JP2004326099A - Electrifying roller, process cartridge and electrophotographic apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrifying roller which is produced by fitting a seamless tube on the peripheral face of an elastic layer covering the peripheral face of a core metal to make a surface layer and which can definitely suppress deposition of a developer on the surface of the roll, and to provide a process cartridge and an electrophotographic apparatus equipped with the above electrifying roll and stably forming a high-quality electrophotographic image. <P>SOLUTION: The electrifying roll for a contact electrification apparatus is used for the process of applying a voltage on an electrifying member and bringing the electrifying member into contact with the surface of the objective body to electrify the body surface. The roll comprises a conductive substrate, an elastic layer covering the peripheral face of the conductive substrate, and a seamless tube externally fitted to cover the peripheral surface of the elastic layer. The seamless tube constitutes the surface layer of the electrifying roll. The electrifying roll has the surface having ≤3.0 μm ten-point average roughness (Rzjis94) and ≤0.10 mm average distance (RSm) in the roughness curve. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a charging roller, a process cartridge, and an electrophotographic apparatus, and more particularly, to a charging roll used for contact charging of an electrophotographic photosensitive member, a process cartridge having the charging roll, and an electrophotographic apparatus.

  In recent years, a contact charging device has been put to practical use as a charging device for an electrophotographic photosensitive member. The contact charging can suppress the generation of ozone due to the charging of the electrophotographic photosensitive member and can reduce the power consumption required for charging, as compared with the corona charging conventionally used. In particular, a roller charging method using a charging roller as a charging member is preferably used in terms of charging stability.

  In the roller charging method, a conductive elastic roller is brought into pressure contact with a member to be charged, and a voltage is applied thereto to charge the member to be charged.

  Meanwhile, in contact charging, charging is performed by discharging from a charging member (charging roller) to a member to be charged, and charging of the member to be charged is started by applying a voltage equal to or higher than a certain threshold voltage to the charging roller. For example, when a charging roller is pressed against an organic photoconductor (OPC photoconductor) having a photosensitive layer having a thickness of 25 μm, a voltage of about 640 V or more in absolute value is applied to the charging roller. Then, the surface potential of the photoconductor starts to increase, and thereafter, the surface potential of the photoconductor increases linearly with a slope of 1 with respect to the applied voltage. Hereinafter, this threshold voltage is defined as a charging start voltage Vth.

  That is, in order to obtain the photoconductor surface potential Vd required for electrophotography, it is necessary to apply a DC voltage of Vd + Vth to the charging roller that is higher than that required for image formation itself. The method of applying only a DC voltage to the charging member and performing charging in this manner is referred to as DC charging.

  However, in DC charging, the resistance value of the charging member tends to fluctuate due to environmental fluctuations and the like. Further, when the thickness of the photosensitive layer changes due to the gradual scraping of the photosensitive layer with the use of the photoconductor, Vth varies. For these reasons, it has not been easy to control the potential of the photoconductor to a desired value.

  For this reason, in order to further uniform the charging, an AC + DC charging method is used in which a voltage obtained by superimposing an AC component having a peak-to-peak voltage of 2 × Vth or more on a DC voltage corresponding to a desired Vd is applied to the charging member. (For example, see Patent Document 1). This is for the purpose of the effect of leveling the potential by AC, and the potential of the member to be charged converges to Vd, which is the center of the peak of the AC voltage, and is hardly affected by disturbances such as the environment.

  As a charging roller, there is an example in which a surface layer is formed by a conductive seamless tube on a conductive support member (for example, see Patent Document 2). Furthermore, a seamless tube made of a fluororesin is disclosed (for example, see Patent Document 3), and a multilayer tube having a layer configuration having different conductivity is also disclosed (for example, see Patent Document 4). As a method for manufacturing such a charging roller, a method of forming the charging roller by insertion is mentioned as the conventional technique. A surface forming method using a crosshead extruder has also been proposed (for example, see Patent Document 5).

  In such a method of forming a charging roller by a seamless tube, even if a foam is used as an elastic layer on a substrate, a smooth surface can be formed by further covering the foam with a seamless tube. The charged body can be more uniformly charged.

  As a specific method of covering the support member with the seamless tube, there is a method of externally fitting the seamless tube to the support member. Specifically, the inner diameter of the seamless tube 22 is made larger than the outer diameter of the support member to be covered, and the tube is contracted and fitted by physical or chemical means, for example, heat, or a support to cover the inner diameter of the seamless tube. There is a method in which the tube is made smaller than the outer diameter of the member and the tube is expanded and fitted by physical or chemical means, for example, air pressure (for example, see Patent Document 6).

By the way, when a developer (toner or external additive) adheres to the surface of the charging roller via the electrophotographic photosensitive member, the resistance value of the surface of the charging roller changes or the resistance varies. In some cases, the photographic photoreceptor is stably and satisfactorily charged, so that a good electrophotographic image cannot be obtained. Therefore, it is important for the charging roller to have a surface property capable of suppressing the adhesion of the developer to the surface of the charging roller in order to stably obtain a high-quality electrophotographic image. Here, in the charging roll having a configuration in which the seamless tube is externally fitted to the peripheral surface of the elastic layer, the surface properties of the charging roller after the external fitting are further improved while reliably covering the elastic layer with the seamless tube. An example has not yet been found by the inventors.
JP-A-63-149669 U.S. Pat. No. 4,967,231 JP-A-5-2313 JP-A-5-96648 JP-A-6-58325 JP-A-10-228156

  Therefore, an object of the present invention is to cover the peripheral surface of the elastic layer covering the peripheral surface of the cored bar by covering the peripheral surface of the elastic layer with a seamless tube, and to prevent the developer from adhering to the surface of the charging roll serving as the surface layer. It is an object of the present invention to provide a charging roll that can be more reliably suppressed.

  Another object of the present invention is to provide a high-quality electronic device comprising a charging roll having a surface layer formed by covering a peripheral surface of an elastic layer covering a peripheral surface of a metal core with a seamless tube. An object of the present invention is to provide a process cartridge and an electrophotographic apparatus that stably provide a photographic image.

  A first aspect according to the present invention is a charging roll for a contact charging device that charges a surface of a member to be charged by applying a voltage to the surface of the member to be charged, the conductive member comprising: a conductive base; An elastic layer covering the outer periphery of the conductive substrate, and a seamless tube externally fitted to cover the outer periphery of the elastic layer, the seamless tube constituting a surface layer of the charging roll, The charging roll has a surface having a ten-point average roughness (Rzjis94) of 3.0 μm or less and an average length of a roughness curve (RSm) of 0.10 mm or less. provide.

  Another aspect of the present invention provides a process cartridge which integrally supports an electrophotographic photosensitive member and the above-described charging roll and is detachable from an electrophotographic apparatus main body.

  Further, another aspect of the present invention provides an electrophotographic apparatus including an electrophotographic photoreceptor and the above-described charging roll.

  As described above, the present invention has a charging roll that prevents a developer (for example, a toner and an external additive, etc.) from adhering to the roller surface and provides stable and good uniform charging characteristics and output image quality. It has become possible to provide a process cartridge and an electrophotographic apparatus.

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

  FIG. 1 illustrates an example of a structure of a charging roll according to one embodiment of the present invention. The charging roll 11 has an elastic layer 2 covering the peripheral surface of the conductive cored bar 1, and a seamless tube 3 fitted on the peripheral surface of the elastic layer 2. The seamless tube forms a surface layer of the charging roll. Here, the seamless tube has a laminated structure of the first layer 31 and the second layer 32. In the present invention, the ten-point average roughness (Rzjis94) of the surface of the charging roll is 3.0 μm or less. Although the lower limit is not particularly limited, about 1.0 μm is a practical lower limit. Further, RSm is 0.10 mm or less, preferably 0.08 mm, and as a practical lower limit, it is about 0.04 mm.

  According to such a configuration, the adhesion of the developer to the surface of the charging roll can be extremely effectively suppressed.

  By the way, the ten-point average roughness (Rzjis94) in the present invention is a value obtained based on JIS B 0601: 1994, and the reference length required for calculating (Rzjis94) is 2.5 mm. Further, RSm is “the average value of the length Xs of the roughness curve element at the reference length” obtained in accordance with JIS B 0601: 2001, and the reference length here is 2.5 mm. The minimum height used for calculating RSm was defined as 10% of the maximum height roughness (maximum height of profile) Rz of the roughness curve in JIS B0601: 2001.

  The seamless tube constituting the surface layer of the charging roll according to the present invention may be a blend of rubber particles and a thermoplastic elastomer. Here, specific examples of the rubber particles include those containing EPDM crosslinked rubber particles contained in impact-resistant polystyrene (HIPS) and the like. The particle size, shape, and the like of the rubber particles are not particularly limited as long as they satisfy the surface roughness (Rzjis94) and the average distance between irregularities (RSm) of the present invention.

  Specific examples of the seamless tube according to the present invention include, for example, a thermoplastic styrene-based elastomer of component (A), a two-component resin of HIPS of component (B), and carbon black of component (C) as a conductive agent. A configured seamless tube.

  Specifically, as the thermoplastic styrene-based elastomer of the component (A), poly (styrene-hydrogenated butadiene-crystalline olefin) ternary block copolymer (SEBC), poly (styrene-hydrogenated butadiene-styrene) ternary Block copolymer (SEBS), poly (styrene-butadiene-styrene) ternary block copolymer (SBS), poly (styrene-hydrogenated isoprene-styrene) ternary block copolymer (SEPS) and poly (styrene- (Vinyl isoprene-styrene) ternary block copolymer.

  On the other hand, as the component (B), impact-resistant polystyrene (HIPS) is preferred, and impact-resistant polystyrene containing EPDM crosslinked rubber particles is particularly preferred.

  The ratio of the component (A) to the component (B) is preferably (A) / (B) = 80/20 to 40/60, more preferably 60/40 to 40/60 by mass ratio. Within this range, a predetermined surface roughness is exhibited, and the adhesion of the developer to the surface of the charging roll is improved. Further, even if the tube is too hard or has poor elastic properties and cannot be coated or can be coated, there is no problem that the roll shape is deteriorated and it is difficult to use as a charging roll.

  By blending a thermoplastic styrenic elastomer and HIPS as the base resin composition in the present invention, the surface roughness can be controlled well. Further, the rubber component contained in the HIPS has an effect of reducing the RSm value (average distance between unevenness) to 0.10 mm or less. In the present invention, by reducing the RSm value, the contact area between the toner and the external additives and the like and the roller surface is reduced, thereby giving an effect of reducing the adhesion.

  The use ratio of the carbon black as the component (C) is preferably from 10 to 60% by mass, and particularly preferably from 20 to 40% by mass. By setting the content ratio of the carbon black of the component (C) within the above range, the durability as a charging roll is reduced due to an increase in resistance during energization use, the tube becomes too hard, the elastic properties are poor, and the elasticity is poor. It is possible to prevent a situation where the outer layer cannot be fitted to the layer.

As the carbon black species of the component (C), any carbon black may be used as long as the volume resistance value of the seamless tube is 1 × 10 ⁶ to 1 × 10 ¹¹ Ω · cm and the above content is satisfied. The above carbon blacks may be used as a mixture.

  As the component (C) carbon black, for example, commercially available products such as Ketjen Black (manufactured by Lion Akzo), Printex, SpecialBlack, ColorBlack (manufactured by Degussa), BLACKPEARLS (manufactured by Cabot), Asahi Carbon (manufactured by Asahi Carbon Co., Ltd.) ), Mitsubishi Carbon (manufactured by Mitsubishi Chemical Corporation), Denka Black (manufactured by Denki Kagaku Kogyo), Seast and Talka Black (all manufactured by Tokai Carbon Co., Ltd.) and the like.

  Other additives include, as necessary, a conductive filler, an antioxidant, a softener, a plasticizer, a reinforcing agent, a filler, and the like. As the conductive filler, the above-mentioned carbon black is indispensable, and graphite or a metal oxide may also be used. Examples of the metal oxide include titanium oxide and lead oxide.

  Next, as one embodiment of the method for producing a seamless tube according to the present invention, first, a styrene-based thermoplastic elastomer, HIPS, and carbon black are kneaded with necessary additives, and then, pelletized. Next, the obtained pellets are formed into a seamless tube by an extruder. Then, the conductive member (charging roller) is formed by externally fitting the formed seamless tube to the support member.

  The thickness of the seamless tube according to the present invention is not particularly limited, but is preferably 100 to 600 μm. Moreover, it is good also as a multilayer simultaneous molding tube.

  The structure, material, or manufacturing method of the support member to which the seamless tube is fitted according to the present invention are exemplified.

  An example of the support member includes an elastic roller. As the material, a metal such as iron, copper, and stainless steel, a carbon-dispersed resin, a metal or a metal oxide-dispersed resin, or the like is used as the conductive substrate. For example, as a configuration of the elastic roller, an elastic layer is provided on a conductive substrate. Further, a conductive layer or a resistance layer may be further provided outside the elastic layer. The elastic layer can be formed of a rubber or sponge such as chloroprene rubber, isoprene rubber, EPDM rubber, polyurethane rubber, epoxy rubber and butyl rubber, or a thermoplastic resin such as styrene butadiene, polyurethane, polyester and ethylene-vinyl acetate. . These rubbers and resins may contain conductive agents such as carbon black, metal and metal oxide particles.

  As the conductive layer, for example, a metal vapor-deposited film, a conductive particle-dispersed resin or a conductive resin, or the like is used. Examples of the metal vapor-deposited film include aluminum, indium, nickel, copper, and iron. Examples thereof include those in which conductive particles such as carbon, aluminum, nickel, and titanium oxide are dispersed in a resin such as urethane, polyester, vinyl acetate-vinyl chloride copolymer, and polymethyl methacrylate. Examples thereof include quaternary ammonium salt-containing polymethyl methacrylate, polyvinylaniline, polyvinylpyrrole, polydiacetylene, and polyethyleneimine.

  As the resistance layer, a conductive resin, a conductive particle-dispersed insulating resin, or the like can be used. As the conductive resin, a resin such as ethyl cellulose, nitrocellulose, methoxymethylated polyamide, ethoxymethylated polyamide, copolymerized polyamide, polyvinyl hydrin, or casein is used. Examples of the conductive particle-dispersed resin include a small amount of conductive particles such as carbon, aluminum, indium oxide and titanium oxide in an insulating resin such as urethane, polyester, vinyl acetate-vinyl chloride copolymer and polymethyl methacrylate. Dispersed materials and the like can be mentioned.

  A charging roll having a support member and a seamless tube according to the present invention, which has a support member and a seamless tube, is excellent in production stability and can stably produce a medium-resistance region which has conventionally been considered difficult to produce stably.

  The method of externally fitting the seamless tube according to the present invention so as to cover the outer periphery of the elastic layer is not particularly limited. For example, after forming a seamless tube such that the inner diameter is smaller than the outer diameter of the elastic roller, the inner diameter of the seamless tube is expanded by using air pressure or the like, and the elastic roller is inserted therein, and the contraction of the seamless tube is performed. There is a method of bringing the elastic tube into close contact with the peripheral surface of the elastic roller by a force, a method of coating the elastic tube with a heat-shrinkable seamless roller, and then heating and shrinking the tube to adhere to the peripheral surface of the elastic roller.

  The electrophotographic photoreceptor, exposure means, developing means, transfer means and cleaning means used in the present invention are not particularly limited.

  FIG. 2 shows a schematic cross section of an electrophotographic apparatus in which a process cartridge 21 having the charging roll 11 of the present invention as a primary charging means is mounted on an electrophotographic apparatus main body by guide means.

  2, the electrophotographic photosensitive member 13 is driven to rotate at a predetermined peripheral speed in the direction of the arrow. In the rotation process, the photoreceptor 13 is uniformly charged at a predetermined positive or negative potential on its peripheral surface by the charging roll 11 of the present invention as a primary charging means provided with a power supply 12, and then subjected to slit exposure or laser beam scanning exposure. And the like, and receives exposure light 14 from exposure means (not shown). Thus, an electrostatic latent image is sequentially formed on the peripheral surface of the photoconductor 13.

  The formed electrostatic latent image is then toner-developed by the developing unit 15, and the developed toner-developed image is transferred between the photoconductor 13 and the transfer unit 16 by a rotation of the photoconductor 13 from a paper feeding unit (not shown). The image is sequentially transferred to the transfer material 17 taken in synchronization and fed by the transfer unit 16.

  The transfer material 17 having undergone the image transfer is separated from the photoreceptor surface, introduced into the image fixing means 18 and subjected to image fixing, thereby being printed out of the apparatus as a copy.

  The surface of the photoreceptor 13 after the image transfer is cleaned by the cleaning unit 19 to remove the untransferred toner, and is used repeatedly for image formation.

  Hereinafter, the present invention will be described in more detail with reference to specific examples. However, embodiments of the present invention are not limited to these. In the examples, “parts” means “parts by mass”.

  In this example, a two-layer simultaneously molded tube was produced by the method described below.

  As shown in FIG. 3, the 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 gas introduction. The inner layer material is injected from the first extruder 8 into the outer channel 7 and the surface layer material from the second extruder 9 is injected into the outer channel 7 under pressure. It is cooled by a water-cooling ring 10 provided on the outer periphery of the two-layered simultaneously formed tube 3 obtained as described above, pulled by a tube take-off device 22 and sequentially cut into a predetermined length to form a seamless tube for a charging roll in the next step. Then, the outer peripheral surface of the elastic roller having the foamed elastic layer 2 covering the periphery of the conductive substrate 1 is fitted.

  As a specific external fitting method, a seamless tube is first produced by extrusion molding with the inner diameter of the tube equal to or smaller than the outer diameter of the support, and then the inner diameter of the tube is expanded by pressure, for example, so that fitting is possible, The support is coated by means of inserting the support.

  As described above, by forming the seamless tube 3 by multi-layer simultaneous extrusion molding, it is possible to easily produce a multi-layered tube including a thin layer which is difficult to cover alone as a tube.

  The obtained seamless tube 3 was externally fitted on the peripheral surface of the elastic roller, and a charging roller 11 as shown in FIG. 1 was produced.

(Example of Seamless Tube and Comparative Example 1)
The resin constituting the surface layer 32 of the seamless tube 3 is such that the mass ratio of SEBC (styrene content 20%) to HIPS is SEBC / HIPS = 0/100, 20/80, 40/60, 60/40. , 80/20, and 100/0, and Ketjen Black EC: 5 parts, Special Black 250: 20 parts, magnesium oxide: 10 parts, and calcium stearate: 1 part were added to each, and a pressurized kneader was added. Is kneaded at 180 ° C. for 15 minutes, cooled and pulverized, and then pelletized by a granulating extruder. The sample number of SEBC / HIPS having a copy number of 0/100 is referred to as sample number 1-1, and hereinafter, 20/80 is 1-2, 40/60 is 1-3, 60/40 is 1-4, and 80/20 is 1-80. 5, 100/0 was 1-6.

  The resin constituting the inner layer 31 of the seamless tube 3 is a thermoplastic polyurethane elastomer (TPU): 100 parts, Ketjen black EC: 16 parts, magnesium oxide: 10 parts, calcium stearate: 1 part, and a pressurized type. The mixture was kneaded at 180 ° C. for 15 minutes using a kneader, cooled and pulverized, and then pelletized by a granulating extruder.

  Using the above-mentioned pellets, after extruding with a two-layer extruder having a die having an inner diameter of 16.5 mm and a point having an outer diameter of 18.5 mm as shown in FIG. 3, through a sizing and cooling process, an inner diameter of 11.1 mm was obtained. Then, a seamless tube having a surface layer thickness of 100 μm and an inner layer thickness of 400 μm was formed.

(Comparative example 2 of seamless tube)
For the tube surface layer, SEBC (styrene content 20%): 60 parts, GPPS: 40 parts, Ketjen black: 5 parts, Special Black 250: 20 parts, magnesium oxide: 10 parts, calcium stearate: 1 part Then, the mixture was kneaded at 180 ° C. for 15 minutes using a pressure kneader, cooled and pulverized, and then pelletized by a granulating extruder (sample No. 2). Thereafter, through the same manufacturing process as the seamless tube example / comparative example 1, a seamless tube having an inner diameter of 11.1 mm, a surface layer thickness of 100 μm, and an inner layer thickness of 400 μm was formed.

  Like the conductive roller shown in FIG. 1, a foamed elastic body made of a conductive elastic material is provided on the outer periphery of a conductive base 1 made of a good conductive material such as stainless steel, plated iron, brass, and conductive plastic. Layer 2 was provided, and a charging roller was prepared in which the seamless tube was fitted around the outer periphery of the foamed elastic layer 2. This charging roller was incorporated in the process cartridge shown in FIG.

  The measurement of the surface roughness (Rzjis94) of the charging roller and the average interval of irregularities (RSm) was performed in accordance with JIS-B-0601: 1994, 2001. The measurement conditions were a measurement length of 2.5 mm, a measurement speed of 0.5 mm / min, and a cutoff wavelength of 0.8 mm.

The toner adhesion was evaluated by assembling into the process cartridge shown in FIG. 2, outputting 1000 images continuously, visually observing the surface of the charging roller after the image was output, and evaluating the toner adhesion according to the following criteria. The results are shown in Table 1 below.
A: Slight toner adhesion is confirmed.
B: Although toner adhesion is confirmed, it is within an allowable range.
C: A large amount of toner components adhere.

Further, in the image evaluation, 10,000 continuous sheets of images were output using the same roller, and the occurrence of image defects due to toner adhesion was evaluated. Table 1 shows the results.
A: Almost no toner-derived matter is observed on the image.
B: Black streaks derived from toner adhesion are slightly observed, but within the allowable range.
C: Image defects (black streaks) due to toner adhesion clearly appear.

  By setting the HIPS content of the component (B) to a predetermined ratio as described above, Rzjis94 can be 3.0 μm or less and RSm can be 0.10 mm or less in terms of surface roughness. Was reduced, and image defects due to toner adhesion were less likely to occur. On the other hand, the charging roller according to Comparative Example 2 using GPPS (general-purpose polystyrene) having no rubber component as the base resin could not sufficiently lower the RSm value. Therefore, adhesion of the developer to the surface of the charging roller was observed, and the electrophotographic image formed using the charging roller was also defective.

FIG. 3 is a diagram illustrating an example of a configuration of a charging roll of the present invention. FIG. 2 is a schematic configuration diagram of an electrophotographic apparatus including a process cartridge having the charging roll of the present invention as a primary charging unit. It is a schematic structure figure of the manufacturing device of the charge roll constituted by the seamless tube of the present invention.

Claims (6)

A charging roller for a contact charging device, which applies a voltage to bring the charging member into contact with the surface of the member to be charged, thereby charging the surface of the member to be charged,
A conductive substrate, an elastic layer covering the outer periphery of the conductive substrate, and a seamless tube fitted externally to cover the outer periphery of the elastic layer;
The seamless tube constitutes a surface layer of the charging roll, and the charging roller has a ten-point average roughness (Rzjis94) of 3.0 μm or less and an average length of a roughness curve (RSm). Has a surface of 0.10 mm or less.   The charging roller according to claim 1, wherein the seamless tube includes high impact polystyrene (HIPS). The seamless tube,
(A) a thermoplastic styrenic elastomer;
(B) impact-resistant polystyrene (HIPS);
Containing
The charging roller according to claim 1, wherein the ratio of the component (A) to the component (B) is (A) / (B) = 80/20 to 40/60 by mass ratio. 4.   The charging roller according to claim 1, wherein the seamless tube is a laminate of a plurality of layers.   A process cartridge which integrally supports an electrophotographic photosensitive member and the charging roller according to any one of claims 1 to 4, and is detachable from an electrophotographic apparatus main body.   An electrophotographic apparatus comprising: an electrophotographic photosensitive member; and the charging roller according to claim 1.

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