JP2006058539A - Charging roller, metallic mold for manufacturing the same, cartridge for electrophotographic apparatus and the electrophotographic apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide respectively a charging roller in which slippage of tube due to high-speed rotation is suppressed and resistance unevenness is also suppressed, a manufacturing method therefor, a cartridge for an electrophotographic apparatus and the electrophotographic apparatus each mounted with the charging roller. <P>SOLUTION: The charging roller comprises a core bar, an elastic body on an outer periphery of the core bar and a seamless covering tube for the charging roller covering the elastic body, wherein ten-point mean roughness (Rzjis) of the inner surface of the tube is 4 to 15 μm. Further the manufacturing method of the charging roller, the cartridge for the electrophotographic apparatus and the electrophotographic apparatus each mounted with the charging roller are also provided. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a charging roller that contacts a member to be charged and charges the member to be charged by applying a voltage, and a mold for manufacturing the same. The present invention further relates to an electrophotographic cartridge and an electrophotographic apparatus having the charging roller.

  In recent years, a contact charging type charging unit has been adopted as a charging unit used in an image forming apparatus such as an electrophotographic apparatus or an electrostatic recording apparatus. Contact charging is to charge a charged body to a predetermined polarity and potential by applying a voltage to a charging member placed in contact with the charged body, and the voltage of a power source can be lowered, such as ozone. There are advantages that the generation of corona products can be reduced, the structure is simple, and the cost can be reduced.

  The voltage applied to the charging member has a peak-to-peak voltage that is at least twice the charging start voltage of the object to be charged when a DC voltage is applied to the contact charging member, in addition to a method in which only DC is applied (DC application method). There is a technique (AC application method) in which an oscillating electric field (electric field whose voltage value changes periodically with time) is formed between the contact charging member and the object to be charged, and the surface of the object to be charged is charged (AC application method). Can be charged easily.

  As a member to be brought into contact with the non-charged body, the charging roller is frequently used because it is rotatably supported by the bearing, is pressed against the body to be charged at a predetermined pressure, and rotates with the movement of the body to be charged.

  This charging roller is usually a multilayer structure having a cored bar provided at the center, a conductive elastic layer provided in a roller shape on the outer periphery of the cored bar, and a surface layer provided on the outer periphery thereof.

  Among the above layers, the cored bar (metal layer) is a rigid body for maintaining the shape of the roller, and has a role as a feeding electrode.

In addition, the elastic layer usually has a volume resistivity of 10 ⁴ to 10 ⁹ Ω · cm, and a function to ensure uniform contact with the member to be charged by elastic deformation. A vulcanized rubber having a softness of 70 degrees or less with a rubber hardness (JIS A) imparted with conductivity is used. Conventional charging rollers include a foam type that uses a rubber foam (or sponge-like rubber) as an elastic layer and a solid type that does not use a rubber foam. The surface layer improves the charging uniformity of the object to be charged, prevents the occurrence of leaks due to pinholes on the surface of the object to be charged, and prevents the adhesion of toner particles, paper powder, etc. In addition, there is a demand for a function for preventing bleeding of softeners such as oil and plasticizer used to reduce the hardness of the elastic layer. The volume resistivity of the surface layer is usually 10 ⁵ to 10 ¹³ Ω · cm, and has been conventionally formed by applying a conductive paint or covering a seamless tube (for example, Patent Document 1). .

  However, when covering a seamless tube, the dispersion of the conductive agent contained in the tube, uneven thickness of the tube, etc., may cause resistance unevenness in the circumferential direction of the roller, resulting in direct image defects. .

In addition, when the charging roller is rotated at a high speed, if the interference between the tube and the elastic layer is increased in order to prevent the tube from being displaced from the elastic layer, the tube forming defect as described above becomes clearer due to the tube being stretched. In some cases, the resistance unevenness deteriorates, and as a result, it is recognized as image unevenness.
Japanese Patent Laid-Open No. 11-125952

  An object of the present invention is to provide a charging roller that suppresses tube displacement due to high-speed rotation and suppresses resistance unevenness, and also provides a manufacturing method thereof.

  Another object of the present invention is to provide an electrophotographic apparatus cartridge and an electrophotographic apparatus provided with the above charging roller.

  According to the present invention, in a charging roller obtained by coating a cored bar, an elastic body on the outer periphery of the cored bar, and a seamless charging roller-coated tube on the elastic body, the 10-point average roughness (Rzjis) of the inner surface of the tube is A charging roller having a thickness of 4 to 15 μm is provided.

Further, according to the present invention, in a seamless charging roller coating tube extrusion die, an average of 10 points of the surface of the die exit portion (nipple) that comes into contact with the coating tube on the inner surface of the charging roller coating tube An extrusion die for a coated tube for a charging roller is provided, wherein the roughness (Rzjis _N ) is 5 to 20 μm.

  Furthermore, according to the present invention, there are provided a cartridge for an electrophotographic apparatus and an electrophotographic apparatus provided with the above charging roller.

  According to the present invention, it is possible to obtain a charging roller in which tube displacement due to high-speed rotation is suppressed and resistance unevenness is suppressed, and a coating tube for the charging roller can be appropriately formed by a mold for manufacturing the charging roller. Furthermore, a high-quality image can be obtained by using an electrophotographic apparatus cartridge and an electrophotographic apparatus on which the charging roller is mounted.

  The present invention relates to a charging roller formed by covering a cored bar, an elastic body on the outer periphery of the cored bar, and a seamless charging roller-coated tube on the elastic body, and having an average roughness (Rzjis) of the inner surface of the tube of 10 points. The charging roller is 4 to 15 μm.

  Hereinafter, the present invention will be described in more detail with reference to the drawings.

  FIG. 1 shows an example of a charging roller 1 'according to the present invention, which is used as a charger for an electrophotographic apparatus. This charging roller is provided with a foamed elastic body layer 2 made of a conductive elastic material on the outer periphery of a core metal 1 made of a highly conductive material such as stainless steel, plated iron, brass and conductive plastic. The outer periphery of the elastic layer 2 is coated with a plurality of seamless small-diameter thin-walled coating tubes 3 for charging rollers (hereinafter, coated tubes). In the case of FIG. 1, the covering tube is composed of an inner layer 3 (i) and an outer layer 3 (o).

  As the core metal (metal layer) in the present invention, for example, a good conductor such as aluminum, copper, iron, or an alloy containing these is preferably used. The metal core used in the present invention may be a metal tube having a thickness of about 0.1 to 1.5 mm, or may be a rod shape.

  As the conductive elastic material constituting the foamed elastic body layer 2, a foamed conductive rubber composition or a conductive polyurethane foam containing a conductive material can be used.

  In this case, the rubber component constituting the foamed conductive rubber composition is not particularly limited, but a conductive material is blended with ethylene-propylene-diene rubber (EPDM), chloroprene, or chlorosulfonated polyethylene. A foam, a foam of a copolymer rubber of epichlorohydrin and ethylene oxide, or a foam of a conductive rubber blended with a copolymer rubber of epichlorohydrin and ethylene oxide can be suitably used.

Examples of the conductive material blended in these rubber compositions include conductive powders such as carbon black, graphite, metals and various conductive metal oxides (such as tin oxide and titanium oxide), short carbon fibers and metal oxides. Various conductive fibers such as fibers can be used. The blending amount is preferably 3 to 100 parts by mass (3 to 50% by mass), particularly preferably 5 to 50 parts by mass (5 to 33% by mass) with respect to 100 parts by mass of the total rubber component, and thereby foaming is performed. The volume resistance of the elastic layer 2 is preferably adjusted to about 10 ¹ to 10 ⁹ Ω · cm. The foamed elastic body layer 2 can be formed by a known vulcanization molding method, and the thickness is appropriately set according to the use of the charging roller, but is usually preferably 1 to 20 mm.

  In the present invention, the foamed elastic layer 2 is covered with a plurality of seamless small-diameter thin-walled coating tubes 3 for charging rollers. In this case, the thermoplastic resin and elastomer constituting the coated tube 3 may be any extrudable thermoplastic resin or elastomer, and specifically, ethylene propylene rubber (EPDM), ethylene acetate Polyamides such as vinyl, ethylene ethyl acrylate, ethylene methyl acrylate, styrene butadiene rubber, polyester, polyurethane, nylon 6, nylon 66, nylon 11, nylon 12 and other copolymer nylons, styrene ethylene butyl, ethylene butyl, nitrile butadiene rubber Ordinary rubber such as chlorosulfonated polyethylene, polysulfide rubber, chlorinated polyethylene, chloroprene rubber, butadiene rubber, 1,2-polybutadiene, isoprene rubber and polynorbornene rubber, or styrene Butadiene - styrene (SBS) and styrene - butadiene - it is possible to use a thermoplastic rubber such as styrene hydrogenated product (SEBS), it is not particularly limited.

  Alternatively, elastomers such as the above resins and copolymers and elastomers such as modified bodies, and saturated polyesters such as polyethylene, polypropylene, polyethylene terephthalate (PET) and polybutylene terephthalate (PBT), polyethers, polyamides, polycarbonates, polyacetals , Acrylonitrile butadiene styrene, polystyrene, high impact polystyrene (HIPS), polyurethane, polyphenylene oxide, polyvinyl acetate, polyvinylidene fluoride, polytetrafluoroethylene, acrylonitrile-butadiene-styrene resin (ABS), acrylonitrile-ethylene / propylene rubber-styrene Resin (AES) and styrene resin such as acrylonitrile-acrylic rubber-styrene resin (AAS) Lil resin, vinyl chloride resin, a combination of vinylidene chloride resin, consisting of the resin and copolymers and the like materials are preferred.

  Furthermore, a polymer alloy or polymer blend composed of two or more polymers selected from the rubber, thermoplastic elastomer and thermoplastic resin can also be used.

  The resin, elastomer, copolymer, and the like used for the coated tube are those described above, and a tube configuration having desired characteristics can be obtained by appropriately blending a conductive material or the like.

  As the conductive material, known materials can be used, for example, carbon fine particles such as carbon black and graphite; metal fine particles such as nickel, silver, aluminum and copper; tin oxide, zinc oxide, titanium oxide, aluminum oxide and silica. Metal oxide fine particles doped with impurity ions having different valences; conductive fibers such as carbon fibers; metal fibers such as stainless steel fibers; the surface of carbon whiskers and potassium titanate whiskers are metal-oxidized Conductive whiskers such as conductive potassium titanate whiskers that have been subjected to a conductive treatment with a material or carbon, and conductive polymer fine particles such as polyaniline and polypyrrole.

  The coated tube concerning this invention forms the conductive polymer composition which consists of said various polymers, the said electrically-conductive material, and another additive if needed by an extrusion method.

  Furthermore, in order to obtain a film having a uniform film thickness of each thin film layer of the tube to be formed and a more uniform dispersibility of the conductive material or the like, a vertical tube extruder (FIG. 2) is used in the present invention.

  If the coated tube used in the present invention is simply molded, it can be obtained by forming a film into a tube by an extrusion molding method, an injection molding method, a blow molding method or the like. For example, for the purpose of obtaining superior durability, environmental resistance, and the like, the seamless tube obtained by the above various molding methods can be further crosslinked to form a conductive crosslinked polymer. As a method of cross-linking the conductive polymer formed into a tube shape, a cross-linking agent such as sulfur, organic peroxide and amines is added in advance according to the kind of the polymer, and the cross-linking is performed at a high temperature. A chemical cross-linking method for generating bismuth, a radiation cross-linking method for cross-linking by irradiating with radiation such as an electron beam or γ-ray is effective. Of the various crosslinking methods described above, the electron beam crosslinking method is preferred because there is no fear of contamination of the charged object due to the migration of the crosslinking agent or its decomposition product, and further, high-temperature treatment is not necessary and safety.

  The diameter of the coated tube used in the present invention is preferably about 5 to 25 mm. When the tube diameter is less than 5 mm, roughening the tube inner diameter tends to cause irregularities on the tube surface, and the coating is also technically difficult. Regarding the coated tube diameter exceeding 25 mm, it is technically possible if there is a demand.

The volume resistance value of the coated tube used in the present invention is preferably 10 ⁴ to 10 ¹⁰ Ω · cm, and particularly preferably 10 ⁵ to 10 ⁹ Ω · cm.

  Further, in the present invention, the ultra-thin layer tube appropriately function-separated is integrally formed at the same time, so that each layer does not have an unnecessarily thick film, and the foamed elastic body can be used in the entire configuration. It is possible to effectively extract the flexibility of the layer.

  The coated tube used in the present invention can be formed by various methods, and the extrusion method is suitable as described above. That is, a compound in which a polymer, a conductive material and, if necessary, a crosslinking agent, a stabilizer and other additives are mixed is manufactured in advance, and the compound is extruded from a die having a ring-shaped slit by an extruder and cooled. Can continuously produce seamless tubes (FIG. 2).

FIG. 3 shows an enlarged view of the vicinity of the roughened mold outlet in the present invention. The exit portion of the mold used in the present invention includes a die 4 that determines the outer surface of the charging roller coating tube, and a nipple 22 that determines the inner surface of the tube. The 10-point average roughness (Rzjis _N ) of the surface of the nipple 22 on the surface in contact with the coated tube is suitably in the range of 5 μm or more and 20 μm or less. As a means for roughening the surface, the surface of the nipple 22 may be a roughening tool such as sandpaper or a file, or may be blasted with abrasive grains. It is also possible to roughen the rough surface by strongly contacting the surface of the nipple 22 with a high hardness. For example, if blasting is used as an example, the predetermined roughness can be easily adjusted by the grain size, shape, material (hardness), etc., pressure, and time of the abrasive grains.

Further, even if the roughness of the mold is slightly larger than the desired roughness of the coated tube, the roughness of the molded product of the high-temperature semi-fluid tends to be less than the roughness of the mold due to the remaining temperature. Therefore, if the surface roughness Rzjis _N of the nipple is less than 5 μm, the tube surface is smoothed and hardly roughened. On the other hand, if the roughness Rzjis _N is larger than 20 μm, the tube surface becomes too larger than the desired roughness, and appears as a streak on the tube surface or as a thickness unevenness in the case of a thin tube.

FIG. 4 shows an inner surface when the tube is cut open, and Rzjis in the circumferential direction of the tube is defined as Rzjis _O and Rzjis in the vertical direction is defined as Rzjis _L. The surface roughness in the present invention is measured by surf coder SE3500 (manufactured by Kosaka Laboratory) based on JIS B0601 (2001) with a measurement length of 2.5 mm.

When the mold is used as a means for roughening the inner surface of the tube, the characteristic of the roughness profile is extrusion molding, so the Rzjis _{O in} the circumferential direction of the tube is slightly larger than Rzjis _{L in the} longitudinal direction, Has a streak pattern roughly parallel to the direction.

  The 10-point average roughness Rzjis of the tube inner surface measured in an arbitrary direction is suitably in the range of 4 μm to 15 μm. When the roughness of the inner surface of the tube is less than 4 μm, the effect of preventing tube displacement is hardly seen, and when the tightening margin is small, the tube is displaced. When the thickness exceeds 15 μm, the thickness of the tube becomes uneven in the case of a thin tube, and the tube cannot be properly molded.

  After extruding the tube, heat-shrinkable tube can be obtained if the tube diameter is expanded using means such as air pressurization in the middle of cooling or after cooling, and a non-heat-shrinkable tube can be obtained if the tube is not expanded. .

  The coated tube used in the present invention employs a non-heat-shrinkable tube in the examples described later. 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 foamed elastic layer in order to ensure adhesion between the foamed elastic layer and the coated tube. By inserting compressed air, the foamed elastic body layer having the core metal is inserted in a state where the diameter of the tube is temporarily enlarged so that the shape can be restored, and the external fitting process is completed if the air pressure is released.

  FIG. 5 shows a schematic configuration of an electrophotographic apparatus having a process cartridge having a charging roller of the present invention.

  In FIG. 5, 13 is an electrophotographic photosensitive member, which is rotationally driven at a predetermined peripheral speed in the direction of the arrow. In the rotation process, the photosensitive member 13 is uniformly charged with a positive or negative predetermined potential on its peripheral surface by the charging roller 1 ′ of the present invention, and then exposure means (not shown) such as slit exposure or laser beam scanning exposure. The image exposure light 14 is received. In this way, electrostatic latent images are sequentially formed on the peripheral surface of the photoreceptor 13.

  The formed electrostatic latent image is then developed with toner by the developing unit 15, and the developed toner developed image is rotated between the photosensitive member 13 and the transfer unit 16 from a sheet feeding unit (not shown). The image is sequentially transferred by the transfer means 16 to the transfer material 17 fed in synchronization.

  The transfer material 17 that has received the image transfer is separated from the surface of the photosensitive member, introduced into the image fixing means 18, and subjected to image fixing, thereby being printed out as a copy (copy).

  The surface of the photoreceptor 13 after the image transfer is cleaned by the removal of the transfer residual toner by the cleaning means 19 and is repeatedly used for image formation.

  In the present invention, a plurality of components such as the electrophotographic photosensitive member 13, the charging member 1 ′, the developing unit 15 and the cleaning unit 19 are integrally combined as a process cartridge. The electrophotographic apparatus main body such as a copying machine or a laser beam printer may be detachable. For example, the developing unit 15 and the cleaning unit 19 are integrally supported together with the photosensitive member 13 and the charging member 1 ′ to form a cartridge, and the process cartridge 21 is detachably attached to the apparatus main body using guide means such as the rail 20 of the apparatus main body. can do.

  Further, when the electrophotographic apparatus is a copying machine or a printer, the image exposure light 14 is a reflected light or transmitted light from a document, or a signal is read from a document by a sensor, and a laser beam performed according to this signal. Light emitted by scanning, LED array driving, liquid crystal shutter array driving, and the like.

  In the present invention, image evaluation and tube deviation evaluation are performed by the electrophotographic apparatus using the process cartridge in which the charging roller is incorporated as described above. In this method, an arbitrary number of sheets (such as the number of cartridges whose quality is guaranteed) is compared with image density unevenness after passing and the amount of deviation of the charging roller tube.

  More specifically, this will be described below with examples and comparative examples.

<Formation of coated tube for charging roller>
As a material for the outer layer of the coated tube, 100 parts by mass (61.3% by mass) of styrene resin (styrene-ethylene / butylene-olefin copolymer resin, trade name: Dynalon, JSR, melting point 100 ° C.), polyethylene 20 parts by mass (12.3% by mass), trade name: Ketjen Black EC (manufactured by Lion Akzo) 12 parts by mass (7.4% by mass) and trade name: Special Black 250 (manufactured by Degussa) 20 parts by mass (12.3% by mass), 10 parts by mass of magnesium oxide (6.1% by mass) and 1 part by mass of calcium stearate (0.6% by mass) were mixed for several minutes with a V-type blender. This was further melt-kneaded at 190 ° C. for 10 minutes using a pressure kneader. Furthermore, after cooling, it was pulverized by a pulverizer and pelletized by a single screw extruder.

  As materials for the inner layer, polyurethane elastomer (melting point: 120 ° C.) 100 parts by mass (76.3% by mass), as carbon black, trade name: Ketjen Black EC 20 parts by mass (15.3% by mass), magnesium oxide 10 parts by mass ( 7.6% by mass) and 1 part by mass (0.8% by mass) of calcium stearate were pelletized in the same process as the material of the outer layer.

Example 1
Using a vertical extruder (special product manufactured by Plastic Giken Co., Ltd., see FIG. 2), these are joined to form a double layer with one crosshead, and a nipple 22 having a Rzjis _N of 10 μm is used. After being extruded into a water-cooling ring 10 having an appropriate temperature at 155 ° C. and further cooled, it was taken up by a tube take-up device 11 comprising a pair of circular rotators. In this way, a coated tube having an inner diameter of 11.30 mm was obtained.

(Example 2)
A coated tube having an inner diameter of 11.30 mm was obtained using a nipple 22 having a Rzjis _N of 5 μm in the same procedure as in Example 1.

(Example 3)
A coated tube having an inner diameter of 11.30 mm was obtained using a nipple 22 having a Rzjis _N of 20 μm in the same procedure as in Example 1.

(Comparative Example 1)
A coated tube having an inner diameter of 11.30 mm was obtained using a nipple 22 having a Rzjis _N of 0 μm in the same procedure as in Example 1.

(Comparative Example 2)
A coated tube having an inner diameter of 11.05 mm was obtained using a nipple 22 having a Rzjis _N of 10 μm in the same procedure as in Example 1.

(Comparative Example 3)
A coated tube having an inner diameter of 11.05 mm was obtained using a nipple 22 having a Rzjis _N of 0 μm in the same procedure as in Example 1.

(Comparative Example 4)
A coated tube having an inner diameter of 11.30 mm was obtained using a nipple 22 having a Rzjis _N of 25 μm in the same procedure as in Example 1.

<Production of roller>
Hose-like foamed elastic layer with an inner diameter of 4.5 mm and an outer diameter of 11.5 mm (ethylene-diene rubber (EPDM) blended with a vulcanizing agent, carbon black (trade name: Ketjen Black EC) and a foaming agent Is extruded into a hose shape with an extruder and foamed in a vulcanized tube, cut to a length of 225 mm, and a core metal (diameter 5 mm x length 260 mm) is formed on an iron metal rod by chemical plating to form a 10 μm plating layer Then, a charged material roller having a diameter of 11.40 mm was obtained. A material obtained by cutting the coated tube manufactured in Examples / Comparative Examples into a length of 230 mm on this raw material roller was fitted on the outer periphery of the foamed elastic layer by a tube coating device (not shown), and pressure-contacted to obtain a charging roller.

<Evaluation>
These charging rollers were used as a primary charger for LBP (Laser Beam Printer; Laser Jet 2-P manufactured by Hewlett-Packard Company), and evaluation of charging uniformity was judged from image density unevenness. Further, a product having a good image was defined as a limit sample, a product having density non-uniformity smaller or smaller than that was indicated by ◯, and a product having a large density by ×. A summary of the evaluation results is shown in Table 2.

It is a longitudinal front view of an example of the charging roller of the present invention. It is a vertical front view of an example of the vertical type extruder of the functional multi-layer tube used for this invention. It is a vertical front view of the metal mold | die exit part used for this invention. It is explanatory drawing of Rzjis _O of the circumferential direction of the tube used for this invention, and Rzjis _L of a longitudinal direction. 1 is a schematic configuration diagram of an electrophotographic apparatus having a process cartridge having a charging roller of the present invention.

Explanation of symbols

1 Core (metal layer)
DESCRIPTION OF SYMBOLS 1 'Charging roller 2 Foaming elastic-body layer 3 Functional multilayer tube 3 (i) Inner layer 3 (o) Outer layer 4 Die 5 Center through-hole 6 Extrusion flow path 7 Extrusion flow path 8 1st extrusion machine 9 2nd pushing Out machine 10 Water-cooled ring 11 Timing pulley (Tube pulling device)
12 Power supply 13 Electrophotographic photoreceptor 14 Image exposure light 15 Developing means 16 Transfer means 17 Transfer material 18 Image fixing means 19 Cleaning means 20 Rail 21 Process cartridge 22 Nipple

Claims (5)

  In a charging roller comprising a cored bar, an elastic body on the outer periphery of the cored bar, and a seamless charging roller-coated tube, the 10-point average roughness (Rzjis) of the inner surface of the tube is 4 to 15 μm. There is a charging roller. The relationship between the 10-point average roughness (Rzjis _O ) in the circumferential direction of the inner surface of the tube and the 10-point average roughness (Rzjis _L ) in the coaxial length direction is Rzjis _O > Rzjis _L. The charging roller according to claim 1, wherein the charging roller has a streak pattern substantially parallel to the line. 10-point average roughness (Rzjis _N ) of the surface of the die that is in contact with the coating tube on the side that is the inner surface of the coating tube for the charging roller at the outlet portion (nipple) of the coating tube for seamless charging roller coating tube Is an extrusion die for a coated tube for a charging roller, wherein the die is 5 to 20 μm.   An electrophotographic apparatus cartridge comprising the charging roller according to claim 1.   An electrophotographic apparatus comprising the charging roller according to claim 1.

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