JP2001099136A - Charging device and image forming device using it - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent generation of unevenness of optional charging in the case where charging is carried out by applying only direct current voltage on a charging member. SOLUTION: In a charging member wherein a charging member is brought into contact with a charged body, voltage is applied on the charging member, and the charged body is charged; A=(R1/R2)<100, when a resistance value of the charging member when measuring voltage is direct current voltage V1=-50 V is identified as R1, a resistance value at the time of direct current voltage V2=-1000 V is identified as R2, the relation between the R1 and R2 is identified as R1>=R2, and a change ratio A of a resistance value of the charging member is identified as R1/R2, in the case where the resistance value between a voltage applying part of the charging member and a part that is brought into contact with the charged body is measured in direct voltage -50 to -1000 V, and the resistance value unevenness of the circumferential direction of the charging member is (a circumferential direction resistance maximum value Rmax)/(a circumferential direction resistance minimum value Rmin) <=3.0.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus employing an electrophotographic method, such as a printer, a facsimile, and a copying machine. The present invention relates to a contact charging member for charging a charged body.

[0002]

2. Description of the Related Art For convenience, an image forming apparatus such as a laser beam printer, a copying machine, and a facsimile of an electrophotographic system will be described as an example.

Conventionally, a charging process in an electrophotographic process involves applying a high voltage (DC voltage of 6 to 8 kV) to a metal wire.
2. Description of the Related Art A corona charger that uniformly charges a surface of a photoreceptor, which is a member to be charged, to a predetermined polarity and potential by a corona shower generated by applying a voltage has been widely used. However, there are problems such as generation of a relatively large amount of ozone that requires a high-voltage power supply.

On the other hand, a contact charging system in which a voltage is applied while a charging member is in contact with a photosensitive member to charge the surface of the photosensitive member has been put to practical use. That is, a charging member as a charge supply member such as a roller type, a blade type, a brush type and a magnetic brush type is brought into contact with the photoreceptor, and a predetermined charging bias is applied to the contact charging member to bring the photoreceptor surface into a predetermined state. This is to uniformly charge to polarity and potential.

This charging method has the advantages of lowering the voltage of the power supply and reducing the amount of ozone generated. Among these, a roller charging system using a conductive roller (charging roller) as a contact charging member is preferably used in terms of charging stability. However, the charging uniformity is slightly inferior to the corona charger.

In order to improve the charging uniformity, as disclosed in Japanese Patent Application Laid-Open No. 63-149669, a charging start voltage (V _TH ) is reduced to a DC voltage corresponding to a desired surface potential Vd of a member to be charged. A voltage (alternating voltage, pulsating voltage, oscillating voltage; voltage whose voltage value changes periodically with time) superimposed with an AC voltage component (AC voltage component) having a peak-to-peak voltage of twice or more is applied to the contact charging member. The “AC charging method” is used. This is for the purpose of the leveling effect of the potential by the AC voltage, and the potential of the member to be charged converges to the potential Vd, which is the center of the peak of the AC voltage, and is not affected by disturbances such as the environment. This is an excellent method as a contact charging method.

However, Japanese Patent Application Laid-Open No. 63-149669
In the publication, charging start voltage (V
_In order to superimpose a high AC voltage which is a peak-to-peak voltage twice or more than _TH ), an AC power source is required separately from a 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 photoreceptor is reduced by consuming a large amount of the alternating current.

Further, these problems can be solved by applying only a DC voltage to the charging roller to perform charging. However, applying only a DC voltage to the charging roller causes the following problems.

When only a DC voltage is applied to the conventional charging member, local charging unevenness which is excessively charged to a charging potential or more on the surface of a member to be charged such as a photoreceptor is generated. 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 image, and there is a problem that image quality is reduced.

[0010] When only a DC voltage is applied to the charging roller, uneven charging potential occurs due to uneven resistance in the circumferential direction of the charging roller. For example, when a halftone image is output by the image forming apparatus using the reversal development method as described above, there is a problem that density unevenness appears on the image and the image quality deteriorates.

Further, in an image forming apparatus using a contact charging method, there is a tendency that unevenness in image density or the like occurs due to poor charging due to contamination of the charging member (adhesion of the surface of the developer), causing a problem in durability. There is an urgent need to prevent the influence of poor charging due to dirt on the prints to enable printing of a plurality of sheets. In particular, in the case of the charging method in which only a DC voltage is applied to the charging member, the influence of contamination on the charging member tends to appear as an image defect more easily than in the AC charging method.

[0012]

SUMMARY OF THE INVENTION The present invention has been made in consideration of the above circumstances, and prevents the occurrence of local charging unevenness even when charging is performed by applying only a DC voltage to a charging member. And an image forming apparatus using the same.

Another object of the present invention is to provide a charging member which suppresses the occurrence of uneven charging potential due to uneven resistance in the circumferential direction of the charging member, and an image forming apparatus using the same.

Still another object of the present invention is to provide a charging member capable of maintaining good charging characteristics for a long period without causing charging failure due to contamination of the charging member, and an image forming apparatus using the same. Is to provide.

[0015]

According to the present invention, there is provided a charging member for applying a voltage to a charging member to directly charge an object to be charged by a direct charging method, and the charging member is provided with a conductive material on a conductive support. In a charging member having a laminated structure in which an elastic layer is formed and at least a coating layer is formed on a conductive elastic layer, a resistance value between a voltage application portion of the charging member and a portion in contact with the member to be charged is determined by a DC voltage. -50 to -1000V
, The measured voltage is DC voltage V ₁ = −
The resistance value of the charging member at 50 V is R ₁ , and the DC voltage V ₂ = −
When the resistance value at 1000 V is R ₂ and R ₁ ≧ R ₂ , when the rate of change A of the resistance value of the charging member is expressed as R ₁ / R ₂ , A = (R ₁ / R ₂ ) <100..., Wherein the circumferential resistance unevenness of the charging member satisfies (maximum circumferential resistance Rmax) / (minimum circumferential resistance Rmin) ≦ 3.0. Is provided.

According to the present invention, there is provided an image forming apparatus having the charging member as a charging unit.

[0017]

Embodiments of the present invention will be described below in detail.

As a result of our intensive studies, the electric resistance of the charging member is usually set to a load voltage (for example, -1000 V) substantially equal to the DC voltage applied for charging the member to be charged with only the DC voltage. When measured under the condition of a smaller load voltage (for example, −50 V), the rate of change of the electrical resistance value of the charging member is represented by (resistance at −50 V application) / (resistance at −1000 V application). When the charging member has a small change rate, that is, a small dependency on the applied voltage (voltage dependency), −100
It was found that local charging unevenness is unlikely to occur even when a charging process is performed on the member to be charged by applying only a DC voltage of about 0 V to -1500 V. Probably, it is considered that since the resistance value of the charging member does not change abruptly with respect to the applied voltage, charging is performed by stable discharge.

That is, by designing a charging member having a small voltage dependency so as to satisfy the relationship of the formula of the present invention, it is possible to solve the problem of local charging unevenness that occurs when only a DC voltage is applied to the charging member. I found it.

Further, the charging member often has a multilayer structure. In this case, it may not be possible to reduce the voltage dependence of the electric resistance value of the entire charging member only by controlling the volume resistivity or the thickness of the high-resistance coating layer or some coating layers. . As a result of our intensive studies, it has been found that in order to control the voltage dependence of the entire charging member, it is particularly effective to design the conductive elastic layer so as to reduce the voltage dependence.

Further, since the charging member is in contact with the member to be charged, the resistance of the charging member at the time of actual charging includes an electrical contact resistance, and further, the contact area between the charging member and the member to be charged, and It depends on the degree of deformation of the charging member and also on the moving speed of the charging member and the member to be charged. Therefore, the electric resistance of the charging member reflects the state at the time of actual charging when the electric resistance measured by making the contact state between the charging member and the electrode the same as that of the member to be charged. Therefore, in the present invention, the electrical resistance value of the charging member close to the actual charging time was obtained by the resistance measuring method as shown in FIG.

It is an important point to reduce the unevenness of the resistance value in the circumferential direction of the charging member as in the equation of the present invention to ensure the uniformity of the image density. When the charging member is in the form of a roller, the rotation is driven by the rotation of the photosensitive drum,
Alternatively, if the roller is driven and rotated, if there is a resistance value unevenness in the circumferential direction of the charging roller, the unevenness appears as charging potential unevenness. In addition, the resistance value unevenness in the circumferential direction of the charging roller can be measured by using the resistance measuring device of FIG.

In a low-temperature, low-humidity environment with a temperature of 15 ° C. and a humidity of 10%, when the measurement voltage DC = −500 V, 5 × 1
If 0 ⁷ Omega following electric resistance of the charging member, the temperature 15 ℃
A stable surface potential of the member to be charged can be obtained in an environment of 10% / humidity of 32.5 ° C./80% of humidity, so that an image defect does not occur due to environmental fluctuation of the electrical resistance of the charging member. Normally, the electrical resistance of the charging member has the largest value in a low-temperature and low-humidity environment. Therefore, it is necessary to control the electrical resistance in a low-temperature and low-humidity environment in order to obtain a good image.
On the other hand, when the electric resistance of the charging member exceeds 5 × 10 ⁷ Ω,
The supply of the current required for charging cannot be made in time, which causes a reduction in the charging efficiency. To compensate for this, a high voltage must be applied to the charging member, but this is not a practical measure because it leads to an increase in power supply capacity.

Further, if the static friction coefficient of the binder resin of the surface layer of the charging member is 0.50 or less, dirt hardly adheres to the surface of the charging member, and poor charging due to dirt on the charging member does not occur. Enables multiple prints.

Further, by designing the surface roughness of the charging member to have a ten-point average surface roughness (Rz) of 10 μm or less, it is possible to prevent the occurrence of uneven charging due to unevenness on the surface of the charging member and to achieve uniformity. It enables a proper charging.

Next, a schematic configuration of the image forming apparatus of the present invention will be described.

(1) Image Forming Apparatus FIG. 1 is a schematic configuration diagram of an example of an image forming apparatus according to the present invention. The image forming apparatus of this example is a reversal developing type apparatus using a transfer type electrophotography.

Reference numeral 1 denotes a rotating drum type electrophotographic photosensitive member as an image carrier, which is rotated at a predetermined peripheral speed (process speed) in the direction of an arrow.

Reference numeral 2 denotes a charging roller (conductive roller) serving as a photosensitive member charging means, which is brought into contact with the photosensitive member 1 with a predetermined pressing force. In this embodiment, the charging roller rotates following the rotation of the photosensitive member 1. . A predetermined DC voltage (in this case, -1200 in this case) is supplied from the charging bias applying power source S1 to the charging roller 2.
V), the surface of the rotating photoconductor 1 is uniformly charged to a predetermined polarity potential (dark potential -600 V) by a contact charging method or a DC charging method.

Reference numeral 3 denotes an exposure unit, for example, a laser beam scanner. Exposure L corresponding to the target image information is performed on the uniformly charged surface of the rotating photoreceptor 1 by the exposing means 3 so that the potential of the exposed light portion on the charged surface of the photoreceptor (bright portion potential -120 V). Is selectively reduced (decay)
As a result, an electrostatic latent image is formed.

Reference numeral 4 denotes a reversal developing means, which selectively adheres a toner (negative toner) charged to the same polarity as the charged polarity of the photoreceptor to the exposed light portion of the electrostatic latent image on the photoreceptor surface to form an electrostatic image. Visualize the latent image as a toner image.

Reference numeral 5 denotes a transfer roller as transfer means.
The transfer nip portion is formed by contacting the photoconductor 1 with a predetermined pressing force, and rotates at a peripheral speed substantially equal to the rotation peripheral speed of the photoconductor in the forward direction with the rotation of the photoconductor. Further, a transfer voltage having a polarity opposite to the charge polarity of the toner is applied from the transfer bias application power source S2. The transfer material P is fed to the transfer nip from a feed mechanism (not shown) at a predetermined control timing.
The back surface of the sheet transfer material P is charged by the transfer roller 5 to which the transfer voltage is applied to a polarity opposite to the charge polarity of the toner, so that the toner image on the photoconductor 1 surface side in the transfer nip portion is transferred to the transfer material P. It is electrostatically transferred to the front side.

The transfer material to which the toner image has been transferred at the transfer nip portion is separated from the surface of the rotating photoreceptor, introduced into a toner image fixing means (not shown), subjected to a toner image fixing process, and output as an image formed product. Is done. In the case of the double-sided image forming mode or the multiple image forming mode, this image-formed product is introduced into a recirculation transport mechanism (not shown) and is again introduced into the transfer nip portion.

Residues on the photoreceptor such as transfer residual toner are as follows:
It is collected from the photoreceptor by cleaning means 6 such as a blade type.

(2) Charging Roller For example, the charging member has a roller shape as shown in FIG. 2, and has a conductive support 2a, an elastic layer 2b integrally formed on the outer periphery thereof, and an outer periphery of the elastic layer. The formed resistance layer 2c
And a surface layer 2d formed on the outer periphery thereof.

FIG. 3 shows another configuration of the charging member of the present invention. As shown in FIG. 3, the charging member may be a two-layer structure including an elastic layer 2b and a surface layer 2d, or a four-layer structure in which a second resistance layer 2e is provided between the resistance layer 2c and the surface layer 2d. The above may be formed on a conductive support.

The conductive support 2a used in the present invention comprises:
Round bars of metal materials 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. . Also, the charging roller 2
Elastic layer 2 to ensure uniform adhesion between
In many cases, b is formed into a shape in which the center is thickest by polishing and becomes thinner toward both ends, that is, a so-called crown shape. A generally used charging roller 2 applies a predetermined pressing force to both ends of a conductive support 2a to apply a photosensitive drum 1
Since the pressing force at the central portion is small and the pressure at both ends is large, there is no problem if the straightness of the charging roller 1 is sufficient. Density unevenness may occur in the image corresponding to the copy. The crown shape is formed to prevent this.

The conductivity of the elastic layer 2b is such that a conductive agent having an electron conducting mechanism such as carbon black, graphite and a conductive metal oxide and an ion conductive material such as an alkali metal salt and a quaternary ammonium salt are contained in an elastic material such as rubber. It is preferable to adjust to less than 10 ⁸ Ωcm by appropriately adding a conductive agent having a mechanism.

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, and further polyamide resins,
Polyurethane resins and silicone resins are also included.

In order to achieve the electrical characteristics of the present invention, it is particularly preferable to use a medium-resistance polar rubber (for example, epichlorohydrin rubber, NBR, CR and urethane rubber) or a polyurethane resin as the elastic material. These polar rubbers and polyurethane resins are considered to have a small amount of conductivity due to moisture and impurities in the rubber and the resin, and these conductive mechanisms are considered to be ionic conduction. Their own resistance values change little with the applied voltage. Therefore, if these polar rubbers or polyurethane resins are used as the material of the elastic layer, a charging member with little voltage dependency can be obtained. However, an elastic layer was formed without adding any conductive agent to these polar rubbers or polyurethane resins, and the obtained charging member had a high resistance value in a low-temperature and low-humidity environment (L / L) and exceeded 10 ⁸ Ωcm. Therefore, a high voltage must be applied to the charging member.

Therefore, in the L / L environment, the resistance of the charging member becomes less than 10 ⁸ Ωcm, and the conductive agent having an electronic conductive mechanism or the conductive agent having an ionic conductive mechanism so as to satisfy the formula of the present invention. Is preferably adjusted by appropriately adding As a result of our intensive studies, it has been found that the voltage dependence can be reduced when the resistance is adjusted by adding a conductive agent having an ionic conduction mechanism. However, a conductive agent having an ionic conduction mechanism has a small effect of lowering the resistance value, and particularly has a small effect in an L / L environment. For this reason, it is preferable to adjust the resistance by adding a conductive agent having an electronic conductive mechanism in addition to the addition of a conductive agent having an ionic conductive mechanism.

Examples of the conductive agent having an electron conductive mechanism include a layered compound having an irregular shape, whiskers and graphite, and among them, an elastic layer to which graphite is added is particularly preferable.

A foam formed by foaming these elastic materials may be used for the elastic layer 2b.

Since the resistance layer 2c is formed at a position in contact with the elastic layer, the resistance layer 2c is provided for the purpose of preventing bleed-out of a softening oil, a plasticizer, or the like contained in the elastic layer to the surface of the charging member. Provided for the purpose of adjusting the overall electric resistance.

The material constituting the resistance layer used in the present invention includes, for example, epichlorohydrin rubber, NBR, polyolefin-based thermoplastic elastomer, urethane-based thermoplastic elastomer, polystyrene-based thermoplastic elastomer, fluororubber-based thermoplastic elastomer, polyester-based thermoplastic elastomer Examples include thermoplastic elastomers, polyamide thermoplastic elastomers, polybutadiene thermoplastic elastomers, ethylene vinyl acetate thermoplastic elastomers, polyvinyl chloride thermoplastic elastomers, and chlorinated polyethylene thermoplastic elastomers. These materials may be used alone or as a mixture of two or more kinds, and may be a copolymer.

The resistance layer 2c used in the present invention 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 required to express conductivity and semi-conductivity.
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, the surface layer 2d is characterized in that the binder resin of the surface layer has a coefficient of static friction of 0.50 or less. In the measurement of the static friction coefficient in the present invention, a coating film similar to the material constituting the surface layer is formed on an aluminum sheet to obtain a surface layer sample sheet, and a static friction coefficient measuring device; HEIDON Tribogear Muse TYPE:
941 "manufactured by Shinto Kagaku Co., Ltd.", which was defined as the static friction coefficient of the binder resin on the surface layer of the charging member.

As a result of our intensive studies, it has been found that when the surface layer of the charging member has the above-mentioned physical properties, the toner hardly adheres to the surface of the charging roller. And no fogging occurs on the image. Further, it was found that even in a low-temperature and low-humidity environment where image fogging is likely to occur due to toner adhesion, image fogging does not occur even when the total number of printed sheets increases. If the coefficient of static friction exceeds 0.50, the releasability of the surface of the charging member becomes small, so that the transfer residual toner that cannot be completely collected by the cleaning unit easily adheres, which causes deterioration of image quality. In particular, it causes deterioration of image quality in a low-temperature and low-humidity environment. Further, the surface layer 2d constitutes the surface of the charging member, and should not be made of a material composition that comes into contact with the photoreceptor that is the charged member and that contaminates the photoreceptor.

Further, when a pinhole occurs in the surface of the charged member, a large amount of current flows through the pinhole, so that the output voltage of the power supply 3 is reduced, and charging failure occurs in the entire nip direction of the charging roller 2. It is provided for the purpose of preventing occurrence.
The resistance value of the surface layer is 10 ⁴ to 10 ¹⁵ Ωcm in order to prevent a large amount of current from flowing through a pinhole generated in the member to be charged.
The degree is preferred.

Surface layer 2 for exhibiting the characteristics of the present invention
As the material of d, for example, fluorine resin, polyamide resin, acrylic resin, polyurethane resin, silicone resin, butyral resin, styrene-ethylene / butylene-
An olefin copolymer (SEBC) and an olefin-ethylene-butylene-olefin copolymer (CEBC) are exemplified. In addition, silicone oil may be added to these resins for the purpose of reducing the coefficient of static friction.

Various conductive agents (conductive carbon, graphite, conductive tin oxide, conductive titanium oxide,
Copper, aluminum, nickel, iron powder, alkali metal salts, ammonium salts, 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.

Ten-point average surface roughness (Rz) of the charging roller
Is not more than 10 μm.

When the charging roller of the present invention is used, if the surface of the charging roller is rough, uneven charging on the surface may cause slight charging unevenness, resulting in an image defect. Alternatively, the photoconductor surface may be eroded (e.g., scraped). Therefore, the surface of the charging roller is preferably smoother, and the ten-point average surface roughness (Rz) in the standard of JIS B0601 surface roughness is preferably 10 μm or less, more preferably 4 μm or less.

[0054]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to Examples.

(Example 1) A charging roller as a charging member of the present invention was prepared in the following manner.

Epichlorohydrin rubber 100 parts by weight Quaternary ammonium salt 2 parts by weight Graphite 20 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 adjusted to 10 by 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 with a closed mixer cooled to 20 ° C. to prepare a raw material compound. To this compound were added 1 part by weight of sulfur as a vulcanizing agent, 1 part by weight of Noxerer DM and 0.5 part by weight of Noxerer TS as a vulcanization accelerator per 100 parts by weight of raw material epichlorohydrin rubber, and cooled to 20 ° C. Knead with a roll machine for 10 minutes. The obtained compound is molded by an extruder so as to form a roller around a stainless steel support having a diameter of 6 mm, and then subjected to heat vulcanization molding, followed by polishing treatment to an outer diameter of 12 mm to form an elastic layer. Obtained.

A resistance layer as shown below was formed on the elastic layer by coating. As a material for the resistance layer 2c, 100 parts by weight of epichlorohydrin rubber and 0.5 parts by weight of a quaternary ammonium salt are dispersed and dissolved in a toluene solvent to prepare a coating for the resistance layer. This coating material was applied on the elastic layer 2b by dipping to form a 100 μm-thick resistive layer 2c.

Further, a surface layer 2d shown below was coated on the resistance layer 2c. As a material for the surface layer 2d, a fluororesin copolymer obtained by copolymerizing fluoroolefin (tetrafluoride type), hydroxyalkyl vinyl ether and vinyl carboxylate is used.
Using a paint obtained by adding 5 parts by weight of isocyanate (HDI) to 00 parts by weight (solids content: 50% by weight), the coating is applied by a dipping method to form a surface layer having a thickness of 3 μm to form a roller. A charging member was obtained.

An aluminum sheet was coated with the same coating material as the coating material on which the surface layer was formed to obtain a surface layer binding resin sample sheet for measuring a static friction coefficient.

The static friction coefficient of the surface layer sample sheet was measured using a static friction coefficient measuring instrument: HEIDON Tribogear Muse TYPE: 941 “manufactured by Shinto Kagaku Co., Ltd.” The coefficient of static friction was defined as the average of the values measured at any five points on the sample sheet. The coefficient of static friction of the surface layer of this example was 0.10.

The ten-point average surface roughness (R) of the charging roller surface
z) was 2.3 μm.

“Measurement of Resistance of Charging Roller Evaluation of Voltage Dependence” The resistance of the charging member (charging roller) is measured in an environment of a temperature of 15 ° C. and a humidity of 10% using an apparatus as shown in FIG. In this contact charging device shown in FIG. 1, the surface moving speed of the cylindrical electrode, the pressing force of the charging member against the cylindrical electrode, and the like are all the same except that a conductive cylindrical electrode having the same shape as the photosensitive drum is used. In the same manner as in Example 1, a DC voltage was applied from an external power supply, and the resistance of the charging roller was determined from the current value flowing at that time. As a result, in the charging roller of the present embodiment, R ₁ (when −50 V is applied) = 3.08 × 10 ⁶ Ω R ₂ (when −1000 V is applied) = 0.45 × 10 ⁶ Ω, and the rate of change A is: Since A = 6.8, the condition of the formula of the present invention is satisfied. In addition, the resistance value unevenness at that time was also 3.
0 or less, which satisfies the condition of the formula of the present invention.

The electric resistance R of the charging roller in an environment of a temperature of 15 ° C. and a humidity of 10% was R (when -500 V was applied) = 0.91 × 10 ⁶ Ω.

"Evaluation of Image When Only DC Voltage Is Applied to Charging Roller" The charging roller obtained above was attached to the electrophotographic image forming apparatus shown in FIG. 1 and environment 1 (temperature 23 ° C./humidity 55 %), Environment 2 (temperature 32.5 ° C./humidity 80%), and environment 3 (temperature 15 ° C./humidity 10%), images were taken out, and horizontal whiteness caused by local charging unevenness of the charging roller was observed. Image evaluation was performed on the occurrence of streaks and white spots. Table 1 shows the results. However, the surface potential V _D of the photosensitive member has output an image changing in each environment applied voltage so that the vicinity of -600 V. In the table, ◎ indicates that the obtained image was excellent, ○ indicates good, Δ indicates practical use, and × indicates bad.

"Evaluation of Image Fogging due to Adhesion of Toner on Charging Roller" The charging roller obtained above was attached to the electrophotographic image forming apparatus shown in FIG.
Environment 3 (temperature 32.5 ° C / humidity 8)
0%) and Environment 3 (temperature: 15 ° C./humidity: 10%).
By observing the obtained image visually, the toner adhered to the charging roller, and the occurrence of fogging on the printing paper due to the toner was evaluated. Table 2 shows the results. In the table, ◎ indicates that the obtained image was excellent, ○ indicates good, Δ indicates practical use, and × indicates bad.

As a result, a good image was obtained from the beginning in all environments, and an image which was almost the same as the initial image was obtained even after outputting 20,000 sheets of images.

(Example 2) A charging roller as a charging member of the present invention was prepared in the following manner.

NBR 100 parts by weight Quaternary ammonium salt 3 parts by weight Graphite 25 parts by weight Calcium carbonate 30 parts by weight Zinc oxide 5 parts by weight Fatty acid 2 parts by weight
After kneading for 15 minutes, 15 parts by weight of 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 by an extruder so as to form a roller around a stainless steel support having a diameter of 6 mm, and then subjected to heat vulcanization molding, followed by polishing treatment to an outer diameter of 12 mm to form an elastic layer. Obtained.

On the above 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 elastomer and 1 part by weight of lithium perchlorate are dispersed and dissolved in a methyl ethyl ketone (MEK) solvent to prepare a coating for the resistance layer. This paint is applied on the elastic layer 2b by dipping to form a resistive layer 2c having a thickness of 100 μm.
Was formed by coating.

Further, the surface layer 2 shown below is formed on the resistance layer 2c.
d was coated. As a material for forming the surface layer 2d, a fluororesin copolymer obtained by copolymerizing fluoroolefin (trifluoride type) and vinyl carboxylate is used, and 100 parts by weight of a solution thereof (solid content of 50% by weight) is used. ) Was applied by a dipping method using a paint to which 5 parts by weight of isocyanate (HDI) was added to form a surface layer having a thickness of 3 μm to obtain a roller-shaped charging member.

An aluminum sheet was coated with the same coating material as the coating material on which the surface layer was formed to obtain a surface layer binder resin sample sheet for measuring a static friction coefficient. The coefficient of static friction in this example was 0.26.

The electric resistances R ₁ (−50 V applied) and R ₂ (−1000 V applied) of the charging roller are represented by R ₁ =
7.52 × 10 ⁶ Ω, R ₂ = 0.57 × 10 ⁶ Ω,
The change rate A of the resistance value is A = 13.2. These satisfy the conditions of the formula of the present invention. In addition, since the resistance value unevenness in the circumferential direction was 3.0 or less, this also satisfied the condition of the formula of the present invention.

The electric resistance R of the charging roller in an environment of a temperature of 15 ° C. and a humidity of 10% was R (when -500 V was applied) = 1.51 × 10 ⁶ Ω.

The ten-point average surface roughness (Rz) of the charging roller surface was 1.8 μm.

This charging roller was evaluated in the same manner as in Example 1, and the results are shown in Tables 1 and 2.

(Example 3) A charging roller as a charging member of the present invention was prepared in the following manner.

100 parts by weight of NBR 15 parts by weight of graphite 5 parts by weight of conductive carbon black 30 parts by weight of calcium carbonate 5 parts by weight of zinc oxide 2 parts by weight of fatty acids 2 parts by weight
After kneading for 15 minutes, 15 parts by weight of 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 wrapped around a stainless steel support having a diameter of φ6 mm and an outer diameter of φ1.
Molded with an extruder so as to form a 2 mm roller,
After heat vulcanization molding, the outer diameter of the rubber part is central φ12mm,
An elastic layer was obtained by polishing to form a crown shape having both ends of φ11.9 mm.

On the above 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 epichlorohydrin rubber and 0.5 parts by weight of a quaternary ammonium salt are dispersed and dissolved in a toluene solvent to prepare a coating for the resistance layer. This coating material was applied on the elastic layer 2b by dipping to form a 100 μm-thick resistive layer 2c.

Further, a surface layer 2d shown below was formed on the resistance layer 2c by coating. Polyvinyl butyral resin is used as a material of the surface layer 2d, and its ethanol solution 100
A roller-shaped charging member is formed by adding 40 parts by weight of conductive titanium oxide to the parts by weight (solid content: 50% by weight) and applying a coating material by a dipping method to form a surface layer having a thickness of 3 μm. I got

The same binder resin (butyral resin) as used for forming the surface layer was formed into a paint, and the clear paint was used to coat it on an aluminum sheet to obtain a surface layer binder resin sample sheet for measuring a static friction coefficient. . The coefficient of static friction in this example was 0.29.

The electric resistance values R ₁ (−50 V applied) and R ₂ (−1000 V applied) of the charging roller are represented by R ₁ =
2.96 × 10 ⁷ Ω, R ₂ = 0.47 × 10 ⁶ Ω,
The rate of change A of the resistance value is A = 63.0, which satisfies the condition of the formula of the present invention. Moreover, the resistance value unevenness in the circumferential direction is 3.0 or less, which satisfies the condition of the formula of the present invention.

The electrical resistance R of the charging roller in an environment of a temperature of 15 ° C. and a humidity of 10% was R (when -500 V was applied) = 1.09 × 10 ⁶ Ω.

The ten-point average surface roughness (Rz) of the charging roller surface was 2.0 μm.

The charging roller was evaluated in the same manner as in Example 1, and the results are shown in Tables 1 and 2.

(Example 4) A charging roller as a charging member of the present invention was prepared in the following manner.

Epichlorohydrin rubber 100 parts by weight Quaternary ammonium salt 2 parts by weight Graphite 20 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. 10
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 with a closed mixer cooled to 20 ° C. to prepare a raw material compound. To this compound were added 1 part by weight of sulfur as a vulcanizing agent, 1 part by weight of Noxerer DM and 0.5 part by weight of Noxerer TS as a vulcanization accelerator per 100 parts by weight of raw material epichlorohydrin rubber, and cooled to 20 ° C. Knead with a roll machine 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 support having a diameter of 6 mm.

A resistance layer as shown below was coated on the elastic layer. As a material of the resistance layer 2c, 100 parts by weight of epichlorohydrin rubber is dispersed and dissolved in a toluene solvent to prepare a coating for the resistance layer. This paint is applied on the elastic layer 2b by dipping to form a resistive layer 2 having a thickness of 80 μm.
c was coated.

Further, a surface layer 2d shown below was formed on the resistance layer 2c by coating. As a material of the surface layer 2c, a paint containing 100 parts by weight of a polyester urethane elastomer and 30 parts by weight of tin oxide is applied by dipping to form a surface layer having a thickness of 3 μm to form a roller-shaped charging member. Obtained.

The same binder resin (polyester urethane elastomer resin) as used for forming the surface layer was formed into a paint, and the clear paint was used to coat it on an aluminum sheet. And The coefficient of static friction in this example was 0.28.

The electric resistance values R ₁ (−50 V applied) and R ₂ (−1000 V applied) of the charging roller are represented by R ₁ =
3.66 × 10 ⁶ Ω, R ₂ = 0.72 × 10 ⁶ Ω,
The rate of change A of the resistance value is A = 5.1, which satisfies the condition of the formula of the present invention. Moreover, the resistance value unevenness in the circumferential direction is 3.0 or less, which satisfies the condition of the formula of the present invention.

The electric resistance R of the charging roller in an environment of a temperature of 15 ° C. and a humidity of 10% was R (when -500 V was applied) = 1.03 × 10 ⁶ Ω.

The ten-point average surface roughness (Rz) of the charging roller surface was 2.6 μm.

This charging roller was evaluated in the same manner as in Example 1, and the results are shown in Tables 1 and 2.

Comparative Example 1 In Comparative Example 1, a charging roller was prepared by the following method.

EPDM 100 parts by weight Conductive carbon black 37 parts by weight Zinc oxide 5 parts by weight Fatty acid 2 parts by weight
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. The compound rubber EPDM100
0.5 part by weight of sulfur as a vulcanizing agent, 1 part by weight of MBT as a vulcanization accelerator, 1 part by weight of TMTD and 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. The obtained compound was placed around a stainless steel support having a diameter of 6 mm and an outer diameter of 12 mm.
An elastic layer was obtained by heat vulcanization molding using a press molding machine so as to form a roller having a diameter of 2 mm.

On the above 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. This paint is applied on the elastic layer 2b by dipping to form a resistive layer 2c having a thickness of 100 μm.
Was formed by coating.

Further, the following surface layer 2d was formed on the resistance layer 2c. As a material for the surface layer 2d, 100 parts by weight of SEBS (styrene-ethylene / butylene-styrene) and 10 parts by weight of conductive carbon black are dispersed and dissolved in a toluene solvent to prepare a coating for the surface layer. The coating material was applied by a dipping method to form a 3 μm-thick surface layer so as to obtain a roller-shaped charging member.

[0098] The same binder resin (S
EBS) was formed into a paint, and the clear paint was coated on an aluminum sheet to obtain a sample sheet of a surface layer binder resin for measuring a static friction coefficient. The coefficient of static friction of Comparative Example 1 was 0.62.

The electric resistances R ₁ (−50 V applied) and R ₂ (−1000 V applied) of the charging roller are represented by R ₁ =
3.26 × 10 ⁸ Ω, R ₂ = 6.00 × 10 ⁴ Ω,
The change rate A of the resistance value is A = 5433, which is out of the condition of the present invention. In addition, the resistance unevenness in the circumferential direction is 3.8, which does not satisfy the condition of the formula of the present invention.

The electrical resistance R of the charging roller in an environment of a temperature of 15 ° C. and a humidity of 10% was R (when -500 V was applied) = 0.28 × 10 ⁶ Ω.

The ten-point average surface roughness (Rz) of the surface of the charging roller was 1.9 μm.

The charging roller was evaluated in the same manner as in Example 1, and the results are shown in Tables 1 and 2.

The image output by the image forming apparatus using the charging roller had horizontal white stripes and white spots due to local charging unevenness. Further, in the durability test for image output on a plurality of sheets, unevenness in image density due to toner adhesion occurred.

[0104]

[Table 1]

[0105]

[Table 2]

[0106]

As described above, according to the present invention, in a charging member in which only a DC voltage is applied to the charging member to charge the charged member by a contact charging method, the surface of the charged member such as a photoreceptor is desired. Is not excessively charged to a charge potential higher than or equal to the above, and uniform charging without local charging unevenness can be realized. Therefore, high image quality can be achieved by using the charging member of the present invention in an image forming apparatus. Further, by using the charging member of the present invention in an image forming apparatus,
It is possible to prevent image density unevenness from occurring due to resistance value unevenness in the circumferential direction of the charging roller.

Further, in the image forming apparatus of the present invention, the amount of toner adhered to the surface of the charging roller is small, so that image fogging and image density unevenness caused by toner adhesion do not occur. As a result, the total number of printed sheets of the image forming apparatus is greatly increased, and the durability stability is improved. Further, even in a low-temperature and low-humidity environment, image fogging caused by toner adhesion does not occur.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of an image forming apparatus of the present invention.

FIG. 2 is a schematic diagram of a charging roller.

FIG. 3 is a schematic view of another charging roller.

FIG. 4 is a schematic view of a method for measuring the resistance of a charging member.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Image carrier (electrophotographic photosensitive member) 2 Charging member (charging roller) 3 Exposure means 4 Developing means 4a Developing roller 4b Transport roller 4c Regulator blade 5 Transfer means (transfer roller) 6 Cleaning means S1, S2, S3 P Transfer material 11 Cylindrical electrode (metal roller) 12 Fixed resistor 13 Tester

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2H003 BB11 CC05 EE11 3J103 AA02 AA14 AA32 AA71 AA85 FA30 GA02 GA57 GA58 GA60 HA03 HA05 HA20 HA33 HA37 HA48 HA53

Claims (6)

[Claims] A charging member configured to apply a voltage to the charging member to perform a charging process on a member to be charged by a contact charging method, wherein the charging member forms a conductive elastic layer on a conductive support; In a charging member having a laminated structure in which at least a coating layer is formed on the conductive elastic layer, a resistance value between a voltage application portion of the charging member and a portion in contact with the member to be charged is set to a DC voltage of -50 to-. When measured at 1000 V, the resistance value of the charging member when the measured voltage is DC voltage V ₁ = −50 V is R ₁ , the resistance value when DC voltage V ₂ = −1000 V is R ₂ , and R ₁ When ≧ R ₂ , when the rate of change A of the resistance value of the charging member is expressed as R ₁ / R ₂ , A = (R ₁ / R ₂ ) <100. The resistance unevenness in the circumferential direction of the charging member is represented by (maximum circumferential resistance Rmax) / ( It said charging member, wherein the direction resistance minimum value Rmin) ≦ 3.0 ... is. 2. The charging member has a temperature of 15 ° C./humidity of 10 ° C.
2. The charging member according to claim 1, wherein the resistance value when the measured voltage DC is −500 V is 5 × 10 ⁷ Ω or less. 3. The charging member according to claim 1, wherein the binder resin of the surface layer of the charging member has a static friction coefficient of 0.50 or less. 4. A ten-point average surface roughness (R) of the charging member.
The charging member according to claim 1, wherein z) is 10 μm or less. 5. The charging member according to claim 1, wherein said charging member has a roller shape. 6. At least a member to be charged, a charging member for charging the surface of the member to be charged in contact with the member to be charged, an exposure unit for exposing the surface of the member to be charged charged by the charging member, and the exposure unit And a developing means for visualizing the latent image formed by the above, the charging member forms a conductive elastic layer on a conductive support, and at least on the conductive elastic layer A charging member having a laminated structure formed by forming a coating layer, and when a resistance value between a voltage application portion of the charging member and a portion in contact with the member to be charged is measured at a DC voltage of −50 to −1000 V, The resistance value of the charging member when the measurement voltage is DC voltage V ₁ = −50 V is R ₁ , and the resistance value when the measurement voltage is DC voltage V ₂ = −1000 V is R _2.
When R ₁ ≧ R ₂ , and the rate of change A of the resistance value of the charging member is expressed as R ₁ / R ₂ , A = (R ₁ / R ₂ ) <100. The image forming apparatus is characterized in that the non-uniform resistance value in the circumferential direction of the charging member is (maximum circumferential resistance Rmax) / (minimum circumferential resistance Rmin) ≦ 3.0.