JP2004258064A - Electrifying device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrifying device that can be processed with high accuracy and prevents discharge that occurs at both ends. <P>SOLUTION: An electrifying roller (electrifying device) 45 has gap retaining members 63 each of which is in contact with an outside A2 of the image forming area of a photoreceptor (image carrier)14 and thereby forms a gap Gp between the main body 62 of the electrifying member and the photoreceptor 14 within an image forming area A1. The electrifying member main body 62 is made of a resin material containing an ionic conductive material. The gap retaining members 63 are are made of heat-shrinkable insulative resin material which has a thickness t2 of 100 to 500 μm and is lower in hardness than the main body 62 of the electrifying member 62. Steps 64 are formed at both ends of the main body 62 of the electrifying member. The gap retaining members 63 are disposed such that the maximum value of the gap Gp is 100 μm or less by adjusting the depths d of the steps 64. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
According to the present invention, a gap is formed between a charging member main body and an image carrier in an image forming area by contacting a gap holding member outside an image forming area of the image carrier to charge the image carrier. The present invention relates to a charging device and an image forming apparatus including the charging device, such as a printer, a facsimile, a copying machine, or a multifunction peripheral thereof.
[0002]
[Prior art]
Conventionally, this type of charging device is mainly a charger system such as a scorotron. However, there is a problem that a large amount of discharge products such as ozone is generated, and in recent years, a charging member body such as a roller or a brush is provided. A contact type in which a charging device is brought into direct contact with a photoreceptor has been widely used.
[0003]
In this contact type charging device, there is a problem that the toner on the surface of the photoreceptor adheres to the surface of the charging member main body due to the contact, thereby causing contamination and uneven charging of the photoreceptor. In addition, the charging member main body is often unitized with the photoreceptor as a photoreceptor unit, and in order to replace the charging member main body, the entire photoreceptor unit must be replaced, which shortens the life of the charging device. It has become a major factor. As a technique for reducing toner adhering to the charging member main body, there is a method of providing a minute gap between the charging member main body and the photoconductor.
[0004]
As one of them, for example, a film-like gap holding member is attached on the periphery of both ends of the charging member main body outside the image forming area, and both ends of the charging device having an outer diameter larger than other portions are attached to the photosensitive member. A method of forming a minute gap between the photosensitive member and the charging device by contacting the photosensitive member with a charging device (for example, Patent Document 1).
[0005]
However, when the charging device is a rubber charging roller, (1) it is difficult to process the outer diameter of the charging roller with high accuracy by cutting, and (2) the expansion rate of the charging roller due to heat is large. There has been a problem that the gap between the charging roller and the photoreceptor fluctuates greatly depending on the ambient temperature, and it is difficult to maintain the gap accurately.
On the other hand, when the charging device is a resin-made charging roller (for example, Patent Document 2 or the like), the outer diameter of the charging roller and the like can be processed with high precision because cutting is easy. However, since the film has a higher hardness than rubber, there is a problem that when a film is used as the gap holding member, the film is worn between the charging roller and the photoconductor.
[0006]
In addition, when an organic photoreceptor is used as the photoreceptor, there is a problem that a portion of the organic photoreceptor that contacts the film is damaged.
Furthermore, if the film is simply attached and used for a long period of time, the film may peel off from the charging roller.If the charging roller and the film are bonded with an adhesive, uneven application of the adhesive may cause the photosensitive member and the charging roller to become uneven. This affects the formation of a small gap of several tens μm between them, which is not preferable.
[0007]
Therefore, steps and grooves are provided at both ends of the charging roller, and an annular gap holding member is fitted and fixed to the steps and grooves, and both ends of the charging roller having an outer diameter larger than other portions are attached to the photosensitive member. A method of forming a gap by abutting is disclosed (for example, Patent Document 3).
[0008]
However, in such a method, a discharge from the charging roller to the photoconductor is generated on the outer side where the gap holding member is attached, as well as on the inner side where the gap holding member is attached. May be worn away. Then, there were problems such as leakage of charging bias between the photosensitive member and the charging roller, and toner sticking due to cleaning failure, widening the charging gap, and easily causing charging unevenness due to abnormal discharge. .
[0009]
For this reason, a technology has been disclosed in which a gap holding member having a high volume resistance is provided on the periphery of both ends of the charging roller to prevent discharge at both ends (for example, Patent Documents 4 and 5).
[0010]
[Patent Document 1]
JP 2001-194868 A
[Patent Document 2]
JP 2001-337515 A
[Patent Document 3]
JP-A-2002-55508
[Patent Document 4]
JP-A-7-104557
[Patent Document 5]
JP-A-7-199599
[0011]
[Problems to be solved by the invention]
However, in such a method, when forming a minute gap between the charging roller and the photoconductor, the thickness of the gap holding member cannot be made too large. For this reason, there has been a problem that a sufficient discharge prevention effect cannot be obtained even when a material having a high volume resistance value is used.
Accordingly, a first object of the present invention is to provide a charging device which can be machined with high accuracy and can prevent discharges generated at both ends.
[0012]
A second object of the present invention is to provide a durable charging device.
[0013]
A third object of the present invention is to prevent charging unevenness and prevent excessive discharge between a charging member and an image carrier.
[0014]
A fourth object of the present invention is to provide an image forming apparatus which achieves each of the above objects.
[0015]
A fifth object of the present invention is to provide an image forming apparatus in which parts can be easily replaced.
[0016]
[Means for Solving the Problems]
For this reason, the invention according to claim 1 is a gap holding member that forms a gap between the charging member main body and the image carrier in the image forming area by abutting outside the image forming area of the image carrier. In the charging device provided with
The charging member body is made of a resin material containing an ion conductive material,
The gap holding member has a hardness lower than that of the charging member main body, and is made of an insulating resin material having a thickness of 100 to 500 μm having heat shrinkability,
A step is formed at both ends of the charging member body, and the gap holding member is provided at the step so that the maximum value of the gap is 100 μm or less.
[0017]
According to a second aspect of the present invention, in the charging device according to the first aspect, the gap holding member covers side surfaces of both ends of the charging member main body.
[0018]
According to a third aspect of the present invention, in the charging device according to the second aspect, the charging member main body is formed in a substantially cylindrical shape by covering a conductive metal core, and extends to both ends of the charging member main body. When the core is rotatably attached to the bearing, a step is provided on the core so that the gap holding member does not contact the bearing, and the step is attached to the bearing.
[0019]
According to a fourth aspect of the present invention, an AC bias is superimposed on the charging member main body, and a peak-to-peak voltage of the AC bias is at least twice a discharge starting voltage between the charging member main body and the image carrier. Between the frequency f [Hz] of the AC bias and the linear velocity v [mm / s] of the image carrier.
7 × v <f <12 × v
The charging device according to any one of claims 1 to 3, wherein the following relationship is satisfied.
[0020]
According to a fifth aspect of the present invention, there is provided an image forming apparatus including the charging device according to any one of the first to fourth aspects.
[0021]
According to a sixth aspect of the present invention, in the image forming apparatus according to the fifth aspect, the image carrier and the charging device are integrally and detachably provided.
[0022]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings. 1 is an overall schematic configuration diagram of a small color printer as an example of an image forming apparatus according to the present invention. Reference numeral A in the figure denotes a printer main body. In the apparatus main body A, a transfer material transport path P is provided diagonally from the lower right to the upper left in the figure. On the transfer material transport path P, four monochromatic image forming means 10Y, 10M, 10C, and 10B of yellow, magenta, cyan, and black are arranged in order from the lower right to the upper left along the transport path P to form a tandem type. Prepare.
[0023]
Each monochrome image forming means 10 is composed of a photoreceptor unit 12Y, 12M, 12C, 12B and a developing unit 13Y, 13M, 13C, 13B. Each of the photoconductor units 12Y, 12M, 12C, and 12B includes a drum-shaped photoconductor (image carrier) 14Y, 14M, 14C, and 14B.
[0024]
Each of the photoconductors 14B, 14Y, 14M, and 14C has a structure in which an undercoat layer, a charge generation layer mainly containing a charge generation material, and a charge transport layer mainly containing a charge transport material are stacked on a conductive support. Is formed.
The conductive support has a volume resistance of 10 ⁴ A material having a conductivity of Ωcm or less, for example, a metal tube such as aluminum or stainless steel, or a metal such as nickel processed into an endless belt shape is used.
[0025]
The undercoat layer generally contains a resin as a main component. However, considering that the photosensitive layer is coated thereon with a solvent, these resins are resins having high solubility resistance to general organic solvents. Is desirable. Examples of such a resin include a water-soluble resin such as a polyvinyl alcohol resin, an alcohol-soluble resin such as a copolymerized nylon, a polyurethane resin, an alkyd-melamine resin, and an epoxy resin, and a curable resin that forms a three-dimensional network structure. No. Further, fine powder of a metal oxide such as titanium oxide, silica, and alumina may be added to the undercoat layer in order to prevent moiré and reduce residual potential. This undercoat layer can be formed using an appropriate solvent and a coating method. The thickness of the undercoat layer is suitably from 0 to 5 μm.
[0026]
The charge generation layer is a layer containing a charge generation material as a main component, and typical examples are a monoazo pigment, a disazo pigment, a trisazo pigment, and a phthalocyanine pigment. The charge generation material can be formed by dispersing the charge generation material together with a binder resin such as polycarbonate using a solvent such as tetrahydrofuran or cyclohexanone, and applying a dispersion. The coating is performed by a dip coating method or a spray coating. The thickness of the charge generation layer is usually 0.01 to 5 μm.
[0027]
The charge transporting layer can be formed by dissolving or dispersing the charge transporting material and the binder resin in an appropriate solvent of tetrahydrofuran, toluene, and dichloroethane, and applying and drying this. Among the charge transport materials, low-molecular charge transport materials include an electron transport material and a hole transport material. Examples of the electron transporting material include chloranil, bromoanil, tetracyanoethylene, tetracyanoquinodimethane, 2,4,7-trinitro-9-fluorenone, 2,4,5,7-tetranitro-9-fluorenone, Electron accepting substances such as 3,7-trinitrodibenzothiophene-5,5-dioxide are exemplified. Examples of the hole transport material include oxazole derivatives, oxadiazole derivatives, imidazole derivatives, triphenylamine derivatives, phenylhydrazones, α-phenylstilbene derivatives, thiazole derivatives, triazole derivatives, phenazine derivatives, acridine derivatives, thiophene derivatives, and the like. Electron donating substances. As the binder resin used for the charge transport layer together with the charge transport material, polystyrene resin, styrene-acrylonitrile copolymer, styrene-butadiene copolymer, polyester resin, polyarylate resin, polycarbonate resin, acrylic resin, epoxy resin, melamine Thermoplastic or thermosetting resins such as resin and phenolic resin are exemplified.
[0028]
The thickness of the charge transport layer may be appropriately selected in the range of 5 to 30 μm according to desired characteristics of the photoreceptor. Further, a protective layer may be formed on the photoreceptor as a surface layer for the purpose of protecting the photosensitive layer and improving durability.
[0029]
The developing units 13Y, 13M, 13C, and 13B have the same configuration, and are a two-component developing system that differs only in the color of the toner used. That is, the developing unit 13Y uses a yellow toner, the developing unit 13M uses a magenta toner, the developing unit 13C uses a cyan toner, and the developing unit 13B uses a black toner. . Then, the two-component developer including the toner and the carrier is accommodated in the developing unit of each color.
[0030]
Each of the developing units 13Y, 13M, 13C, and 13B includes a developing roller facing the photoconductors 14Y, 14M, 14C, and 14B, a screw that conveys and agitates the developer, a toner density sensor, and the like. The developing roller includes a magnet fixed inside a rotatable sleeve. Then, the toner is supplied from the toner supply device in accordance with the output of the toner concentration sensor.
[0031]
The toner includes a binder resin, a colorant, and a charge control agent as main components, and is further configured to include other additives as necessary. As specific examples of the binder resin, polystyrene, styrene-acrylate copolymer, polyester resin, and the like can be used. As a coloring material (for example, yellow, magenta, cyan, and black) used for the toner, those known for toner can be used. The amount of the coloring material is suitably from 0.1 to 15 parts by weight based on 100 parts by weight of the binder resin.
[0032]
Specific examples of the charge control agent include a nigrosine dye, a chromium-containing complex, a quaternary ammonium salt, and the like, which are used depending on the polarity of the toner particles. The amount of the charge control agent is 0.1 to 10 parts by weight based on 100 parts by weight of the binder resin.
It is advantageous to add a fluidity imparting agent to the toner particles. Examples of the fluidity-imparting agent include fine particles of a metal oxide such as silica, titania, and alumina, and those obtained by subjecting the fine particles to a surface treatment with a silane coupling agent, a titanate coupling agent, or the like; polystyrene, polymethyl methacrylate, Polymer fine particles such as vinylidene are used. These fluidity imparting agents have a particle size in the range of 0.01 to 3 μm. The addition amount of these fluidity-imparting agents is preferably in the range of 0.1 to 7.0 parts by weight based on 100 parts by weight of the toner particles.
[0033]
As a method for producing the toner for a two-component developer according to the present invention, it can be produced by various known methods or a method combining them. For example, in the kneading and pulverizing method, a binder resin and a coloring material such as carbon black and necessary additives are dry-mixed, heated and kneaded with an extruder or a two-roll, three-roll, or the like, and then cooled and solidified. The toner is obtained by pulverizing with a pulverizer such as a jet mill and classifying with an airflow classifier. Further, a toner can be directly produced from a monomer, a colorant, and an additive by a suspension polymerization method or a non-aqueous dispersion polymerization method.
[0034]
As the carrier, a core material itself or a core material provided with a coating layer is generally used. The core material of the resin-coated carrier that can be used in the present invention is ferrite or magnetite. The particle size of the core material is suitably about 20 to 60 μm.
[0035]
Materials used for forming the carrier coating layer include vinylidene fluoride, tetrafluoroethylene, hexafluoropropylene, perfluoroalkyl vinyl ether, vinyl ether substituted with a fluorine atom, and vinyl ketone substituted with a fluorine atom. As a method of forming the coating layer, a resin may be applied to the surface of the carrier core material particles by a spraying method, a dipping method, or the like, as in the related art.
[0036]
On such a single-color image forming means 10Y, 10M, 10C, 10B, a writing unit 16 is provided obliquely along the single-color image forming means 10. The writing unit 16 is provided with four laser diode (LD) type light sources prepared for each color, a set of polygon scanners composed of six polygon mirrors and polygon motors, and a route for each light source. It is composed of an fθ lens, a lens such as a long WTL, and a mirror. The laser light emitted from the laser diode is deflected and scanned by a polygon scanner, and is irradiated on a photosensitive member.
[0037]
On the other hand, an endless belt-shaped transfer belt 18 is stretched under the single-color image forming means 10Y, 10M, 10C, and 10B with the transfer material conveyance path P interposed therebetween. In the illustrated example, the transfer belt 18 is wrapped around four support rollers 19A, 19B, 19C, and 19D, is brought into contact with the photoconductors 14Y, 14M, 14C, and 14B, and is partially provided along the transfer material transport path P. A driving device (not shown) can rotate and convey in a counterclockwise direction in the figure.
[0038]
As a material of the transfer belt 18, a resin material such as polyvinylidene fluoride, polyimide, polycarbonate, and polyethylene terephthalate can be molded into a seamless belt and used. These materials can be used as they are, or the resistance can be adjusted with a conductive material such as carbon black. In addition, a surface layer may be formed by using a method such as spraying or dipping using these resins as a base layer to form a laminated structure.
[0039]
Inside the transfer belt 18, backup rollers 20Y, 20M, 20C, and 20B and transfer brushes 21Y, 21M, 21C, and 21B are disposed corresponding to the photoconductors 14Y, 14M, 14C, and 14B, respectively. The backup rollers 20Y, 20M, 20C, and 20B bring the transfer belt 18 and the transfer paper into close contact with the respective photoconductors 14Y, 14M, 14C, and 14B. A transfer bias is supplied to the transfer brushes 21Y, 21M, 21C, and 21B from a power source (not shown). In the illustrated example, the transfer brush is used, but a non-contact charger may be used.
[0040]
Along the transfer material transport path P, a pair of registration rollers 23 is provided at an upstream position of the transfer belt 18, and a fixing unit 24 is provided at a downstream position. The fixing unit 24 is configured such that a pressure roller 26 is pressed against a fixing belt 25 which is an endless belt, and a discharge roller pair 27 is provided at an outlet.
A reversing unit 29 is provided downstream of the fixing unit 24 and attached to the apparatus main assembly A. The reversing unit 29 is composed of a plurality of transport rollers forming a pair and a plurality of transport guide plates forming a pair. The reversing unit 29 discharges the transfer paper as it is, reverses and discharges the transfer paper, or returns the transfer paper to the apparatus main body A again. .
Further, at another downstream side of the fixing unit 24, a reversing discharge path P1 is formed by branching off from the transfer material transport path P, and the transfer paper is discharged to the discharge stack unit 30 on the apparatus main body A first. A discharge roller pair 31 is provided.
[0041]
On the other hand, under the transfer belt 18, a duplex unit 33 that guides the transfer paper inverted by the reversing unit 29 between the pair of guide plates 32 and re-feeds the transfer paper is disposed obliquely along the extending direction. .
The duplex unit 33 includes a pair of transport guide plates and four pairs of transport rollers, and in a duplex image forming mode for forming images on both sides of a transfer sheet, an image is formed on one side and a reversing unit is formed. The transfer paper transported by the transfer paper 29 and transported by the switchback is received and transported to the separation paper feeding unit 35.
[0042]
Below the duplex unit 33, a paper feed cassette 34 is provided in upper and lower two stages. In the paper feed cassette 34, transfer papers of different sizes, such as papers and OHP films, are stacked and stored. Then, there is provided a separation sheet feeding section 35 for separating and feeding the transfer sheets one by one.
[0043]
The transfer paper fed from the separation paper feed unit 35 and the transfer paper fed again through the duplex unit 33 are guided to the registration roller pair 23 of the transfer material transport path P on the right side of the separation paper feed unit 35 in the drawing. A paper feed path P2 is provided.
A manual feed portion is provided on the right side of the apparatus main body A in the figure, and a manual feed tray 36 is attached to the manual feed portion so as to be freely opened and closed. The manual feed unit is provided with a paper feed unit 37 that separates and feeds the transfer paper on the manual feed tray 36 one by one, and guides the transfer paper fed from the paper feed unit 37 to the registration roller pair 23. A paper path P3 is provided.
[0044]
When a color image is formed on transfer paper using this color printer, the separation paper feed unit 35 is selectively driven based on, for example, a signal from a personal computer to transfer one transfer paper in one paper feed cassette 34 The sheet is fed out separately, and is fed into the sheet feeding path P2, and is stopped against the registration roller pair 23. Alternatively, the manual paper feed unit 37 is driven to separate and feed out the transfer papers on the manual paper feed tray 36 one by one, and then the transfer papers are put into the manual paper feed path P3 and hit against the registration roller pair 23 to be stopped.
[0045]
On the other hand, in the single-color image forming means 10Y, 10M, 10C and 10B, the individual photoconductors 14Y, 14M, 14C and 14B are rotated to form yellow, magenta, cyan and black single-color toner images on the respective photoconductors. I do. At the same time, the support roller 19A is rotationally driven by a drive motor (not shown), and the other support rollers 19B, 19C, and 19D are driven to rotate, and the transfer belt 18 is rotationally conveyed.
[0046]
Then, the registration roller pair 23 is rotated in synchronization with the rotation of the photoconductor, the transfer paper is put into the transfer material conveyance path P, and the transfer belt 18 is placed between the monochrome image forming means 10Y, 10M, 10C, and 10B. The transfer paper is conveyed by feeding and rotating and conveying the transfer belt 18. At this time, the transfer paper is charged by the support roller 19B disposed near the entrance of the transfer belt 18, and is thereby electrostatically attracted to the surface of the transfer belt 18. Along with the conveyance, the single-color toner images on the individual photoconductors 14Y, 14M, 14C, and 14B are transferred by the transfer brushes 21Y, 21M, 21C, and 21B to form a synthetic full-color image on the transfer paper.
[0047]
The transfer paper after the image transfer is sent to the fixing unit 24, where the transfer image is fixed, and then discharged by the discharge roller pair 27. When the paper is discharged in a face-down state, the paper is switched by a switching claw (not shown) to the reverse paper discharge path P1, discharged by the discharge roller pair 31, and stacked on the paper discharge stacking section 30 in the page order. When the paper is discharged in a face-up state, it is switched by a switching claw (not shown), guided to the reversing unit 29, and directly discharged as it is.
[0048]
When recording is performed on the back side of the transfer paper on which single-side recording has been performed, similarly, switching is performed by a switching claw (not shown) to guide the sheet to the reversing unit 29, and after reversing by the reversing unit 29, guiding the sheet to the double-side unit 33, The sheet is inserted into the sheet feeding path P2 and is stopped by abutting against the registration roller pair 23. Then, the sheet is again put into the transfer material conveying path P, sent between the single-color image forming means 10Y, 10M, 10C, and 10B and the transfer belt 18 to form a synthetic full-color image on the back surface, and then fixed by the fixing unit 24. Then, for example, the sheet is discharged by the discharge roller pair 31 through the reversing sheet discharge path P <b> 1 and stacked on the sheet discharge stack unit 30.
[0049]
Next, the operation of forming a black and white image on transfer paper using this color printer will be described. When the color printer receives black and white image data based on a signal from, for example, a personal computer, the transfer belt 18 rotates clockwise around the drive roller 19A in FIG. 1, and the magenta, cyan, and yellow photoconductors are rotated. Separate from 14M, 14C, 14Y. The black photoconductor 14B rotates clockwise, and the surface of the photoconductor 14B is uniformly charged by the charging roller. Then, the photoconductor 14B of the photoconductor unit 12B is further irradiated with a laser beam corresponding to a black image to form a latent image. When the latent image reaches the position of the developing unit 13B, the latent image is developed with black toner to become a toner image. At this time, the image forming units for the three colors other than black are stopped to prevent unnecessary consumption.
[0050]
On the other hand, the transfer paper is fed from the paper feed cassette 34 by the separation paper feed unit 35, and the toner is formed on the black photoconductor 14 B by the registration roller pair 23 provided immediately before the transfer belt 18. The sheet is conveyed at the same timing as the image. The transfer paper is charged by a support roller 19 </ b> B disposed near the entrance of the transfer belt 18, and is thereby electrostatically attracted to the surface of the transfer belt 18. Since the transfer paper is conveyed while being attracted to the transfer belt 18, even if the transfer belt 18 is separated from the magenta, cyan, and yellow photoconductors 14M, 14C, and 14Y, it is conveyed to the black photoconductor 14B. , A black toner image is transferred. The transfer paper is fixed by the fixing unit 24 as in the case of the full-color image, and is processed through a paper discharge system according to the designated mode. Thereafter, when an instruction to form two or more images is given, the above-described image forming process is repeated.
[0051]
In order to stably transfer the transfer paper by electrostatic attraction, the transfer belt 18 needs to be made of a material having at least a surface layer having a high electric resistance value. As a material of the transfer belt 18, a resin material such as polyvinylidene fluoride, polyimide, polycarbonate, and polyethylene terephthalate can be molded into a seamless belt and used. These materials can be used as they are, or the resistance can be adjusted with a conductive material such as carbon black. In addition, a surface layer may be formed by using a method such as spraying or dipping using these resins as a base layer to form a laminated structure.
[0052]
Next, the photoconductor units 12Y, 12M, 12C, and 12B will be described in detail. The photoconductor units 12Y, 12M, 12C, and 12B of this example have the same configuration and operation except that the color of the toner is different. Therefore, for convenience, the photoconductor units 12Y, 12M, 12C, and 12B will be described below. The photoconductors 14Y, 14M, 14C, and 14B will be referred to as the photoconductor 14, and will be described.
[0053]
As shown in FIG. 2, the photoreceptor unit 12 contacts the photoreceptor 14 having an outer diameter of 30 mm, which rotates at a linear velocity of 125 mm / sec in the direction of arrow C, and a charging roller (charging device) 45, a brush roller 46, A cleaning blade 47 is provided along the C direction. The brush roller 46 rotates clockwise in synchronization with the rotation of the photoconductor 14. In addition, a cleaning brush 49 is provided in contact with the charging roller 45 on a side substantially opposite to a position where the charging roller 45 contacts the photoconductor 14. Further, a toner transport auger 48 is provided on a side of the brush roller 46 substantially opposite to a position where the brush roller 46 contacts the photoconductor 14.
[0054]
The brush roller 46 is for cleaning toner and the like adhered to the surface of the photoconductor 14, and the cleaning blade 47 is for scraping the toner and the like also adhered to the surface of the photoconductor 14. The charging roller 45 charges the surface of the photoconductor 14.
[0055]
Further, the cleaning brush 49 is for cleaning toner and the like adhered to the surface of the charging roller 45. The cleaning brush 49 is formed by electrostatically implanting conductive fibers having a hair length of 0.5 mm on a metal core having a diameter of 6 mm. The cleaning brush 49 is rotatably in contact with the charging roller 45 only by its own weight, and cleans the surface of the charging roller 45 while rotating along with the rotation of the charging roller 45. Since the contact is made only by its own weight without using a pressing means such as a spring or the like, even if the diameter of the metal core is small, the bending does not pose a problem.
[0056]
The toner transport auger 48 collects the waste toner scraped off by the cleaning blade 47 via the brush roller 46 and transports the waste toner to the waste toner storage unit 38 shown in FIG.
[0057]
Further, the photoconductor unit 12 is provided with a positioning main reference portion 51 as a reference when the photoconductor unit 12 is attached to and detached from the image forming apparatus main body A, and a front positioning sub-reference portion 52 and a rear positioning sub-reference portion 53 are connected. The photoconductor unit 12 is provided integrally with the bracket 50 so that the photoconductor unit 12 can be reliably positioned at a predetermined mounting position by the reference portions when the photoconductor unit 12 is mounted on the apparatus main body A.
[0058]
In this example, since the photoconductor 14 and the charging roller 45 are integrally disposed in the respective photoconductor units 12, when the photoconductor unit 12 is replaced, the gap between the photoconductor 14 and the charging roller 45 is adjusted. There is no need to perform this operation, and the user can easily replace the photoconductor unit 12. In this example, the photoconductor unit in which the photoconductor 14, the charging roller 45, the brush roller 46, the cleaning blade 47, the toner conveying auger 48, and the like are integrated, but the brush roller 46, the cleaning blade 47, the toner conveying The cleaning device for the photoconductor 14 such as the auger 48 may be configured as another unit. Further, the developing unit 13 may be a unit integrated with the photoconductor 14 and the charging roller 45.
[0059]
The charging roller 45 of this example is as shown in FIG. That is, the charging roller 45 is formed into a cylindrical conductive core 61 having an outer diameter of 6 to 10 mm and a cylindrical shape having a thickness t1 of 1 to 3 mm by covering the core 61 so as to extend from both ends. And a gap holding member 63 having a thickness t2 of 100 to 500 μm provided on a step 64 formed at both ends of the charging member main body 62.
[0060]
The core 61 is made of a metal such as stainless steel. If the cored bar 61 is too thin, the influence of bending when cutting or pressing against the photoreceptor cannot be ignored, and it is difficult to obtain the necessary gap accuracy. On the other hand, if the cored bar 61 is too thick, the charging roller 45 becomes large, Since the weight of the roller 45 becomes heavy, it is preferable that the roller 45 is formed of a metal such as stainless steel in a cylindrical shape having an outer diameter of 6 to 10 mm.
[0061]
Further, the charging member main body 62 ⁶ -10 ⁹ Materials having a medium volume resistivity of Ωcm are preferred. If the volume resistance is too low, leakage of the charging bias tends to occur when the photoconductor 14 has a defect such as a pinhole, and if the volume resistance is too high, the discharge does not sufficiently occur and a uniform charging potential is obtained. I can't. In forming the charging member main body 62, a desired volume resistance value can be obtained by mixing a conductive material with a resin serving as a base material.
[0062]
The resin used as the base material has good moldability and is easy to mold. Therefore, resins such as polyethylene, polypropylene, polymethyl methacrylate, polystyrene, ABS (acrylonitrile-butadiene-styrene copolymer), polycarbonate, and the like are used. Should be used.
[0063]
Further, as the conductive material, an ion conductive material such as a polymer compound having a quaternary ammonium base is preferable.
Examples of the polymer compound having a quaternary ammonium base include polyethylene, polypropylene, polybutene, polyisoprene, ethylene-ethyl acrylate copolymer, ethylene-methyl acrylate copolymer, ethylene-san vinyl acetate copolymer, ethylene-propylene having a quaternary ammonium base. And polyolefins such as copolymerization and ethylene-hexene copolymerization. In addition, the polymer compound having a quaternary ammonium base may be a polymer compound other than the above-mentioned polyolefin.
[0064]
The ion conductive material is uniformly blended with the above-mentioned base resin by using a means such as a biaxial kneader or a kneader. Injection molding or extrusion molding of the blended material into the cored bar 61 allows easy molding into a cylindrical shape. The compounding amount of the ion conductive material and the base resin is preferably 30 to 80 parts by weight based on 100 parts by weight of the base resin.
[0065]
If the thickness t1 of the cylindrical charging member main body 62 is too small, molding is difficult and the strength is low. If the thickness t1 is too thick, the charging roller 45 becomes large, and the charging efficiency decreases because the volume resistance value of the charging member main body 62 increases. Further, the charging member main body 62 may be formed with a protective layer having a thickness of several tens of μm to which toner or the like is hardly attached by coating or the like. The steps 64 may be formed at both ends of the charging member main body 62 when the charging member main body 62 is cut and the outer diameter is adjusted in the process molding.
[0066]
The gap holding member 63 is a heat-shrinkable tube made of an insulating fluororesin material such as PFA (tetrafluoroethylene-perfluoroalkylvinylether copolymer) or FEP (tetrafluoroethylene-hexafluoropropylene copolymer). is there. If the thickness of the gap holding member 63 is too small, the gap holding member 63 extends due to friction with the photoconductor 14 and separates from the charging member main body 62. The hardness of the gap holding member 63 is set lower than that of the charging member main body 62.
[0067]
Since the charging member main body 62 having such a configuration is excellent in releasability, it is difficult to apply an adhesive to the surface of the charging member main body 62. Therefore, the gap holding member 63 thermally shrinks the charging member main body 62. And attached to the step 64. Therefore, the gap holding member 63 can be provided without using the adhesive, and the gap holding member 63 can be provided without considering the thickness of the adhesive.
[0068]
The outer diameter φa of the charging roller 45 where the gap holding member 63 is attached is larger than the outer diameter φb of the charging roller 45 where the gap holding member 63 is not attached, that is, where the charging member main body 62 is exposed. Next, the depth d of the step 64 and the thickness t2 of the gap holding member 63 are adjusted.
[0069]
Then, a gear (not shown) is attached to the end of the core 61 of the charging roller 45 so as to mesh with a gear formed on the flange of the photoconductor 14 and to be rotatably attached to a bearing (not shown) of the photoconductor unit 12. Become. Then, the gap holding member 63 contacts the outside A2 of the image forming area of the photoconductor 14, and a gap Gp is formed between the charging member main body 62 and the photoconductor 14 in the inside A1 of the image forming area.
[0070]
Here, if the gap Gp between the charging roller 45 and the photoconductor 14 is too wide, abnormal discharge occurs and the surface of the photoconductor 14 cannot be uniformly charged, so that the maximum value of the gap Gp is 100 μm or less. , Φa and φb must be set. This setting is performed by appropriately adjusting the thickness t2 of the gap holding member 63 and the depth d of the step 64. As described above, since the photoconductor 14 and the charging roller 45 are required to have high-precision dimensions, the straightness of each of the photoconductor 14 and the charging roller 45 needs to be 20 μm or less.
[0071]
To charge the surface of the photoconductor 14 using the charging roller 45 configured as described above, when the photoconductor 14 is rotated by a drive motor, the gear formed on the flange of the photoconductor 14 The charging roller 45 rotates substantially synchronously with the photoconductor 14 via a gear attached to the end. Then, a charging bias supplied from a power supply (not shown) is applied to the charging member main body 62. Then, a discharge is generated between the surface of the charging member main body 62 provided with the gap Gp and the surface of the photoconductor 14. At this time, since the insulating gap holding members 63 are provided at both ends of the charging roller 45, the discharge does not occur intensively at both ends of the charging roller 45, and the surface of the photoconductor 14 is uniformly formed. Be charged. Then, after the writing unit 16 writes the electrostatic latent image, the image is developed by the developing unit.
[0072]
By the way, the gap holding member 63 is in contact with the photoconductor 14 outside the image forming area A2 of the photoconductor 14 to form the gap Gp between the charging member main body 62 and the photoconductor 14. And does not affect the image formation. In addition, since the charging member main body 62 is made of a material having a lower hardness than the charging member main body 62, even if the charging member main body 62 is formed of a hard resin material and an organic photoconductor is used as the photoconductor 14, There is no scratch on the surface.
[0073]
As described above, the thickness t2 of the gap holding member 63 and the depth d of the step 64 are appropriately adjusted to set φa and φb so that the maximum value of the gap Gp is 100 μm or less. When the gap holding member 63 of 100 to 500 μm is provided on the charging member main body 62, the depth d of the step 64 may be adjusted.
[0074]
In the charging roller 45 of this example, the gap Gp with the photoconductor 14 is formed by contacting the gap holding member 63 with the photoconductor 14 outside the image forming area A2. The body 14 rotates synchronously and generates frictional heat between the gap holding member 63 and the photoconductor 14. However, since the thickness t2 of the gap holding member 63 is 100 to 500 μm, the gap holding member 63 is unlikely to be stretched or deformed by frictional heat, and can always maintain a stable gap Gp.
[0075]
Further, by making the length of the cleaning brush 49 in the rotation axis direction longer than the length of the charging roller 45 in the rotation axis direction, the surface of the gap holding member 63 can be cleaned at the same time. The outer diameter φb of the portion of the charging member main body 62, which is the image area of the charging roller 45, and the outer diameter φa of the portion of the gap holding member 63, which is the coating portion of the heat-shrinkable tube, differ by about several tens to 100 μm. Since it is sufficiently smaller than the length of the bristle feet of the brush 49, the cleaning performance of the surface of the charging member main body 62 in the image forming area A1 does not deteriorate.
[0076]
As shown in FIG. 4, the gap holding member 65 of the charging roller 55 may cover a part of the side surface 62s at both ends of the charging member main body 62.
This makes it possible to more reliably prevent discharge from both ends of the charging roller 55. Further, since the gap holding member 65 has heat shrinkability, it is possible to easily cover the side surface 62s of the charging member main body 62 without requiring a special process.
[0077]
Incidentally, the charging roller 55 has a core 61 extending to both ends of the charging roller 55, which is rotatably attached to a bearing (not shown) of the photosensitive unit 12. Then, the bearing is pressed by a spring so that the gap holding member 65 of the charging roller 55 is brought into contact with the photoconductor 14 outside the image forming area A2, and a gap Gp is formed between the charging member main body 62 of the charging roller 55 and the photoconductor 14. Form. In the charging roller 55 having such a configuration, it is also possible to make the bearing and the spring conductive, and to apply a bias to the charging roller 55 via the bearing. When it is not necessary to apply a bias via a bearing, an insulating bearing may be used.
[0078]
The charging roller 55 is provided with a gear (not shown) attached to the end of the cored bar 61, meshes with a gear formed on a flange of the photoconductor 14, and rotates the photoconductor 14 by a drive motor of the photoconductor 14. The roller 55 rotates at substantially the same speed as the photoconductor 14. At this time, when the gap holding member 65 provided to protrude from the side surface 62s of the charging member main body 62 comes into contact with the bearing, the gap holding member 65 is deteriorated, deformed or broken, and the gap between the charging roller 55 and the photoconductor 14 is reduced. There is a risk of becoming unstable. Therefore, as shown in FIG.
In forming the step portion 67, the width B is larger than the thickness A of the gap holding member 65 provided to protrude from the side surface 62s of the charging member main body 62. Accordingly, the gap holding member 65 does not contact the bearing, and the durability of the charging roller 55 can be improved.
[0079]
Generally, the gap Gp between the photoconductor 14 and the charging roller 45 slightly fluctuates within a certain range as the photoconductor 14 and the charging roller 45 rotate. In order to uniformly charge the photosensitive member 14 in such a situation, in addition to the charging bias of the DC voltage applied to the charging roller 45, the charging start voltage between the charging roller 45 and the photosensitive member 14 is twice or more. It is effective to superimpose an AC bias having a peak-to-peak voltage.
[0080]
Here, when the frequency of the applied AC bias is low, stripe-shaped charging unevenness is conspicuous on the surface of the photoconductor 14, and therefore the frequency f [Hz] of the AC bias is at least the linear velocity v [mm / s] of the photoconductor 14. ] Is preferably set to 7 times or more. If the frequency of the AC bias to be applied is too high, excessive discharge occurs, increasing the abrasion amount of the photoreceptor 14 and filming of the toner or the toner external additive on the photoreceptor 14 easily occurs. Therefore, it is desirable to set the frequency f [Hz] to 12 times or less the linear velocity v [mm / s] of the photoconductor 14.
[0081]
In the above example, a small color printer as an example of the image forming apparatus has been described. However, the present invention is not limited to this, and may be a facsimile, a copier, or a multifunction machine of a printer, a facsimile, and a copier. Can be applied to any electrophotographic image forming apparatus.
[0082]
Further, in the above-described example, the photoconductor 14 and the charging roller 45 are provided integrally with the photoconductor unit 12, and the photoconductor unit 12 is detachably provided to the color printer. However, the present invention is not limited to this. Alternatively, the photoconductor 14 and the charging roller 45 may be provided separately.
[0083]
【The invention's effect】
As described above in detail, according to the first aspect of the present invention, since the charging member main body is made of a resin material containing an ion conductive material, it is easy to perform cutting, so that it can be processed with high precision. In addition, the gap holding member is made of an insulating resin material having a thickness of 100 to 500 μm having a hardness lower than that of the charging member main body and having heat shrinkability, forming a step at both ends of the charging member main body, and forming a maximum gap in the step. Since the gap holding member is provided so as to have a value of 100 μm or less, intensive discharge generated at both ends of the charging member main body can be prevented.
Therefore, it is possible to provide a charging device that is easy to process and that can prevent intensive discharge occurring at both ends.
[0084]
According to the second aspect of the present invention, since the gap holding member covers the side surfaces at both ends of the charging member main body, intensive discharge occurring at both ends of the charging member main body can be further prevented.
[0085]
According to the third aspect of the present invention, when the charging member main body is formed in a substantially cylindrical shape by covering the conductive core, and the core extending to both ends of the charging member main body is rotatably attached to the bearing. A step is provided on the core bar so that the gap holding member does not contact the bearing, and the step is attached to the bearing, so that the gap holding member does not contact the bearing and does not wear out, and a durable charging device is provided. Can be.
[0086]
According to the fourth aspect of the present invention, an AC bias is superimposed on the charging member main body, and a peak-to-peak voltage of the AC bias is equal to or more than twice a discharge start voltage between the charging member main body and the image carrier. Since the frequency f [Hz] of the AC bias satisfies the relationship of 7 × v <f <12 × v with the linear velocity v [mm / s] of the image carrier, charging unevenness is prevented and charging is performed. Excessive discharge between the member and the image carrier can be prevented.
[0087]
According to the fifth aspect of the present invention, since the image forming apparatus includes the charging device according to any one of the first to fourth aspects, it is possible to provide an image forming apparatus having the above-described respective effects.
[0088]
According to the sixth aspect of the present invention, since the image forming apparatus integrally includes the image carrier and the charging device in a detachable manner, it is possible to provide an image forming apparatus in which parts can be easily replaced.
[Brief description of the drawings]
FIG. 1 is a sectional view of an image forming apparatus as an example of the present invention.
FIG. 2 is a schematic sectional view of a photoreceptor unit used in the present invention.
FIG. 3 is a partial sectional view of a charging roller used in the present invention.
FIG. 4 is a partial cross-sectional view of another example of a charging roller used in the present invention.
FIG. 5 is a partial cross-sectional view of a charging roller as still another example used in the present invention.
[Explanation of symbols]
10Y, 10M, 10C, 10B imaging means
12, 12Y, 12M, 12C, 12B Photoconductor unit
13Y, 13M, 13C, 13B developing unit
14, 14Y, 14M, 14C, 14B Photoconductor (image carrier)
18 Transfer belt
19A, 19B, 19C, 19D Support roller
45 Charging roller (charging device)
46 brush roller
47 Cleaning blade
48 Toner Transport Auger
49 Cleaning brush
50 bracket
51 Positioning main reference part
52 Front-side positioning reference part
53 Back side positioning reference part
61,66 core
62 Charging member body
62s side
63, 65 Gap holding member
64 steps
67 steps
A1 Inside the image forming area
A2 Outside image forming area
d depth
Gp gap
t1, t2 thickness

Claims (6)

A charging device including a gap holding member that forms a gap between the charging member main body and the image carrier in the image forming region by abutting outside the image forming region of the image carrier;
The charging member body is made of a resin material containing an ion conductive material,
The gap holding member has a hardness lower than that of the charging member main body, and is made of an insulating resin material having a thickness of 100 to 500 μm having heat shrinkability,
A charging device, wherein a step is formed at both ends of the charging member main body, and the gap holding member is provided at the step so that the maximum value of the gap is 100 μm or less. The charging device according to claim 1, wherein the gap holding member covers both side surfaces of the charging member main body. When the charging member main body is formed in a substantially cylindrical shape by covering a conductive core metal, and when the core metal extending to both ends of the charging member main body is rotatably attached to a bearing, the gap holding member includes the bearing. The charging device according to claim 2, wherein a stepped portion is provided on the core bar so as not to contact with the bearing, and is attached to the bearing. An AC bias is superimposed on the charging member main body, and a peak-to-peak voltage of the AC bias is at least twice a discharge starting voltage between the charging member main body and the image carrier, and a frequency f [Hz of the AC bias is applied. Is between 7 × v <f <12 × v and the linear velocity v [mm / s] of the image carrier.
The charging device according to any one of claims 1 to 3, wherein the following relationship is satisfied. An image forming apparatus comprising the charging device according to claim 1. The image forming apparatus according to claim 5, wherein the image carrier and the charging device are integrally and detachably provided.

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