrylate (PMMA) fine particles, “Tech Polymer” (trade name) manufactured by Sekisui Plastics Co., Ltd. and “Chemisnow” (trade name) manufactured by Soken Kagaku Co., Ltd. were used. As the silicone rubber fine particles, “Tospearl” (trade name) manufactured by Momentive Performance Materials Japan GK was used.

  In this example and the comparative example, the outer layer thickness was 10 μm or more in the present example and the comparative example. At this time, as the material of the outer layer of the coating layer, 80 parts by mass of styrene-based thermoplastic elastomer SEBC having a styrene content of 20% by mass, 20 parts by mass of acrylonitrile-styrene copolymer resin, 50 parts by mass of acidic carbon black, A specified amount (described in Tables 1 to 3) of spherical organic fine particles having a predetermined average particle diameter, 10 parts by mass of magnesium oxide, 1 part by mass of calcium stearate and 2 parts by mass of PP wax. This was kneaded in a pressure kneader at 180 ° C. for 30 minutes. After cooling it, it was pulverized with a pulverizer and pelletized with a single screw extruder.

  The material of the inner layer in the coating layer is 100 parts by weight of thermoplastic polyurethane elastomer (TPU), 50 parts by weight and 5 parts by weight of two types of carbon black, 20 parts by weight of conductive titanium oxide, and 10 parts by weight of magnesium oxide. Part and 1 part by mass of calcium stearate were added, kneaded at 180 ° C. for 15 minutes using a pressure kneader, and pelletized in the same process as the outer layer of the coating layer.

  A cross-head was attached to the vertical extruder to obtain the configuration shown in FIG. Using this extruder, the pellets for the inner layer and the pellets for the outer layer were merged to form a double layer with one crosshead (temperature 160 ° C.) and extruded into a water-cooled ring 10 having an appropriate temperature. After further cooling, it was taken up by a roll type tube take-up device 21 and cut by a cutting machine 23. In this way, a tube for a covering layer having an outer diameter of about 8.5 mm and a tube length of 300 mm was obtained. The film thicknesses of the outer layer and the inner layer in the tube for the coating layer are as shown in Tables 1 to 3.

(Production of charging roller)
The length of the cut tube for covering is longer than that of the conductive shaft core on which the conductive elastic layer is formed. Both were set in a tube coating apparatus (not shown), and the tube was fitted into the outer periphery of the conductive elastic body layer of the raw material roller and brought into pressure contact. Thereafter, the end of the tube protruding outward from the conductive elastic layer was cut off with a margin of 1 mm to obtain a charging roller. Here, when the resistance was measured by contacting a metal drum having a diameter of 30 mm and rotating it while supporting both ends of the conductive shaft core, the resistance when 200 V was applied was about 10 ⁶ Ω · cm.

(Image evaluation)
Image evaluation was performed using a prototype of an electrophotographic apparatus before market introduction. A charging roller is incorporated into the cartridge, and an intermittent sheet passing mode in which the image forming body stops every time one sheet is passed, 250 sheets are passed at an interval of outputting one sheet every 10 seconds, and then stopped for 1 hour. . This was repeated 4 times, and after passing 1000 sheets, it was left overnight, and a halftone image for evaluation was output the next day. Furthermore, after repeating the same type of paper to the 1500th sheet, a halftone image was output for final evaluation. In the halftone images obtained after passing 1000 sheets and 1500 sheets, whether or not charging lateral streaks / starting streaks / cleaning defects occurred was visually confirmed.

  The charged horizontal streak is a thin black streak that randomly extends left and right on the output image. If the degree is poor, a large amount appears on the entire image. Further, the starting stripe is caused by the adhesion of toner, external additives, etc. to the surface of the charging roller. The toner or the like sandwiched between the charging roller and the image forming body adheres to the roller surface when stopped for a long time, and remains stuck for a while even during image output. Appears. In addition, the cleaning failure is caused by the toner, external additive, drum scraping powder, etc. remaining on the image forming body without being removed by the cleaning means 35 in FIG. It is what is caused. Many vertical stripes appear thin and thin around the edge of the image.

These evaluations were judged according to the following criteria.
<Common to charged horizontal streaks and poor cleaning>
A: Not recognized.
◯: Recognized, but very slight and acceptable.
Δ: Recognized. Impossible.
X: Obviously recognized. Impossible.
<Start line>
A: Not recognized.
◯: Recognized, but disappeared with few images output. It is within the allowable range.
Δ: Recognized. A large number of image outputs are required until disappearance. Impossible.
X: Obviously recognized. Impossible.

[Examples 1, 8, and 15 / Comparative Examples 1, 8, and 15]
(Formation of conductive shaft core and conductive elastic layer)
Conductive shaft cores and conductive elastic layers are formed in the same manner as in other examples and comparative examples.

(Formation of coating layer)
The coating layer was formed by using both a tube coating layer and a paint coating layer. First, a tube for the inner layer was prepared using a vertical extruder having only a single layer using the material for the inner layer described in the above example. Next, a coating for the outer layer was produced by the method described below.

(Preparation of paint)
First, a lactone-modified acrylic polyol (trade name “Placcel DC2009” manufactured by Daicel Chemical Industries, Ltd.) was dissolved in methyl isobutyl ketone (MIBK) to obtain a solution having a solid content of 10%. A ball mill is prepared by blending 70 parts by mass of carbon black with 100 parts by mass of the original acrylic polyol, and further blending 0.1 parts by mass of silicone oil (SH-28PA: manufactured by Toray Dow Corning Silicone). For 5 hours. Thereafter, 80 parts by weight of spherical particles having an average particle diameter of 2 μm (Examples 1, 8 and 15) and 80 parts by weight of spherical particles having an average particle diameter of 1.5 μm (Comparative Examples 8 and 15) Were made separately and dispersed for another 3 hours. At this time, polyurethane particles, PMMA particles, and silicone rubber particles were used as the spherical particles. Thereafter, a 1: 1 (equivalent ratio) mixture of hexamethylene diisocyanate (HDI) and isophorone diisocyanate (IPDI) was added to each solution so that NCO / OH = 1.0, dissolved, and finally The solution was filtered through a mesh of 500 mesh to prepare various outer layer coatings.

(Production of charging roller)
The length of the cut | disconnected tube | cover is longer than the electroconductive axial core body in which said electroconductive elastic body layer was formed. Both were set in a tube coating apparatus (not shown), and the tube was fitted into the outer periphery of the conductive elastic body layer of the raw material roller and brought into pressure contact. Thereafter, the roller covered up to the inner layer was set in a roller coating device (not shown), and the outermost layer was formed by dipping using the above-described paint. Thereafter, the tube end protruding outward from the conductive elastic layer was cut off with a margin of 1 mm to obtain a charging roller. Two types of outermost layer thicknesses of 3 μm and 2.5 μm were prepared. In a resistance measurement performed by contacting a metal drum with a diameter of 30 mm and rotating while supporting both ends of the conductive shaft core, the resistance when 200 V was applied was about 10 ⁶ Ω · cm.

(Image evaluation)
Image evaluation was performed in exactly the same manner as in Examples 2-7, 9-14, 16-21 and Comparative Examples 2-7, 9-14, 16-21.

The results are summarized in Tables 1 to 3 below. Those using polyurethane fine particles as spherical organic fine particles are shown in Table 1, those using polymethyl methacrylate fine particles (PMMA) are shown in Table 2, and those using silicone rubber fine particles are shown in Table 3. The average particle diameter and input amount of the spherical organic fine particles contained in the outer coating layer are as shown in each table. The average particle diameter is a volume average particle diameter measured using a Multisizer 3 manufactured by Beckman Coulter, Inc. ISOTON II was used as the electrolyte during the measurement. Regarding the film thickness, a tube of the same lot as that used for the roller was observed and measured with a field emission scanning electron microscope S-4300 manufactured by Hitachi, Ltd. However, the outermost layer having a thickness of 3 μm or less was cut out from the roller and measured. Rz (JIS) is shown as data representing the surface roughness of the charging roller.

As can be seen from the examples and comparative examples, in the charging roller having a conductive elastic layer formed around the conductive shaft core and having at least two conductive coating layers on the outer side, the conductive coating is provided. When the thickness of the outermost layer of the layer is a, and the total thickness of the inner layers in the conductive coating layer is b, the ratio is in the range of the following values, and the average particle diameter is a / By containing fine particles having a particle size of 4 or more and 3a / 4 or less, the outermost layer can have high resistance and high hardness, and the surface of the roller can be roughened, and sufficient chargeability and adhesion resistance can be ensured. Therefore, it is possible to manufacture a low-cost and high-performance charging roller excellent in charging horizontal stripes, starting stripes, and poor cleaning.
0.016 ≦ a / b ≦ 0.300
However, 3 μm ≦ a ≦ 50 μm and b ≧ 150 μm

Sectional drawing of an example of a charging roller. An example (schematic cross section) of a vertical extruder used for manufacturing a tube for coating. Sectional drawing of a coating layer. Schematic of Coulter counter. The conceptual diagram which shows the data processing of a Coulter counter. Schematic which shows the relationship between the particle pulse of a Coulter counter, and a passing particle. The enlarged view of the coating layer part of the charging roller which concerns on this invention. 1 is a schematic view showing an example of an electrophotographic apparatus having a charging roller according to the present invention. FIG. 3 is a schematic view showing an example of a process cartridge on which a charging roller according to the present invention is mounted. Schematic which shows the shape of a conductive elastic body layer.

Explanation of symbols

1: Conductive shaft core body 1 ′: Charging roller 2: Conductive elastic body layer 3: Coating layer (tube)
3 (i): Inner layer 3 (o): Outer layer 4: Die 5: Central through hole 6: Extrusion channel 7: Extrusion channel 8: First extruder 9: Second extruder 10: Water cooling ring 11: Spherical Particle 12: Film thickness of outermost layer 13: Film thickness of inner layer in coating layer 21: Timing pulley (take-off machine)
22: Nipple 23: Cutting machine 24: Mold 31: Image forming body 32: Power source 33: Image exposure light 34: Developing means 35: Cleaning means 36: Transfer means 37: Transfer material 41: Process cartridge 42: Rail 51: End Part diameter 52: Center diameter 61: Power source 62: Electrode 63: Aperture (pores; partially enlarged view)
64: Volume measuring device 65: Passing particle 66: Aperture outer edge portion 67: Threshold value determined to be a particle

Claims (8)

In a charging roller having a conductive elastic layer formed around a conductive shaft core and having at least two conductive coating layers outside the conductive elastic layer,
When the film thickness of the outermost layer of the conductive coating layer is a and the total film thickness of the inner layers in the conductive coating layer is b, the ratio is in the range of the following values, and the average particle diameter is in the outermost layer. A charging roller characterized by containing fine particles having an a / 4 to 3a / 4.
0.016 ≦ a / b ≦ 0.300
However, 3 μm ≦ a ≦ 50 μm and b ≧ 150 μm   2. The charging roller according to claim 1, wherein a surface roughness Rz (JIS) of the outermost layer is 6 μm or more and 24 μm or less. The charging roller according to claim 1, wherein the total film thickness of the a and the b is in the range of the following values.
160 ≦ a + b ≦ 1000   The charging roller according to claim 1, wherein the fine particles are spherical organic fine particles.   The charging roller according to claim 4, wherein the spherical organic fine particles are made of polyurethane, polystyrene, polymethyl methacrylate, or silicone rubber.   6. A process cartridge for electrophotography, wherein the charging roller according to claim 1 is incorporated therein.   An electrophotographic apparatus comprising the process cartridge according to claim 6 incorporated therein.   An electrophotographic apparatus in which the charging roller according to any one of claims 1 to 5 is incorporated in a main body.

Images