JP5201886B2 - Electrophotographic equipment - Google Patents

Description

  The present invention relates to a charging roller mainly used in an electrophotographic apparatus such as a laser printer and a copying machine, and an electrophotographic apparatus having the charging roller.

  Conventionally, an image forming unit is installed inside an electrophotographic apparatus, and a recorded image is formed through processes of cleaning, charging, latent image, development, transfer, and fixing. The image forming unit includes a photosensitive drum that is an electrophotographic photosensitive member, and includes a cleaning unit, a charging unit, a latent image forming unit, a developing unit, and a transfer unit. The image on the photosensitive drum formed by the image forming unit is transferred to a recording material by a transfer unit, conveyed to the fixing unit, heated and pressed by the fixing unit, and output as a recording image fixed on the recording material. Is done.

  Next, charging, latent image formation, development, and transfer processes will be described.

  In the charging unit, the charging roller performs primary charging on the surface of the photoconductor so that the potential is uniform with a predetermined polarity. Next, by receiving exposure of target image information, an electrostatic latent image corresponding to the target image is formed on the surface of the photoreceptor. This electrostatic latent image is visualized as a toner image from the developing member in the developing unit. The visualized toner image is transferred from the surface of the photosensitive member to the recording material by the transfer member at the transfer portion. The transferred unfixed toner image is conveyed to a fixing unit, fixed by the fixing unit, and output as a recorded image.

  There are a corona charging method and a roller charging method as charging methods used in image forming apparatuses such as electrophotographic apparatuses and electrostatic recording apparatuses. The corona charging method is a charging method in which a voltage is applied to a corona wire or the like to form a charged product, and the surface of the photoreceptor is charged with the charged product. On the other hand, the roller charging method is a charging method in which the surface of the photosensitive member is charged by discharging by bringing the charging roller into contact with or close to the photosensitive member (the distance between the charging roller and the photosensitive member is several tens of μm).

  The roller charging method has an extremely small amount of ozone and discharge products generated compared to the corona charging method. Therefore, by using the roller charging method, it is possible to reduce the space for attaching the ozone filter and to reduce image blur due to the discharge product.

  The roller charging method is classified into AC + DC charging in which alternating current (AC) is superimposed on direct current (DC), and DC charging only in DC. DC charging is a suitable technique for achieving downsizing and low cost, but the charging bias region for keeping the drum potential of the photoconductor constant is narrow, and the roller resistance is uneven due to circumferential unevenness and dirt, and roller non-uniformity. It is technically difficult to achieve image quality stability such as non-uniform charging due to uniformity. If this is a high-speed and long-life office copying machine with a printing speed of 50 sheets or more and a maintenance interval of 250,000 sheets or more, it is more difficult to maintain image quality with the DC charging system, so the AC + DC charging system is suitable.

  However, a problem in roller charging by the AC + DC charging system is deterioration of energization of the charging roller. The deterioration of energization means that the roller resistance is changed by passing a current through the charging roller. If the roller resistance changes, the charging roller cannot give a desired drum potential to the photoreceptor. In general, when energization deterioration occurs, the roller resistance increases, so that the drum potential decreases. Related art has been reported in Patent Documents 1 to 3 as a study for solving energization deterioration.

  In recent years, an electrophotographic apparatus is required to have high image quality and a long life.

  As an approach from the electrophotographic photosensitive member to satisfy the high image quality, for example, the following two can be mentioned. (1) A method of increasing the electrostatic capacitance of the electrophotographic photosensitive member by thinning the electrophotographic photosensitive member to make the contrast of the latent image clearer. (2) A method of employing an electrophotographic photosensitive member corresponding to a short wavelength laser (particularly 380 to 500 nm).

Moreover, as an approach from the electrophotographic photosensitive member for satisfying the long life, for example, the following two methods are exemplified. (1) A method using a photoconductor composed of an amorphous material having a silicon atom as a base, for example, an amorphous silicon photoconductor. (2) A method of providing a surface protective layer for protecting the photosensitive layer.
Special registration 03018906 Special registration 03638008 JP 2000-003086 A

  However, when a roller charging method is employed in an electrophotographic process using an amorphous silicon photoreceptor or a thin film organic photoreceptor, a large current is required for charging because the electrostatic capacity of the photoreceptor is large. When a large current flows through the charging roller, the charging roller tends to increase in resistance (energization deterioration), and a long life cannot be achieved. Therefore, countermeasures against energization deterioration in a large current energizing condition of the charging roller (for example, a DC current of 0.2 mA or more and an AC current of 2 mA or more) are an important issue.

  Patent Documents 1 to 3 describe inventions relating to a charging roller having a small resistance change before and after energization. However, since the energization conditions described in these patent documents are low current, the problems of the present invention are solved. It is not a means.

  Accordingly, an object of the present invention is to provide a charging roller in which energization deterioration does not occur even when a large current is applied.

The inventors of the present invention diligently studied to solve the above-mentioned problems, and the cause of the deterioration of energization is the molecular motion of the base polymer and conductive particles that form the conductive layer by Joule heat generated when a large current is passed. It was discovered that the dispersion state of the conductive particles in the conductive layer is changed by this molecular motion. Thus, it has been found that the deterioration of energization can be suppressed by setting the hydrogen nucleus spin-spin relaxation time T ₂ that is an index of molecular motion within a specific range.

That is, the charging roller according to the present invention is a charging roller having a conductive layer containing conductive particles on a conductive support, and the hydrogen nucleus spin-spin relaxation time T ₂ of the conductive layer at 23 ° C. 20 μs <T ₂ <300 μs.

  In addition, an electrophotographic apparatus according to the present invention includes the charging roller.

  In the charging roller according to the present invention, even when a large current is passed, the roller resistance does not change, and energization deterioration does not occur. Therefore, the charging roller according to the present invention can be used in an electrophotographic apparatus equipped with an amorphous silicon photoconductor or a thin film organic photoconductor that requires a large current energization condition without causing a problem of energization deterioration.

  As a result of intensive studies, the present inventors have found that a charging roller containing conductive particles and having a low molecular mobility conductive layer is indispensable as a means for solving the deterioration in energization under large current energization conditions. It became clear.

As a result of studying the energization deterioration mechanism, it has been found that the cause of the energization deterioration under a large current energization condition is a change in the dispersion state of the conductive particles. That is, the molecular motion of the base polymer (polymer, rubber, etc.) that forms the conductive layer is activated by Joule heat generated by passing a large current through the charging roller, and this molecular motion disperses in the conductive layer. The dispersion state of the conductive particles changes before and after energization. For this reason, it has been found that the roller resistance changes. From this mechanism, it has been found that the following two are very effective as material countermeasures for suppressing current deterioration.
(1) A conductive layer made of a low molecular mobility material.
(2) Use conductive particles having a relatively large particle size that are hardly affected by thermal motion of molecules.

  First, the condition (1) was examined.

Here, the low molecular mobility material means a material (polymer, resin or rubber) composed of molecules having small thermal motion. In addition, as a resistance value of the conductive layer, for example, 10 ⁴ Ω to 10 ⁷ Ω can be selected.

Here, the molecular mobility can be expressed by the hydrogen nuclear spin-spin relaxation time (T ₂ ) of pulse NMR. This is the average value of the hydrogen nuclear spin-spin relaxation time (T ₂ ) obtained from the FID (Free Induction Decay) intensity curve or the echo intensity attenuation curve obtained by analysis by proton nuclear magnetic resonance. is there. When measuring the T ₂ of the conductive layer, not only T ₂ components derived from the base polymer, T ₂ components derived from components (additives such as carbon black) contained in the conductive layer is also observed. An average of these observed components was used as an index of molecular mobility as T ₂ of the conductive layer. When T ₂ is small, the molecular mobility of the conductive layer is small, and when T ₂ is large, the molecular mobility is large.

Therefore, the present inventors examined the relationship between T ₂ exhibiting molecular mobility and the conductive layer. As a result, when T _{2 of the} conductive layer is within a predetermined range, the roller resistance value does not change even when a large current is passed. It was found that there was no deterioration of energization.

Therefore, the charging roller according to the present invention is a charging roller having a conductive layer containing conductive particles on a conductive support, and the hydrogen nucleus spin-spin relaxation time T ₂ at 23 ° C. of the conductive layer is 20 μs. The charging roller is characterized in that <T ₂ <300 μs.

The conductive layer is characterized in that T ₂ (μs) at 23 ° C. is in the range of more than 20 and less than 300. If it is 20 or less, the conductive layer becomes too hard and it is not suitable as a charging roller. On the other hand, when T ₂ is 300 or more, the dispersion state of the conductive particles existing inside the conductive layer changes due to the movement of molecules caused by Joule heat generated when a large current flows through the conductive layer. Such a change in the dispersion state of the conductive particles is a cause of deterioration of energization under a large current energization condition. That is, the conductive layer having T ₂ (μs) at 23 ° C. of more than 20 and less than 300 can maintain the dispersed state of the conductive particles even when a large current flows, and the roller resistance hardly changes due to the large current flow.

Regarding the measured temperature of T ₂ (.mu.s), since the varying value of the temperature changes T ₂ (.mu.s), it was defined as 23 ° C.. This temperature is a standard room temperature, and it is considered that a charging roller, a cartridge equipped with a charging roller, or an electrophotographic apparatus is most used at this temperature. It has also been confirmed that the magnitude relationship of T ₂ (μs) does not change even at different temperatures.

The base polymer constituting the conductive layer is not particularly limited as long as the T ₂ (μs) of the conductive layer at 23 ° C. can be in the range of more than 20 and less than 300. Usually, butadiene rubber, styrene rubber, ethylene propylene rubber, acrylonitrile-butadiene rubber, epichlorohydrin rubber, or the like can be used. Of these, acrylonitrile-butadiene rubber (hereinafter abbreviated as NBR) having an acrylonitrile content of more than 25% and less than 49% is particularly preferred in the present invention. A nitrile group has an effect of lowering molecular mobility, and when the acrylonitrile content in NBR increases, T ₂ (μs) of the conductive layer decreases. When this phenomenon was confirmed, when the acrylonitrile content in NBR is 49% or more, T ₂ (μs) of the conductive layer may be 20 or less, and the conductive layer tends to be hard. When the conductive layer becomes hard, defects such as cracks are likely to occur in the conductive layer during vulcanization, polishing or UV treatment. The cause of the occurrence of cracks is unknown, but if the conductive layer becomes too hard, it is considered that the conductive layer cracks due to internal stress such as external stress or contraction of the conductive layer. On the other hand, when the acrylonitrile content of NBR is 25% or less, T ₂ (μs) becomes 300 or more, and the electric conductivity existing inside the conductive layer is caused by the movement of molecules that occurs when a large current flows through the conductive layer. The dispersion state of the conductive particles changes. In addition, the acrylonitrile content rate (%) in NBR refers to the mass% of acrylonitrile in the case of synthesizing NBR by polymerizing acrylonitrile and butadiene. For example, NBR having an acrylonitrile content of 25% refers to a polymer of 25% by mass of acrylonitrile and 75% by mass of butadiene.

  Next, the condition (2) was examined.

  The conductive particles are used for the conductive layer of the present invention to exhibit suitable conductivity, and are not particularly limited. Examples thereof include carbon materials such as carbon black, graphite and carbon fibers, metal powders such as aluminum and magnesium, metal materials such as metal fibers, and surface-treated metal oxide powders. Among these, carbon black is particularly preferable in consideration of material cost and dispersibility. As carbon black, MT carbon is particularly preferable from the viewpoint of material cost and dispersibility. Moreover, in this invention, a different kind of electroconductive particle can be used together.

  The average particle diameter (arithmetic average particle diameter by electron microscope) (hereinafter abbreviated as average particle diameter) of the conductive particles is not particularly limited, but from the viewpoint of preventing energization deterioration, more than 75 nm and less than 300 nm. It is preferable that it is 80 nm or more and 230 nm or less. The conductive particles having a relatively large particle diameter are unlikely to change in dispersion state due to the molecular motion of the base polymer. Therefore, by using conductive particles having a relatively large average particle size (over 75 nm) as a conductivity-imparting agent, it is possible to suppress a change in the dispersion state of the conductive particles caused by molecular motion of the conductive layer under a large current conduction condition. It is possible to prevent the electrification deterioration of the charging roller. On the other hand, in the case of conductive particles having an average particle size of 75 nm or less, it is easily affected by the molecular motion of the base polymer, and there is a possibility that the effect of reinforcing the conductive path by the highly conductive particles due to the change in the dispersion state may be reduced. . Furthermore, in the case of conductive particles having an average particle size of 300 nm or more, if such large particle size conductive particles exist in the vicinity of the surface of the conductive layer, it is easy to leak against minute scratches on the photosensitive drum. Detrimental effects may occur. Therefore, the conductive particles having an average particle diameter of more than 75 nm and less than 300 nm are less likely to cause a change in dispersion state, exhibit an effect of reinforcing the conductive path, and are less likely to cause a photoconductor drum leak. It is suitable as.

  As a compounding quantity of the said electroconductive particle, 20 mass parts or more and 100 mass parts or less are preferable with respect to 100 mass parts of base polymers, and 40 mass parts or more and 60 mass parts or less are more preferable. If it is less than 20 parts by mass, the effect of reinforcing the conductive path may be reduced. If it exceeds 100 parts by mass, the effect of reinforcing the conductive path can be obtained, but the conductive layer may become too hard and defects such as cracking may easily occur.

Further, the conductive particles are preferably those having high conductivity, and particularly suitably used carbon blacks include, for example, carbon black having a large nitrogen adsorption specific surface area (N ₂ SA) and DBP (dibutyl phthalate) oil absorption. Etc. Furthermore, examples of carbon black having an average particle size of more than 75 nm and less than 300 nm include MT carbon and FT carbon.

  In addition to the above base polymer and conductive particles, a filler, a plasticizer, a vulcanizing agent, a vulcanization accelerator, an antiaging agent, and the like can be arbitrarily added to the charging roller of the present invention. .

  A method for manufacturing the charging roller of the present invention will be described.

  The charging roller manufacturing process is divided into a kneading process, a molding process, and a polishing process.

  In the kneading step, for example, the base polymer, the conductive particles, the vulcanization aid, the plasticizer, the filler, and the like are kneaded with a pressure kneader, and then the vulcanizer, the vulcanization accelerator, and the like are mixed with a roll kneader. Knead.

  In the molding process, the mixture produced in the kneading process is extruded into a roll with a single screw extruder, vulcanized with a vulcanizing can, and press-fitted into a conductive support (core metal) coated with an adhesive. Alternatively, the extrudate can be directly coated on the core and vulcanized in a hot air furnace. Here, the heat treatment of the conductive layer is preferably 140 to 170 ° C. and 50 to 130 minutes.

  In the polishing step, the surface of the unpolished conductive layer obtained in the molding step is polished to manufacture the charging roller according to the present invention. Examples of the polishing method include the following methods. (1) A method of polishing the longitudinal direction at once using a grindstone having the same size as the length (longitudinal width) of the charging roller. (2) A method of polishing while traversing a thin grindstone in the longitudinal direction.

The charging roller of the present invention can be provided with a surface layer as long as the effects of the invention are not impaired. For example, by applying a resin curable with ultraviolet light or an electron beam to the surface and curing it, the friction coefficient, water repellency, oil repellency, etc. of the surface can be controlled, and the charging roller can be prevented from contamination. It is also possible to perform surface modification by ultraviolet light irradiation, electron beam irradiation, or the like. Here, as surface treatment (UV treatment) by ultraviolet light irradiation, for example, light having a wavelength of 200 to 450 nm can be uniformly irradiated on the surface of the conductive layer. The UV treatment time may be about 1 to 30 minutes. It is preferable to irradiate the surface of the conductive layer uniformly with the ultraviolet light irradiation. For example, a method of rotating the conductive layer with respect to the ultraviolet light source or irradiating the ultraviolet light from above and below while feeding the conductive layer by a conveyor. Can be used. At this time, the T ₂ value of the surface portion of the conductive layer may change due to the UV treatment. In this case, as T ₂ according to the present invention will measure the conductive layer inside the T ₂ unaffected by the UV treatment.

  Next, an example of an electrophotographic apparatus using the charging roller of the present invention will be described. FIG. 5 shows a schematic configuration as an example of an electrophotographic apparatus incorporating the charging roller 1 according to the present invention.

  In FIG. 5, reference numeral 6 denotes an electrophotographic photosensitive member, which is rotationally driven at a predetermined peripheral speed. In the rotation process, the photosensitive member 6 is uniformly charged with a predetermined positive or negative potential on its peripheral surface by the charging roller 1 and then receives image exposure light from an exposure means 8 such as slit exposure or laser beam scanning exposure. . In this way, electrostatic latent images are sequentially formed on the peripheral surface of the photoreceptor 6.

  The formed electrostatic latent image is then developed with toner by the developing means 9, and the developed toner image is rotated between the photosensitive member 6 and the transfer means 10 from a paper supply unit (not shown). The images are sequentially transferred by the transfer means 10 to the transfer material P that is fed in synchronization.

  The transfer material P that has received the image transfer is separated from the photoreceptor surface, introduced into the fixing means 12, and subjected to image fixing, thereby being printed out as a copy (copy).

  The surface of the photoreceptor 6 after the image transfer is cleaned by the transfer unit 11 after the transfer residual toner is removed, and is repeatedly used for image formation.

  Among the constituent elements such as the photosensitive member 6, the charging roller 1, the developing means 9 and the cleaning means 11 described above, a plurality of such constituent elements are combined together to form an electrophotographic apparatus main body such as a copying machine or a laser beam printer. And a removable process cartridge. For example, the developing unit 9 and the cleaning unit 11 are integrally supported together with the photosensitive member 6 and the charging roller 1 to form a cartridge, and a process cartridge that can be attached to and detached from the apparatus main body using guide means such as a rail of the apparatus main body is obtained. it can.

  The image exposure light is as follows when the electrophotographic apparatus is a copying machine or a printer. (1) Reflected light or transmitted light from a document. (2) Light irradiated by scanning a laser beam, driving an LED array, driving a liquid crystal shutter array, and the like performed by reading a document with a sensor and converting the signal into a signal.

The electrophotographic apparatus according to the present invention includes the following components as described above.
(1) An electrophotographic photoreceptor. (2) Charging means for charging the surface of the electrophotographic photosensitive member with the charging roller according to the present invention. (3) Latent image forming means for exposing the electrophotographic photosensitive member to form a latent image. (4) Developing means for supplying toner onto the photoreceptor. (5) Transfer means for transferring the toner image on the photosensitive member to the transfer target. (6) Cleaning means for cleaning the transfer residual toner on the photosensitive member. (7) A means for fixing the transfer body on which the toner image is formed.

As the electrophotographic photoreceptor, it is desirable to employ the following two types of photoreceptors.
(1) An electrophotographic photosensitive member having a photoconductive layer formed of an amorphous material mainly containing silicon atoms (2) An organic photosensitive member having a total thickness of the surface protective layer and the photosensitive layer of 20 μm or less (1) For example, a photoconductive layer and a surface protective layer are sequentially laminated on a base made of a conductive material such as aluminum (Al) or stainless steel. In addition to these layers, various functional layers such as a blocking layer, an antireflection layer, or an interface layer may be provided as necessary. For example, by providing a blocking layer, an interface layer and the like and selecting a dopant such as a group III element or a group V element, it is possible to control the charging polarity such as positive charging and negative charging. In the electrophotographic apparatus according to the present invention, a positively chargeable silicon drum is desirable from the viewpoint of image defects such as image blur due to a chargeable product.

  The substrate shape may be as desired according to the driving method of the electrophotographic photosensitive member. As the base material, conductive materials such as Al and stainless are generally used. However, for example, various conductive materials such as various plastics and ceramics, particularly those having no conductivity, are deposited to be conductive. Those provided with can also be used.

  Examples of the photoconductive layer include an amorphous material in which silicon atoms include hydrogen atoms and halogen atoms (abbreviated as “a-Si (H, X)”). Further, the thickness of the photoconductive layer is not particularly limited, but about 15 to 50 μm is appropriate in consideration of the manufacturing cost. Furthermore, in order to improve the characteristics, a plurality of layers may be formed such as a lower photoconductive layer and an upper photoconductive layer. In particular, for a light source having a relatively long wavelength and almost no wavelength variation, such as a semiconductor laser, an epoch-making effect appears by devising such a layer structure.

  The surface protective layer is generally formed of a-SiC (H, X), but may be a-C (H, X). Further, it is preferable to control so that the interface reflection between the photoconductive layer and the surface protective layer is continuously changed to suppress the interface reflection of the portion.

  The above (2) is an electrophotographic photosensitive member in which a conductive layer, an intermediate layer, a photosensitive layer, and a surface protective layer are provided in this order on a substrate made of a conductive material such as Al or stainless steel.

  The binder resin for the conductive layer is preferably a thermosetting phenol resin.

As the intermediate layer, the volume resistivity of the intermediate layer is preferably set to 1 × 10 ⁹ to 1 × 10 ¹³ Ω · cm in order to prevent charge injection from the conductive layer to the photosensitive layer. Non-crystalline copolymerizable nylon and the like are preferable. The film thickness of the intermediate layer is preferably 0.1 to 2 μm.

  The photosensitive layer is separated into a charge generating layer containing a charge generating material and a charge transporting layer containing a charge transporting material even if it is a single layer type photosensitive layer containing the charge transporting material and the charge generating material in the same layer. The laminated photosensitive layer may be used. From the viewpoint of electrophotographic characteristics, the laminated photosensitive layer is preferred. The laminated photosensitive layer includes a normal layer type photosensitive layer laminated in the order of the charge generation layer and the charge transport layer from the support side, and a reverse layer type photosensitive layer laminated in the order of the charge transport layer and the charge generation layer from the support side. However, a normal photosensitive layer is preferred from the viewpoint of electrophotographic characteristics. The film thickness of the photosensitive layer is desirably 15 μm or less.

  The surface protective layer is formed by applying a chain polymerizable compound having an unsaturated double bond onto the photosensitive layer and then curing it. The chain polymerizable compound can be cured by heat, but can also be cured using ultraviolet rays or electron beams. The thickness of the protective layer is desirably 1 to 5 μm.

  As the latent image forming means, a laser exposure apparatus using a semiconductor laser is preferably employed. As for the latent image forming method, for example, it is preferable to adopt a back scan method when an amorphous silicon photoconductor is used, and an image scan method when a thin film organic photoconductor is used.

  As the developing means, in the case of an amorphous silicon photoreceptor, it is preferable to use a two-component developing system using a developing carrier.

  The toner is a pulverized toner containing a styrene copolymer and an ester wax, and is negatively charged. Further, it is preferable to use titanium oxide, silica, or strontium titanate as the external additive.

  As the carrier, it is desirable to use magnetic dispersion type carrier particles. Regarding the developing system, in the case of an electrophotographic apparatus using an amorphous silicon photoconductor, a regular developing system using a positively charged photoconductor and a negatively chargeable toner is used. In the case of an electrophotographic apparatus using a thin film organic photoconductor, a developing carrier is used. It is preferable to adopt a two-component development system using

  The toner includes colored resin particles containing a binder resin, a colorant, and other additives as necessary, and colored particles to which an external additive such as colloidal silica fine powder is externally added. Yes. The toner is a negatively charged polyethylene resin, and the weight average particle diameter (D4) is preferably 5 μm or more and 8 μm or less.

As the carrier, for example, surface-oxidized or non-oxidized iron, nickel, cobalt, manganese, chromium, rare earth and other metals, and their alloys, or oxide ferrite can be preferably used. The production method is not particularly limited. The carrier has a weight average particle diameter (D4) of 20 to 50 μm, preferably 30 to 40 μm, and a resistivity of 10 ⁷ Ωcm or more, preferably 10 ⁸ Ωcm or more.

  The developing system of the electrophotographic apparatus using the thin film organic photoreceptor in the present invention is a regular developing system using a negatively charged photoreceptor and a negatively chargeable toner. As the transfer unit, it is preferable to use a transfer unit that directly transfers to a transfer target (paper, medium such as OHP) using a transfer roller, or a transfer unit that primarily transfers to an intermediate transfer member such as a transfer belt.

  As the cleaning means, it is preferable to use a blade cleaning method using a blade-shaped member, a brush cleaning method using a brush-shaped member, or a method using both.

  As the charging roller, an electronic roller in which the base polymer forming the conductive layer is composed of at least acrylonitrile-butadiene rubber and the acrylonitrile content is more than 34% and less than 49% is preferable. When the electrophotographic apparatus is used in a high-temperature and high-humidity environment, the deterioration of energization of the charging roller becomes more severe than in a normal environment. Therefore, the molecular mobility of the conductive layer of the charging roller is preferably lower, and the acrylonitrile content is preferably more than 34% and less than 49%.

  The present invention will be described below with reference to production examples and examples, but the present invention is not limited to these unless it exceeds the gist.

"Example 1"
(Production of charging roller)
The following materials were mixed and kneaded with a pressure kneader for 30 minutes (see Table 1).
Acrylonitrile-butadiene rubber (manufactured by JSR: trade name “N215SL”, bonded acrylonitrile 48%) (hereinafter abbreviated as NBR1): 100 parts by mass.
-Zinc flower: 5 mass parts.
-Zinc stearate: 1 part by mass.
-Plasticizer: 10 mass parts.
Calcium carbonate (manufactured by Maruo Calcium Co., Ltd .: trade name “Nanox # 30”): 20 parts by mass.
Carbon black 1 (manufactured by Ketjen Black International Co., Ltd .: trade name “Ketjen Black EC600JD”, average particle size 40 nm): 4 parts by mass.
Carbon black 2 (Asahi Carbon Co., Ltd .: trade name “Asahi Thermal”, average particle size 80 nm): 40 parts by mass.

  Thereafter, 2 parts by mass of sulfur and 2 parts by mass of vulcanization accelerator TMTM (manufactured by Ouchi Shinsei Chemical Co., Ltd., tetrathiuram monosulfide) were added, and the mixture was further kneaded with an open roll for 15 minutes. This rubber mixture was extruded into a cylindrical shape with a rubber extruder, cut into a length of 400 mm, and primary vulcanized at 160 ° C. for 40 minutes using a vulcanizing can to obtain a primary vulcanized tube of a conductive layer.

Next, a thermosetting adhesive is applied to the surface of the conductive support made of SUS (FIG. 1A) and inserted into the resulting primary vulcanization tube, and then 160 ° C. using an electric oven. Then, secondary vulcanization and curing of the adhesive were carried out for 1 hour to form an unpolished conductive layer on the conductive support. Both ends were cut so that the length of the unpolished conductive layer was 320 mm, and then the surface of the conductive layer was polished with a rotating grindstone. Next, the surface of the conductive layer after polishing was irradiated with ultraviolet rays for 5 minutes using a low-pressure mercury lamp (manufactured by Harrison Toshiba Lighting), and UV treatment (ultraviolet ray integrated light amount: about 6000 mJ / cm ² ) was performed. This low-pressure mercury lamp mainly emits ultraviolet light having a wavelength of 254 nm. As described above, the charging roller of Example 1 was obtained (FIG. 1B). In addition, although the dimension was described in FIG. 1 as an example of embodiment, it is not specifically limited.

  The surface of the completed charging roller was visually evaluated for the presence of cracks. In the case where the crack could not be confirmed visually, it was marked as ◯, and in the case where the crack could be confirmed visually, it was marked as x. Subsequent evaluation was not performed on the charging roller that was evaluated as x in the crack evaluation. The evaluation of cracks in the charging roller of Example 1 was good.

"Example 2"
The carbon black formulation was changed to a mixed system of carbon black 1 and carbon black 3 (manufactured by Cancarb, N990, average particle size 230 nm), and the compounding amounts were changed to 3.4 parts by mass and 40 parts by mass, respectively (see Table 1). ). Other than that, a charging roller was produced in the same manner as in Example 1. The evaluation of the crack was ○.

"Example 3"
A charging roller was produced in the same manner as in Example 1 except that only carbon black 1 was used and the blending amount was changed to 4.5 parts by mass (see Table 1). The evaluation of the crack was ○.

Example 4
NBR1 is changed to acrylonitrile-butadiene rubber (manufactured by JSR: trade name “N232S”, bonded acrylonitrile 35%) (hereinafter abbreviated as NBR2), and the carbon black content is 2.8 parts by mass and 60 parts by mass, respectively. Changed (see Table 1). Other than that, a charging roller was produced in the same manner as in Example 1. The evaluation of the crack was ○.

"Example 5"
Except for changing NBR1 to NBR2 and changing the carbon black formulation to a mixed system of carbon black 1 and carbon black 3 and changing the amount of carbon black to 2.2 parts by mass and 60 parts by mass, respectively (see Table 1). A charging roller was produced in the same manner as in Example 1. The evaluation of the crack was ○.

"Example 6"
A charging roller was produced in the same manner as in Example 1 except that NBR1 was changed to NBR2, the carbon black formulation was changed to only carbon black 1, and the blending amount thereof was changed to 4.6 parts by mass (see Table 1). The evaluation of the crack was ○.

"Example 7"
NBR1 is changed to acrylonitrile-butadiene rubber (manufactured by JSR: trade name “N240S”, 26% bonded acrylonitrile) (hereinafter abbreviated as NBR3), and the amount of carbon black is 3.8 parts by mass and 40 parts by mass, respectively. (See Table 1). Other than that, a charging roller was produced in the same manner as in Example 1. The evaluation of the crack was ○.

"Example 8"
NBR1 was changed to NBR3, the carbon black formulation was changed to a mixed system of carbon black 1 and carbon black 3, and the amounts of carbon black were changed to 3.2 parts by mass and 40 parts by mass, respectively (see Table 1). Other than that, a charging roller was produced in the same manner as in Example 1. The evaluation of the crack was ○.

"Example 9"
A charging roller was produced in the same manner as in Example 1 except that NBR1 was changed to NBR3, the carbon black formulation was changed to only carbon black 1, and the blending amount thereof was changed to 4.6 parts by mass (see Table 1). The evaluation of the crack was ○.

“Comparative Example 1”
NBR1 is changed to acrylonitrile-butadiene rubber (manufactured by JSR: trade name “N640”, 25% bonded acrylonitrile) (hereinafter abbreviated as NBR5), and the amount of carbon black is 3.4 parts by mass and 40 parts by mass, respectively. (See Table 1). Other than that, a charging roller was produced in the same manner as in Example 1. The evaluation of the crack was ○.

“Comparative Example 2”
Except that NBR1 was changed to NBR5, the carbon black formulation was changed to a mixed system of carbon black 1 and carbon black 3, and the carbon black content was changed to 3.6 parts by mass and 40 parts by mass, respectively (see Table 1). A charging roller was produced in the same manner as in Example 1. The evaluation of the crack was ○.

“Comparative Example 3”
A charging roller was produced in the same manner as in Example 1 except that NBR1 was changed to NBR5, the carbon black formulation was changed to only carbon black 1, and the blending amount thereof was changed to 4.3 parts by mass (see Table 1). The evaluation of the crack was ○.

“Comparative Example 4”
Except for changing NBR1 to hydrin (Daiso Co., Ltd .: trade name “Epichromer CG102”) and changing the amount of carbon black to 1.4 parts by mass and 40 parts by mass, respectively (see Table 1), the same as Example 1 In this way, a charging roller was produced. The evaluation of the crack was ○.

“Comparative Example 5”
Except for changing NBR1 to hydrin and changing the carbon black formulation to a mixed system of carbon black 1 and carbon black 3 and changing the amount of carbon black to 0.9 parts by weight and 40 parts by weight, respectively (see Table 1). A charging roller was produced in the same manner as in Example 1. The evaluation of the crack was ○.

“Comparative Example 6”
A charging roller was produced in the same manner as in Example 1 except that NBR1 was hydrin, the carbon black formulation was only carbon black 1, and the blending amount was changed to 2.5 parts by mass (see Table 1). The evaluation of the crack was ○.

“Comparative Example 7”
NBR1 is changed to acrylonitrile-butadiene rubber (manufactured by Zeon Corporation: trade name “NipolDN003”, bonded acrylonitrile 50%) (hereinafter abbreviated as NBR4), and the blending amounts of carbon black are 3.5 parts by mass and 40 parts by mass, respectively. (See Table 1). Other than that, a charging roller was produced in the same manner as in Example 1. The evaluation of the crack was x.

“Comparative Example 8”
Except that NBR1 was changed to NBR4, the carbon black formulation was changed to a mixed system of carbon black 1 and carbon black 3, and the carbon black content was changed to 3.8 parts by mass and 40 parts by mass, respectively (see Table 1). A charging roller was produced in the same manner as in Example 1. The evaluation of the crack was x.

"Comparative Example 9"
A charging roller was produced in the same manner as in Example 1 except that NBR1 was changed to NBR4, the carbon black formulation was changed to only carbon black 1, and the blending amount thereof was changed to 4.1 parts by mass (see Table 1). The evaluation of the crack was x.

ＮＢＲ１：ＪＳＲ社製Ｎ２１５ＳＬ（結合アクリロニトリル４８％）、
ＮＢＲ２：ＪＳＲ社製Ｎ２３２Ｓ（結合アクリロニトリル３５％）、
ＮＢＲ３：ＪＳＲ社製Ｎ２４０Ｓ（結合アクリロニトリル２６％）、
ＮＢＲ４：日本ゼオン社製ＮｉｐｏｌＤＮ００３（結合アクリロニトリル５０％）、
ＮＢＲ５：ＪＳＲ社製Ｎ６４０（結合アクリロニトリル２５％）、
ヒドリン：ダイソー社製エピクロマーＣＧ１０２、
カーボンブラック１：ケッチェンブラックＥＣ６００ＪＤ（平均粒径４０ｎｍ）、
カーボンブラック２：アサヒサーマル（平均粒径８０ｎｍ）、
カーボンブラック３：ＭＴカーボンＮ９９０（平均粒径２３０ｎｍ）。

NBR1: N215SL (bonded acrylonitrile 48%) manufactured by JSR,
NBR2: J232 N232S (bonded acrylonitrile 35%),
NBR3: N240S manufactured by JSR (26% bonded acrylonitrile),
NBR4: Nipol DN003 (bound acrylonitrile 50%) manufactured by Nippon Zeon Co., Ltd.
NBR5: N640 manufactured by JSR (bound acrylonitrile 25%),
Hydrin: Daiso Epichromer CG102,
Carbon black 1: Ketjen black EC600JD (average particle size 40 nm),
Carbon black 2: Asahi thermal (average particle size 80 nm),
Carbon black 3: MT carbon N990 (average particle size 230 nm).

(Measurement of T ₂ )
The measurement of T _2, and subjected Examples 1 to 9, which scraped the conductive layer of the charging roller prepared in Comparative Examples 1 to 6 (excluding UV treated surface) as a sample. The measuring apparatus used was a JEOL Ltd. (trade name: MU25A) pulse NMR apparatus. The value of T ₂ is obtained from the echo intensity S obtained using the solid echo method with a hydrogen nucleus as a measurement nucleus by pulse NMR measurement. The measurement conditions were a measurement frequency of 20 MHz, a 90 ° pulse width (Pw1) of 2.0 μsec, a pulse interval (Pi1) = 12 μsec, a temperature of 23 ° C., and a solid echo method (90 ° _x τ90 ° _y ) was used. T ₂ is obtained from the observed echo intensity S by the least square method. The observed echo intensity S is given by the following equation (1).

S (t) = _{ΣS 0i} exp (−t / T _2i ) (1)
Here, t represents time (τ), S _0i represents the echo intensity at t = 0 of each i component, T _2i represents T _{2 of} each i component, and Σ represents the sum for i. For example, when the number of i components is 3, the echo intensity S is given by the following equation (2).

S (t) = S _0S exp (−t / T _2S ) + S _0M exp (−t / T _2M ) + S _0L exp (−t / T _2L ) (2)
The relationship between the components S, M, and L is T _2S <T _2M <T _2L , and the fraction of each component in the conductive layer is given by the ratio of S _0S , S _0M , and S _0L . Therefore, the average value of T ₂ of the conductive layer is given by the following equation (3).

T ₂ = (S _0S × T _2S + S _0M × T _2M + S _0L × T _2L ) / ΣS ₀ (3)
_{(ΣS 0 = S 0S + S} 0M + S 0L)
About the number of the components i, it changes with kinds and addition amount of the base polymer and additive (carbon black etc.) which are contained in a conductive layer. In this example, the number of component i was 2 or 3.

Table 2 shows the results of measuring T ₂ for the conductive layers of the charging rollers prepared in Examples 1 to 9 and Comparative Examples 1 to 6.

(Measurement of energization degradation index)
The charging roller produced in Examples 1 to 9 and Comparative Examples 1 to 6 is attached to the apparatus shown in FIG. 2, and an energization deterioration acceleration test is performed in a room temperature and low humidity environment (N / L: 23 ° C./5% RH). The degradation index was determined. In the apparatus shown in FIG. 2, the charging roller 1 is brought into contact with the aluminum drum 2, and the aluminum drum is driven by the drum driving motor 4 while DC + AC current is supplied from the charging bias power source 3, and fixed by the spring pressure 5. This device rotates the charged roller.

  As energization conditions, a DC current of 290 μA, an AC total current of 3.3 mA, and 8 hours / 1 day were energized for 3 days.

The electric resistance value of the charging roller was measured seven times as follows, and the electric resistance value plotted for each time is shown in FIG.
(1) Before energization on the first day, (2) After energization for 8 hours on the first day (after 8 hours), (3) Before energization on the second day (8 hours in the morning), (4) After energization for 8 hours on the second day ( 16 hours later), (5) Before the third day energization (16 hours morning), (6) After the third day 8 hours energization (after 24 hours), and (7) The fourth day morning (24 hours morning). In addition, 8 hours, 8 hours morning, 16 hours, 16 hours morning, 24 hours, and 24 hours morning are plotted at the same time of 8, 16, 24 respectively. Moreover, it fitted using following Formula (4) (FIG. 3).

R (electric resistance value: Ω) = R ₀ × exp (0.0001 × A × T) (4)
[R (Measured electrical resistance value: Ω), R ₀ (Initial electrical resistance value: Ω), A (Electrical degradation index), T (Time)]
The value of the power deterioration index (A) was used as an index of power deterioration. As an evaluation of A,
A: 0 <| A | (Absolute value of A) <100: Deterioration of energization is very good.
○: 100 ≦ | A | ≦ 220: Deterioration of energization is a level that can withstand practical use.
×: 220 <| A |: Deterioration of energization deteriorates and is not at a level that can withstand practical use.
It was.

  Table 2 shows the results of evaluating the energization deterioration index of the charging rollers manufactured in Examples 1 to 9 and Comparative Examples 1 to 6.

The electrical resistance value (Ω) was determined by the following method.
While applying 300 g of weight to both ends of the conductive support 5 so that the contact area between the aluminum drum 2 and the charging roller 1 is uniform, the aluminum drum 2 is rotated and the charging roller is driven to rotate, and the direct current of 300 V is applied. A voltage was applied between the aluminum drum and the conductive support, and the current flowing between them was measured (FIG. 4).

(Evaluation of drum potential stability by paper endurance test)
(1) Paper passing durability test using amorphous silicon photoconductor (a-Si) The Canon copier GP405 was remodeled, and the charging rollers produced in Examples 1 to 9 and Comparative Examples 1 to 6 were attached. The process speed of the copying machine was set to 400 mm / s, and the charging bias was supplied from an external power source. The charging conditions were a DC voltage of +600 V, an AC voltage of 1.5 kV, and an AC frequency of 3.5 kHz. The exposure method was changed to the back scan method. As the developing means, those shown below according to the photosensitive drum (amorphous silicon photosensitive member) were used.

The charging roller prepared in Examples 1 to 9 and Comparative Examples 1 to 6 and the amorphous silicon photoconductor are mounted, and paper is passed under the above conditions in a room temperature and low humidity environment (N / L: 23 ° C./5% RH). A durability test (printing 250,000 sheets) was performed, and the decrease in drum potential before and after the test was evaluated. The results are shown in Table 2. The drum potential evaluation method is shown below.
○: The drum potential before and after the paper passing durability test was measured, and no decrease in drum potential was observed.
X: A decrease in drum potential occurred during the paper passing durability test.

  The amorphous silicon photoconductor is a positively charged a-Si type photoconductor that is sequentially laminated on the surface of a conductive support made of Al, and is composed of a negative charge blocking layer, a photoconductive layer, and a surface protective layer. A photosensitive drum was used.

  As the toner, a negatively charged pulverized toner in which an ester wax and a colorant are dispersed in a styrene copolymer was used, and silica, titanium oxide, and strontium titanate were used as external additives. The weight average particle diameter (D4) of the toner was 6.8 μm.

As the carrier, magnetic particle-dispersed carrier particles in which magnetite was dispersed in a phenol resin were used. The carrier had a weight average particle diameter (D4) of 35 μm and a resistivity of 10 ⁹ Ωcm.

  As the developing means, a two-component developing system using a developing carrier was used.

(2) Paper-passing durability test using a thin-film organic photoreceptor (thin film OPC) The charging conditions were changed to the DC voltage -750 V, the AC voltage 2.0 kV, the AC frequency 3.2 kHz, the exposure method to the image scan method, and the thin film A paper passing durability test was performed in the same manner as the paper passing durability test using the amorphous silicon photosensitive member except that the organic photosensitive member was mounted. The results are shown in Table 2.

  Here, the thin-film organic photoreceptor has an intermediate layer containing an electron-transporting organic compound on an aluminum cylinder, a 1 μm thick intermediate layer, a 0.15 μm thick phthalocyanine charge generating layer, and a 10 μm thick triarylamine charge. It is a photoreceptor having a photosensitive layer composed of a transport layer and a photopolymerizable protective layer having a layer thickness of 5 μm.

  The toner used was a pulverized toner in which carbon black was dispersed as a colorant in a negatively charged polyethylene resin externally added with silica and titanium oxide. The weight average particle diameter (D4) of the toner was 7.0 μm.

The carrier used oxide ferrite. The carrier had a weight average particle diameter (D4) of 30 μm and a resistivity of 10 ⁸ Ωcm. As the developing means, a two-component developing system using a developing carrier was used.

(A) It is the schematic of the shape of an electroconductive support body. (B) It is the schematic of the shape of a charging roller. FIG. 6 is a graph of electric resistance values and energization times of charging rollers manufactured in Examples 1 and 8 and Comparative Example 3. It is the schematic of the electrical resistance measuring apparatus of a charging roller. 1 is a schematic diagram illustrating an example of an electrophotographic apparatus of the present invention.

Explanation of symbols

1 Charging roller 2 Aluminum drum 3 Charging bias power supply (AC + DC)
4 Drum Drive Motor 5 Spring Pressure 6 Electrophotographic Photoreceptor 7 Axis 8 Exposure Unit 9 Development Unit 10 Transfer Unit 11 Cleaning Unit 12 Fixing Unit P Transfer Material

Claims (2)

A photoreceptor having a photoconductive layer formed of an amorphous material mainly composed of silicon atoms, a charging roller in contact with or close to the photoreceptor, and forming a latent image by exposing an image Means, a developing means for forming a toner image on the photosensitive member, and a transferring means for transferring the toner image to the transfer member, and applying a direct current and an alternating current between the photosensitive member and the charging roller. In an electrophotographic apparatus for charging the surface of the photoreceptor by
The charging roller is
A conductive support and a conductive layer formed on the conductive support;
The conductive layer includes acrylonitrile-butadiene rubber as a base polymer and carbon black as conductive particles,
The acrylonitrile-butadiene rubber has an acrylonitrile content of more than 25% and less than 49%. The electrophotographic apparatus according to claim 1, wherein an arithmetic average particle diameter of the conductive particles is more than 75 nm and less than 300 nm.

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