JP6641828B2 - Charging member, image forming apparatus and process cartridge - Google Patents

Description

  The present invention relates to a charging member, an image forming apparatus, and a process cartridge.

  2. Description of the Related Art In recent years, electrophotographic image formation has been widely used in image forming apparatuses such as copying machines and laser printers.

  In an image forming apparatus using an electrophotographic method, for example, first, the surface of an electrophotographic photosensitive member is charged by a charging device, and an electrostatic latent image is formed by a laser beam or the like that modulates an image signal. The toner image developed by developing the electrostatic latent image on the surface of the electrophotographic photoreceptor is formed. Then, for example, a reproduced image is obtained by electrostatically transferring the toner image to a recording material such as recording paper via an intermediate transfer member or directly, and fixing the toner image to the recording material.

For example, in Patent Document 1, a conductive foam layer and a resistance adjustment layer are laminated in this order on the outer periphery of a shaft body, and furthermore, both ends in the axial direction between the conductive foam layer and the resistance adjustment layer. A low-resistance layer is provided, and the following formulas (1) and (2) are satisfied.
0.01 ≦ R2 / R1 ≦ 0.9 (1)
1 × 10 ⁴ ≦ R1 ≦ 1 × 10 ⁶ (2)
Here, R1 [Ω · cm]: Volume electric resistance of the conductive foam layer, R2 [Ω · cm]: Volume electric resistance of the low resistance layer

JP 2009-210981 A

  An object of the present invention is to provide a charging member having a conductive substrate, a conductive elastic layer disposed on the conductive substrate, and a conductive surface layer disposed on the conductive elastic layer, from 1 MHz to 1 mHz. When the AC impedance of the conductive elastic layer and the charging member is measured by the AC impedance method in the range up to, at least one of the frequencies at which the phase difference θ in the conductive elastic layer and the charging member is minimal is less than 63 Hz or exceeds 1600 Hz. The generation of minute color lines from the initial stage of image formation, which occurs when charging is performed by a contact charging method to which only a DC voltage is applied (hereinafter, sometimes referred to as a “DC contact charging method”), is suppressed as compared with the case of The purpose of the present invention is to provide a charging member.

  The above problem is solved by the following means.

< 1 >
A conductive substrate, and a conductive elastic layer disposed on the conductive substrate, and a conductive surface layer disposed on the conductive elastic layer,
When the AC impedance of the conductive elastic layer and the charging member is measured by the AC impedance method in the range of 1 MHz to 1 mHz, the frequency at which the phase difference θ in the conductive elastic layer and the charging member is minimized is 63 Hz or more. A charging member having a frequency of 1600 Hz or less.

< 2 >
The charging member according to < 1 > , wherein the conductive surface layer contains polyamide particles, carbon black, and dimethylpolysiloxane.

< 3 >
A charging device comprising the charging member according to < 1 > or < 2 > .

< 4 >
An electrophotographic photoreceptor,
A charging device having the charging member according to < 1 > or < 2 > , and charging a surface of the electrophotographic photosensitive member by a contact charging method of applying only a DC voltage to the charging member;
An electrostatic latent image forming apparatus for forming an electrostatic latent image on the surface of the charged electrophotographic photosensitive member,
A developing device that forms a toner image by developing an electrostatic latent image formed on the surface of the electrophotographic photoreceptor with a developer containing a toner;
A transfer device for transferring the toner image to a surface of a recording medium,
An image forming apparatus comprising:

< 5 >
The image forming apparatus according to < 4 > , wherein the total thickness of the charge transporting surface layer of the electrophotographic photosensitive member is 20 μm or more and 50 μm or less.

< 6 >
The image forming apparatus according to < 4 > or < 5 > , wherein the image forming apparatus does not include a static eliminator for eliminating residual charges on the surface of the electrophotographic photosensitive member.

< 7 >
A charging device that has the charging member according to < 1 > or < 2 > and charges a surface of the electrophotographic photosensitive member by a contact charging method of applying only a DC voltage to the charging member;
A process cartridge that is attached to and detached from the image forming apparatus.

According to the invention according to < 1 > or < 2 > , the conductive substrate, the conductive elastic layer disposed on the conductive substrate, and the conductive surface layer disposed on the conductive elastic layer The frequency at which the phase difference θ between the conductive elastic layer and the charging member is minimized when the AC impedance of the conductive elastic layer and the charging member is measured by the AC impedance method in the range of 1 MHz to 1 mHz in the charging member having A charging member that suppresses the generation of minute color lines from the initial stage of image formation, which occurs when at least one of the above is less than 63 Hz or exceeds 1600 Hz, when charging is performed by the DC contact charging method.

According to the invention according to < 3 > , it has a conductive base material, a conductive elastic layer disposed on the conductive base material, and a conductive surface layer disposed on the conductive elastic layer. When the AC impedance of the conductive elastic layer and the charging member is measured by the AC impedance method in the range from to 1 mHz, at least one of the frequencies at which the phase difference θ in the conductive elastic layer and the charging member is minimal is less than 63 Hz or There is provided a charging device that suppresses the generation of minute color lines from the initial stage of image formation as compared with a case where a charging member of 1600 Hz or more is provided.

According to the invention according to < 4 > , the charging device of the DC contact charging system comprises: a conductive base; a conductive elastic layer disposed on the conductive base; and a conductive elastic layer disposed on the conductive elastic layer. When the AC impedance of the conductive elastic layer and the charging member is measured by the AC impedance method in the range of 1 MHz to 1 mHz, the phase difference θ in the conductive elastic layer and the charging member is extremely small. An image forming apparatus is provided that suppresses the generation of minute color lines from the beginning of image formation as compared with the case where a charging member having at least one of the following frequencies is lower than 63 Hz or higher than 1600 Hz.

According to the invention according to < 5 > , the charging device of the DC contact charging system includes: a conductive base; a conductive elastic layer disposed on the conductive base; and a conductive elastic layer disposed on the conductive elastic layer. When the AC impedance of the conductive elastic layer and the charging member is measured by the AC impedance method in the range of 1 MHz to 1 mHz, the phase difference θ in the conductive elastic layer and the charging member is extremely small. In comparison with the case where at least one of the following frequencies is provided with a charging member of less than 63 Hz or more than 1600 Hz, even if the electrophotographic photosensitive member having a total thickness of the surface layer having a charge transporting property of 20 μm or more and 50 μm or less is provided from the beginning of image formation. And an image forming apparatus for suppressing the generation of minute color lines.

According to the invention according to < 6 > , the charging device of the DC contact charging method includes a conductive base, a conductive elastic layer disposed on the conductive base, and a conductive elastic layer disposed on the conductive elastic layer. When the AC impedance of the conductive elastic layer and the charging member is measured by the AC impedance method in the range of 1 MHz to 1 mHz, the phase difference θ in the conductive elastic layer and the charging member is extremely small. The generation of minute color lines from the early stage of image formation without providing a static eliminator for removing residual charges on the surface of the electrophotographic photosensitive member, compared to a case where at least one of the following frequencies is provided with a charging member of less than 63 Hz or more than 1600 Hz. An image forming apparatus is provided which suppresses the image formation.

According to the invention according to < 7 > , the charging device of the DC contact charging method comprises: a conductive base; a conductive elastic layer disposed on the conductive base; and a conductive elastic layer disposed on the conductive elastic layer. When the AC impedance of the conductive elastic layer and the charging member is measured by the AC impedance method in the range of 1 MHz to 1 mHz, the phase difference θ in the conductive elastic layer and the charging member is extremely small. A process cartridge is provided which suppresses the generation of minute color lines from the beginning of image formation as compared with the case where a charging member having at least one of the following frequencies is less than 63 Hz or more than 1600 Hz.

FIG. 2 is a schematic diagram illustrating an example of a configuration of a charging member according to the embodiment. FIG. 1 is a schematic diagram illustrating an example of a basic configuration of an image forming apparatus according to an embodiment. FIG. 4 is a schematic diagram illustrating another example of the basic configuration of the image forming apparatus according to the embodiment. FIG. 2 is a schematic diagram illustrating an example of a basic configuration of a process cartridge according to the embodiment. FIG. 3 is a schematic Bode diagram showing a relationship between a frequency and a phase difference θ obtained by an AC impedance method.

  Hereinafter, embodiments will be described in detail. In the drawings, the same or corresponding portions have the same reference characters allotted, and duplicate description may be omitted.

[Charging member]
The charging member according to the present embodiment has a conductive base material, a conductive elastic layer disposed on the conductive base material, and a conductive surface layer disposed on the conductive elastic layer. When the AC impedance of the conductive elastic layer and the charging member is measured by the AC impedance method in the range of 1 MHz to 1 mHz, the frequency at which the phase difference θ in the conductive elastic layer and the charging member is minimum is 63 Hz or more and 1600 Hz or less. It is.

  In the charging member according to the exemplary embodiment, the above configuration suppresses the generation of minute color lines from the beginning of image formation. The reason is presumed as follows.

In the current field of electrophotography, a long-life and inexpensive device is required. For example, a charging device of a DC contact charging system (a contact charging system to which only a DC voltage is applied) is employed. However, when a charging device of a DC contact charging system (a contact charging system to which only a DC voltage is applied) is employed, a minute color line may be generated as an image defect from the beginning of image formation.
The occurrence of the minute color line depends on the magnitude of the frequency of the discharge phenomenon (post-discharge) occurring immediately after the contact portion between the electrophotographic photosensitive member (hereinafter also referred to as “photosensitive member”) and the charging member (hereinafter referred to as “discharge frequency”). It is thought that it is caused. In the case of a charging method in which only a direct current is applied, the frequency of discharge immediately after the contact portion between the photoconductor and the charging member is likely to be reduced, and a region that is not sufficiently charged is irregularly generated, and a minute color line may become apparent. . The decrease in the “discharge frequency immediately after the contact between the photoconductor and the charging member”, which causes the generation of the minute color line, is due to the electrical responsiveness between the conductive elastic layer and the conductive surface layer in the charging member. It is considered that the difference is large.

  Therefore, when the AC impedance of the conductive elastic layer and the charging member is measured by the AC impedance method in the range of 1 MHz to 1 mHz, the frequency at which the phase difference θ in the conductive elastic layer and the charging member is minimized is 63 Hz. At least 1600 Hz. Thereby, the electrical responsiveness of the conductive elastic layer alone and the electrical responsiveness of the state in which the conductive elastic layer and the conductive surface layer are stacked are both close to each other. That is, the electrical responsiveness of the conductive elastic layer and the electrical responsiveness of the conductive surface layer are both close, and the electrical response difference is reduced. For this reason, the “discharge frequency immediately after the contact portion between the photosensitive member and the charging member” increases, and the generation of minute color lines is suppressed.

  From the above, it is presumed that the charging member according to the present embodiment suppresses the generation of minute color lines from the beginning of image formation by the above configuration.

In the charging member according to this embodiment, the frequency at which the phase difference θ in the conductive elastic layer and the charging member is minimized is both 63 Hz or more and 1600 Hz or less.
On the other hand, the frequency at which the phase difference θ in the conductive elastic layer is minimized is preferably 63 Hz or more and 500 Hz or less, more preferably 120 Hz or more and 500 Hz or less, from the viewpoint of suppressing generation of minute color lines from the beginning of image formation. Further, the frequency at which the phase difference θ in the charging member is minimized is preferably 300 Hz or more and 1590 Hz or less, more preferably 1000 Hz or more and 1580 Hz or less.

  Further, the difference (absolute value) between the frequency at which the phase difference θ in the conductive elastic layer is minimized and the frequency at which the phase difference θ in the charging member is minimized is a point of suppressing the generation of minute color lines from the beginning of image formation. From this, 0 Hz or more and 1500 Hz or less are preferable, and 0 Hz or more and 1000 Hz or less are more preferable.

  Here, in the Bode diagram showing the relationship between the frequency and the phase difference θ obtained by measuring the AC impedance by the AC impedance method in the range of 1 MHz to 1 mHz, the impedance decreases from the high frequency of 1 MHz to the low frequency of 1 mHz. Toward this point, a phase diagram is drawn in which the phase difference θ decreases once and then rises (see FIG. 5). The frequency at which the phase difference θ becomes the minimum indicates the frequency at which the phase difference θ becomes the smallest when the phase difference θ increases after the decrease (see “Min” in FIG. 5).

  The method for measuring the AC impedance by the AC impedance method is the measurement method described in the column of [AC impedance measurement] described in [Examples]. Then, a Bode diagram is created from the phase difference θ and the frequency obtained by the measurement, and the frequency at which the phase difference θ is minimized is determined.

  In addition, as a method of controlling the frequency at which the phase difference θ in the conductive elastic layer and the charging member is minimized to the above range, 1) a method of adjusting the types and amounts of components of the conductive elastic layer and the conductive surface layer (For example, a method for adjusting the type and amount of the conductive agent, a method for adjusting the type (for example, dimethylpolysiloxane) and the amount of the dispersant), and 2) a method for adjusting the formation conditions of the conductive elastic layer and the conductive surface layer (for example, And a method for adjusting the drying temperature of the surface layer).

Hereinafter, details of the charging member according to the present embodiment will be described.
FIG. 1 shows an example of the configuration of the charging member according to the present embodiment. The charging member shown in FIG. 1 includes a conductive base material 30 formed of a cylindrical or columnar rod-shaped member (shaft), a conductive elastic layer 31 disposed on the outer peripheral surface of the shaft 30, and a conductive elastic layer 31. And a conductive surface layer 32 disposed on the outer peripheral surface of the charging roller 208. The shaft 30 and the conductive elastic layer 31 are adhered, for example, by an adhesive layer (not shown).

  The shape of the charging member according to the exemplary embodiment is not particularly limited, and examples thereof include a roll shape, a brush shape, a belt (tube) shape, and a blade shape. Among these, the roll-shaped charging member described in the present embodiment is preferable, that is, a so-called charging roll form is preferable. Hereinafter, as an example of the charging member according to the present embodiment, a roll-shaped charging member (hereinafter, sometimes referred to as a charging roll) will be mainly described.

In addition, in this specification, conductivity means that the volume resistivity at 20 ° C. is less than 1 × 10 Ωcm, and semiconductivity means that the volume resistivity at 20 ° C. is 1 × 10 Ωcm or more and 1 × 10 ¹⁰ Ωcm. Ωcm or less. The volume resistivity in this specification is a value measured by a TREK volume resistance meter MODEL 152-1 or the like.

  Next, each component of the charging member according to the present embodiment will be described. In the following description, the “conductive base” may be referred to as a “base”, the “conductive elastic layer” may be referred to as an “elastic layer”, and the “conductive surface layer” may be referred to as a “surface layer”.

(Base material)
The base material 30 functions as an electrode and a support member of the charging roll. For example, as a material thereof, a metal or alloy such as iron (free-cutting steel), copper, brass, stainless steel, aluminum, nickel; Iron plated with nickel or the like; a conductive material such as a conductive resin.
The base material 30 is a conductive rod-shaped member, and includes a member (for example, a resin or a ceramic member) in which an outer peripheral surface is plated, a member (for example, a resin or a ceramic member) in which a conductive agent is dispersed, and the like. .
The substrate 30 may be a hollow member (tubular member) or a non-hollow member.

(Elastic layer)
The elastic layer 31 is arranged in a roll shape on the outer peripheral surface of the conductive substrate (shaft) 30.
The elastic layer 31 includes, for example, an elastic material, a conductive agent, and if necessary, other additives.

  As the elastic material, isoprene rubber, chloroprene rubber, epichlorohydrin rubber, butyl rubber, polyurethane, silicone rubber, fluorine rubber, styrene-butadiene rubber, butadiene rubber, nitrile rubber, ethylene propylene rubber, epichlorohydrin-ethylene oxide copolymer rubber, epichlorohydrin-ethylene oxide- Examples include allyl glycidyl ether copolymer rubber, ethylene-propylene-diene terpolymer rubber (EPDM), acrylonitrile-butadiene copolymer rubber (NBR), natural rubber, and a blend rubber thereof. Among them, polyurethane, silicone rubber, EPDM, epichlorohydrin-ethylene oxide copolymer rubber, epichlorohydrin-ethylene oxide-allyl glycidyl ether copolymer rubber, NBR, and a blend rubber thereof are preferably used. These elastic materials may be foamed or non-foamed.

Examples of the conductive agent include an electronic conductive agent and an ionic conductive agent.
Examples of the electronic conductive agent include carbon black such as Ketjen black and acetylene black; pyrolytic carbon, graphite; various conductive metals or alloys such as aluminum, copper, nickel, and stainless steel; tin oxide, indium oxide, and titanium oxide. And various conductive metal oxides such as a tin oxide-antimony oxide solid solution and a tin oxide-indium oxide solid solution;
Examples of the ionic conductive agent include perchlorates and chlorates such as tetraethylammonium and lauryltrimethylammonium; alkali metals such as lithium and magnesium, and perchlorates and chlorates of alkaline earth metals. No.
The conductive agent may be used alone or in combination of two or more.

  Here, specific examples of the carbon black include “Special Black 350”, “Special Black 100”, “Special Black 250”, “Special Black 5”, and “Special Black” manufactured by Orion Engineered Carbons. 4, "Special Black 4A", "Special Black 550", "Special Black 6", "Color Black FW200", "Color Black FW2", "Color Black FW2V", "MONARCH1000" manufactured by Cabot Corporation "MONARCH1300" manufactured by Cabot Corporation, "MONARCH1400" manufactured by Cabot Corporation, "MOGUL-L", and "REGAL400R" manufactured by Cabot Corporation.

  The average particle size of the conductive agent is preferably from 1 nm to 200 nm. The average particle diameter is defined as the average particle diameter by observing the conductive agent with an electron microscope, measuring the diameter of 100 conductive agents, and taking the average.

The amount of the conductive agent added to the elastic layer 31 is not particularly limited. In the case of an electronic conductive agent, the amount is preferably in the range of 1 part by mass to 30 parts by mass, and more preferably 15 parts by mass with respect to 100 parts by mass of the elastic material. More preferably, it is in the range of not less than 25 parts by mass.
On the other hand, in the case of the ionic conductive agent, the amount is preferably in the range of 0.1 to 5.0 parts by mass, and more preferably 0.5 to 3.0 parts by mass with respect to 100 parts by mass of the elastic material. Is more preferable.

  As other additives to be blended in the elastic layer 31, for example, a softener, a plasticizer, a curing agent, a vulcanizing agent, a vulcanization accelerator, an antioxidant, a surfactant, a coupling agent, a filler (silica, A material that can be added to a known elastic layer, such as calcium carbonate, may be used.

  In forming the elastic layer 31, the method and order of mixing the conductive agent, the elastic material, and other components (each component such as a vulcanizing agent and a foaming agent added as necessary) constituting the elastic layer 31 are particularly specified. Although not limited, a general method includes a method in which all components are mixed in advance using a tumbler or a V blender, melt-mixed with an extruder, and extruded.

The thickness of the elastic layer 31 is preferably about 1 mm or more and 10 mm or less, more preferably about 2 mm or more and 5 mm or less.
Further, the volume resistivity of the elastic layer 31 is desirably from 10 ³ Ωcm to 10 ¹⁴ Ωcm.

(Surface layer)
The surface layer 32 is a layer formed mainly for preventing contamination by toner and the like, and is formed by dispersing particles in a binder resin.

  Examples of the binder resin used for the surface layer 32 include a polyamide resin, a urethane resin, a polyester resin, a phenol resin, an acrylic resin, an epoxy resin, and cellulose. Among these, a polyamide resin is preferable. Examples of the polyamide resin include polyamide resins described in a polyamide resin handbook, Osamu Fukumoto (Nikkan Kogyo Shimbun). Among these, alcohol-soluble polyamides are preferable as the polyamide resin, since alcohol-soluble polyamides are preferable, since the contamination of the conductive outermost layer 32 is suppressed and the generation of fine color streaks is easily suppressed, and alkoxymethylated polyamide (alkoxymethylated nylon) is preferable. Is more preferable, and methoxymethylated polyamide (methoxymethylated nylon) is still more preferable.

  The particles contained in the surface layer 32 perform resistance control by using a conductive material, reduce environmental fluctuations in the resistance value of the surface layer 32, obtain stable charging characteristics, and control irregularities on the roll surface. It is used for the purpose of lowering the coefficient of friction with the photoconductor and improving the wear resistance between the photoconductors. Further, an additive or the like can be used for the purpose of improving the adhesiveness with a lower layer (for example, the elastic layer 31) and controlling the dispersion of particles in the binder resin.

The conductive particles preferably have a particle size of 3 μm or less and a volume resistivity of 10 ⁹ Ωcm or less. For example, particles made of a metal oxide such as tin oxide, titanium oxide, zinc oxide, or an alloy thereof, or carbon black can be used.
As other particles, fluorine-based or silicone-based, alumina, silica, or polyamide-based particles can be used, and those having a particle size of 3 μm or more and 10 μm or less are desirable.

  In particular, the conductive particles contained in the surface layer 32 affect the volume resistivity of the charging roll, and the type and content of the particles may be selected according to the target volume resistivity. Usually, conductive particles are blended in the range of 2 to 20 parts by mass with respect to 100 parts by mass of the binder resin contained in the surface layer 32.

The surface layer 32 desirably contains carbon black and polyamide particles as particles and dimethylpolysiloxane as an additive from the viewpoint of suppressing generation of minute color lines.
Examples of the polyamide particles include polyamide resin particles described in Polyamide Resin Handbook, Osamu Fukumoto, 8400, (Nikkan Kogyo Shimbun). Among them, particularly, as the polyamide resin, alcohol-soluble polyamide particles are preferable, alkoxymethylated polyamide particles (alkoxymethylated nylon particles) are more preferable, and methoxymethylated polyamide particles (methoxymethylated nylon particles) are further preferable.

The surface layer 32 is formed by applying a coating liquid (coating liquid for forming a surface layer) containing the above-described binder resin and particles, and an additive that is added as necessary, onto the conductive elastic layer.
As a method for applying the coating solution for forming the surface layer, there are common methods such as a roll coating method, a blade coating method, a wire bar coating method, a spray coating method, a dip coating method, a bead coating method, an air knife coating method, and a curtain coating method. Can be used.

  After applying the coating liquid for forming a surface layer, the coating solution is dried to form a surface layer. The drying temperature is, for example, 80 ° C. or more and 200 ° C. or less.

The thickness of the surface layer 32 is preferably about 5 μm or more and 20 μm or less, more preferably about 7 μm or more and 13 μm or less.
Further, the volume resistivity of the surface layer is desirably from 1 × 10 ³ Ωcm to 1 × 10 ¹⁴ Ωcm.

[Image forming apparatus (and process cartridge)]
The image forming apparatus according to the present exemplary embodiment includes an electrophotographic photoreceptor and the charging member according to the exemplary embodiment. The surface of the electrophotographic photoreceptor is formed by a contact charging method that applies only a DC voltage to the charging member. A charging device for charging; an electrostatic latent image forming device for forming an electrostatic latent image on the charged surface of the electrophotographic photosensitive member; and a static electricity formed on the surface of the electrophotographic photosensitive member by a developer containing toner. The image forming apparatus includes a developing device that develops an electrostatic latent image to form a toner image, and a transfer device that transfers the toner image to a surface of a recording medium.

  The image forming apparatus according to the present embodiment includes a fixing device that fixes a toner image transferred to the surface of a recording medium; direct transfer that directly transfers a toner image formed on the surface of an electrophotographic photosensitive member to a recording medium. -Type device; intermediate transfer in which a toner image formed on the surface of an electrophotographic photosensitive member is primarily transferred to the surface of an intermediate transfer member, and the toner image transferred on the surface of the intermediate transfer member is secondarily transferred to a surface of a recording medium. -Type device; device with a cleaning device for cleaning the surface of the electrophotographic photosensitive member after transfer of the toner image and before charging; electrophotographic photosensitive member for increasing the temperature of the electrophotographic photosensitive member and reducing the relative temperature A known image forming apparatus such as an apparatus having a heating member is applied.

  In the case of an intermediate transfer type device, the transfer device includes, for example, an intermediate transfer body on which a toner image is transferred on the surface, and a primary transfer for primarily transferring the toner image formed on the surface of the image holding body to the surface of the intermediate transfer body. A configuration including a device and a secondary transfer device that secondary-transfers the toner image transferred on the surface of the intermediate transfer member to the surface of the recording medium is applied.

  The image forming apparatus according to the present embodiment may be either a dry developing type image forming apparatus or a wet developing type (developing type using a liquid developer) image forming apparatus.

  In the image forming apparatus according to the present embodiment, for example, the portion including the charging member according to the present embodiment may have a cartridge structure (process cartridge) that is detachably attached to the image forming apparatus. As the process cartridge, for example, a process cartridge including the charging member according to the present embodiment is preferably used. The process cartridge may include, for example, at least one selected from the group consisting of an electrophotographic photosensitive member, an electrostatic latent image forming device, a developing device, and a transfer device, in addition to the charging member according to the exemplary embodiment. Good.

  Hereinafter, an example of the image forming apparatus according to the present embodiment will be described, but the present invention is not limited thereto. The main parts shown in the figure will be described, and the description of the other parts will be omitted.

<First embodiment>
FIG. 2 schematically illustrates a basic configuration of the image forming apparatus according to the first embodiment. The image forming apparatus 200 shown in FIG. 2 is a DC contact charging type charging device that is connected to the electrophotographic photosensitive member 1 and a power supply 209 and charges the electrophotographic photosensitive member 1, and an electrophotographic photosensitive member charged by the charging device. Exposure device 210 (an example of an electrostatic latent image forming device) for exposing 1 to form an electrostatic latent image, and developing the electrostatic latent image formed by exposure device 210 with a developer containing toner A developing device 211 for forming a toner image, a transfer device 212 for transferring the toner image formed on the surface of the electrophotographic photosensitive member 1 to the recording medium 500, and a toner remaining on the surface of the electrophotographic photosensitive member 1 after the transfer. The image forming apparatus includes a toner removing device 213 for removing the toner, and a fixing device 215 for fixing the toner image transferred to the recording medium 500 to the recording medium 500.

  The image forming apparatus 200 shown in FIG. 2 does not include a charge removing device that removes a charge remaining on the surface of the electrophotographic photosensitive member 1 after a toner image on the surface of the electrophotographic photosensitive member 1 has been transferred, and has an erase-less type image. It is a forming device. If there is no charge eliminator for removing charges remaining on the surface of the electrophotographic photoreceptor 1, minute color lines are likely to occur in the image. This is because the surface of the electrophotographic photoreceptor 1 that has not undergone charge elimination is considered to have a variation in charge, and the discharge frequency immediately after the contact portion between the electrophotographic photoreceptor 1 and the charging roll 208 is likely to decrease. . However, since the image forming apparatus 200 (that is, the image forming apparatus according to the present embodiment) includes the charging member according to the present embodiment as the charging roll 208, the generation of minute color lines is suppressed even without including the charge removing device. Is done.

(Electrophotographic photoreceptor)
The electrophotographic photosensitive member 1 is not particularly limited, and a known electrophotographic photosensitive member can be used. For example, on a conductive substrate, an undercoat layer, a charge generation layer, and a charge transport layer are laminated in this order, and a function separation type photosensitive layer in which the charge generation layer and the charge transport layer are separately provided is provided. And a photoreceptor. Further, a function-integrated photoconductor having a photosensitive layer in which a charge generation layer and a charge transport layer are integrally formed may be used.
The photoreceptor 1 may not have an undercoat layer, may have an intermediate layer between the undercoat layer and the photosensitive layer, or may have a protective layer containing a charge transport material on the photosensitive layer. It may be provided.

  In addition, in the electrophotographic photoreceptor 1, the total thickness of the surface layer having the charge transporting property is preferably 20 μm or more and 50 μm or less, more preferably 24 μm or more and 50 μm or less, and more preferably 28 μm More preferably, it is 38 μm or less.

For example, in a case where a function-separated type photosensitive member having a charge transport layer as the outermost surface layer is used in an image forming apparatus having a DC contact charging type charging device, the longer the thickness of the charge transport layer, the longer the life can be achieved. , A minute color line is easily generated. In the case where a second charge transporting layer, which is more wear-resistant than the first charge transporting layer, is provided on the first charge transporting layer, the first charge transporting layer and the second charge transporting layer may be provided. The longer the total thickness of the (protective layer), the longer the service life can be achieved, while the minute color lines are more likely to occur.
In other words, in the case of a photoreceptor of a function-integrated type, the longer the total thickness of the surface layer having the charge transporting property, the longer the life of the photoreceptor can be. That is, as the total thickness of the surface layer having the charge transporting property is larger, the electrical responsiveness of the surface layer becomes lower, and the discharge frequency immediately after the contact portion between the electrophotographic photosensitive member 1 and the charging roll 208 is easily reduced. It is because it is considered that it becomes.

  However, when the charging member according to the present embodiment is used as the charging roll 208, the generation of minute color lines is suppressed even when the total thickness of the surface layer having charge transportability of the electrophotographic photosensitive member 1 is 20 μm or more and 50 μm or less. And a longer service life. In this embodiment, the surface layer having the charge transporting property of the electrophotographic photoreceptor 1 refers to a charge transporting layer and a protective layer when a protective layer containing a charge transporting material is provided on the functional separation type photosensitive layer. This is the total thickness, and in the case where a protective layer containing a charge transport material is provided on the function-integrated photosensitive layer, the total thickness of the photosensitive layer and the protective layer.

(Charging device)
The charging device is a DC contact charging type charging device that has the charging member according to the present embodiment as the charging roll 208 and applies a DC voltage to charge the surface of the electrophotographic photosensitive member 1. The applied voltage may be a positive or negative DC voltage of 50 V or more and 2000 V or less, depending on the required photoconductor charging potential.

  The pressure at which the charging roll 208 comes into contact with the electrophotographic photosensitive member 1 is, for example, in the range of 250 mgf to 600 mgf.

  By bringing the charging roll 208 into contact with the surface of the photoconductor 1, the charging device rotates following the photoconductor 1 even if the charging device does not have a driving device. It may be rotated at a different peripheral speed.

(Exposure equipment)
As the exposure device 210, a known exposure device is used. Specifically, for example, an optical system device that performs exposure with a light source such as a semiconductor laser, an LED (Light Emitting Diode), and a liquid crystal shutter is used. The amount of time writing, for example, range from 0.5 mJ / ^{m 2} or more 5.0mJ / ^{m 2} and the like on the photosensitive member surface.

(Developer)
As the developing device 211, for example, a two-component developing type developing device in which a developing brush (developer holding member) to which a developer including a carrier and a toner is attached is brought into contact with the electrophotographic photosensitive member 1 to perform development, a conductive rubber elasticity Examples include a contact type one-component developing type developing device in which toner is adhered to a body transport roll (developer holding member) to develop the toner on the electrophotographic photosensitive member.
The toner is not particularly limited as long as it is a known toner. Specifically, for example, the toner may include at least a binder resin and, if necessary, a colorant and a release agent.

  The method for producing the toner is not particularly limited, but includes, for example, a known pulverization method, a wet melt spheroidization method in a dispersion medium, suspension polymerization, dispersion polymerization, and emulsion polymerization aggregation method. Examples of the method include a method for producing a toner by a polymerization method.

  When the developer is a two-component developer consisting of a toner and a carrier, the carrier is not particularly limited, and examples thereof include a core material such as a magnetic metal such as iron oxide, nickel, and cobalt; and a magnetic oxide such as ferrite and magnetite. Carrier (non-coated carrier) composed only of these, and a resin-coated carrier in which a resin layer is provided on the surface of these core materials. In the case of the two-component developer, for example, the mixing ratio (mass ratio) of the toner and the carrier is in the range of toner: carrier = 1: 100 to 30: 100, and even in the range of 3: 100 to 20: 100. Good.

(Transfer device)
The transfer device 212 includes, in addition to a roll-shaped contact-type charging member, a contact-type transfer charger using a belt, a film, a rubber blade, or the like, or a scorotron transfer charger or a corotron transfer charger using corona discharge. No.

(Toner removal device)
The toner removing device 213 is for removing residual toner adhering to the surface of the electrophotographic photoreceptor 1 after the transfer step, and the electrophotographic photoreceptor 1 having a cleaned surface is repeatedly used in the above-described image forming process. Provided. As the toner removing device 213, in addition to a foreign matter removing member (cleaning blade), brush cleaning, roll cleaning, and the like are used. Among them, a cleaning blade is preferably used. Examples of the material for the cleaning blade include urethane rubber, neoprene rubber, and silicone rubber.
When residual toner does not cause a problem, for example, when the toner hardly remains on the surface of the photoconductor 1, the toner removing device 213 does not need to be provided.

A basic image forming process of the image forming apparatus 200 will be described.
First, the charging device charges the surface of the photoconductor 1 to a predetermined potential. Next, the charged surface of the photoconductor 1 is exposed by the exposure device 210 based on an image signal to form an electrostatic latent image.
Next, the developer is held on the developer holding body of the developing device 211, and the held developer is transported to the photoconductor 1, and at a position where the developer holding body and the photoconductor 1 approach (or come into contact with). Supplied to the electrostatic latent image. Thereby, the electrostatic latent image is visualized and becomes a toner image.
The developed toner image is transported to the position of the transfer device 212, and is directly transferred to the recording medium 500 by the transfer device 212.
Next, the recording medium 500 to which the toner image has been transferred is conveyed to the fixing device 215, and the toner image is fixed to the recording medium 500 by the fixing device 215. The fixing temperature is, for example, 100 ° C. or more and 180 ° C. or less.
On the other hand, after the toner image is transferred to the recording medium 500, the toner particles remaining on the photoconductor 1 without being transferred are carried to a position where the toner image contacts the toner removing device 213, and collected by the toner removing device 213.
As described above, image formation by the image forming apparatus 200 is performed. When performing the next image formation, the next image formation process is performed without passing through the step of removing the charge on the surface of the photoconductor 1.

<Second embodiment>
FIG. 3 schematically shows a basic configuration of the image forming apparatus according to the second embodiment. An image forming apparatus 220 shown in FIG. 3 is an intermediate transfer type image forming apparatus, and four electrophotographic photosensitive members 1 a, 1 b, 1 c, and 1 d are arranged in a housing 400 in parallel with each other along an intermediate transfer belt 409. ing. For example, the photoconductor 1a forms an image of yellow, the photoconductor 1b forms an image of magenta, the photoconductor 1c forms an image of cyan, and the photoconductor 1d forms an image of black.
The image forming apparatus 220 shown in FIG. 3 is also an erase-less type image forming apparatus that does not include a charge removing device that removes the charge remaining on the photoconductor surface after the toner image on the photoconductor surface is transferred.

  The electrophotographic photosensitive members 1a, 1b, 1c, and 1d rotate in one direction (counterclockwise on the paper), and along the rotating direction, the charging rolls 402a, 402b, 402c, and 402d, and the developing devices 404a, 404b, and 404b. 404c, 404d, primary transfer rolls 410a, 410b, 410c, 410d, and cleaning blades 415a, 415b, 415c, 415d are arranged. Each of the charging rolls 402a, 402b, 402c, and 402d is the charging roll according to the above-described embodiment, and employs a contact charging method in which only a DC voltage is applied.

  The developing devices 404a, 404b, 404c, 404d supply the four color toners of black, yellow, magenta, and cyan stored in the toner cartridges 405a, 405b, 405c, 405d, respectively. 410c and 410d are in contact with the electrophotographic photosensitive members 1a, 1b, 1c and 1d via the intermediate transfer belt 409, respectively.

A laser light source (exposure device) 403 is disposed in the housing 400, and irradiates the laser light emitted from the laser light source 403 to the surfaces of the charged electrophotographic photosensitive members 1a, 1b, 1c, and 1d.
As a result, in the rotation process of the electrophotographic photosensitive members 1a, 1b, 1c, 1d, respective processes of charging, exposure, development, primary transfer, and cleaning (removal of foreign matter such as toner) are sequentially performed, and the toner image of each color is intermediate. The image is transferred onto the transfer belt 409 in an overlapping manner. After the toner image is transferred onto the intermediate transfer belt 409, the electrophotographic photoreceptors 1a, 1b, 1c, and 1d are subjected to the next image forming process without passing through the step of removing the charge on the surface.

  The intermediate transfer belt 409 is supported with tension by a drive roll 406, a back roll 408, and a support roll 407, and rotates without bending due to rotation of these rolls. Further, the secondary transfer roll 413 is arranged so as to be in contact with the back roll 408 via the intermediate transfer belt 409. The intermediate transfer belt 409 that has passed through a position sandwiched between the back roll 408 and the secondary transfer roll 413 is cleaned, for example, by a cleaning blade 416 disposed to face the drive roll 406, and then forms the next image. It is repeatedly submitted to the process.

  Further, a container 411 for storing a recording medium is provided in the housing 400, and the recording medium 500 such as paper in the container 411 is sandwiched between the intermediate transfer belt 409 and the secondary transfer roll 413 by the transfer roll 412. After being sequentially transferred to a position, and further to a position sandwiched between two fixing rolls 414 that are in contact with each other, the sheet is discharged to the outside of the housing 400.

  In the above description, the case where the intermediate transfer belt 409 is used as the intermediate transfer body has been described. However, the intermediate transfer body may be a belt shape like the intermediate transfer belt 409 or a drum shape. Good. In the case of a belt shape, a known resin is used as the resin material constituting the base material of the intermediate transfer body. For example, polyimide resin, polycarbonate resin (PC), polyvinylidene fluoride (PVDF), polyalkylene terephthalate (PAT), ethylene tetrafluoroethylene copolymer (ETFE) / PC, ETFE / PAT, blended material of PC / PAT, polyester And resin materials such as polyetheretherketone and polyamide, and resin materials containing these as main raw materials. Further, a resin material and an elastic material may be blended and used.

  The recording medium according to the embodiment is not particularly limited as long as the medium transfers a toner image formed on an electrophotographic photosensitive member.

<Process cartridge>
The process cartridge according to the present embodiment includes the charging member according to the present embodiment, and charges the surface of the electrophotographic photosensitive member by a contact charging method (DC contact charging method) in which only a DC voltage is applied to the charging member. And has a configuration detachable from the image forming apparatus.
FIG. 4 schematically shows a basic configuration of an example of the process cartridge according to the present embodiment. The process cartridge 300 includes a DC contact charging type charging device that applies a DC voltage to the electrophotographic photosensitive member 1 and a charging roll to charge the surface of the electrophotographic photosensitive member 1, and the electrophotographic photosensitive member 1 by exposure. A developing device 211 for developing the electrostatic latent image formed thereon with a developer containing toner to form a toner image; a toner removing device 213 for removing toner remaining on the surface of the electrophotographic photosensitive member 1 after transfer; An opening 218 for exposure is combined with a mounting rail 216 and integrated.

The process cartridge 300 includes a transfer device 212 that transfers the toner image formed on the surface of the electrophotographic photosensitive member 1 to the recording medium 500, and a fixing device that fixes the toner image transferred to the recording medium 500 to the recording medium 500. It is detachable from an image forming apparatus main body composed of the apparatus 215 and other components (not shown), and forms an image forming apparatus together with the image forming apparatus main body.
The process cartridge 300 of the present embodiment includes an electrophotographic photosensitive member 1, a charging device, a developing device 211, a toner removing device 213, and an opening 218 for exposure, and an exposure for exposing the surface of the electrophotographic photosensitive member 1. An apparatus (not shown) may be provided.

  Hereinafter, the present invention will be described specifically with reference to Examples, but the present invention is not limited to these Examples.

<Example 1>
[Preparation of charging roll]
-Formation of conductive elastic layer-
-Epichlorohydrin rubber (3106, manufactured by Zeon Corporation): 100 parts by mass-Carbon black (Asahi No. 60, manufactured by Asahi Carbon Co.): 6 parts by mass-Calcium carbonate (Whiteton SB, manufactured by Shiraishi Calcium): 20 parts by mass Parts: ionic conductive agent (BTEAC, manufactured by Lion Corporation): 5 parts by mass. Vulcanization accelerator: stearic acid (manufactured by NOF Corporation): 1 part by mass. Vulcanizing agent: sulfur (PARNOC R, manufactured by Ouchi Shinko Chemical Co., Ltd.) ): 1 part by mass, vulcanization accelerator: zinc oxide: 1.5 parts by mass A mixture having the composition shown above was kneaded with an open roll, and a conductive base material (metal shaft) having a diameter of 8 mm formed by SUS303. A roll having a diameter of 15 mm was formed on the surface with a press molding machine via an adhesive layer, and then a conductive elastic roll having a diameter of 14 mm was obtained by polishing.

-Formation of conductive surface layer-
-Binder resin: N-methoxymethylated nylon 1 (trade name: F30K, manufactured by Nagase ChemteX Corporation): 100 parts by mass-Particle A: carbon black (trade name: MONAHRCH1000, manufactured by Cabot Corporation): 15 parts by mass-Particle B : Polyamide particles (polyamide 12, manufactured by Arkema): 20 parts by mass. Additive: dimethylpolysiloxane (BYK-307, manufactured by Altana): 1 part by mass. The mixture having the above composition was diluted with methanol and dispersed by a bead mill. The obtained dispersion is applied by dip coating on the surface of the conductive elastic roll, and then dried by heating at 130 ° C. for 30 minutes to form a surface layer having a thickness of 9 μm. The charging member of Example 1 (charging roll 1) I got

<Example 2>
In the formation of the conductive surface layer, a charging roll of Example 2 was obtained in the same manner as in Example 1, except that the additive was used in an amount of 0 parts by mass.

<Example 3>
A charging roll of Example 3 was obtained in the same manner as in Example 1, except that carbon black was used in an amount of 10 parts by mass in forming the conductive surface layer.

<Example 4>
In the formation of the conductive elastic layer, a charging roll of Example 5 was obtained in the same manner as in Example 1, except that the ionic conductive agent was used in an amount of 3.5 parts by mass.

<Comparative Example 1>
In the formation of the conductive surface layer, a charging roll of Comparative Example 1 was obtained in the same manner as in Example 1, except that carbon black was used in an amount of 20 parts by mass.

<Comparative Example 2>
In the formation of the conductive surface layer, the charging roll of Comparative Example 2 was obtained in the same manner as in Example 1 except that the temperature for heating and drying was set to 160 ° C.

<Comparative Example 3>
In the formation of the conductive elastic layer, a charging roll of Comparative Example 3 was obtained in the same manner as in Example 1, except that the ionic conductive agent was changed to 2 parts by mass.

<Comparative Example 4>
In the formation of the conductive surface layer, a charging roll of Comparative Example 4 was obtained in the same manner as in Example 2 except that the additive was changed to 1 part by mass of an ion conductive agent (BTEAC, manufactured by Lion Corporation).

<Measurement / Evaluation>
The following various measurements and evaluations were performed on the charging rolls obtained in the above Examples and Comparative Examples. The results are shown in Tables 1 and 2.

[AC impedance measurement]
-Measurement method-
For measuring the AC impedance, an SI 1260 impedance / gain phase analyzer (manufactured by Toyo Technica) was used as a power supply and an ammeter, and a 1296 dielectric interface (manufactured by Toyo Technica) was used as a current amplifier.
A conductive base (metal shaft) was used as a cathode, and a 1.5 cm-wide aluminum plate was wrapped around the charging roll around the charging roll obtained in the above Examples and Comparative Examples as a sample for impedance measurement. As an anode, an AC voltage of 1 Vp-p was applied from the high frequency side in a frequency range of 1 MHz to 1 mHz, and the AC impedance of each charging roll was measured. Then, a Bode diagram was created from the phase difference θ and the frequency obtained by this measurement, and the frequency at which the phase difference θ was minimized was determined.
On the other hand, a frequency at which the phase difference θ was minimized was determined in the same manner as described above, using the conductive elastic roll from which the surface layer was removed from each charging roll as a sample for impedance measurement.

[Evaluation of minute color line]
Modified image forming apparatus "DocuCenter 505a (manufactured by Fuji Xerox)" having a contact charging device in which only a DC voltage is applied to the charging device (equipped with a photoconductor having a total thickness of 28 μm of a surface layer having charge transportability) Then, the charging rolls obtained in the above Examples and Comparative Examples were incorporated into an erase-less type remodeling machine without a static eliminator. Then, using this remodeled machine, an entire surface halftone image having an image density of 30% was output on A4 paper under high temperature and high humidity conditions. The number of fine color lines generated in an area of 94 mm in length and 200 mm in width from the upper left of the output image was evaluated according to the following evaluation criteria. Here, “high temperature and high humidity” refers to a surrounding environment of 28 ° C. and 85 RH%.
The evaluation of the minute color line was referred to as “Evaluation 1”. In Evaluation 1, except that the total thickness of the charge transporting surface layer of the photoreceptor mounted on the remodeling machine was changed to a thin 16 μm. Evaluation 2 was performed in the same manner.
In Evaluation 1, Evaluation 3 was performed in the same manner as Evaluation 1 except that the static eliminator was mounted on the modified machine.

−Evaluation criteria for minute color lines−
G0: No minute color line is generated G1: One to three or less minute color line generation G2: Four to ten minute color line generation G3: 11 to 20 minute color line generation G4: 21 points Above minute color line generation

  Hereinafter, the details and evaluation results of each of the examples and comparative examples are listed in Tables 1 and 2.

From the above results, it can be seen that the generation of minute color lines in the initial stage of image formation is suppressed in the charging roll of the present example as compared with the charging roll of the comparative example.
Also, from the comparison between the evaluation 1 of the minute color line when the total thickness of the charge transporting surface layer of the photoreceptor mounted on the remodeling machine is as thick as 28 μm and the evaluation 2 of the minute color line when the total thickness is as thin as 16 μm. In the case of the evaluation 1 of the minute color line, the minute color line is more likely to occur (see the comparative example), and it is understood that the minute color line is suppressed in the present embodiment.
Furthermore, comparing the evaluation 1 of the minute color line when the static eliminator is not mounted on the remodeled machine and the evaluation 3 of the minute color line when the static eliminator is mounted, the evaluation of the minute color line 1 indicates that the minute color line is smaller. Easily occur (see the comparative example), and it can be seen that in this example, this minute color line is suppressed.

1, 1a, 1b, 1c, 1d Electrophotographic photoreceptor, 30 conductive substrate, 31 conductive elastic layer, 32 conductive surface layer, 200 image forming device, 208 charging roll, 210 exposure device, 211 developing device, 212 Transfer device, 213 Toner removal device, 215 fixing device, 220 image forming device, 300 process cartridge, 402a, 402b, 402c, 402d Charging roll, 404a, 404b, 404c, 404d Developing device, 500 recording medium

Claims (7)

A conductive substrate, and a conductive elastic layer disposed on the conductive substrate, and a conductive surface layer disposed on the conductive elastic layer,
When the AC impedance of the conductive elastic layer and the charging member is measured by the AC impedance method in the range of 1 MHz to 1 mHz, the frequency at which the phase difference θ in the conductive elastic layer and the charging member is minimized is 63 Hz or more. A contact charging type charging member to which only a DC voltage of 1600 Hz or less is applied. 2. The charging member according to claim 1, wherein the frequency at which the phase difference θ in the conductive elastic layer is a minimum is 63 Hz or more and 500 Hz or less, and the frequency at which the phase difference θ in the charging member is a minimum is 300 Hz or more and 1590 Hz or less. .   A charging device comprising the charging member according to claim 1. An electrophotographic photoreceptor,
A charging device having the charging member according to claim 1 or 2, and charging a surface of the electrophotographic photosensitive member by a contact charging method of applying only a DC voltage to the charging member,
An electrostatic latent image forming apparatus for forming an electrostatic latent image on the surface of the charged electrophotographic photosensitive member,
A developing device that forms a toner image by developing an electrostatic latent image formed on the surface of the electrophotographic photoreceptor with a developer containing a toner;
A transfer device for transferring the toner image to a surface of a recording medium,
An image forming apparatus comprising:   The image forming apparatus according to claim 4, wherein the total thickness of the surface layer having a charge transporting property of the electrophotographic photosensitive member is 20 μm or more and 50 μm or less. The image forming apparatus according to claim 4, wherein the image forming apparatus does not include a charge removing device that removes a residual charge on a surface of the electrophotographic photosensitive member. A charging device, comprising: the charging member according to claim 1 or 2; and a charging device that charges a surface of the electrophotographic photosensitive member by a contact charging method that applies only a DC voltage to the charging member.
A process cartridge that is attached to and detached from the image forming apparatus.