JP2003107851A - Member and device for electrostatic charging and image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrostatic charging device which can stably maintain uniform direct injection electrostatic charging, an electrostatic charging member used for the electrostatic charging device, and an image forming device equipped with the electrostatic charging device for a device which electrostatically charges an electrostatically charged body by applying a voltage to the electrostatic charging member while interposing conductive particles between the electrostatic charging member and electrostatically charged body. SOLUTION: The electrostatic charging member which is arranged forming a nip part with the electrostatically charged body is formed of a sponge roller while the conductive particles are interposed in the nip part and also characterized in that when (n) cells are present on the surface of the sponge roller, the value of standard deviation (s) shown by an equation (1) of s=(Σ(Ai-A)2/(n-1))1/2 is <=0.03, where Ai (i=1, 2, n, etc.), are circle equivalent radii (mm). The electrostatic charging device uses the electrostatic charging member and the image forming device is equipped with the electrostatic charging device.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a charging member, a charging device, and an image forming apparatus, and more particularly, to a charging member that contacts an object to be charged for charging and a nip portion between the charging member and the object to be charged. The present invention relates to a charging device and an image forming apparatus that interpose conductive particles.

[0002]

2. Description of the Related Art Conventionally, for example, in an image forming apparatus such as an electrophotographic apparatus or an electrostatic recording apparatus, required polarities and potentials of an image carrier (charged body) such as an electrophotographic photosensitive member or an electrostatic recording dielectric. A corona charger (corona discharger) has been widely used as a charging device for uniformly charging (including sticking). The corona charger is a non-contact type charging device, and includes, for example, a discharge electrode such as a wire electrode and a shield electrode surrounding the discharge electrode, and the discharge opening is opposed to the image carrier, which is a member to be charged, and is not in contact. The surface of the image carrier is exposed to the generated discharge current (corona shower) by applying a high voltage between the discharge electrode and the shield electrode so that the surface of the image carrier is charged in a predetermined manner.

Recently, the ozone level is lower than that of corona chargers.
Due to advantages such as low power consumption, a contact type charging device (contact charging device) for charging a charged member by bringing a charging member to which a voltage has been applied into contact with the charged member is put into practical use as described above. ing.

The contact charging device contacts a charged member such as an image bearing member with a conductive charging member such as a roller type (charging roller), a fur brush type, a magnetic brush type or a blade type, and the charging member (contact type). A predetermined charging bias is applied to a charging member / contact charger (hereinafter, referred to as a contact charging member) to charge the surface of the body to be charged to a predetermined polarity / potential.

Contact charging electrification hole (charging mechanism,
In (charging principle), two types of charging mechanisms (1) discharge charging mechanism and (2) direct injection charging mechanism are mixed, and each characteristic appears depending on which one is dominant. FIG. 3 shows typical charging characteristics of each.

<Discharge Charging Mechanism> This is a mechanism in which the surface of the member to be charged is charged by a discharge phenomenon that occurs in a minute gap between the contact charging member and the member to be charged.

In the discharge charging mechanism, since the contact charging member and the member to be charged have a constant discharge threshold, it is necessary to apply a voltage higher than the charging potential to the contact charging member. Further, compared with a corona charger, the generation amount is remarkably small, but generation of a discharge product is inevitable in principle, so that a harmful effect due to active ions such as ozone is unavoidable.

For example, a roller charging method using a conductive roller (charging roller) as a contact charging member is preferable from the viewpoint of stability of charging and is widely used. In this roller charging method, the charging mechanism is discharge charging. The mechanism is dominant.

That is, the charging roller is made of a conductive or medium-resistance rubber material or foam. Further, there is also one in which these are laminated to obtain desired characteristics. The charging roller has elasticity in order to obtain a constant contact with the body to be charged. Therefore, the friction roller has a large friction resistance, and in many cases, is driven by the body to be charged or driven with a slight speed difference. . Therefore, the non-contact state cannot be avoided due to the unevenness of the roller shape and the adhered matter on the body to be charged, and therefore the discharge charging mechanism is the predominant charging mechanism in the conventional roller charging. More specifically, since charging is performed by discharging from the charging member to the member to be charged, charging is started by applying a voltage equal to or higher than a certain threshold voltage. For example,
When the charging roller is pressed against the 25 μm-thick OPC photosensitive member as the member to be charged to perform the charging process, a voltage of about 640 V or more is applied to the charging roller. The surface potential starts to rise, and thereafter the surface potential of the photoconductor linearly increases with a slope of 1 with respect to the applied voltage.

<Direct Injection Charging Mechanism> This is a mechanism for charging the surface of the member to be charged by directly injecting charges from the contact charging member to the member to be charged. It is disclosed in JP-A-6-3921 and JP-A-11-65231.

The medium-resistance contact charging member comes into contact with the surface of the body to be charged, and directly injects the charge into the surface of the body to be charged without a discharge phenomenon, that is, basically without using a discharge mechanism. . Therefore, even if the voltage applied to the contact charging member is equal to or lower than the discharge threshold value, the body to be charged can be charged to a potential corresponding to the applied voltage (solid line in FIG. 3). This direct injection charging mechanism does not cause the generation of ions, and therefore does not cause a harmful effect due to discharge generation.

More specifically, a voltage is applied to a contact charging member such as a charging roller, a charging brush or a charging magnetic brush,
This is a mechanism for directly injecting charges by injecting charges into a charge holding member such as conductive particles in a trap order or charge injection layer on the surface of an object to be charged (image carrier). Since the discharge phenomenon is not dominant, the voltage required for charging is only the desired surface of the image carrier, and ozone is not generated. When a porous roller such as a sponge roller coated with conductive particles for improving the contact charging property is used as the contact charging member, the contact between the contact charging member and the body to be charged should be tight. It is possible to improve the charging property. Further, as the charging member, the degree of promotion of injection charging by the conductive particles is proportional to the number of conductive particles held in the nip portion between the charging member and the body to be charged. The mesh cell wall is
Since it is flat, the holding force of the conductive particles is small, and many conductive particles cannot exist in the cell wall portion.

On the other hand, in the cell portion, the holding force for the conductive particles is large, and a large amount of conductive particles can exist. Therefore, JP-A-200
The size of the cell is small as in Japanese Patent Publication No. 1-242605,
It is better to increase the number of cells as much as possible in order to promote injection charging. In addition, when the charging member and the charged body move by sliding while forming a nip portion, the conductive particles held in the cell part are swept to one edge of the cell by the sliding contact with the charged body. Therefore, when the cell size is large, the injection charging by the conductive particles is likely to be non-uniform. Therefore, it is advantageous that the cell size is as small as possible in that uniform injection charging is generated. However, if the cell size is too small, the holding force of the conductive particles becomes small. Therefore,
As the charging member in the injection charging, a member having an appropriately small cell diameter and a thin cell wall is suitable.

[0014]

However, the simple structure using the charging roller has no problem in the performance in light durability, but under the high durability, specifically, the usage condition of 10,000 sheets or more, the cleanerless system is not affected. It is not easy to sufficiently charge the charged body, and local contamination of the surface of the charging member by the untransferred toner may occur, resulting in uneven charging due to poor charging. So-called local contamination means that when the cells on the roller surface vary, there is a difference in the degree of toner contamination between the large cell area and the small cell area, so there is a difference in resistance in a minute area on the roller surface. When the image is output, it appears as a black dot image at a portion where the degree of contamination is large, and the image quality is deteriorated because the charging property becomes non-uniform. As described above, a method using a microcapsule such as Japanese Patent Laid-Open No. 2001-97594 is used to form a sponge having a smaller cell diameter than a sponge made of a chemical foaming agent and having a small cell diameter. It is advantageous. However, although the size and shape of the cell itself is stable, high filling is difficult and it is difficult to obtain a sponge body having a thin cell wall. Further, when the method using elution as disclosed in JP-A No. 11-198250 is used, it is easy to make the cell small, but it is extremely difficult to include the material cost and the processing cost as compared with the sponge made of the chemical foaming agent. There is a problem that the cost becomes high.

An object of the present invention is to perform uniform direct injection charging in a device in which conductive particles are interposed between a charging member and a member to be charged and a voltage is applied to the charging member to charge the member to be charged. An object of the present invention is to provide a charging device that can be stably maintained.

Another object of the present invention is to provide an image forming apparatus equipped with the above charging device.

Still another object of the present invention is to provide a charging member used in the above charging device.

[0018]

According to the present invention, in a charging member arranged to form a nip portion with a member to be charged, conductive particles are interposed in the nip portion, and the charging member is constituted by a sponge roller. When there are n cells on the surface of the sponge roller, assuming that the true circle equivalent diameters (mm) are Ai (i = 1, 2, ... N) and the average is A, the following formula (1 ), The value of standard deviation s is 0.0
A charging member is provided which is 3 or less. s = {Σ (Ai-A) 2 / (n-1)} 1/2 (1)

According to the present invention, there are also provided a charging device using the above charging member and an image forming apparatus equipped with the charging device.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below.

The reason why the charging device of the present invention can maintain an excellent uniform charging property is considered as follows.

Since the charging method of the present invention does not have a cleaning mechanism in the apparatus, a part of the toner is not transferred and is collected by the charging roller. The collected toner is again made negative on the charging roller, discharged onto the body to be charged, and collected by the developing sleeve. However, since the standard deviation of the cell diameter is small, that is, the variation in the cell diameter is small, the variation in the collection of the untransferred toner into the cells on the roller surface is small, and the irregularity of the roller resistance in a minute range is small. Since the size is small and an extreme density difference is hard to appear on the image, image defects are less noticeable. At the same time, the conductive particles present on the roller surface can be uniformly distributed, which is advantageous for charging uniformity.

Further, the injection charging of the present invention is a process of charging a charged body through conductive particles, and it is important that the conductive particles efficiently contact the charged body,
It is considered that the size of the conductive particles should be as small as possible, and the size variation should be small for uniform contact. From such a point of recovery of toner on the charging roller during the injection charging and stabilization of ejection, and efficient and uniform injection charging, the standard deviation s of the true circle equivalent diameter of the cells present on the surface of the charging roller is determined. In the injection charging method of the present invention, the average particle diameter of the conductive particles is set to 0.03 or less and the standard deviation s ′ of the average particle diameter of the conductive particles is set to 0.001 or less.
It is possible to stably realize uniform charging.

Further, as a means for obtaining a sponge roller in which the variation in cell size is suppressed to a low level, the foaming cells are affected by the dispersibility of the foaming agent. It is possible to obtain the charging member of the present invention having a small cell and a thin cell wall by using the azodicarbonamide, which decomposes relatively slowly as compared with other foaming agents, as a foaming agent. It will be possible. As described above, the problems in the injection charging method of the present invention can be achieved.

A typical structure of the charging device of the present invention is shown in FIG. The charging roller 2 includes a charging roller 2 as a charging member and a photoconductor 1 that is a member to be charged. The charging roller 2 forms a nip portion n with the photoconductor 1. It is preferable that the charging roller 2 that constitutes the characteristic part of the present invention is a porous roller such as a sponge roller, and the sponge shape has a small cell diameter and that there are as many cells as possible. By using a foam having a sharp size distribution, the surface can sufficiently rub against the surface of the photoconductor while holding the conductive particles, and the surface of the charging member and the surface of the photoconductor can be sufficiently contacted with each other. Therefore, it is possible to realize stable and safe direct charging (injection charging) that does not substantially use the discharge phenomenon due to the direct transfer of the charge to the charged body, and it is also possible to maintain the charging performance for a long time.

It is preferable to drive the charging roller and the photosensitive member so that they are moved by rubbing against each other. Therefore, the charging roller and the photosensitive member may be moved at different surface speeds. It may move in the opposite direction as indicated by. The charging roller 2 is manufactured by forming the elastic layer 2b on the core metal 2a. The elastic layer 2b is made of rubber (eg EPD).
M), conductive particles (for example, carbon black), a vulcanizing material, a foaming agent, etc., and is formed into a roller shape on the core metal 2a through the processes of extrusion and heating. Then, the surface is polished to produce the charging roller 2. The surface shape of the charging roller is an uneven shape formed by a sponge rubber cell and a cell wall by polishing.

Further, it is preferable to use vulcanized foaming under pressure, such as in-mold foaming using press heating or a vulcanizing can using heating under steam pressure for the foaming treatment. The size of the foam cells is suppressed, and it is possible to produce a large number of small cells. When the EPDM rubber is vulcanized and foamed by a vulcanization can, a thermally decomposable one is preferable as the foaming agent, and particularly azodicarbonamide is preferable. Also, by increasing the expansion ratio,
Since the hardness of the roller is lowered and the nip width required for the charging roller to charge the charged body (photosensitive body) can be secured, the charging efficiency can be improved. However, if the foaming ratio is increased too much, the strength of the charging roller is insufficient, so that deformation easily occurs and the charging performance deteriorates.
The expansion ratio is preferably 1.5 to 5 times.

The expansion ratio is calculated by the formula using the specific gravity (g / cm ³ ) before and after expansion as shown below: Expansion ratio = (specific gravity before vulcanization expansion) / (after vulcanization expansion) specific gravity)

It is important for the charging roller 2 to function as an electrode, and it is necessary to have elasticity so as to obtain a sufficient contact state and at the same time have a resistance sufficiently low to charge a moving member to be charged. However, on the other hand, it is necessary to prevent voltage leakage when there is a defective portion such as a pinhole on the charged body. Therefore, when an electrophotographic photosensitive member is used as the member to be charged, in order to obtain sufficient charging property and leak resistance, 1
It preferably has a resistance of 0 ⁴ to 10 ⁷ Ω.

If the hardness of the charging roller is too low, the shape is not stable, resulting in poor contact. If it is too high, not only the charging nip cannot be secured, but also the microscopic contact with the surface of the photoreceptor is deteriorated. Therefore, the Asker C hardness is preferably in the range of 15 to 50 degrees.

The elastic layer 2b of the charging roller is EPD.
M (ethylene propylene rubber), urethane, NBR (nitrile butadiene rubber), SBR (styrene butadiene rubber), CR (chloroprene rubber), silicone rubber or IR (butyl rubber), carbon black or metal oxide for resistance adjustment A rubber layer in which a conductive substance such as is dispersed is used. It is also possible to adjust the resistance by using an ion conductive material without particularly dispersing a conductive substance, and further, by adjusting the resistance by mixing a metal oxide and an ion conductive material. Is also possible.

Next, the conductive particles m shown in FIG. 1 will be described.

As the conductive particles m, various conductive particles such as particles of metal oxides, mixtures with organic substances, or those surface-treated can be used. Examples of the metal oxide include zinc oxide, tin oxide / antimony oxide composite oxide, and titanium oxide / tin oxide composite oxide. Examples of the organic compound include polypyrrole and polyaniline.

The resistance of the conductive particles is preferably 10 ¹² Ω · cm or less in order to transfer charges through the particles. The particle resistance was measured by the tablet method and normalized. Approximately 0.5 in a cylinder with a base area of 2.26 cm ^2.
A powder sample of g is put into the upper and lower electrodes, a pressure of 15 kg is applied to the upper and lower electrodes, a voltage of 100 V is applied at the same time, the resistance value is measured, and then the resistance value is normalized to calculate the specific resistance.

The average particle size is preferably 0.05 mm (50 μm) or less in order to obtain good charging uniformity. The lower limit of the particle size is 10 nm as a limit for stably obtaining the particles. Further, in terms of particle size control,
3 μm or more is preferable. In the present invention, the particle size when the particles are formed as an aggregate is defined as the average particle size of the aggregate.

For classifying the particles, a commercially available general classifying device was used. For example, classification can be performed using a centrifugal separation system (Beckman Coulter, Inc.). In order to measure the particle size thus obtained, 100 or more particles were extracted from observation with an optical or electron microscope, the volume particle size distribution was calculated with the maximum chord length in the horizontal direction, and the 50% average particle size was used to calculate the average particle size. The diameter. Further, the standard deviation of the particle size was obtained from the volume particle size distribution.

Next, a structural example of an image forming apparatus equipped with the charging device of the present invention will be described with reference to FIG. This configuration example is an electrophotographic image forming apparatus that enables toner recycling without the need for cleaning the photosensitive member. This image forming apparatus includes a charging device 2, an exposing device 3, a developing device 4, a transfer charging device 5, which are arranged around the photoconductor 1.
It comprises a fixing device 6. Here, the developing means may be integrally formed into a cartridge together with the photoconductor and the charging means, and the process cartridge may be detachable from the main body of the image forming apparatus.

Next, the toner image forming process in the embodiment described later will be described with reference to FIG.

The charging roller 2 is arranged in pressure contact with the photosensitive member 1 as a member to be charged with a predetermined pressing force against elasticity. Reference numeral n is a charging nip portion which is a nip portion between the photoconductor 1 and the charging roller 2, and the width of the charging nip portion is 3 mm. The charging roller 2 was rotationally driven in the arrow direction at about 80 rpm so that the charging roller surface and the photosensitive member surface were moved in the charging nip portion n in opposite directions at a constant speed.

The core metal 2a of the charging roller 2 is applied with a DC voltage of -620V from the charging bias applying power source S1 as a charging bias. In this example, the surface of the photoconductor 1 is charged to a potential (−600 V) substantially equal to the voltage applied to the charging roller 2.

The basic structure of the photoconductor 1 has a charge generation layer, a charge transport layer and a charge injection layer in this order on the surface of an aluminum cylinder having an outer diameter of 30 mm. The charge generation layer is a layer having a film thickness of 1 μm in which a disazo charge generation pigment is dispersed in a polyvinyl butyral resin at a ratio of 2: 1 (mass ratio). The charge transport layer has a thickness of 2 in which a hydrazone-based charge transport compound is dispersed in a polycarbonate resin at a ratio of 1: 1.
It is a layer of 0 μm. The charge injection layer is a layer that facilitates injection of charges from the charging roller into the charge transport layer, and SnO ₂ powder is used as a conductive filler in phosphazene resin, and 7:
It is a layer having a film thickness of 10 μm dispersed in a ratio of 10. The photoconductor rotates in the arrow direction at a peripheral speed of 50 mm / sec.

The exposure device 3 is a laser beam scanner including a laser diode, a polygon mirror and the like. This laser beam scanner outputs laser light whose intensity is modulated corresponding to a time-series electric digital pixel signal of target image information, and scans and exposes the uniformly charged surface of the rotating photoconductor 1 with the laser light. To do. By this scanning exposure L, an electrostatic latent image corresponding to the target image information is formed on the surface of the rotating photoconductor 1.

The electrostatic latent image on the surface of the photosensitive member 1 is developed as a toner image by the developing device 4. The developing device of this example is a reversal developing device using magnetic one-component insulating toner (negative toner). 4a includes a magnet roll 4b,
The developer carrying / conveying member is a non-magnetic rotary developing sleeve, and the rotary developing sleeve 4a is coated with the developer 4d in a thin layer by the regulating blade 4c. The layer thickness of the toner of the developer 4d with respect to the rotary developing sleeve 4a is regulated by the regulation blade 4c, and an electric charge is applied. The developer coated on the rotary developing sleeve 4a is conveyed to the developing portion (developing area portion) a which is an opposed portion of the photosensitive member 1 and the sleeve 4a by the rotation of the sleeve 4a. A developing bias voltage is applied to the sleeve 4a by a developing bias applying power source S2. As the developing bias voltage, a DC voltage of -500 V and an AC voltage having a frequency of 1800 Hz and a peak-to-peak voltage of 1600 V were superposed. As a result, the electrostatic latent image on the side of the photoconductor 1 is developed with the toner.

The developer 4d is a mixture of the toner t and the conductive particles m, and the toner t is prepared by mixing a binder resin, magnetic particles and a charge control agent, and kneading, pulverizing and classifying the toner.
It is produced by adding conductive particles and a fluidizing agent as an external additive to this. The toner t has a weight average particle diameter (D
4) was 7 μm. The conductive particles m have a particle size of 3 μm.
Conductive zinc oxide particles with a specific resistance of 10 ⁶ Ω · c
m, the average particle size including secondary aggregates is 3 μm. Further, the conductive particles are 2 parts by mass with respect to 100 parts by mass of the toner.

A medium resistance transfer roller 5 as a contact transfer means is pressed against the photoconductor 1 at a predetermined pressure to form a transfer nip portion b. A transfer material P as a recording medium is fed to the transfer nip portion b from a paper feed portion (not shown) at a predetermined timing, and a predetermined transfer bias voltage is applied to the transfer roller 5 from a transfer bias applying power source S3. The toner image on the side of the photoconductor 1 is fed to the transfer nip portion b, and the transfer material P
Are sequentially transferred to the surface. Roller resistance is 5 × 10
Transfer was carried out by applying a DC voltage of +2000 V using an ⁸ Ω one. That is, the transfer material P introduced into the transfer nip portion b is nipped and conveyed in the transfer nip portion b, and the toner image formed and carried on the surface of the rotary photosensitive member 1 is electrostatically and pressed in order on the surface side thereof. Will be transcribed.

The transfer material P fed to the transfer nip portion b and having received the toner image on the side of the photoconductor 1 is separated from the surface of the rotary photoconductor 1 and introduced into a fixing device 6 such as a heat fixing system. ,
After the toner image is fixed, it is ejected outside the apparatus as an image-formed product (print or copy).

The toner image on the photoconductor 1 is attracted and actively transferred to the transfer material P side under the influence of the transfer bias in the transfer nip portion b, but the conductive particles m on the photoconductor 1 are conductive. As a result, they are not positively transferred to the transfer material P side, and are substantially attached and retained on the photoconductor 1 and remain.

The transfer residual toner remaining on the surface of the photoconductor 1 after transfer and the above-mentioned conductive particles m are carried as they are to the charging nip portion n between the photoconductor 1 and the charging roller by the rotation of the photoconductor 1 and the charging roller 2 Adheres to and mixes with.

Therefore, the contact charging of the photosensitive member 1 is performed with the conductive particles m existing in the nip portion n between the photosensitive member 1 and the charging roller 2. Since the conductive particles are not supplied to the surface of the charging roller at the initial stage of printing and thus charging cannot be performed, the surface of the charging roller is coated with the conductive particles in advance. Also,
The toner transferred to the charging roller is gradually discharged from the charging roller, collected in the developing device 4, and used again for development.

[0050]

EXAMPLES The present invention will be described in more detail below with reference to examples.

The compositions of the materials of the charging rollers of Examples 1 to 6 and Comparative Examples 1 to 4 were the following materials, in which the foaming agent azodicarbonamide was arbitrarily blended according to the target cell diameter. It was done. Further, the azodicarbonamide used in the present invention is subjected to a surface treatment in order to improve the dispersibility in order to improve the dispersion in kneading. The surface treatment may be any one that improves the dispersibility of particles such as commonly used coupling agents.

As a method for producing the charging roller, rubber obtained by kneading with an open roll is extruded into a tube shape, and primary vulcanization is performed at 160 ° C. for 30 minutes to obtain a foam, and further 160 Secondary vulcanization was performed at 120 ° C. for 120 minutes. A core metal coated with an adhesive having an outer diameter of 6 mm and a length of 250 mm was press-fitted into the tube thus obtained, and after bonding, the surface was polished to manufacture a charging roller having an outer diameter of 18 mm. In the steam vulcanization method, during heating, vulcanization and expansion of the cells generated by the steam pressure are suppressed when the foaming progresses, so that fine cells can be formed, and the foaming agent is used. By adding the following amount, the progress of vulcanization is not delayed and a large amount of generated gas is obtained, so that it is possible to obtain a sponge rubber having a high expansion ratio and a thin cell wall.

[0053]   <Composition>   Ethylene propylene diene rubber 100 parts by mass   [Product name: EPT8075E, manufactured by Mitsui Chemicals, Inc.]   Zinc white 5 parts by mass   Stearic acid 2 parts by mass   65 parts by mass of carbon black   Calcium carbonate 10 parts by mass   Paraffin oil 55 parts by mass   [Product name: PW-380, manufactured by Idemitsu Kosan Co., Ltd.]   2 parts by mass of mercaptobenzothiazole (vulcanization accelerator)   Zinc di-n-butyl dithiocarbamate (vulcanization accelerator) 1 part by mass   Tetraethyl thiuram disulfide (vulcanization accelerator) 3 parts by mass   Sulfur (vulcanizing agent) 0.5 to 2 parts by mass   Azodicarbonamide (foaming agent) 15 to 25 parts by mass [With surface treatment ... Product name: Vinyl Hall AC # 1L-K3 manufactured by Eiwa Chemical Co., Ltd.] [No surface treatment ... Product name: Vinyl Hall AC # 3 manufactured by Eiwa Kasei Co., Ltd.]

10 according to Examples 1 to 6 and Comparative Examples 1 to 4.
A book charging roller was manufactured, and this charging roller was applied to the toner image forming process described above to evaluate the formed toner image. The toner image is a thin line image with a width of 1 mm.
A large number of images are formed at intervals of 0 mm. A solid white image is output every 500 sheets, and it is evaluated whether there is a black dot image (fog image) on the image, and a three-level evaluation of ◯, Δ, and × is performed. It was O indicates that no black dot image appears even after passing 10,000 sheets or more, Δ indicates that no black dot image appears up to 7,000 sheets, and X indicates that a black dot image appears before 5000 sheets.

Regarding the charging rollers of Examples 1 to 6 and Comparative Examples 1 to 4, average cell diameter, standard deviation of cell diameter, average particle diameter of conductive particles, standard deviation of particle diameter, specific resistance of conductive particles, roller resistance. , Specific gravity and foaming ratio, and measure the above "fog"
The evaluation results are shown in Table 1.

As shown in FIG. 2, the roller resistance is 100 V applied to the core metal 41 and the aluminum drum 43 while being pressed to the aluminum drum 43 having a diameter of 30 mm so that a total pressure of 1 kg is applied to the core metal 41 of the charging roller. The voltage was applied and the measurement was performed. The cell edge length was measured by observing the surface of the sponge roller with an optical microscope (DMRHC metallurgical microscope manufactured by Leica Microsystems Co., Ltd.) at a magnification of 200 times, and the obtained roller surface image was subjected to image processing (Q5001W manufactured by Leica Microsystems Co., Ltd.).
-EX image analysis / measurement system), the cells were binarized, converted into a true circle equivalent diameter, and at least 100 cell diameters were measured, and the average cell diameter and the standard deviation s of the cell diameters were obtained from the data.

[0057]

[Table 1]

[0058]

As described above, according to the present invention, in a charging member arranged so as to form a nip portion with a member to be charged, conductive particles intervening in the nip portion are provided, and the charging member is sponge. The sponge roller is composed of a roller, and the standard deviation s of the true circle equivalent diameter (mm) of the cell is s
By setting the ratio to 0.03 or less, it is possible to provide a charging member that can realize uniform charging and maintain the performance for a long period of time, a charging device including the charging member, and an image forming apparatus.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing the configuration and operation of a charging roller used in a charging device of the present invention.

FIG. 2 is a configuration diagram of an apparatus for measuring roller resistance in an example.

FIG. 3 is a graph showing charging characteristics of a direct injection charging mechanism and a discharge charging mechanism.

FIG. 4 is a cross-sectional view of an image forming apparatus including the charging device of the present invention.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Jun Murata             3-30-2 Shimomaruko, Ota-ku, Tokyo             Non non corporation F-term (reference) 2H200 FA02 GA14 GA16 GA23 GA34                       GA46 GA57 GA59 GB25 HA03                       HA28 HB12 HB17 HB45 HB46                       HB47 MA04 MA08 MA14 MA20                       MB02 MB04 MC11 MC15 MC16                 3J103 AA02 BA41 GA02 GA52 GA58                       HA11 HA12 HA20 HA53

Claims (19)

[Claims] 1. A charging member arranged to form a nip portion with a member to be charged, wherein conductive particles are interposed in the nip portion, and the charging member is constituted by a sponge roller, and the surface of the sponge roller. When there are n cells in each of the circles, the diameter (mm) corresponding to each true circle is Ai (i = 1,
2, ... N), where the average is A, the value of the standard deviation s shown in the following formula (1) is 0.03 or less. s = {Σ (Ai-A) 2 / (n-1)} 1/2 (1) 2. The charging member according to claim 1, wherein the average A of the true circle equivalent diameters of the cells existing on the surface of the sponge roller is 0.05 mm to 0.2 mm. 3. The conductive particles have an average particle diameter of 0.05 mm.
And the standard deviation s'of the average particle size is 0.001
The charging member according to claim 1, which is as follows. 4. The rubber forming the sponge roller is E
The charging member according to any one of claims 1 to 3, which is a PDM and is formed using a thermally decomposable foaming agent. 5. The charging member according to claim 1, wherein a vulcanization can of a steam heating system is used as a means for vulcanizing and foaming the sponge roller. 6. The azodicarbonamide which is surface-coated with a coupling agent as the foaming agent.
The charging member according to any one of to 5. 7. The charging member according to claim 1, wherein the foaming ratio of the sponge of the sponge roller is 1.5 to 5 times. 8. The resistance of the sponge roller is 10 ⁴ to 10 ⁷ Ω.
The charging member according to any one of claims 1 to 7. 9. The charging member according to claim 1, wherein the conductive particles have a specific resistance of 10 ¹² Ω · cm or less. 10. A charging device comprising a charging member arranged to form a nip portion with a member to be charged and conductive particles interposed in the nip portion, wherein the charging member is constituted by a sponge roller, When there are n cells on the roller surface, the diameter of each true circle (mm)
Is Ai (i = 1, 2, ... N) and the average is A, the value of the standard deviation s shown in the following formula (1) is 0.03 or less. s = {Σ (Ai-A) 2 / (n-1)} 1/2 (1) 11. An average A of true circle equivalent diameters of cells existing on the surface of the sponge roller is 0.05 mm to 0.2 mm.
The charging device according to claim 10, wherein 12. The average particle diameter of the conductive particles is 0.05 m.
m or less and the standard deviation s'of the average particle size is 0.00
The charging device according to claim 10 or 11, which is 1 or less. 13. The charging device according to claim 10, wherein the rubber forming the sponge roller is EPDM and is formed by using a thermally decomposable foaming agent. 14. The charging device according to claim 10, wherein a steam heating vulcanization can is used as a means for vulcanizing and foaming the sponge roller. 15. The charging device according to claim 10, wherein the foaming agent is azodicarbonamide subjected to a surface coating treatment with a coupling agent. 16. The charging device according to claim 10, wherein the foaming ratio of the sponge of the sponge roller is 1.5 to 5 times. 17. The sponge roller has a resistance of 10 ⁴ to 10 ^7.
The charging device according to any one of claims 10 to 16, which has an Ω. 18. The charging device according to claim 10, wherein the specific resistance of the conductive particles is 10 ¹² Ω · cm or less. 19. An image forming apparatus comprising a charging member arranged to form a nip portion with a member to be charged and a charging device having conductive particles interposed in the nip portion, wherein the charging member is composed of a sponge roller. When there are n cells on the surface of the sponge roller, the diameter (mm) corresponding to each true circle is Ai (i = 1, 2, ... N), and the average is A. An image forming apparatus characterized in that the value of the standard deviation s shown in 1) is 0.03 or less. s = {Σ (Ai-A) 2 / (n-1)} 1/2 (1)