JP2002229300A - Electrifying member and image forming device having the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a partial electrifying irregularity and degradation in electrifying capability and maintain stable electrifying characteristics for a long time even when electrifying is performed by the application of only a DC voltage. SOLUTION: The resistance value between an elastic layer 2b and a surface layer 2c is measured while a DC voltage of -50 to -1,000 V is applied to a core metal 2a. R1 is a resistance value between the elastic layer 2b and the surface layer 2c when a DC voltage V1 of -50 V is applied, and R2 is a resistance value between the elastic layer 2b and the surface layer 2c when a DC voltage V2 of -1,000 V is applied. If a change rate A of the resistance value between the elastic layer 2b and the surface layer 2c when R1>=R2 is R1/R2, A=(R1/R2)<100 is satisfied. Also, when a resistance value R1 between the elastic layer 2b and the surface layer 2c when a DC voltage V1 of 50 V is applied, R1<=8×107 Ω is satisfied. In such a manner, a resistance between the elastic layer 2b and the surface layer 2c is adjusted. Accordingly, partial electrification irregularity and degradation in electrifying capability are prevented, and the stable electrifying characteristics can be maintained for a long time.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a charging member and an image forming apparatus provided with the charging member. More specifically, the present invention relates to a charging member which contacts a member to be charged and charges the member by applying a voltage, and an image bearing member. The present invention relates to an image forming apparatus such as a copying machine, a printer, and a facsimile which includes a body and a charging member for charging the image carrier and forms an image by an electrophotographic system or an electrostatic recording system.

[0002]

2. Description of the Related Art An electrophotographic image forming apparatus (copier,
In a printer, a facsimile, etc.), a corona charger has been generally used as a charging unit for uniformly charging a photosensitive drum as an image carrier to a required polarity and potential. In this method, a corona charger is arranged to face a photosensitive drum in a non-contact manner, and the surface of the photosensitive drum is exposed to corona discharged from the corona charger to charge the photosensitive drum surface to a predetermined polarity and potential.

Further, in recent years, since there are advantages such as low ozone and low power as compared with the above-mentioned non-contact corona charger, a voltage is applied while a charging member which is a conductive member is in contact with the photosensitive drum. Thus, a contact charging system for charging the surface of the photosensitive drum has been put to practical use. In this method, a charging member such as a roller type, a blade type, a brush type, or a magnetic brush type is brought into contact with the photosensitive drum, and a predetermined charging bias is applied to the charging member so that the surface of the photosensitive drum has a predetermined polarity.・ It is charged uniformly to the potential.

[0004] This charging system has the advantages of lowering the voltage of the power supply and generating less ozone. Among them, a roller charging method using a charging roller (conductive roller) as a contact charging member is particularly preferably used from the viewpoint of charging stability. However, the charging uniformity is slightly inferior to the corona charger.

[0005] Therefore, in order to improve the charging uniformity, as disclosed in Japanese Patent Application Laid-Open No. 63-149669, a DC voltage corresponding to a desired surface potential of a member to be charged is reduced by a charging start voltage of 2%. A voltage (alternating voltage, pulsating voltage, oscillating voltage; voltage whose voltage periodically changes with time) on which an AC voltage component (AC voltage component) having a peak-to-peak voltage that is twice or more is applied to the contact charging member. The “AC charging method” is used. This is for the purpose of the effect of leveling the potential by the AC voltage. The potential of the charged body (photosensitive drum) converges to the potential at the center of the peak of the AC voltage, and is affected by disturbances such as the environment. This is an excellent method as a contact charging method.

[0006]

However, in the "AC charging system" disclosed in Japanese Patent Application Laid-Open No. 63-149669, the peak-to-peak voltage that is twice or more the charging start voltage when a DC voltage is applied. In order to superimpose a high AC voltage, an AC power source is required separately from the DC power source, which leads to an increase in the cost of the device itself. Further, there is a problem that the durability of the charging roller and the photosensitive drum is reduced by consuming a large amount of the alternating current.

[0007] These problems can be solved by applying only a DC voltage to the charging roller to perform charging. However, if only a DC voltage is applied to the charging roller, the following problems occur.

That is, when only a DC voltage is applied to the charging roller as described above, local charging unevenness that is excessively charged to a charge potential or more on the surface of the photosensitive drum as a member to be charged occurs. For example, when a halftone image is output by an image forming apparatus using the reversal developing method, the local charging unevenness appears as horizontal white stripes or white spots on the output image, and there is a problem that image quality is degraded.

When the photosensitive drum is charged by a charging roller having a low charging ability, as shown in FIG. 7, the saturation potential (dark portion potential V) after the first and second rounds of charging of the photosensitive drum is obtained.
_D1 and V _D2 ). At this time, as shown in FIG. 8, a predetermined charging bias is applied from the charging bias power supply S1 to the charging roller 2 in contact with the photosensitive drum 1, and the photosensitive drum 1 is And a surface electrometer 1
It was measured at zero.

As described above, when a potential difference occurs between the saturation potential (dark portion potentials V _D1 and V _D2 ) of the first and second rounds of charging of the photosensitive drum, the influence on the image may be, for example, as follows. However, in the case of the reversal development method, if a halftone image is continuously output immediately after forming an electrostatic latent image on a character or a black figure, the previous character or black figure on the halftone image is slightly left behind. Appears as a phenomenon (ghost image). That is, as shown in FIG.
A ghost image occurs due to a phenomenon on the halftone potential (V _HT1 , V _HT2 ) plane immediately after the bright portion potential (V _L ).

When only a DC voltage is applied to the charging roller as described above, particularly in a low-humidity environment, the charging roller deteriorates due to continuous use, and the resistance value of the charging roller tends to increase (charge-up). Then, there is a problem that the charging potential on the surface of the photosensitive drum subjected to the charging process decreases accordingly.

As described above, in an image forming apparatus in which a photosensitive drum is charged by applying only a DC voltage to a charging roller and an image is formed using, for example, a reversal developing method, a plurality of images are continuously output. However, there is a problem in that the image quality of a plurality of successively output images is lower than that of the initial image.

Accordingly, the present invention prevents the occurrence of local charging unevenness, prevents the charging performance from deteriorating, and provides stable charging characteristics for a long period of time, even when charging a charged object by applying only a DC voltage. And an image forming apparatus provided with the charging member.

[0014]

According to a first aspect of the present invention, there is provided a charging member which contacts a member to be charged and charges the member by applying a DC voltage. A conductive elastic layer mainly composed of a medium-resistance elastic material having an ion conduction mechanism, and a coating containing a conductive agent which is in contact with the member to be charged and surface-treated on the elastic layer. A DC voltage V1 when a resistance between the elastic layer and the coating layer is measured by applying a DC voltage of −50 to −1000 V to the support. = -50 V, the resistance between the elastic layer and the coating layer is R1, DC voltage V2
When the resistance between the elastic layer and the coating layer at −1000 V is R2, when R1 ≧ R2, the rate of change A of the resistance between the elastic layer and the coating layer is R1. /
When R2 is satisfied, A <100 is satisfied, and the resistance value R1 between the elastic layer and the coating layer when the measurement voltage is DC voltage V1 = −50 V is R1 ≦ 8 × 10 ⁷ Ω. The resistance of the elastic layer and the coating layer is adjusted so as to satisfy the following.

According to a tenth aspect of the present invention, there is provided an image forming apparatus comprising at least an image carrier and a charging member that contacts the image carrier and charges the image carrier by applying a DC voltage. The charging member contains, on a conductive support, a conductive elastic layer mainly composed of a medium-resistance elastic material having an ion conduction mechanism, and a conductive agent surface-treated on the elastic layer. At least a coating layer that is in contact with the image carrier is laminated, and a resistance value between the elastic layer and the coating layer is set to a DC voltage of -50 to-
When a measurement is performed by applying 1000 V, a measurement voltage; a resistance value between the elastic layer and the coating layer when the DC voltage V1 = -50 V is R1, and the elastic layer when the DC voltage V2 is -1000 V; When the resistance value between the elastic layer and the coating layer is R1 ≧ R2, and when the rate of change A of the resistance value between the elastic layer and the coating layer is R1 / R2,
A = (R1 / R2) <100 and the measured voltage; When the DC voltage V1 = −50 V, the resistance value R1 between the elastic layer and the coating layer is R1 ≦ 8 × 10 ⁷ Ω. The resistance of the elastic layer and the coating layer is adjusted so as to satisfy the following.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below based on the illustrated embodiment.

FIG. 1 is a schematic configuration diagram showing an image forming apparatus (for example, an electrophotographic laser beam printer) provided with a charging roller as a charging member according to an embodiment of the present invention.

This image forming apparatus includes a photosensitive drum 1 as an image carrier, around which a charging roller 2, an exposing device 3, a developing device 4, a transfer roller 5, and a cleaning device 6 are provided.

The photosensitive drum 1 is driven to rotate at a predetermined process speed (peripheral speed) in a direction indicated by an arrow (clockwise) by a driving means (not shown). As the photosensitive drum 1,
A commonly used organic photoreceptor or an amorphous photoreceptor can be used.

The charging roller is in contact with the photosensitive drum 1 with a predetermined pressing force. In the present embodiment, the charging roller 2 is driven to rotate by the rotation of the photosensitive drum 1. Charging roller 2
The surface of the photosensitive drum 1 is applied with a predetermined DC voltage (-1200 V in the present embodiment) from the charging bias power supply S1 to apply a predetermined polarity potential (in the present embodiment,
The charging is uniformly performed by a contact charging method and a DC charging method at a dark area potential of -600 V (the charging roller 2 as a charging member, which is a feature of the present invention, will be described in detail later).

The exposure device 3 can use, for example, a laser beam scanner, and outputs laser light modulated according to a time-series digital image signal of input image information from a laser output unit (not shown). By performing the image exposure L on the surface of the photosensitive drum 1, the exposed bright portion potential (the bright portion potential −120 V in the present embodiment) on the charged photosensitive drum 1 surface is selectively reduced (attenuated). An electrostatic latent image corresponding to the image information is formed on the surface of the photosensitive drum 1.

The developing device 4 is a reversal developing device in the present embodiment, and applies a developing bias between the developing sleeve 4a and the photosensitive drum 1 so that the developing device 4 is rotatable on the surface of the photosensitive drum 1 by the developing sleeve 4a. A toner (negative toner) charged to the same polarity (negative polarity) as the charged polarity of the photosensitive drum 1 is selectively adhered to the exposed light portion of the formed electrostatic latent image, and is visualized as a toner image by reversal development. I do. A toner supply roller 4b and a toner regulating blade 4c are provided in contact with the periphery of the developing sleeve 4a, and the toner is supplied to the peripheral surface of the rotating developing sleeve 4a by the toner supply roller 4b and the toner regulating blade 4c. Applying layer and applying charge to toner (friction charging)
I do.

A transfer roller 5 as a contact transfer means contacts the photosensitive drum 1 with a predetermined pressing force to form a transfer nip N, and is substantially at a rotational peripheral speed of the photosensitive drum 1 in an arrow direction (counterclockwise). They rotate at the same peripheral speed. To the transfer roller 5, a transfer bias having a polarity opposite to the charge polarity of the toner is applied from a transfer bias power supply S2, and the toner image formed on the surface of the photosensitive drum 1 at the transfer nip N is transferred onto a transfer material P such as paper. Transcribe.

Further, in the present embodiment, the photosensitive drum 1,
Charging roller 2, developing device 4, and cleaning device 6
Are integrated into a cartridge to form a process cartridge (not shown), and are detachably mounted on the image forming apparatus.

Next, an image forming operation by the image forming apparatus will be described.

At the time of image formation, the photosensitive drum 1 is driven to rotate in a direction indicated by an arrow (clockwise) by a driving means (not shown), and a charging bias (-1200 V in this embodiment) is applied from a charging bias power supply S1. In the present embodiment, the charging roller 2 charges to about −600 V.

The image exposure L by the laser beam corresponding to the image signal input from the exposure device 3
The potential on the photosensitive drum 1 is reduced, and the potential of the portion exposed to the image L is reduced to form an electrostatic latent image. Then, the electrostatic latent image is reversely developed with the toner formed in a thin layer on the surface of the developing sleeve 4a of the developing device 4 to be visualized as a toner image.

When the toner image on the photosensitive drum 1 reaches the transfer nip N, a transfer material P such as paper is fed and conveyed to the transfer nip N at this timing. Then, the transfer roller 5 to which a transfer bias of a polarity (positive polarity) opposite to that of the toner is applied from the transfer bias power source S2
Accordingly, the toner image on the photosensitive drum 1 is transferred to the transfer material P conveyed to the transfer nip N by the electrostatic force generated between the photosensitive drum 1 and the transfer roller 5.

The transfer material P to which the toner image has been transferred is conveyed to a fixing device (not shown), and the toner image is heated and added to the transfer material P by a fixing nip between a fixing roller and a pressure roller (not shown). After pressing and heat fixing, the sheet is discharged to the outside, and a series of image forming operations is completed. The transfer residual toner remaining on the surface of the photosensitive drum 1 after the transfer of the toner image is removed and collected by the cleaning device 6.

Next, the charging roller 2 will be described.

According to the experimental results of the present inventors, by setting the resistance value of the charging roller 2 to 8 × 10 ⁷ Ω or less when a low voltage (for example, −50 V) is applied, sufficient charging ability can be obtained. (The rise of the charged potential can be made faster), which proved to be very effective in preventing ghost images.

According to the experimental results of the present inventors, to control the voltage dependency of the entire charging roller 2,
In particular, it has been found that it is effective to reduce the voltage dependency of the conductive elastic layer constituting the charging roller 2. The resistance of the elastic layer is adjusted to an electron conductive type (a) to which conductive particles are added, an ion conductive type (b) to which an ionic conductive agent is added, or an ion conductive type (c) in which the polymer itself has a medium resistance. It can be broadly divided.

It has been found that the three types (a), (b) and (c) of the elastic layer have a smaller voltage dependency in the order of (a)>(b)> (c).

Accordingly, the elastic layer of the charging roller 2 is made of a material having a medium resistance of the polymer itself, so that the voltage dependency can be extremely reduced. If only the elastic layer is used for the charging roller 2, the voltage dependency is very small. However, since the material used for the elastic layer has adhesiveness, if used as it is, the toner or the like adheres to the surface, causing a problem that the chargeability is reduced. Therefore,
In order to prevent toner from adhering, a coating layer (surface layer) having releasability is required.

In consideration of the voltage dependency, if the coating layer is made of a material having an ion conduction mechanism, the voltage dependency of the entire charging roller 2 can be reduced. However, if the outermost layer is formed of a material having an ion conduction mechanism, it is not preferable because the environmental fluctuation of the resistance value is affected by disturbance such as the environment and the environmental fluctuation of the resistance value is increased. Further, since the outermost layer (surface layer) is in contact with the photosensitive drum, there is a risk of contamination due to transfer of the ionic substance to the photosensitive drum, which is not preferable.

Therefore, the outermost layer, in particular, must be formed of a material having an electron conduction mechanism and having a resistance adjusted. In this case, the outermost layer has voltage dependency, but by including the acicular conductive agent, the voltage dependency can be reduced. In addition, by making the thickness of the outermost layer as thin as possible, voltage dependency can be reduced to some extent.

According to the experimental results of the present inventors, in order to prevent the electrification deterioration due to continuous use of the charging roller 2, the surface of the conductive agent used for the coating layer (surface layer) is coated with a coupling agent or the like. It has been found that hydrophobic treatment is very effective.

Based on the above results, the charging roller 2 as a charging member in the present embodiment is
As shown in the figure, a core metal 2a as a conductive support, an elastic layer 2b integrally formed on the outer periphery thereof, and a surface layer as a coating layer formed on a peripheral surface of the elastic layer 2b and as an outermost layer 2
c.

As another configuration of the charging roller 2 in the present embodiment, as shown in FIG. 3A, three layers including an elastic layer 2b, a resistance layer 2d, and a surface layer 2c may be used. As shown in FIG. 3B, the resistance layer 2d and the surface layer 2c
A configuration in which four or more layers having a second resistance layer 2e provided therebetween are formed on the cored bar 2a may be employed.

As the core metal 2a of the charging roller 2, a round bar made of a metal material such as iron, copper, stainless steel, aluminum and nickel can be used. Further, these metal surfaces may be subjected to plating treatment for the purpose of rust prevention and imparting scratch resistance, but it is necessary that the conductivity is not impaired.

In the charging roller 2, the elastic layer 2b has appropriate conductivity and elasticity to supply power to the photosensitive drum 1 as a member to be charged and to ensure good uniform adhesion of the charging roller 2 to the photosensitive drum 1. I have. In addition, in order to ensure uniform adhesion between the charging roller 2 and the photosensitive drum 1, the elastic layer 2b is often formed by polishing so that the center portion is thickest and becomes thinner toward both ends, that is, a so-called crown shape. .

Since the generally used charging roller 2 is brought into contact with the photosensitive drum 1 by applying a predetermined pressing force to both ends of the metal core 2a, the pressing force at the center is small, and the pressing force at the both ends is large. Therefore, if the straightness of the charging roller 1 is sufficient, there is no problem. However, if the straightness is not sufficient, density unevenness may occur in images corresponding to the center and both ends. The crown shape is formed to prevent this.

The conductivity control (resistance adjustment) of the elastic layer 2b of the charging roller 2 is performed by using a conductive agent having an electron conductive mechanism such as carbon black, graphite, or conductive metal oxide in an elastic material such as rubber; It is preferable to adjust to less than 10 ⁸ Ω by adding a conductive agent having an ion conduction mechanism such as a salt or a quaternary ammonium salt.

In order to reduce the voltage dependency of the elastic layer 2b, it is best to use a material in which the polymer itself has a medium resistance. Further, even when a material to which a conductive agent having an ion conduction mechanism is added is used, the voltage dependency is relatively small. Note that when a conductive agent having an electron conduction mechanism is used to reduce the voltage dependency, an advanced dispersion technique is required.

Specific elastic materials of the elastic layer 2b include, for example, natural rubber, EPDM, SBR, silicone rubber,
Urethane rubber, epichlorohydrin rubber, IR, BR,
Synthetic rubbers such as NBR and CR, as well as polyamide resins, polyurethane resins, silicone resins and the like are also included.

In order to achieve good electrical properties of the elastic layer 2b, a medium-resistance rubber (for example, epichlorohydrin rubber, NBR, CR,
It is preferable to use urethane rubber) or a polyurethane resin as the elastic material. These medium-resistance rubbers and polyurethane resins are considered to have conductivity, albeit slightly, due to moisture and impurities in the rubbers and resins, and these conductive mechanisms are considered to be ionic conduction. Therefore, if such a medium-resistance rubber or polyurethane resin is used as the material of the elastic layer 2b, a conductive member having little voltage dependency can be obtained.

However, when an elastic layer is formed without adding any conductive agent to these medium resistance rubbers or polyurethane resins, the obtained charging roller has a high resistance value in a low temperature and low humidity environment (L / L). It may exceed 10 ⁸ Ω, and a high voltage must be applied to the charging roller.

Therefore, in the present embodiment, the charging roller 2
Of the elastic layer 2b and the photosensitive drum 1 (the surface layer 2
c), the DC voltage; -50 to -1000
When measured at V, measured voltage; DC voltage V1 =
The resistance value R1 of the charging roller 2 at −50 V was set to satisfy R1 ≦ 8 × 10 ⁷ Ω (1).

Furthermore, according to the experimental results of the present inventors, the electric resistance value of the charging roller 2 is usually set to a load voltage (for example, approximately the same as the DC voltage applied to charge the photosensitive drum 1 with only the DC voltage). When measured under conditions of −1000 V) and a smaller load voltage (for example, −50 V), the rate of change of the electric resistance of the charging roller 2 is represented by (resistance at −50 V application) / (− 1000 V application). When the charge roller 2 has a small change rate, that is, a small dependency on the applied voltage (voltage dependency),
It was found that even when a charging process of the photosensitive drum 1 was performed by applying only a DC voltage of about 1000 V to -1500 V, local charging unevenness hardly occurred. This is because the resistance value of the charging roller 2 does not change abruptly with respect to the applied voltage, and it is considered that charging is performed by stable discharge.

Therefore, when the resistance value between the elastic layer 2b of the charging roller 2 and the portion (surface layer 2c) in contact with the photosensitive drum 1 is measured at a DC voltage of -50 to -1000V, the measured voltage is DC. When the voltage V1 = −50 V, the resistance value of the charging roller 2 is R1, and the DC voltage V2 = −1000.
The resistance value of the charging roller 2 at V is R2, where R1
When ≧ R2, when the rate of change A of the resistance value of the charging roller 2 is represented by R1 / R2, the following equation (2) is satisfied.
It is adjusted by appropriately adding a conductive agent having the above-described ionic conductive mechanism.

A <100 (2) A foam obtained by foaming and molding these elastic materials may be used for the elastic layer 2b.

Further, since the charging roller 2 is in contact with the photosensitive drum 1, the resistance of the charging roller 2 during actual charging includes an electrical contact resistance, and the contact area between the charging roller 2 and the photosensitive drum 1 , And the degree of deformation of the charging roller 2, and also the moving speed of the charging roller 2 and the photosensitive drum 1.
Therefore, the electric resistance of the charging roller 2 is
The electrical resistance measured by making the contact state between the electrode and the cylindrical electrode the same as the contact with the photosensitive drum 1 reflects the state at the time of actual charging.

Therefore, in the present embodiment, the electric resistance value of the charging roller 2 close to the actual charging time was obtained by the resistance measuring method as shown in FIG.

That is, a DC voltage is applied to the charging roller 2 from the power source S3 to charge the rotating conductive cylindrical electrode 21. At this time, both ends of the resistor 22 connected between the cylindrical electrode 21 and the power source S3 are processed. The potential difference is measured by the ammeter 23,
The value of the current flowing through the entire circuit was determined from the potential difference at this time. Further, the electric resistance value of the charging roller 2 was calculated from the current value and the voltage value applied to the charging roller. The resistance value of the charging roller 2 was measured by this method. The shape of the cylindrical electrode 21 is the same as that of the photosensitive drum 1.

As shown in FIGS. 3A and 3B, the resistance layer 2d (2e) of the charging roller 2 is
Formed on the surface of the charging roller 2 to prevent softening oil or plasticizer contained in the elastic layer 2b from bleeding out to the surface of the charging roller 2, or to adjust the electric resistance of the entire charging roller 2. It is provided in.

Examples of the material constituting the resistance layer 2d (2e) include epichlorohydrin rubber, NBR, polyolefin-based plastic elastomer, urethane-based thermoplastic elastomer, polystyrene-based thermoplastic elastomer, fluoro-rubber-based thermoplastic elastomer, and polyester-based thermoplastic elastomer. Examples thereof include a thermoplastic elastomer, a polyamide-based thermoplastic elastomer, a polybutadiene-based thermoplastic elastomer, an ethylene-vinyl acetate-based thermoplastic elastomer, a polyvinyl chloride-based thermoplastic elastomer, and a chlorinated polyethylene-based thermoplastic elastomer. These materials may be used alone or as a mixture of two or more kinds, and may be a copolymer.

The resistance layer 2d (2e) needs to have conductivity or semi-conductivity. Various conductive agents (conductive carbon, graphite, conductive metal oxides, copper, aluminum, nickel, iron powder, alkali metal salts, ammonium salts, etc.) are used as appropriate to achieve conductivity and semi-conductivity. Can be. In this case, in order to obtain a desired electric resistance, two or more of the above-mentioned various conductive agents may be used in combination. Further, in order to reduce the voltage dependency, it is preferable to use a rubber having a medium resistance of the polymer itself such as epichlorohydrin rubber or NBR. Further, when the resistance is adjusted with a conductive agent, it is particularly preferable to add an ionic conductive agent such as an alkali metal salt or an ammonium salt.

The surface layer 2c of the charging roller 2 constitutes the outermost layer of the charging roller 2 and is in contact with the photosensitive drum 1, which is a member to be charged. .

For this reason, as the material of the surface layer 2c, fluorine resin, polyamide resin, acrylic resin, polyurethane resin, silicone resin, butyral resin, styrene-
Ethylene / butylene-olefin copolymer (SEB
C), olefin-ethylene / butylene-olefin copolymer (CEBC) and the like. Silicone oil may be added to these resins for the purpose of reducing the coefficient of static friction.

For the surface layer 2c, various conductive agents (conductive carbon, graphite, conductive tin oxide, conductive titanium oxide, copper, aluminum, nickel, iron powder, etc.) can be used as appropriate. In this case, in order to obtain a desired electric resistance, two or more of the above-mentioned various conductive agents may be used in combination.
In the present invention, it is particularly preferable to add a needle-like conductive agent in order to reduce the voltage dependency.

In the present invention, it is preferable that the conductive agent is subjected to a hydrophobic treatment in order to prevent the deterioration of the electric conduction. As the hydrophobizing agent, coupling agents (silicon, titanium,
The central element such as aluminum and zirconium is not particularly limited), oil, varnish, organic compound and the like. In particular, it is preferable that the coupling agent has been subjected to a hydrophobic treatment.

The charging roller 2 according to the embodiment of the present invention has a ten-point average surface roughness Rz of the surface layer 2c.
Is set to 10 μm or less.

That is, the surface of the charging roller 2 (surface layer 2c)
If the surface is rough, charging unevenness may be delicately caused by unevenness of the surface, and as a result, an image defect may occur. Alternatively, there is a possibility that the surface of the photosensitive drum 1 is eroded (cut, etc.). Therefore, the surface of the charging roller 2 (surface layer 2c) is preferably smoother, and the ten-point average surface roughness Rz in the JIS B0601 surface roughness standard is preferably 10 μm or less, more preferably 4 μm or less.

Hereinafter, the charging roller 2 of the present invention will be described in more detail with reference to the following embodiments.

Example 1 In this example, a charging roller 2 as a charging member was manufactured in the following manner.

Epichlorohydrin rubber (ternary copolymer) 100 parts by weight Light calcium carbonate 30 parts by weight Plasticizer (molecular weight 8000) 10 parts by weight Stearic acid 1 part by weight Antioxidant MB 0.5 part by weight Zinc oxide 5 parts by weight Four Grade ammonium salt 2 parts by weight The above materials were mixed in a closed mixer adjusted to 45 ° C for 10 minutes.
Knead for a minute to adjust the raw material compound. To this compound was added 1 part by weight of sulfur as a vulcanizing agent, 1 part by weight of DM as a vulcanization accelerator, and 0.5 part by weight of TS with respect to 100 parts by weight of raw material epichlorohydrin rubber, and cooled to 20 ° C. on a two-roll machine. And knead for 10 minutes. The obtained compound is formed around a cored bar 2a made of stainless steel having a diameter of 6 mm by using an extruder so as to form a roller having an outer diameter of 15 mm.
Polishing was performed to a thickness of 2 mm to obtain an elastic layer 2b on the peripheral surface of the cored bar 2a.

Then, a surface layer 2c as shown below was formed on the surface of the elastic layer 2b.

As the material of the surface layer 2c, 100 parts by weight of a caprolactone-modified acrylic polyol solution (solid content: 20% by mass, solvent: MEK) 20 parts by weight of acicular conductive tin oxide (hydrophobized with a titanium coupling agent) Glass beads (average particle size; diameter 1 mm)
Was dispersed for 5 hours using a rigid sand mill as a dispersion medium. Thereafter, hexamethylene diisocyanate (HDI) is added to the dispersion solution obtained by filtering the glass beads and separating.
Was added so as to have a molar ratio of (NCO of HDI / OH of caprolactone-modified acrylic polyol) = 0.7 to prepare a coating material for the surface layer.

Then, the surface layer coating material is coated on the surface of the elastic layer 2b by a dipping method, and then dried at 150 ° C. for 1 hour in a hot air circulating drier to form a film having a thickness of 18 μm.
To form a charging roller 2. The surface (surface layer 2c) of the obtained charging roller 2 had a ten-point average surface roughness Rz of 1.8 μm.

The resistance of the charging roller 2 of the present embodiment manufactured as described above was measured by the apparatus shown in FIG.
Also in this case, the surface moving speed of the cylindrical electrode 21, the pressing force of the charging roller 2 against the cylindrical electrode 21, and the like are all the same as those in FIG. A DC voltage (-50 V and -1000 V) was applied from a power source S3, and the resistance value of the charging roller 2 was obtained from the current value flowing at that time.

As a result, the resistance value of the charging roller 2 of this embodiment is: R1 (when -50 V is applied) = 2.48 × 10 ⁶ Ω R2 (when −1000 V is applied) = 6.20 × 10 ⁵ Ω Was.

Therefore, the rate of change (R1 / R2) A of the resistance value of the charging roller 2 is A = 4.0, which satisfies the conditions of the above equations (1) and (2).

The charging roller 2 is attached to the image forming apparatus shown in FIG.
%), Environment 2 (temperature 32.5 ° C, humidity 80%), environment 3
In each environment (temperature 15 ° C., humidity 10%), an image is output by the above-described image forming operation, and the charging roller 2
(A) Occurrence of horizontal white stripes and white spots due to local charging unevenness, and (b) Occurrence of ghost image due to charging ability
Was evaluated for images.

FIG. 5 shows the evaluation results. However, the surface potential V _D of the photosensitive drum 1 has output an image by changing the applied charge voltage so that approximately -600V in each environment. In addition,
In the evaluation of FIG. 5, ◎ indicates that the obtained image was excellent, は indicates that the image was excellent, Δ indicates that there was a slight occurrence of horizontal white streaks or white spots on the halftone image, and x indicates that the occurrence of horizontal white streaks or white spots occurred. stand out,
It is shown that.

The charging roller 2 is attached to the image forming apparatus shown in FIG.
Under the conditions (temperature: 15 ° C., humidity: 10%), a continuous test was carried out by outputting a plurality of images. When the energization deterioration occurs, the electric resistance of the charging roller 2 increases. The electrical resistance value of the charging roller 2 was compared and evaluated before and after the continuous multiple-image image output durability test. However, the charging roller 2 after the durability test
Was wiped dry to remove dirt such as toner from the surface.

FIG. 6 shows the results of this comparative evaluation. In the comparative evaluation of FIG. 6, if the change in electrical resistance is less than one digit, the result is ranked as ◎ if it is 1 digit or more and less than 1 and a half digits, △ if it is 1 digit or more and less than 2 digits, or × if it is 2 digits or more.

By using the charging roller 2 of the present embodiment thus configured, as is apparent from the above-described evaluations, the local charging that occurs when a charging bias of only a DC voltage is applied to the charging roller 2 is performed. The occurrence of unevenness was prevented, and a high-quality image was obtained.

Further, by setting the resistance value of the charging roller 2 when a low voltage (for example, -50 V) is applied to 8 × 10 ⁷ Ω or less, the charging ability can be made sufficient (the charging potential can be reduced). The rise can be made faster), and generation of a ghost image can be prevented.

Further, even when a continuous image was formed in a low humidity environment where deterioration of current flow is apt to occur, it was possible to prevent an increase in the electric resistance of the charging roller 2 and maintain good charging performance for a long period of time.

Example 2 In this example, a charging roller 2 as a charging member was manufactured in the following manner.

100 parts by weight of NBR 3 parts by weight of quaternary ammonium salt 25 parts by weight of graphite 30 parts by weight of calcium carbonate 5 parts by weight of zinc oxide 2 parts by weight of fatty acid 2 parts by weight
After kneading for 15 minutes, 15 parts by weight of a DOS plasticizer is added to 100 parts by weight of NBR, and the mixture is further kneaded for 20 minutes by a closed mixer cooled to 20 ° C. to prepare a raw material compound. To this compound, 1 part by weight of sulfur as a vulcanizing agent and 3 parts by weight of Noxeller TS as a vulcanization accelerator were added to 100 parts by weight of NBR of raw rubber, and the mixture was cooled to 20 ° C.
Knead with this roll machine for 10 minutes. The obtained compound is molded in a roller shape around a cored bar 2a made of stainless steel having a diameter of 6 mm using an extruder, heated and vulcanized, and then polished to an outer diameter of 12 mm. Thus, an elastic layer 2b was obtained.

Then, a resistance layer 2d as shown below was formed on the surface of the elastic layer 2b.

As a material for the resistance layer 2d, 100 parts by weight of epichlorohydrin rubber and 2 parts by weight of a quaternary ammonium salt are dispersed and dissolved in a methyl ethyl ketone (MEK) solvent to form a coating for the resistance layer. This paint is applied on the elastic layer 2b by dipping to form a resistive layer 2d having a thickness of 100 μm.
Was formed by coating.

Then, a surface layer 2c shown below was formed on the surface of the resistance layer 2d.

As a material for the surface layer 2c, a fluororesin copolymer obtained by copolymerizing a fluoroolefin (trifluoride type) and a vinyl carboxylate was used, and 100 parts by weight of the solution (solid content: 50% by mass) was used. ), 55 parts by weight of acicular conductive tin oxide (hydrophobized with n-hexyltrimethoxysilane coupling agent) is added, and isocyanate (HDI) is further added to the NCO / fluorine copolymer of HDI. (OH) = 1.0, and the surface layer paint was adjusted. Using the coating material, a surface layer 2c having a film thickness of 10 μm was formed by coating by a dipping method to obtain a charging roller 2. The ten-point average surface roughness Rz of the surface (surface layer 2c) of the obtained charging roller 2 is as follows:
It was 1.8 μm.

The resistance of the charging roller 2 of this embodiment manufactured as described above was measured by the apparatus shown in FIG.
Also in this case, the surface moving speed of the cylindrical electrode 21, the pressing force of the charging roller 2 against the cylindrical electrode 21, and the like are all the same as those in FIG. A DC voltage (-50 V and -1000 V) was applied from a power source S3, and the resistance value of the charging roller 2 was obtained from the current value flowing at that time.

As a result, the resistance value of the charging roller 2 of this embodiment is R1 (when -50 V is applied) = 8.34 × 10 ⁶ Ω R2 (when −1000 V is applied) = 7.81 × 10 ⁵ Ω Was.

Therefore, the rate of change (R1 / R2) A of the resistance value of the charging roller 2 is A = 10.7, which satisfies the conditions of the above equations (1) and (2).

The charging roller 2 is attached to the image forming apparatus shown in FIG.
%), Environment 2 (temperature 32.5 ° C, humidity 80%), environment 3
In each environment (temperature 15 ° C., humidity 10%), an image is output by the above-described image forming operation, and the charging roller 2
(A) Occurrence of horizontal white stripes and white spots due to local charging unevenness, and (b) Occurrence of ghost image due to charging ability
Was evaluated for images.

FIG. 5 shows the evaluation results. However, the surface potential V _D of the photosensitive drum 1 has output an image by changing the applied charging voltage so that approximately -600V in each environment.

The charging roller 2 is attached to the image forming apparatus shown in FIG.
Under the conditions (temperature: 15 ° C., humidity: 10%), a continuous test was carried out by outputting a plurality of images. When the energization deterioration occurs, the electric resistance of the charging roller 2 increases. The electrical resistance value of the charging roller 2 was compared and evaluated before and after the continuous multiple-image image output durability test. However, the charging roller 2 after the durability test
Was wiped dry to remove dirt such as toner from the surface. FIG. 6 shows the results of this comparative evaluation.

By using the charging roller 2 of the present embodiment thus configured, as is apparent from the above-described evaluations, the local charging generated when a charging bias of only a DC voltage is applied to the charging roller 2 is obtained. The occurrence of unevenness was prevented, and a high-quality image was obtained.

Further, by setting the resistance value of the charging roller 2 to 8 × 10 ⁷ Ω or less when a low voltage (for example, −50 V) is applied, the charging ability can be made sufficient and the ghost image can be displayed. The occurrence could be prevented.

Further, even when continuous images were formed in a low-humidity environment where energization deterioration was liable to occur, it was possible to prevent an increase in the electrical resistance of the charging roller 2 and maintain good charging properties for a long period of time.

Embodiment 3 In this embodiment, a charging roller 2 as a charging member was manufactured in the following manner.

NBR 100 parts by weight Graphite 15 parts by weight Conductive carbon black 10 parts by weight Calcium carbonate 30 parts by weight Zinc oxide 5 parts by weight Fatty acid 2 parts by weight The above materials were mixed in a closed mixer adjusted to 60 ° C. 20
After kneading for 1 minute, 15 parts by weight of a DOS plasticizer is added to 100 parts by weight of NBR, and the mixture is further kneaded with a closed mixer cooled to 20 ° C. for 25 minutes to prepare a raw material compound. To this compound, 1 part by weight of sulfur as a vulcanizing agent and 3 parts by weight of Noxeller TS as a vulcanization accelerator were added to 100 parts by weight of NBR of raw rubber, and the mixture was cooled to 20 ° C.
Knead with this roll machine for 10 minutes.

Then, the obtained compound was treated with a diameter of 6
mm around the core 2a made of stainless steel.
mm, and then heat vulcanization molding, the outer diameter of the rubber part is 12.0 m at the center.
Then, the elastic layer 2b was obtained by performing a polishing treatment so as to form a crown shape of 11.9 mm at both ends.

Then, a resistance layer 2d as shown below was formed on the surface of the elastic layer 2b.

As a material for the resistance layer 2d, 100 parts by weight of a polyurethane elastomer and 10 parts by weight of conductive carbon are dispersed and dissolved in a toluene solvent to prepare a coating for a resistance layer. Then, this coating material was applied to the surface of the elastic layer 2b by dipping to form a 130 μm-thick resistive layer 2d.

Then, a surface layer 2c shown below was formed on the surface of the resistance layer 2d.

A polyvinyl butyral resin was used as a material for the surface layer 2d, and a needle-like conductive titanium oxide (n-hexyltrimethoxysilane coupling agent) was added to 100 parts by weight (solid content: 50% by mass) of the ethanol solution. The surface of the surface layer 2c having a thickness of 22 μm was coated by dipping using a paint to which 40 parts by weight was added. The ten-point average surface roughness Rz of the surface (surface layer 2c) of the obtained charging roller 2 is 2.0
μm.

The resistance of the charging roller 2 of this embodiment manufactured as described above was measured by the apparatus shown in FIG.
Also in this case, the surface moving speed of the cylindrical electrode 21, the pressing force of the charging roller 2 against the cylindrical electrode 21, and the like are all the same as those in FIG. A DC voltage (-50 V and -1000 V) was applied from a power source S3, and the resistance value of the charging roller 2 was obtained from the current value flowing at that time.

As a result, the resistance value of the charging roller 2 of this embodiment is: R1 (when −50 V is applied) = 4.60 × 10 ⁷ Ω R2 (when −1000 V is applied) = 5.10 × 10 ⁵ Ω Was.

Therefore, the rate of change (R1 / R2) A of the resistance value of the charging roller 2 is A = 90.2, which satisfies the conditions of the above equations (1) and (2).

The charging roller 2 was attached to the image forming apparatus shown in FIG.
%), Environment 2 (temperature 32.5 ° C, humidity 80%), environment 3
In each environment (temperature 15 ° C., humidity 10%), an image is output by the above-described image forming operation, and the charging roller 2
(A) Occurrence of horizontal white stripes and white spots due to local charging unevenness, and (b) Occurrence of ghost image due to charging ability
Was evaluated for images.

FIG. 5 shows the evaluation results. However, the surface potential V _D of the photosensitive drum 1 has output an image by changing the applied charging voltage so that approximately -600V in each environment.

The charging roller 2 is attached to the image forming apparatus shown in FIG.
Under the conditions (temperature: 15 ° C., humidity: 10%), a continuous test was carried out by outputting a plurality of images. FIG. 6 shows the results of this comparative evaluation.

By using the charging roller 2 of the present embodiment configured as described above, in the case of the environment 3 (temperature 15 ° C., humidity 10%) which is a low humidity environment, the charging roller 2 according to the first and second embodiments is used.
Although the result was inferior to the case of, the occurrence of local charging unevenness could still be suppressed to a level that would not cause a practical problem,
A good image could be obtained.

Further, by setting the resistance value of the charging roller 2 when a low voltage (for example, -50 V) is applied to 8 × 10 ⁷ Ω or less, the charging ability can be made sufficient and the ghost image can be displayed. The occurrence could be prevented.

Further, even when continuous images were formed in a low-humidity environment in which energization deterioration was liable to occur, it was possible to prevent an increase in the electrical resistance of the charging roller 2 and maintain good charging properties for a long period of time.

Embodiment 4 In this embodiment, a charging roller 2 as a charging member was manufactured in the following manner.

Epichlorohydrin rubber 100 parts by weight Quaternary ammonium salt 2 parts by weight Calcium carbonate 30 parts by weight Zinc oxide 2 parts by weight Fatty acid 2 parts by weight The above materials were mixed in a closed mixer adjusted to 60 ° C.
After kneading for 15 minutes, 15 parts by weight of an ether ester plasticizer was added to 100 parts by weight of epichlorohydrin rubber,
The mixture is further kneaded for 20 minutes by a closed mixer cooled to 20 ° C. to adjust the raw material compound. To this compound, 1 part by weight of sulfur as a vulcanizing agent, 1 part by weight of Noxeller DM as a vulcanization accelerator, and 0.5 part by weight of Noxeller TS were added to 100 parts by weight of raw material epichlorohydrin rubber, and the mixture was cooled to 20 ° C. Knead with this roller machine for 10 minutes. The obtained compound was heated and vulcanized by a press molding machine so as to form a roller having an outer diameter of 12 mm around a cored bar 2a made of stainless steel having a diameter of 6 mm to obtain an elastic layer 2b.

The surface of the elastic layer 2b was coated with a resistance layer 2d as shown below.

As a material for the resistance layer 2d, 100 parts by weight of a caprolactone-modified acrylic polyol solution (solid content: 20% by mass, solvent: MEK) Needle-shaped conductive tin oxide (hydrophobized with a titanium coupling agent) 15 parts by weight Particles Conductive tin oxide (hydrophobic treatment with titanium coupling agent) 5 parts by weight This mixed solution is mixed with glass beads (average particle diameter, diameter 1 m).
m) as a dispersion medium and 5
Time dispersed. Then, hexamethylene diisocyanate (HD) was added to the dispersion solution obtained by filtering and separating the glass beads.
I) was added at a molar ratio of (NCO of HDI / OH of caprolactone-modified acrylic polyol) = 0.7 to prepare a coating for the surface layer.

Then, after coating the surface layer paint on the surface of the elastic layer 2b by dipping, the coating is dried at 150 ° C. for 1 hour in a hot air circulating drier to cover the surface layer 2c having a thickness of 15 μm. Thus, a charging roller 2 was obtained. The surface (surface layer 2c) of the obtained charging roller 2 had a ten-point average surface roughness Rz of 2.6 μm.

The resistance of the charging roller 2 of the present example manufactured as described above was measured by the apparatus shown in FIG.
Also in this case, the surface moving speed of the cylindrical electrode 21, the pressing force of the charging roller 2 against the cylindrical electrode 21, and the like are all the same as those in FIG. A DC voltage (-50 V and -1000 V) was applied from a power source S3, and the resistance value of the charging roller 2 was obtained from the current value flowing at that time.

As a result, the resistance value of the charging roller 2 of this embodiment is R1 (when -50 V is applied) = 1.66 × 10 ⁶ Ω R2 (when -1000 V is applied) = 7.60 × 10 ⁵ Ω Was.

Therefore, the rate of change (R1 / R2) A of the resistance value of the charging roller 2 is A = 2.6, which satisfies the conditions of the above equations (1) and (2).

The charging roller 2 is attached to the image forming apparatus shown in FIG.
%), Environment 2 (temperature 32.5 ° C, humidity 80%), environment 3
In each environment (temperature 15 ° C., humidity 10%), an image is output by the above-described image forming operation, and the charging roller 2
(A) Occurrence of horizontal white stripes and white spots due to local charging unevenness, and (b) Occurrence of ghost image due to charging ability
Was evaluated for images.

FIG. 5 shows the evaluation results. However, the surface potential V _D of the photosensitive drum 1 has output an image by changing the applied charge voltage so that approximately -600V in each environment.

The charging roller 2 is attached to the image forming apparatus shown in FIG.
Under the conditions (temperature: 15 ° C., humidity: 10%), a continuous test was carried out by outputting a plurality of continuous images. When the energization deterioration occurs, the electric resistance of the charging roller 2 increases. The electrical resistance value of the charging roller 2 was compared and evaluated before and after the continuous multiple-image image output durability test. However, the charging roller 2 after the durability test
Was wiped dry to remove dirt such as toner from the surface. FIG. 6 shows the results of this comparative evaluation.

By using the charging roller 2 of the present embodiment configured as described above, as is apparent from the above evaluations, the local charging caused when a charging bias of only a DC voltage is applied to the charging roller 2 is obtained. The occurrence of unevenness was prevented, and a high-quality image was obtained.

Further, by setting the resistance value of the charging roller 2 when a low voltage (for example, -50 V) is applied to 8 × 10 ⁷ Ω or less, the charging ability can be made sufficient, and the ghost image can be displayed. The occurrence could be prevented.

Further, even when a continuous image was formed in a low humidity environment in which the deterioration of the power supply was apt to occur, it was possible to prevent an increase in the electrical resistance of the charging roller 2 and maintain good charging performance for a long period of time.

(Comparative Example) Each of the above Examples 1, 2, 3,
The charging roller of Comparative Example 4 was prepared in the following manner.

EPDM 100 parts by weight Conductive carbon black 37 parts by weight Zinc oxide 5 parts by weight Fatty acid 2 parts by weight The above materials were mixed in a closed mixer adjusted to 60 ° C.
After kneading for 15 minutes, 15 parts by weight of paraffin oil is added to 100 parts by weight of EPDM, and the mixture is further kneaded with a closed mixer cooled to 20 ° C. for 20 minutes to prepare a raw material compound. In this compound, the raw rubber EPDM10
0.5 parts by weight of sulfur as a vulcanizing agent, 1 part by weight of MBT as a vulcanization accelerator, 1 part by weight of TMTD, Z
1.5 parts by weight of nMDC is added, and the mixture is kneaded with a two-roll mill cooled to 20 ° C. for 10 minutes.

An elastic layer was obtained by subjecting the obtained compound to heat vulcanization molding using a press molding machine so as to form a roller having an outer diameter of 12 mm around a stainless steel core having a diameter of 6 mm.

Then, on the surface of the elastic layer, a resistance layer as shown below was formed by coating.

As a material for the resistance layer 2c, 100 parts by weight of a polyurethane resin and 20 parts by weight of a conductive carbon black are dispersed and dissolved in a methyl ethyl ketone (MEK) solvent to prepare a coating for the resistance layer. The coating was applied to the surface of the elastic layer by dipping to form a 100 μm-thick resistive layer.

The surface of the resistance layer was coated with the following surface layer.

As a material for the surface layer, 100 parts by weight of a polyamide resin and 10 parts by weight of conductive carbon black are dispersed and dissolved in a mixed solvent of methanol / toluene to prepare a coating for the surface layer. Using this paint, a surface layer having a thickness of 6 μm was formed by coating by a dipping method to obtain a charging roller. The ten-point average surface roughness Rz of the surface (surface layer) of the obtained charging roller was 10.9 μm.

The resistance of the charging roller of the comparative example manufactured as described above was measured using the apparatus shown in FIG. Also in this case, the surface moving speed of the cylindrical electrode 21, the pressing force of the charging roller 2 against the cylindrical electrode 21, and the like are all the same as those in FIG. As in the case of the forming apparatus, a DC voltage (-50 V and -1000 V) was applied from the power supply S3, and the resistance value of the charging roller was determined from the current flowing at that time.

As a result, the resistance value of the charging roller of the comparative example was R1 (when −50 V was applied) = 4.09 × 10 ⁸ Ω R2 (when −1000 V was applied) = 1.56 × 10 ⁵ Ω.

Therefore, the rate of change (R1 / R2) A of the resistance value of the charging roller of the comparative example is A = 2622, which does not satisfy the conditions of the above equations (1) and (2).

The charging roller was attached to the image forming apparatus shown in FIG.
%), Environment 2 (temperature 32.5 ° C, humidity 80%), environment 3
In each environment (temperature 15 ° C., humidity 10%), an image is output by the above-described image forming operation, and the occurrence of horizontal white stripes or white spots due to local charging unevenness of the charging roller (a), and the charging ability Occurrence of ghost image due to (b)
Was evaluated for images.

FIG. 5 shows the evaluation results. However, the surface potential V _D of the photosensitive drum 1 has output an image by changing the applied charge voltage so that approximately -600V in each environment.

Further, this charging roller is attached to the image forming apparatus shown in FIG.
Under the conditions (temperature: 15 ° C., humidity: 10%), a continuous test was carried out by outputting a plurality of images. When the energization deterioration occurs, the electric resistance of the charging roller 2 increases. The electrical resistance value of the charging roller 2 was compared and evaluated before and after the continuous multiple-image image output durability test. However, the charging roller 2 after the durability test
Was wiped dry to remove dirt such as toner from the surface. FIG. 6 shows the results of this comparative evaluation.

When the charging roller 2 of the comparative example having such a configuration is used, as is apparent from the above-described evaluations, horizontal white stripes and white spots are generated on the output image due to the occurrence of local charging unevenness. did.

Further, in the charging roller of the comparative example, in environment 3 (temperature 15 ° C., humidity 10%), which is a low humidity environment, a ghost image was generated due to a decrease in charging ability.

Further, the resistance value of the charging roller when a low voltage (for example, -50 V) was applied was 8 × 10 ⁷ Ω or more, the charging ability was low, and a ghost image was generated.

Further, when continuous images were formed in a low humidity environment where deterioration of current flow was apt to occur, the electrical resistance of the charging roller was increased, and good charging properties could not be maintained.

As described above, by charging the photosensitive drum 1 with the charging roller 2 of each of the above-described embodiments, the occurrence of local charging unevenness is prevented, and the occurrence of a ghost image is prevented by a sufficient charging ability. In addition, stable charging characteristics can be maintained for a long time.

[0143]

As described above, according to the charging member of the present invention, the surface of the member to be charged is prevented from being excessively charged to a desired charging potential or more, and uniform charging without local charging unevenness is realized. In addition, the member to be charged can be favorably charged with a sufficient charging ability. Furthermore, according to the charging member of the present invention, even when the object to be charged is charged by applying only a DC voltage for a long time, the resistance of the charging member is prevented from increasing, and stable charging characteristics are maintained over a long period of time. be able to.

Further, according to the image forming apparatus of the present invention, it is possible to suppress the surface of the image carrier from being excessively charged to a desired charging potential or more, and to realize uniform charging without causing local charging unevenness. In addition, since the object to be charged can be favorably charged with a sufficient charging ability, a high-quality image can be obtained, and generation of a ghost image can be prevented. Furthermore, according to the image forming apparatus of the present invention, even when the image carrier is charged by applying only a DC voltage for a long time, the resistance of the charging member is prevented from increasing, and stable charging characteristics are maintained for a long period of time. Therefore, a high-quality image can be obtained over a long period of time.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing an image forming apparatus provided with a charging member according to an embodiment of the present invention.

FIG. 2 is a schematic sectional view showing a charging roller according to the embodiment of the present invention.

FIGS. 3A and 3B are schematic cross-sectional views showing a modification of the charging roller according to the embodiment of the present invention.

FIG. 4 is a schematic configuration diagram illustrating a resistance roller measuring device.

FIG. 5 is a diagram showing evaluation results of an example of the present invention and a comparative example.

FIG. 6 is a diagram showing evaluation results of an example of the present invention and a comparative example.

FIG. 7 is a schematic diagram of a measurement chart of a surface potential of a photosensitive drum.

FIG. 8 is a schematic diagram illustrating measurement of a surface potential of a photosensitive drum.

[Description of Signs] 1 Photosensitive drum (charged member, image carrier) 2 Charging roller (charging member) 2a Core bar (support) 2b Elastic layer 2c Surface layer (coating layer) 2d, 2e Resistance layer 3 Exposure device 4 Developing device 4a Developing sleeve 5 Transfer roller 6 Cleaning device S1 Charging bias power supply

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Hiroyuki Osada 3-30-2 Shimomaruko, Ota-ku, Tokyo Inside Canon Inc. (72) Inventor Seiji Tsuru 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Incorporated (72) Inventor Satoshi Taniguchi 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. F-term (reference) 2H003 AA12 BB11 CC05

Claims (19)

[Claims] 1. A charging member that contacts an object to be charged and charges the object to be charged by applying a DC voltage, wherein the charging member mainly comprises a medium-resistance elastic material having an ion conduction mechanism on a conductive support. At least a conductive elastic layer, and a coating layer containing a conductive agent that has been surface-treated on the elastic layer in contact with the member to be charged, are laminated at least, and between the elastic layer and the coating layer When a resistance value is measured by applying a DC voltage of −50 to −1000 V to the support, a measurement voltage; a resistance value between the elastic layer and the coating layer when the DC voltage V1 is −50 V; R1, DC voltage V2 =-
When the resistance between the elastic layer and the coating layer at 1000 V is R2, when R1 ≧ R2, the rate of change A in the resistance between the elastic layer and the coating layer is R1 / R2.
When A <100 is satisfied, and the measurement voltage; the resistance value R1 between the elastic layer and the coating layer when the DC voltage V1 = −50 V, R1 ≦ 8 × 10 ⁷ Ω The charging member, wherein the resistance of the elastic layer and the coating layer is adjusted to satisfy the requirements. 2. The charging member according to claim 1, wherein the conductive agent contained in the coating layer is a metal oxide. 3. The charging member according to claim 2, wherein the conductive agent has been subjected to a coupling treatment. 4. The charging member according to claim 2, wherein the conductive agent has been subjected to a hydrophobic treatment with a coupling agent. 5. The charging member according to claim 1, wherein the coating layer contains an acicular conductive agent. 6. The ten-point average surface roughness Rz of the coating layer is 1
The charging member according to claim 1, 2, 3, 4, or 5, wherein the thickness is 0 μm or less. 7. The medium-resistance elastic material having an ion conduction mechanism constituting the elastic layer is made of epichlorohydrin rubber.
The charging member according to claim 1, wherein the charging member is a material selected from nitrile butadiene rubber and urethane rubber. 8. The method according to claim 1, wherein the elastic layer and the covering layer are formed in a roller shape.
The charging member as described in the above. 9. The semiconductor device according to claim 1, further comprising a conductive or semiconductive resistance layer between the elastic layer and the coating layer. 9. The charging member according to 7 or 8. 10. An image forming apparatus comprising: an image carrier; and a charging member that contacts the image carrier and charges the image carrier by applying a DC voltage. A conductive elastic layer mainly composed of a medium-resistance elastic material having an ion conduction mechanism on a support, and a coating layer containing a conductive agent which is in contact with the image carrier and surface-treated on the elastic layer. When at least a resistance value between the elastic layer and the coating layer is measured by applying a DC voltage of −50 to −1000 V to the support, a measurement voltage; DC voltage V1 = R1 is a resistance value between the elastic layer and the coating layer at −50 V, and DC voltage V2 = −
When the resistance between the elastic layer and the coating layer at 1000 V is R2, when R1 ≧ R2, the rate of change A in the resistance between the elastic layer and the coating layer is R1 / R2.
When A <100 is satisfied, and when the measured voltage; DC voltage V1 = −50 V, the resistance value R1 between the elastic layer and the coating layer is R1 ≦ 8 × 10 ⁷ Ω. An image forming apparatus, wherein the resistance of the elastic layer and the coating layer is adjusted to satisfy the requirements. 11. The image forming apparatus according to claim 10, wherein the conductive agent contained in the coating layer is a metal oxide. 12. The image forming apparatus according to claim 11, wherein the conductive agent has been subjected to a coupling process. 13. The image forming apparatus according to claim 11, wherein the conductive agent has been subjected to a hydrophobic treatment with a coupling agent. 14. The image forming apparatus according to claim 10, wherein the coating layer contains a needle-shaped conductive agent. 15. The ten-point average surface roughness Rz of the coating layer is 10 μm or less.
5. The image forming apparatus according to 4. 16. The medium resistance elastic material having an ion conduction mechanism constituting the elastic layer is a material selected from any of epichlorohydrin rubber, nitrile butadiene rubber, and urethane rubber. An image forming apparatus according to claim 10. 17. The apparatus according to claim 10, wherein said elastic layer and said coating layer are formed in a roller shape.
17. The image forming apparatus according to 4, 15, or 16. 18. The semiconductor device according to claim 10, further comprising a conductive or semiconductive resistance layer between said elastic layer and said coating layer.
18. The image forming apparatus according to 4, 15, 16, or 17. 19. The image forming apparatus according to claim 10, wherein the image carrier and the charging member are at least integrally formed as a cartridge, and are configured as a process cartridge detachably mounted to the image forming apparatus. 11, 12, 13, 1
19. The image forming apparatus according to 4, 15, 16, 17 or 18.