JP2001188404A - Electrifier, image forming device and electrifying roller - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize uniform direct injection electrification in a device to elec trify a member to be electrified by applying a voltage to an electrifying member by disposing conductive particles between the electrifying member and the member to be electrified. SOLUTION: An electrifying member which possesses a surface of a fine mesh structure having recessed cells and whose cell edge length is 15 mm/mm2-60 mm/mm2 is used.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a charging device for a member to be charged, and more particularly to an electrophotographic device such as a copying machine and a printer and a process cartridge detachable from the device. The present invention relates to a contact charging device that performs charging. Further, the present invention relates to an image forming apparatus provided with a charging device and a charging roller used for the charging device.

[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, an image carrier (a charged body) such as an electrophotographic photosensitive member or an electrostatic recording dielectric has a required polarity.
A corona charger (a corona discharger) has often been used as a charging device for uniformly charging (including charge elimination) to a potential. 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 applying a high voltage between the discharge electrode and the shield electrode, thereby exposing the surface of the image carrier to a discharge current (corona shower) generated, thereby charging the surface of the image carrier in a predetermined manner.

[0003] In recent years, low ozone and low compared to corona chargers.
Because of the advantages of low power and the like, a contact-type charging device (contact charging device) for charging a member to be charged by bringing a charging member applied with a voltage into contact with the member to be charged as described above has been put to practical use. ing.

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

A contact charging mechanism (charging mechanism,
In the charging principle), two types of charging mechanisms, (1) discharge charging mechanism and (2) direct injection charging mechanism, coexist, and each characteristic appears depending on which is dominant. FIG. 4 shows typical charging characteristics.

(1) Discharge Charging Mechanism This is a mechanism in which the surface of a charged band is charged by a discharge phenomenon generated in a minute gap between a contact charging member and a member to be charged.

Since the discharge charging mechanism has a fixed discharge threshold for the contact charging member and the member to be charged, it is necessary to apply a voltage higher than the charging potential to the contact charging member. Further, although the amount of generation is much smaller than that of the corona charger, it is in principle unavoidable to generate a discharge product, so that the harmful effects of active ions such as ozone are inevitable.

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

That is, the charging roller is formed using a conductive or medium-resistance rubber material or foam. In some cases, these are laminated to obtain desired characteristics. The charging roller has elasticity in order to obtain a constant contact with the member to be charged, but has a large frictional resistance, and is often driven by the member to be charged or with a slight speed difference.
Therefore, a non-contact state is unavoidable due to unevenness of the shape on the roller and the adhered matter on the member to be charged. Therefore, in the conventional roller charging, the discharging mechanism is dominant in the charging mechanism. More specifically, since the charging is performed by discharging from the charging member to the member to be charged, the charging is started by applying a voltage equal to or higher than the threshold voltage. As an example, when the charging roller is pressed against the OPC photosensitive member having a thickness of 25 μm as the member to be charged to perform charging processing,
When a voltage of about 640 V or more is applied to the charging roller, the surface potential of the photoconductor starts to increase, and thereafter, the surface potential of the photoconductor increases linearly with a slope of 1 with respect to the applied voltage.

(2) Direct injection charging mechanism This is a mechanism for charging the surface of the object to be charged by directly injecting charges from the contact charging member to the object to be charged. JP-A-6-3
921 and JP-A-11-65231.

A medium-resistance contact charging member contacts the surface of a member to be charged, and charges are directly injected into the surface of the member without a discharge phenomenon, that is, without using a discharge mechanism. . Therefore, the voltage applied to the contact charging member is equal to or lower than the discharge threshold, and the member to be charged can be charged to a potential corresponding to the applied voltage (solid line in FIG. 4). Since this direct injection charging mechanism does not involve the generation of ions, there is no adverse effect due to discharge generation.

More specifically, a voltage is applied to a contact charging member such as a charging roller, a charging brush, and a charging magnetic brush,
This is a mechanism for directly injecting and charging by injecting a charge into a charge holding member such as conductive particles in a trapping order or a charge injection layer on a surface of a member 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 no ozone is generated. When using a porous roller such as a sponge roller coated with conductive particles for improving the contact charging property as the contact charging member, the contact between the contact charging member and the member to be charged is densely maintained. And it is effective in improving the chargeability.

However, with a simple configuration using a charging roller, it is not easy to sufficiently charge an object to be charged, and uneven charging due to poor charging occurs. Charging unevenness appears as image unevenness when an image is output. The cause of such charging unevenness is that when a sponge roller, which is a foamed elastic roller, is used as a charging member, the sponge cell is generally formed by gas generation accompanying the decomposition of the foaming agent. Becomes lower. Therefore, it is considered that the conductive particles for promoting the injection charging were not effectively held on the roller surface.

[0014]

SUMMARY OF THE INVENTION Accordingly, the present invention provides an apparatus for charging a member to be charged by applying a voltage to the member by interposing conductive particles between the member and the member to be charged. It is a main object of the present invention to provide a charging device capable of realizing direct injection charging.

Another object of the present invention is to provide an image forming apparatus provided with such a charging device. Another object of the present invention is to provide a charging roller used in such a charging device.

[0016]

SUMMARY OF THE INVENTION The present invention is directed to a charging device having a charging member arranged to form a nip portion with a member to be charged, conductive particles interposed in the nip portion, and a charging member having the member to be charged. The member has a fine mesh structure surface having concave cells, and the cell edge length is 15 mm / mm ²
帯 電 60 mm / mm ² .

According to another aspect of the present invention, there is provided an image forming apparatus having a charging member arranged to form a nip portion with a photoreceptor, conductive particles interposed in the nip portion, and a photoreceptor, wherein the charging member has a concave shape. It has a cell and has a fine network structure surface, and the cell edge length is 15 mm / mm ^{2 to} 60 mm /
mm ² .

According to the present invention, there is provided an image forming apparatus having a charging member arranged to form a nip portion with a photosensitive member, conductive particles interposed in the nip portion, and a photosensitive member.
The charging member has a fine mesh structure surface having concave cells, and the cell edge length is 15 mm / mm ^{2 to} 60 mm.
/ Mm ² .

Further, according to the present invention, in a process cartridge in which a developing means is integrally formed with a photosensitive member and a charging means into a cartridge, and which is detachable from an image forming apparatus main body, the charging means forms a nip portion with the photosensitive member. Charging member and conductive particles interposed in the nip portion, the charging member has a fine mesh structure surface having concave cells, and the cell edge length is 15 mm / mm ² to
A process cartridge characterized by having a thickness of 60 mm / mm ² .

Further, the present invention has a fine mesh structure surface having concave cells, and has a cell edge length of 15 mm / m.
m ^{2 to} 60 mm / mm ² .

In the charging device according to the present invention, the charging unit
The surface of the material has a fine mesh structure, and the mesh structure
, The sum of the perimeters of the cell edges of
mm ^Two By setting it to 15 mm to 60 mm
In charging methods where incoming charging is dominant, uniform charging
Can be realized.

The cell edge is the periphery of the cell forming a concave portion having a mesh structure on the surface of the charging member. Taking a case where the mesh structure is a sponge as an example in FIG. 2, the mesh structure is constituted by cells 31 and cell walls 32. The cell 31 refers to a concave portion forming a sponge, and a cell wall 32
Denotes a convex portion forming a sponge. The cell edge 33 is around the cell (recess). It is considered that the reason why the charging device of the present invention has excellent uniform charging properties can be explained as follows. Unit area of network structure (1mm
² ) The sum of cell edges per cell, ie, cell edge length is 1
It is 5mm / mm ² ~60mm / mm ² indicates that the cell size is small, and and the number of cells often exist. For example, assuming the cells are round cells,
With a cell edge length of 15 mm / mm ² per 1 mm ² area, cells having a diameter of about 100 μm exist at a cell density (area occupied by cells with respect to the total surface area) of about 40%. 60m
At m / mm ² , about 25 μm in diameter is present at a cell density of about 40%. With a cell edge length of 20 mm / mm ² , cells having a diameter of about 100 μm exist at a cell density of about 50%. The degree of promotion of injection charging by the conductive particles is proportional to the number of conductive particles held in the nip between the charging member and the member to be charged. Since the cell wall of the network structure is flat, the holding power of the conductive particles is small, and a large amount of conductive particles cannot be present in the cell wall. On the other hand, in the cell portion, the holding power of the conductive particles is large, and many conductive particles can be present. Therefore, it is better that the area of the cell is as large as possible as compared with the area of the cell wall in order to promote the injection charging. In addition, when the charging member and the member to be charged move by rubbing while forming a nip portion, the conductive particles held in the cell portion are swept to one edge of the cell by rubbing with the member to be charged. Therefore, when the cell size is large, the interval between the edges where the conductive particles are present increases, and the injection charging by the conductive particles tends to be non-uniform. Therefore, it is advantageous to make the cell size as small as possible in order to generate uniform injection charging. However, if the cell size is too small, the holding power of the conductive particles becomes small.
From the viewpoint of efficient and uniform injection charging from the holding power of the conductive particles by the cell, the cell edge length is 15 mm /
mm ^{2 to} 60 mm / mm ² is effective.

A typical configuration of the charging device according to the present invention is shown in FIG. The charging roller 21 includes a charging roller 21 and a photoreceptor 1 that is a member to be charged.
And a nip portion n. The charging roller 21 constituting a characteristic part of the present invention is constituted by a porous roller such as a sponge roller, and the cell edge length of the sponge surface exposed on the surface thereof is 15 mm / mm ^{2 to} 60 mm / mm.
² , particularly preferably 20 mm / mm ^{2 to} 50 mm / mm
^{By making} the foam ² , the surface of the charging roller slidably rubs the surface of the photoconductor without leakage while sufficiently holding the conductive particles. The transfer of charges becomes possible. Therefore, in the present invention, a high charging performance, which cannot be obtained by the conventional roller charging mainly for discharging, can be obtained, and a potential substantially equal to the potential applied to the charging member 21 can be given to the photosensitive member 1. Therefore, the bias required for charging is sufficient to be a voltage corresponding to the potential required for the member to be charged, and stable and safe direct charging (injection charging) substantially using no discharge phenomenon can be realized.

It is preferable that the charging roller and the photoconductor are driven so as to slide and move. For this purpose, the charging roller and the photoconductor may move at different surface speeds. It may move in the opposite direction as shown by arrows A and B. The charging roller 21 is formed by forming an elastic layer 2b on a cored bar 2a. The elastic layer 2b is made of rubber (for example, E
PDM), conductive particles (for example, carbon black), a vulcanizing agent, a foaming agent, and the like, and are formed in a roller shape on the cored bar 2a through a process of extrusion and heating. afterwards,
The charging roller 21 is prepared by polishing the surface. The surface shape of the charging roller is formed into an uneven shape formed by sponge rubber cells and cell walls by polishing. cell,
As described later in Examples and Comparative Examples, cell walls can be obtained in various states by selecting a vulcanizing agent, a foaming agent, or a heating means. Means for obtaining a fine network structure having an uneven shape include a method in which a low-molecular substance mixed in a high-molecular substance is eluted with a solvent to obtain a porous body, and a method in which a non-foamed body is polished, etched, etc. It can also be obtained by processing.

When foaming and oxidizing rubber to form an elastic layer having a network structure, the type of foaming agent, the vulcanization accelerator,
By appropriately selecting foaming conditions and vulcanization conditions,
A network structure having a predetermined cell edge length can be formed. For example, at a stage where the curing reaction of the rubber has progressed to some extent, that is, when the rubber is thermally decomposed with a foaming agent in a high viscosity state, the cells formed by the large generated gas become small. By performing with steam heating, the size of the foam is suppressed by the pressure of steam, small,
Moreover, a large number of cells can be generated. EPDM
When a rubber is foamed to form a network structure, it is particularly preferable to use azodicarbonamide as a foaming agent, a thiazole compound and a dithiocarbamate compound as a vulcanization accelerator, and sulfur as a vulcanizing agent. . At this time, it is preferable that the compounding amount of the thiazole compound and the dithiocarbamic acid compound is 3 to 5 parts by weight based on 100 parts by weight of EPDM. The specific gravity of the foam is such that the cell edge length is 15 mm / mm ^{2 to} 60 mm / m
To m ^2, the range of 0.2 to 0.65 are preferred.

Also, by increasing the expansion ratio, the hardness of the roller is reduced, and the nip width required for the charging roller to charge the member to be charged (photosensitive member) can be secured. Can be. However, if the foaming ratio is too high, the charging roller has insufficient strength to easily deform, and the charging performance deteriorates. Therefore, the foaming ratio is preferably 1.5 times or more and 5 times or less.

The expansion ratio is calculated by an equation using the specific gravities (g / cm ³ ) before and after foaming as shown below.

Expansion ratio = (specific gravity before vulcanization / foaming) / (specific gravity after vulcanization / foaming) It is important that the charging roller 21 functions as an electrode. It is necessary to have a resistance low enough to charge the moving object to be charged. However, on the other hand, it is necessary to prevent voltage leakage when a defect site such as a pinhole is present in the member to be charged. Therefore, when an electrophotographic photosensitive member is used as a member to be charged, 10 ⁴ to 10 ⁴ to obtain sufficient chargeability and leak resistance.
It is desirable to have a resistance of 10 ⁷ Ω.

If the hardness of the charging roller is too low, the contact becomes poor because the shape is not stable. If the hardness is too high, not only the charging nip cannot be secured, but also the micro contact with the photoreceptor surface becomes poor. And a Asker C hardness of 25 to 50 degrees is a preferable range.

As the elastic layer 2b of the charging roller, EPD
M (ethylene propylene rubber), urethane, NBR (nitrile butadiene rubber), silicone rubber, IR (butyl rubber), etc., a rubber layer in which a conductive substance such as carbon black or metal oxide is dispersed for resistance adjustment. Can be In addition, it is also possible to adjust the resistance using an ionic conductive material without dispersing a conductive substance, and furthermore, to adjust the resistance by mixing a metal oxide and an ionic conductive material. Is also possible.

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

As the conductive particles, various kinds of conductive particles such as a mixture of particles such as metal oxides and organic substances, or a surface-treated mixture thereof can be used.

Examples of the metal oxide include zinc oxide, tin oxide / antimony oxide composite oxide, and examples of the titanium oxide / tin oxide composite oxide organic compound include polypyrrole and polyaniline.

The resistance of the conductive particles is desirably 10 ¹² Ω · cm or less in order to transfer electric charges via the particles. The resistance of the particles was measured by a tablet method and normalized. Approximately 0.5 g in a cylinder with a bottom area of 2.26 cm ²
And pressurizing the upper and lower electrodes with 15 kg, simultaneously applying a voltage of 100 V, measuring the resistance value, and then normalizing to calculate the specific resistance. The particle size is desirably 50 μm or less in order to obtain good charging uniformity. The lower limit of the particle size is limited to 10 nm as long as the particles can be obtained stably. Further, from the viewpoint of controlling the particle size, it is preferable that the thickness is 0.3 μm or more. 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. In the measurement of the particle size, 100 or more samples are extracted from observation by an optical or electron microscope, the volume particle size distribution is calculated based on the maximum chord length in the horizontal direction, and the 50% average particle size is defined as the average particle size.

Next, an example of the configuration of an image forming apparatus using 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 equipping the photosensitive member with cleaning. This image forming apparatus is arranged around the photoconductor 1,
It comprises a charging device 2, an exposure device 3, a developing device 4, a transfer charging device 5, and a fixing device 6. Here, the developing unit may be integrally formed as a cartridge together with the photosensitive member and the charging unit, and may be a process cartridge detachable from the image forming apparatus main body.

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

The charging roller 2 includes a photosensitive member 1 as a member to be charged.
Are pressed against each other with a predetermined pressing force against the elasticity. n is a charging nip portion which is a nip portion between the photosensitive member 1 and the charging roller 2. The width of the charging nip is 3 mm. The charging roller 2 was rotated at about 80 rpm in a direction indicated by an arrow B at approximately 80 rpm so that the surface of the charging roller and the surface of the photoreceptor moved at opposite speeds in the charging nip n.

Further, a DC voltage of -620 V was applied as a charging bias from the charging bias applying power source S1 to the core 2a of the charging roller 2. 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 photoreceptor 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 thickness of 1 μm in which a disazo charge generation pigment is dispersed in a polyvinyl butyral resin at a ratio (weight ratio) of 2: 1. The charge transport layer is a layer having a thickness of 20 μm in which a hydrazone-based charge transport compound is dispersed in a polycarbonate resin at a ratio of 1: 1. The charge injection layer is a layer for facilitating the injection of charges from the charging roll into the charge transport layer, and is a 10 μm thick layer in which SnO ₂ powder as a conductive filler is dispersed in a phosphazene resin at a ratio of 7:10. . The photoconductor 1 rotates in the direction A at a peripheral speed of 50 mm / sec.

The exposure unit 3 is a laser beam scanner including a laser diode, a polygon mirror and the like. This laser beam scanner outputs a laser beam whose intensity is modulated in accordance with a time-series electric digital pixel signal of target image information, and scans and exposes the uniformly charged surface of the rotary photoreceptor 1 with the laser beam. This scanning exposure L allows the rotating photoconductor 1
An electrostatic latent image corresponding to the target image information is formed on the surface.

Reference numeral 4 denotes a developing device. The electrostatic latent image on the surface of the photoconductor 1 is developed as a toner image by this developing device.
The developing device of this example is a magnetic one-component insulating toner (negative toner).
Is a reversal developing device. Reference numeral 4a denotes a non-magnetic rotary developing sleeve as a developer carrying member carrying a magnet roll 4b. The developer 4d is thinly coated on the rotary developing sleeve 4a by a 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 regulating blade 4c, and an electric charge is applied. The developer coated on the rotary developing sleeve 4a is conveyed to the developing section (developing area) a, which is the opposing 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 from a developing bias applying power source S2. The developing bias voltage is -500
V DC voltage, frequency 1800 Hz, peak-to-peak voltage 1
A superimposed rectangular AC voltage of 600 V was used. Thus, the electrostatic latent image on the photoconductor 1 is developed with the toner.

The developer 4d is a mixture of the toner t and the conductive particles m. The toner t is prepared by mixing a binder resin, magnetic particles, and a charge control agent, and performing kneading, pulverizing, and classifying processes.
It is prepared by adding conductive particles m and a fluidizing agent as external additives. Weight average particle diameter of toner t (D
4) was 7 μm. Conductive particles m have a particle size of 3 μm
Was used. The conductive particles m are 2 parts by weight based on 100 parts by weight of the toner t.

The specific resistance of the conductive particles m is 10 ⁶ Ω · c
m, the average particle size including the secondary aggregates is 3 μm.

Reference numeral 5 denotes a transfer roller of medium resistance as a contact transfer means, which is brought into pressure contact with the photoreceptor 1 to form a transfer nip portion b. Transfer paper P as a recording medium is supplied to the transfer nip b from a paper supply unit (not shown) at a predetermined timing.
Is supplied, and a predetermined transfer bias voltage is applied to the transfer roller 5 from a transfer bias application power source S3.
The toner image on the photoconductor 1 side is sequentially transferred onto the surface of the transfer paper P fed to the transfer nip portion b. Roller resistance value is 5
The transfer was performed by applying a DC voltage of +2000 V using a capacitor of × 10 ⁸ Ω. That is, the transfer paper P introduced into the transfer nip b is nipped and conveyed by the transfer nip b,
The toner image formed and carried on the surface of the rotating photoreceptor 1 is sequentially transferred to the surface side by electrostatic force and pressing force.

Reference numeral 6 denotes a fixing device such as a heat fixing system. The transfer paper P fed to the transfer nip b and receiving the transfer of the toner image on the photoconductor 1 side is separated from the surface of the rotary photoconductor 1 and introduced into the fixing device 6, where the toner image is fixed. It is discharged out of the apparatus as an image formed product (print, copy).

The toner image on the photosensitive member 1 is transferred to a transfer nip b
In the above, due to the influence of the transfer bias, the toner particles are attracted to the transfer paper P and positively transferred, but the conductive particles m on the photoreceptor 1 are not positively transferred to the transfer paper P due to the conductivity. The toner remains substantially adhered and held on the photoconductor 1.

The untransferred toner remaining on the surface of the photoreceptor 1 after the transfer and the conductive particles m are carried to the charging nip n of the photoreceptor 1 and the charging roller 2 by the rotation of the photoreceptor 1 as they are, Attached and mixed into

Therefore, in the state where the conductive particles m exist in the nip portion n between the photosensitive member 1 and the charging roller 2, the photosensitive member 1
Is performed. In the initial stage of printing, since the charge accelerating particles are not supplied to the surface of the charging roller and charging cannot be performed, the surface of the charging roller is coated with conductive particles in advance.

The toner transferred to the charging roller is gradually released from the charging roller and collected by the developing device 4,
Used again for development.

[0050]

(Examples and Comparative Examples) Tables 1 to 3
The rubber obtained by kneading the material for each example using an open roll is formed into a tube by extrusion, and is subjected to primary vulcanization at 160 ° C. for 30 minutes to form a foam. Secondary vulcanization was performed for 30 minutes.

The tube thus obtained has an outer diameter of 6 mm.
A core metal having a diameter of 250 mm and a length of 250 mm was press-fitted and the surface was polished to produce a charging roller having an outer diameter of 12 mm.

In the steam vulcanization method, when heating, vulcanization,
As the foaming progresses, the expansion of the cells generated by the water vapor pressure is suppressed, so that fine cells can be formed, and by adding the foaming agent in the above amount,
Since the progress of vulcanization is not delayed and a large amount of generated gas is obtained, it is possible to obtain a sponge rubber having a high expansion ratio and a thin cell wall.

According to Examples 1 to 8 and Comparative Examples 1 to 4, 1
Two charging rollers were manufactured, and these charging rollers were applied to the above-described toner image forming process, and the formed toner images were evaluated. When a large number of fine line images having a width of 100 μm are formed at intervals of 100 μm, 20 toner fine line images actually formed on the transfer paper are arbitrarily selected and observed with a microscope for 20 times. The maximum thickness and the minimum thickness are measured and evaluated as △, Δ and ×.

○ indicates a level at which the maximum thickness and the minimum thickness are all within the range of 100 μm ± 10 μm for the 20 toner images, and Δ indicates the maximum thickness and the minimum thickness for the 20 toner images. Not applicable to ○, but all levels within the range of 100 μm ± 20 μm, and × indicates the maximum thickness and minimum thickness of 20 toner images which do not correspond to Δ, but are all 100 μm ± 60 μm.
The level is within the range of m.

A toner image of a level (halftone image by a thin line) is observed as a uniform halftone image without unevenness.

The △ level is slightly inferior to the 、 level,
It is observed as a practically uniform halftone without unevenness.

The X level toner image is observed as a halftone image in which unevenness is conspicuous.

With respect to the charging rollers of Examples and Comparative Examples, the roller resistance, the cell edge length, the specific gravity and the expansion ratio were measured, and together with the evaluation of “100 μm line reproducibility” described above,
The results are shown in Tables 1 to 3. As shown in FIG. 3, the roller resistance is such that a voltage of 100 V is applied to the metal core 41 and the aluminum drum 43 in a state where the core metal 41 and the aluminum drum 43 are pressure-bonded to the φ30 aluminum drum 43 so that a load of 1 kg in total pressure is applied to the metal core 41 of the charging roller. Was measured by a method of measuring by applying a voltage.

The cell edge length was measured as follows.

The surface of the sponge roller is irradiated with visible light (halogen lamp), and the magnification is 20 with an optical microscope (DMR HC metal microscope manufactured by Leica Microsystems, Inc.).
Observed at 0x, image processing of the obtained roller surface image (Q5001WE manufactured by Leica Microsystems, Inc.)
X image analysis measurement system), and binarize the cell and the cell wall according to the intensity of the reflected light from the sponge roller surface (a high intensity portion is a cell wall and a low intensity portion is a cell). Convert each cell to a true circle equivalent diameter cell,
Find the circumference of each perfect circle. Then, each circumference of a perfect circle existing in 1 mm ² is integrated to obtain a cell edge length. However, the cell edge length is calculated excluding cells having a diameter of 10 μm or less in terms of a diameter equivalent to a perfect circle.

[0061]

[Table 1]

[0062]

[Table 2]

[0063]

[Table 3]

[0064]

As described above, in a charging device having a charging member provided to form a nip portion with a member to be charged, conductive particles interposed in the nip portion, and a member to be charged, Cell edge length of 15mm / mm ²
By setting the thickness to 600 mm / mm ² , uniform charging can be realized and a good toner image without unevenness can be formed.

[Brief description of the drawings]

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

FIG. 2 is a configuration diagram of a foam showing cells, cell walls, and cell edges.

FIG. 3 is a configuration diagram of an apparatus for measuring a roller resistance in an embodiment.

FIG. 4 is a graph showing charging characteristics of two types of charging mechanisms.

FIG. 5 is a cross-sectional view of an image forming apparatus using the charging device of the present invention.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) // C08L 23:16 C08L 23:16

Claims (18)

[Claims] 1. A charging device having a charging member arranged to form a nip portion with a member to be charged, conductive particles interposed in the nip portion, and a member to be charged, wherein the charging member comprises:
Has a surface of fine mesh structure with a concave shape of the cell, a charging device, wherein the cell edge length is ^{15mm / mm 2 ~60mm / mm 2} . 2. The charging device according to claim 1, wherein the charging member and the member to be charged move by sliding. 3. The cell edge length is 20 mm / mm ² to 50.
^2. The charging device according to claim 1, wherein the ratio is mm / mm ² . 4. The charging device according to claim 1, wherein the fine network structure on the surface of the charging member is made of a foam. 5. The charging device according to claim 4, wherein the specific gravity of the foam is 0.2 to 0.65. 6. The charging device according to claim 1, further comprising a foamed elastic layer having a fine network structure on a surface of the charging member. 7. The charging device according to claim 1, wherein the resistance of the foamed elastic layer is 10 ⁴ to 10 ⁷ Ω. 8. The charging device according to claim 1, wherein the specific resistance of the conductive particles is 10 ¹² Ω · cm or less. 9. The charging device according to claim 1, wherein the particle size of the conductive particles is 50 μm or less. 10. An image forming apparatus having a charging member arranged to form a nip portion with a photosensitive member, conductive particles interposed in the nip portion, and a photosensitive member, wherein the charging member has a concave cell. Has a fine network structure surface,
Image forming apparatus, wherein the cell edge length is ^{15mm / mm 2 ~60mm / mm 2} . 11. The image forming apparatus according to claim 10, wherein the charging member is a roller. 12. A developing device comprising: a photosensitive member and a charging device;
The cartridge is integrated into a
Process cartridge that can be removed by
Charging means is arranged so as to form a nip with the photoconductor.
Charged member and conductive particles interposed in the nip portion.
The charging member has a fine mesh structure with concave cells.
Has surface and cell edge length is 15mm / mm^Two ~ 60m
m / mm ^Two Process cartridge
Di. 13. The process cartridge according to claim 12, wherein the charging member is a roller. 14. A cell having a fine network structure surface and having a concave cell having a cell edge length of 15 mm / mm ^{2 to} 60 m.
m / mm ² . 15. A cell edge length of 20 mm / mm ^{2 to} 5
15. The charging roller according to claim 14, wherein the charging roller has a thickness of 0 mm / mm < ² >. 16. The charging roller according to claim 14, further comprising a foamed elastic layer having a fine network structure on the surface of the roller. 17. The method according to claim 17, wherein the foamed elastic layer comprises EPD as a rubber base material.
M, foamed and vulcanized using azodicarbonamide as a foaming agent, a thiazole compound and a dithiocarbamate compound as a vulcanization accelerator, and sulfur as a vulcanizing agent. The charging roller as described in the above. 18. The charging roller according to claim 17, wherein the compounding amount of the thiazole compound and the dithiocarbamic acid compound is 3 to 5 parts by weight based on 100 parts by weight of EPDM.