JPH11143178A - Electrifying member, process cartridge and image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate the resistance unevenness of the surface of a roller and to prevent the generation of an image having a failure in electrifying by making the outside diameter of an electrifying member larger, as it goes from the end parts to the vicinity of the central part, in the longitudinal direction of the electrifying member. SOLUTION: The outside diameter of the electrifying member is larger as it goes from the vicinities of the end parts to the vicinity of the central part in the longitudinal direction of an electrifying roller as the electrifying member provided with a conductive metallic core metal 2a made of stainless steel, as a supporting member, a conductive foamed member 2b formed like a roller, on the outer periphery of the core metal 2a, to be concentric and integral and a resistance layer 2c having middle resistance, on the outer periphery of the foamed member 2b. When the contact pressure of the electrifying roller with a drum is uniform in the longitudinal direction, at the time of sticking fine powder toner remaining without being completely removed in a cleaner, to the electrifying roller, the fine powder toner is uniformly stuck and has sticking saturation, in some degree. Since the electrifying roller is in such a crown shape that the central part of the roller is larger than its end parts, the sticking of the toner is uniform and the occurrence of irregularities in the image caused by the failure in electrifying can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a charging member capable of contacting a member to be charged such as a photoreceptor or a dielectric, a process cartridge using the member, and a charging member using the member. The present invention relates to an image forming apparatus.

[0002]

2. Description of the Related Art In a contact charging system, a charging member to which a voltage is applied is brought into contact with an image carrier (hereinafter, referred to as a photosensitive drum) as a member to be charged, and charges are transferred directly to the photosensitive drum. It charges the photosensitive drum surface to a required potential. Compared with a corona discharge device that has been widely used as a charging device, a lower applied voltage is required to obtain a desired potential on the photosensitive drum surface. Voltage is applied, the amount of ozone generated during the charging process is very small, and the necessity of an ozone removal filter is eliminated.Therefore, the configuration of the exhaust system of the device is simplified, and maintenance is free. It has advantages such as simplicity.

[0003] For example, in an image forming apparatus such as an electrophotographic apparatus (copier, laser beam printer) or an electrostatic recording apparatus, corona discharge is used as a means for charging an image carrier such as a photosensitive member or a dielectric, or other photosensitive drums. It has attracted attention as a substitute for the device and has been put to practical use.

In order to uniformly charge the contact charging method or device, an oscillating voltage obtained by superimposing a DC voltage on an AC voltage is applied to the contact charging member, and the contact charging member is brought into contact with the photosensitive drum to perform charging. Method (Japanese Unexamined Patent Publication No.
149669).

FIG. 7 shows one embodiment. Reference numeral 1 denotes a photosensitive drum, which is, for example, a drum-shaped electrophotographic photosensitive member or an electrostatic recording derivative which is driven to rotate at a predetermined peripheral speed (process speed) in a clockwise direction indicated by an arrow A.

Reference numeral 2 denotes a charging roller as a contact charging member, which comprises a metal core rod 2a and a conductive roller body 2b formed of a conductive rubber or the like formed on the outer periphery thereof. The charging roller 2 is pressed against the photosensitive drum 1 with a predetermined pressing force by a pressing force of a pressing spring 3 serving as an urging member, which is applied to both ends of the core bar 2a. It rotates following the rotation.

Reference numeral 4 denotes a power supply for applying a voltage to the charging roller 2, and the photosensitive drum 1 is contacted by the power supply 4 via a contact leaf spring (not shown) brought into contact with a metal rod 2 a of the charging roller 2.
A voltage (Vac + Vdc) obtained by superimposing a oscillating voltage Vac having a peak-to-peak voltage Vpp which is twice or more the charging start voltage of the photosensitive drum 1 and a DC voltage Vdc is applied to the charging roller 2, and the outer peripheral surface of the photosensitive drum 1 being driven to rotate. Are uniformly charged.

Thereafter, the photosensitive drum 1 is exposed to the laser beam 5 to form an electrostatic latent image, and the developing sleeve 6 of the developing device is formed.
From 0, the electrostatic latent image is visualized by receiving the supply of the insulating toner as the developer.

Further, the toner image visualized by the developer is transferred to a transfer material 7 such as paper by a transfer roller 8 as transfer means. The toner image is fixed on the transfer material 7 by a fixing unit (not shown). After the transfer of the toner image, the photosensitive drum 1 is charged by the charging roller 2 again after the transfer residual toner is removed by the cleaning blade 90 as a cleaning unit, and the above-described image forming process is repeated.

In such a contact charging system, a structure in which the conductive roller body 2b is made of a conductive foam has been put to practical use in order to suppress a vibration sound called "charging sound" caused by a vibration voltage. .

It is also advantageous that the roller body 2b is made of foam because the contact between the charging roller and the photoconductor can be improved without increasing the pressure between the charging roller and the photoconductor.

[0012]

In recent years, laser beam printers as output devices for personal computers have been developed in the direction of higher pixel density and higher definition of images. In order to cope with such a tendency, there is a tendency that the particle diameter of the toner as a developer is reduced to more faithfully develop the electrostatic latent image. Specifically, a developer having an average particle diameter (weight average particle diameter) of about 10 μm in the past has become about 7 μm in recent years, and a developer having a particle diameter of 7 μm or less has been studied.

When the toner having such a fine particle size is used, the following problem occurs in the above-described contact charging type image forming apparatus.

Since the particle size of the developer has a certain distribution, if the average particle size is reduced, the ratio of the fine powder toner having a smaller particle size increases accordingly. Specifically, when the average particle diameter is 7 μm, several percent or more of fine powder toner having a particle diameter of 3.5 μm or less is present in the number distribution. When the average particle size is further reduced, the ratio of the fine powder toner further increases.

When such a toner having a small particle diameter is used in the above-described image forming process, a small amount of the fine powder toner may not be completely cleaned and may remain on the photosensitive drum in the step of cleaning the transfer residual toner.
When the fine powder toner remaining on the drum is transferred and accumulated on the contact charging member, the resistance unevenness of the roller surface is caused, so that there is a problem that a poor charging image is generated.

In order to avoid this problem, it is conceivable to remove the fine powder components of the toner as much as possible. However, it is not preferable because the production capacity of the developer is reduced and the cost is increased.

[0017]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and is a charging member capable of contacting a member to be charged to charge the member. , A surface layer, and a foaming member provided between the substrate and the surface layer, in the longitudinal direction of the charging member, from the vicinity of the end to the vicinity of the center of the charging member. A charging member having a large outer diameter, a process cartridge including the charging member, and an image forming apparatus.

The present invention also relates to a process cartridge detachably mountable to an image forming apparatus, comprising: an image carrier; a charging member capable of contacting the image carrier for charging the image carrier; The latent image on the carrier was converted to a weight average particle size of 6.5 μm.
A developing means for developing with the following toner, wherein the outer diameter of the charging member is increased from near the end to near the center in the longitudinal direction of the charging member. And an image forming apparatus characterized by the above configuration.

[0019]

Embodiments of the present invention will be described below with reference to the drawings.

(Embodiment 1) FIG. 2 is a schematic cross-sectional view of one embodiment of the contact charging member of the present invention, and FIG. 3 is a vertical cross-sectional view of one end side. The charging member of the present example is incorporated in the image forming apparatus shown in FIG. 7, but the configuration and operation are as described above, and thus description thereof will be omitted.

Reference numeral 1 denotes a rotating photosensitive drum having a negative or positive charging polarity as a member to be charged. In this example, the organic photoconductive layer having a negatively charged polarity is provided. Reference numeral 2 denotes a charging roller as a contact charging member. The charging roller 2 includes a conductive metal core 2a made of stainless steel or the like as a support member,
A conductive foam member (foam layer) 2b formed concentrically and integrally in the form of a roller on the outer periphery of the cored bar 2a and a resistance layer 2c of medium resistance provided on the outer peripheral surface of the foam member 2b.

The foam member 2b has a low volume efficiency of 10 ⁴ Ωc.
m or less. For example, conductive powder such as carbon or tin oxide is dispersed in a foamed member such as polystyrene / polyolefin / polyester / polyurethane / polyamide or a flexible member formed by foaming EPDM or urethane. This is a member whose volume reduction efficiency has been adjusted. Reference numeral 2b 'denotes a bubble portion (enclosed bubble of air, nitrogen, argon gas or the like) of the foamed member.

The medium resistance layer has a low volume efficiency of 1%.
0 ⁵ -10 well to the ⁹ [Omega] cm, for example, urethane resins, polyester resins, vinyl acetate - vinyl chloride copolymer, polyvinyl butyral resin, the N- methoxymethylated nylon, conductive carbon, tin oxide, Kneading the above-mentioned conductive powder in a film formed by dispersing conductive powder such as titanium and indium oxide, or synthetic rubber such as urethane resin, polyester resin, polyethylene resin, EPDM, styrene butadiene rubber, etc. After dispersion, a conductive tube or the like formed by extrusion or the like is used.

This charging roller 2 is, like the conventional charging roller 2 shown in FIG.
Both ends of the cored bar 2a are held by bearing members (not shown), and the bearing members are urged toward the photosensitive drum by a pressing spring 3, which is an urging member, so that a predetermined pressing force is applied to the charging roller and one surface of the photosensitive drum. In this embodiment, the photosensitive drum 1 is brought into pressure contact with a total pressure of 1000 g, and rotates in accordance with the rotation of the photosensitive drum 1. The charging roller 2 is supplied from a power supply 4 via a sliding electrode (not shown) in contact with the charging roller core 2a. An AC voltage; 2.0 KVpp in this embodiment, 1500 Hz DC voltage; equivalent to a target charging potential DC voltage (eg-
(700 V) and a superimposed oscillation voltage (Vac + Vdc). Thus, the peripheral surface of the rotary photosensitive drum 1 is uniformly contact-charged to the target charging potential by the AC application method. In order to make the charging property uniform, it is preferable that the oscillation voltage has a peak-to-peak voltage that is at least twice the charging start voltage of the photoconductor. The charging start voltage is a minimum applied DC voltage value when charging of the member to be charged starts when only a DC voltage is applied to the charging member.

The charging roller of this embodiment is characterized in that the shape of the charging roller 2 is defined in combination with the developer used. Hereinafter, specific contents of the present invention will be described.

FIG. 1 is a longitudinal sectional view of the charging roller used in the first embodiment.

In FIG. 1, 2a has a diameter of 6 mm and a length of 2 mm.
It is a stainless steel round bar which is a core bar of 56 mm. 2b
Is a carbon-dispersed foamed EPDM as a foamed member
It is rubber and has a layer thickness of 2.8 mm at the center in the longitudinal direction.
Is a conductive polyester resin tube which is a medium resistance layer having a volume resistivity of 10 ⁹ Ωcm. FIG. 1 shows the effective charging width in the longitudinal direction of the charging member,
1, D2, D3, D4, and D5 represent roller diameters of portions at distances of L1, L2, L3, L4, and L5 from the ends of the effective charging width, respectively. In the present embodiment, the charging roller No. having the roller diameters D1 to D5 is varied by coating the resin tube after polishing the surface of the foamed EPDM rubber. No. 1 to No. 8 were prepared. The roller diameter is changed by changing the thickness of the foam member. Table 1 summarizes the dimensions of the charging roller prepared in this embodiment.

Next, a molecular weight of 5600 and a glass transition point of 57
60 parts by weight of magnetite is added to a styrene acrylic resin at 40 ° C., kneaded and then pulverized to obtain a toner having a weight average particle size of 6.5 μm, a particle size of 3.2 μm or less and a number distribution of 4%, and a weight average particle size. A toner having a particle size of 6.0 μm and a number distribution of 10% with a particle size of 3.0 μm or less was prepared.

The average particle size and particle size distribution of the toner can be measured by various methods such as Coulter Counter TA-II or Coulter Multisizer (manufactured by Coulter). ), An interface (manufactured by Nikkaki) for outputting the number distribution and volume distribution and a PC9801 personal computer (manufactured by NEC) are connected, and a 1% aqueous NaCl solution is prepared using primary-grade sodium chloride as an electrolytic solution. For example, ISOTON R-II (manufactured by Coulter Scientific Japan) can be used.
As a measurement method, 0.1 to 5 ml of a surfactant, preferably an alkylbenzene sulfonate, is added as a dispersant to 100 to 150 ml of the aqueous electrolytic solution, and 2 to 20 mg of a measurement sample is further added. The electrolytic solution in which the sample is suspended is subjected to a dispersion treatment for about 1 to 3 minutes by an ultrasonic disperser, and the volume and the number of toner particles having a size of 2 μm or more are measured using the Coulter Multisizer with an aperture of 100 μm as an aperture. The number distribution was calculated. Then, the weight-based weight average particle diameter (D ₄ : the median value of each channel is taken as a representative value of the channel) obtained from the volume distribution according to the present invention was obtained.

According to the present inventors, it has been recognized that the adhesion of the toner remaining after transfer to the charging member has a correlation with the shape of the charging member. I understood that. Further, it was found that when the contact pressure at the contact portion between the charging member and the photosensitive drum was uneven, the amount of the adhered toner was large in the portion where the pressure was partially reduced. The reason is considered to be as follows. In other words, the fine powder toner that could not be completely removed by the cleaner adheres to the charging roller, and if the contact pressure of the charging roller with the drum is uniform in the longitudinal direction, the toner is adhered and saturated to the extent that it adheres uniformly. If the pressure distribution becomes non-uniform due to the presence of a surface dent or the like, the residual toner on the drum selectively accumulates and accumulates in low pressure areas. As described above, a non-uniform image due to poor charging is generated in a portion where the amount of the attached toner is partially increased. Such an image defect is at a temperature of 15 ° C. or less, and occurs remarkably in a low-temperature and low-humidity environment of a humidity of 30% or less.

According to the present inventor, by making the shape of the charging roller a crown shape that is thicker at the center than at the roller end, the amount of adhered toner becomes uniform, and the occurrence of image unevenness due to poor charging is prevented. I found that I could do it.

No. 1 to No. The charging roller No. 8 and the toner described above were placed in the image forming apparatus described with reference to FIG. 7, and an image output durability test was performed to test the occurrence of image defects due to charging defects.

In the test, up to 10,000 sheets of A4 size paper as a transfer material were imaged and passed in a low-temperature and low-humidity environment to check for occurrence of charging failure. Further, the effective charging width L =
230 mm charging roller (No. 1 to No. 6) is A4
The size paper is fed vertically (the longer side of the paper coincides with the paper traveling direction), and the charging roller (No. 7 to No. 8) with an effective charging width L = 320 mm feeds A4 paper horizontally. Passed by.

Table 2 summarizes the test results.

As is clear from Table 2, the diameter of the central portion (D2) of the charging roller (No. 1, 2, 3, 4) is larger than the diameter (D1, D3) of the end portion of the charging roller. ,
In the case of 7.8), it can be seen that even when the toner having an average particle diameter of 6.5 μm or less is used, a good image without image defects can be obtained.

As described above, the weight average particle diameter of the toner is 6.5.
Even when the number distribution of toner particles having a particle diameter of not more than μm and not more than half of the weight average particle diameter of the toner was 4% or more, no image defect due to defective charging occurred.

(Embodiment 2) FIG. 4 shows a second embodiment of the charging member of the present invention. In FIG. 4, reference numeral 2 a denotes a stainless steel round bar which is the same core metal as in the first embodiment, and 2 b denotes the same carbon-dispersed foamed EPDM rubber as in the first embodiment. Also,
2c is a carbon-dispersed NBR rubber which is a medium resistance layer, and 2d is a dispersion of particles of a fluorine compound such as PTFE (polytetrafluoroethylene), tin oxide and carbon in methoxymethylated nylon (trade name: resin). This is a surface layer formed by film formation.

Also, L, L1 to L5, D1 to D5 in the figure
The meaning of the symbol is the same as in the first embodiment, and the description is omitted.

The feature of this embodiment is that the foam layer 2
b is a two-layer structure composed of 2c and 2d.
The charging roller having roller diameters D1 to D5 is prepared by changing the thickness of the charging roller in the longitudinal direction of the charging roller.

Table 3 shows the charging roller N prepared in this embodiment.
o. 9-No. 16 dimensions are summarized.

The charging roller and the toner prepared in Example 1 were put in the image forming apparatus described in FIG. 7 in the same manner as in Example 1, and an image endurance test was carried out to test the occurrence of image defects due to charging failure. did.

In the test, as in Example 1, up to 10,000 sheets of A4 paper were imaged and passed in a low-temperature and low-humidity environment, and the presence or absence of occurrence of charging failure was examined. Further, the effective charging width L = 230
mm-size charging rollers (No. 9 to No. 14) feed A4 size paper by vertical feed, and the effective charging width L = 320 mm charging roller (No. 15 to No. 16) crosses A4 size paper horizontally. The paper passed by feed.

Table 4 summarizes the test results.

As is clear from Table 4, the diameter of the central portion (D2) of the charging roller (No. 9, 10, 11, 11) is larger than the diameter (D1, D3) of the end portion of the charging roller.
12, 15.16), it can be seen that even when a toner having an average particle diameter of 6.5 μm or less is used, a good image without image defects can be obtained.

(Embodiment 3) FIG. 5 shows a third embodiment of the charging member of the present invention. In FIG. 5, reference numeral 2a denotes a stainless steel round bar which is the same core metal as in the first embodiment, and reference numeral 2b denotes an NBR solid rubber in which carbon is dispersed. 2c is a carbon-dispersed epichlorohydrin rubber which is a medium resistance layer, and 2d is a surface layer formed by dispersing fluorine compound particles, tin oxide and carbon in resin and forming a film. Further, the meanings of the symbols L, L1 to L5, and D1 to D5 in the drawing are the same as those in the first embodiment, and thus description thereof is omitted.

The feature of this embodiment is that a two-layer surface layer 2c and 2d is provided on the solid rubber layer 2a.
The surface of the solid rubber layer 2c is polished and the polishing amount is changed to prepare a charging roller having roller diameters D1 to D5.

Table 5 shows the charging roller N prepared in this embodiment.
o. 17-No. 24 dimensions are summarized.

These charging rollers and the toner prepared in Example 1 were placed in the image forming apparatus described with reference to FIG. 7 in the same manner as in Example 1, and an image endurance test was performed to test the occurrence of charging failure.

In the test, in the same manner as in Example 1, up to 10,000 sheets of A4 paper were imaged and passed in a low-temperature and low-humidity environment to check for occurrence of charging failure. Further, the effective charging width L = 230
mm charging roller (No. 17 to No. 22) feeds A4 size paper by vertical feed, and the effective charging width L = 320 mm
(No. 23 to No. 24) passed A4 paper sideways.

Table 6 summarizes the test results.

As is apparent from Table 6, the diameter of the central portion (D2) of the charging roller (No. 17, 18, 1) is larger than the diameter (D1, D3) of the end portion of the charging roller.
9, 20, 23.24), it can be seen that even if a toner having an average particle diameter of 6.5 μm or less is used, a good image without image defects can be obtained.

(Embodiment 4) In this embodiment, a process cartridge of an image forming apparatus using the contact charging member or contact charging device shown in Embodiments 1 to 3 as a charging means for an image carrier is provided. .

The process cartridge of the present embodiment includes four process devices including a drum-shaped electrophotographic photosensitive member 1 as an image carrier, a charging roller 2 as a contact charging member, a developing device 6 and a cleaning device 9. It is detachable from the image forming apparatus. The process cartridge may include the photoconductor 1 and the charging member 2.

The charging roller 2 has the same configuration as that of the first, second, or third embodiment.

In the developing device 6, reference numeral 60 denotes a developing sleeve, 61 denotes a container for storing a developer (toner) T, and 62 denotes a toner stirring bar in the container 61, which serves to stir the toner T and send it out toward the developing sleeve. You are. Reference numeral 63 denotes a developing blade for coating the developing sleeve 60 with the toner T to a uniform thickness.

The developer 61 has a weight average particle size of 6.5 μm or less as described in the first embodiment.

In the cleaning device 9, reference numeral 90 denotes a cleaning blade, and reference numeral 91 denotes a waste toner container for storing the toner collected by the cleaning blade 90.

When the process cartridge is mounted on the mounting portion of the image forming apparatus main body, the process cartridge and the image forming apparatus main body are mechanically and electrically coupled, and the driving mechanism of the image forming apparatus main body side drives the process cartridge. The photosensitive drum 1, the developing sleeve 60, the stirring bar 62, etc. can be driven, and the charging roller 2 on the process cartridge side can be driven by the electric circuit of the power supply on the image forming apparatus main body side.
It is possible to apply a charging bias to the developing sleeve 60, apply a developing bias to the developing sleeve 60, and the like, so that an image forming operation can be performed.

Reference numeral 12 denotes an exposure window provided between the cleaning device 90 and the developing device 60 of the process cartridge, and the output laser light 5 from a laser scanner (not shown) on the image forming apparatus main body side receives this exposure light. After passing through the window 12 and entering the process cartridge, the surface of the rotating photosensitive drum 1 is scanned and exposed.

With this configuration, a high-definition image can be obtained by using a fine particle size toner.
In addition, it is possible to provide a compact process cartridge that does not cause image failure due to poor charging even in a low-temperature and low-humidity environment.

In the roller-shaped contact charging members of Examples 1 to 3, when the roller diameter at the center of the length of the roller is D2 and the diameters at both ends are D1 and D3, respectively, It is preferable that the configuration satisfy the expression.

10 (μm) ≦ D2− (D1 + D3) / 2
≦ 100 (μm)

Where D1 and D3 are the effective charging width of the roller = L
(Mm), 0.2 × L / 2 from the effective charging end
Is a roller diameter at an arbitrary point in a portion within a distance of 0.3 × L / 2 from the roller. Further, D1, D2, D3 and D1
It is more preferable that the roller diameter at an arbitrary position between D2 and D2 be D4 and the roller diameter at an arbitrary position between D2 and D3 be D5, and that the following expression be satisfied between them.

10 (μm) ≦ D2− (D1 + D3) / 2
≦ 100 (μm) 100 (μm) ≧ D4−D1 ≧ 0 (μm), 100 (μm)
m) ≧ D5−D3 ≧ 0 (μm)

[0065]

[Table 1]

[0066]

[Table 2]

[0067]

[Table 3]

[0068]

[Table 4]

[0069]

[Table 5]

[0070]

[Table 6]

[0071]

As described above, according to the present invention, in the charging member provided with the foam member, the outer diameter of the charging member is increased from near the end to near the center in the longitudinal direction of the charging member. Thereby, charging failure can be prevented. Further, according to the present invention, the weight average particle size is 6.
Even when a toner of 5 μm or less is used, by increasing the outer diameter of the charging member from near the end to near the center in the longitudinal direction of the charging member, a stable image free from image defects due to poor charging can be obtained. Obtainable.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of a first embodiment of a charging member.

FIG. 2 is a cross-sectional view of a charging member according to a first embodiment in a longitudinal direction and a vertical direction.

FIG. 3 is a cross-sectional view of a charging member according to a first embodiment in a longitudinal direction and an end portion.

FIG. 4 is a longitudinal sectional view of a charging member according to a second embodiment.

FIG. 5 is a longitudinal sectional view of a charging member according to a third embodiment.

FIG. 6 is a cross-sectional view of a process cartridge including a charging member.

FIG. 7 is a side view of an image forming apparatus including a charging member.

[Explanation of symbols]

 Reference Signs List 1 photosensitive drum as image carrier 2 charging member 4 bias power supply 60 developing sleeve 7 transfer material 8 transfer roller 90 cleaning blade

Claims (20)

[Claims] 1. A charging member capable of contacting a member to be charged to charge the member, comprising: a base; a surface layer; a foaming member provided between the base and the surface layer; The charging member according to claim 1, wherein, in a longitudinal direction of the charging member, an outer diameter of the charging member is increased from near an end to near a center. 2. The charging member according to claim 1, wherein the charging member has a roller shape. 3. In the longitudinal direction of the charging member, assuming that the outer diameter at the center is D2 and the outer diameters at both ends are D ₁ and D ₃ ,
0 (μm) ≦ D2− (D1 + D3) / 2 ≦ 100 (μ
m), where D1 and D3 are 0.2 × L / 2 to 0.3 × L / 2 from the end of the effective charging width when the effective charging width of the charging member is L (mm). The charging member according to claim 2, wherein an outer diameter of the charging member at an arbitrary point in a distance portion of the range. 4. An outer diameter of the charging member at an arbitrary position between the position of the outer diameter D1 and the position of the outer diameter D2 is D4, and the outer diameter is D2.
If the outer diameter of the charging member at an arbitrary position between the position of the charging member and the position of the outer diameter D3 is D5, 100 (μm) ≧ D4−D1 ≧ 0 (μm), 100 (μm)
4. The charging member according to claim 3, wherein m) ≧ D5−D3 ≧ 0 (μm). 5. A process cartridge detachable from an image forming apparatus, comprising: an image carrier; a charging member capable of contacting the image carrier to charge the image carrier; A charging member including a layer and a foam member provided between the substrate and the surface layer. In the process cartridge, in the longitudinal direction of the charging member, from near the end to near the center. An outer diameter of the charging member is increased. 6. The process cartridge according to claim 5, wherein said charging member has a roller shape. 7. A process cartridge detachable from an image forming apparatus, comprising: an image carrier; a charging member capable of contacting the image carrier to charge the image carrier; Developing means for developing an image with a toner having a weight average particle diameter of 6.5 μm or less, wherein in the longitudinal direction of the charging member, the outer diameter of the charging member is changed from near the end to near the center in the longitudinal direction of the charging member. Process cartridge characterized by being enlarged. 8. The process cartridge according to claim 7, wherein said charging member has a roller shape. 9. The process cartridge according to claim 7, wherein the number distribution of the toner having a particle diameter equal to or less than half of the weight average particle diameter of the toner is 4% or more of the whole toner. 10. The longitudinal direction of the charging member, the outer diameter of the central portion D2, the outer diameter of the both end portions and _{D 1, D 3 10 (μm} ) ≦ D2- (D1 + D3) / 2 ≦ 100 (μ
m), where D1 and D3 are 0.2 × L / 2 to 0.3 × L / 2 from the end of the effective charging width when the effective charging width of the charging member is L (mm). 9. The process cartridge according to claim 8, wherein an outer diameter of the charging member at an arbitrary point in a distance portion of the range. 11. The external diameter of the charging member at an arbitrary position between the position of the external diameter D1 and the position of the external diameter D2 is D4, and the external diameter is D.
Assuming that the outer diameter of the charging member at an arbitrary position between the position 2 and the position of the outer diameter D3 is D5, 100 (μm) ≧ D4−D1 ≧ 0 (μm), 100 (μm)
11. The process cartridge according to claim 10, wherein m) ≧ D5−D3 ≧ 0 (μm). 12. The charging member includes a base, a surface layer,
A foam member provided between the substrate and the surface layer,
The process cartridge according to claim 7, further comprising: 13. An image carrier, and a charging member capable of contacting the image carrier to charge the image carrier, wherein a charging member is provided between the substrate, the surface layer, and the substrate and the surface layer. An image forming apparatus comprising: a charging member provided with a foam member provided in the image forming apparatus, wherein an outer diameter of the charging member is increased from near an end to near a center in a longitudinal direction of the charging member. Image forming apparatus. 14. The image forming apparatus according to claim 13, wherein said charging member has a roller shape. 15. An image bearing member, a charging member capable of contacting the image bearing member for charging the image bearing member, and a latent image of the image bearing member with a toner having a weight average particle diameter of 6.5 μm or less. An image forming apparatus comprising: developing means for developing, wherein the outer diameter of the charging member is increased from near an end to near a center in a longitudinal direction of the charging member. 16. The image forming apparatus according to claim 15, wherein said charging member has a roller shape. 17. The image forming apparatus according to claim 15, wherein the number distribution of the toner having a particle diameter equal to or less than half of the weight average particle diameter of the toner is 4% or more of the whole toner. 18. The longitudinal direction of the charging member, the outer diameter of the central portion D2, the outer diameter of the both end portions and _{D 1, D 3 10 (μm} ) ≦ D2- (D1 + D3) / 2 ≦ 100 (μ
m), where D1 and D3 are 0.2 × L / 2 to 0.3 × L / 2 from the end of the effective charging width when the effective charging width of the charging member is L (mm). 18. The image forming apparatus according to claim 17, wherein an outer diameter of the charging member at an arbitrary point in a distance portion of the range. 19. An outer diameter of the charging member at an arbitrary position between the position of the outer diameter D1 and the position of the outer diameter D2 is D4, and the outer diameter is D.
Assuming that the outer diameter of the charging member at an arbitrary position between the position 2 and the position of the outer diameter D3 is D5, 100 (μm) ≧ D4−D1 ≧ 0 (μm), 100 (μm)
19. The image forming apparatus according to claim 18, wherein m) ≧ D5−D3 ≧ 0 (μm). 20. The charging member, comprising: a base, a surface layer,
A foam member provided between the substrate and the surface layer,
The image forming apparatus according to claim 15, further comprising: