JP2004198621A - Charging device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a low-cost highly durable charging device which ensures the durability of members for forming gaps between a charging member and an image carrier and makes the accuracy of the gaps between the charging member and the image carrier adequate, and to provide an image forming apparatus having the charging device. <P>SOLUTION: Ringlike members are fitted in annular grooves 105 formed at both ends of a charging roller 14 used for charging the image carrier. In addition, gap retention members 103 for forming gaps between the charging roller 14 and the image carrier are provided. Each of the gap forming members 103 has an area of 1.0 x 10<SP>-6</SP>to 3.0 x 10<SP>-6</SP>m<SP>2</SP>in a section containing the axis O of the charging roller 14. Accordingly, soiling of the charging roller can be prevented by the gaps formed between the charging roller 14 and the image carrier. This provides the low-cost highly durable charging device in which the durability of the members for forming the gaps between the charging roller and the image carrier is ensured and, at the same time, the accuracy of the gaps between the charging roller and the image carrier is made adequate. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a charging device provided with a charging roller for charging an image carrier such as a photoconductor, and an image forming apparatus such as a copying machine, a facsimile, or a printer having the same.
[0002]
[Prior art]
2. Description of the Related Art In an image forming apparatus such as a copying machine, a printer, or a facsimile, a toner image is formed and carried on a sheet-shaped recording medium by a transfer method or a direct method by an image forming process mechanism such as an electrophotographic method. Such an image forming process mechanism forms a toner image carried on a recording medium on an image carrier such as a photoreceptor. In one of the toner image forming processes, the image carrier is charged. The image forming process mechanism includes a charging device as a charging unit for performing the charging process.
[0003]
Conventionally, as a charging device, a charging device such as a scorotron which performs charging is mainly used, but this method has a problem that a large amount of discharge products such as ozone is generated. A charging device of a type that comes into contact with an image carrier has been widely used. In a charging device of this type, contamination such as toner adheres to a roller or the like with time, and if uneven charging occurs due to the adhesion of the stain, adversely affects image formation. This was a major factor in determining the life of the device.
[0004]
Therefore, as shown in [Patent Document 1], in a charging device using a roller, a film is attached to an end of the roller to reduce dirt on the roller, and a small gap is formed between the photoconductor and the roller. There has been proposed a technique for forming an image and suppressing adhesion of dirt. Further, as a technique for forming a gap by means other than a film, a technique has been proposed in which a step or a groove is provided at an end of a roller and a member for forming a gap is attached, as shown in [Patent Document 2]. On the other hand, as a material of the roller, an elastic member such as rubber or sponge is generally used, but a roller using a resin is also known as shown in [Patent Document 3].
[0005]
However, when the roller is made of rubber, it is difficult to perform machining with high precision by cutting, and there is a problem that the gap tends to fluctuate due to the environment due to large thermal expansion. On the other hand, a resin-made roller is high in hardness and easy to cut, but because of high hardness, when a film-shaped member is used as a member for forming a gap, this member is worn over time. There was a problem such as. When an organic photoreceptor is used as an image carrier, the photoreceptor may be damaged when a member forming a gap comes into contact.
[0006]
Therefore, in [Patent Document 2], a step is provided at the end of the roller so that the member forming the gap and the photoreceptor do not deteriorate and good durability is obtained, and the member forming the gap is made thicker. A technique of using an elastic body has been proposed. By providing a groove by a concave step at the end of the roller and attaching a member that forms a gap in this way, it is possible to prevent deterioration of this member and a contacting portion of the member of the photoconductor, Further, by attaching the member in a concave shape, it is possible to prevent the member from coming off.
[0007]
[Patent Document 1]
JP 2001-194868 A [Patent Document 2]
JP 2002-55508 A [Patent Document 3]
JP 2001-337515 A
[Problems to be solved by the invention]
However, when a thick member is used to form such a gap, although the durability is improved, there is a problem that a deviation in the thickness leads to a change in the gap and a change in the gap increases. It is conceivable to prevent such a change in the gap by cutting after attaching such a member to the roller body, but there is a problem that it takes time and costs.
[0009]
The present invention has a low cost, ensures the durability of a member forming a gap between a charging member and an image carrier, and improves the accuracy of the gap between the charging member and the image carrier. An object of the present invention is to provide a durable charging device and an image forming apparatus having the same.
[0010]
[Means for Solving the Problems]
In order to achieve the above object, the invention according to claim 1 includes a charging roller having peripheral grooves at both ends for charging the image carrier, and a ring-shaped member engaged with each of the peripheral grooves. In a charging device having a gap holding member for forming a gap between the charging roller and the image carrier, the gap holding members each have an area in a cross section including a rotation center axis of the charging roller, 1.0 × 10 ^{−6 to} 3.0 × 10 ⁻⁶ m ² .
[0011]
According to a second aspect of the present invention, in the charging device according to the first aspect, the gap holding member is made of a heat-shrinkable material.
[0012]
According to a third aspect of the present invention, in the charging device according to the first or second aspect, a ratio of a width of the gap holding member in an axial direction of the charging roller to a thickness of the gap holding member is 25 to 100. It is characterized by the following.
[0013]
According to a fourth aspect of the present invention, in the charging device according to any one of the first to third aspects, the charging roller has a resin layer.
[0014]
According to a fifth aspect of the present invention, in the charging device according to the fourth aspect, the resin layer contains an ion conductive material.
[0015]
According to a sixth aspect of the present invention, in the charging device according to the fourth or fifth aspect, a ratio of a thickness of the resin layer to a thickness of the gap holding member is 5 to 20.
[0016]
According to a seventh aspect of the present invention, in the charging device according to any one of the first to sixth aspects, the gap holding member is made of a fluorine-based resin.
[0017]
According to an eighth aspect of the present invention, in the charging device according to the seventh aspect, the fluorine-based resin has an insulating property.
[0018]
According to a ninth aspect of the present invention, in the charging device according to any one of the first to eighth aspects, the peak of the discharge starting voltage between the charging roller and the image carrier is twice or more by the charging roller. It is characterized by having a voltage applying means for applying a voltage obtained by superimposing an AC voltage having an intermediate voltage on a DC voltage to the image carrier.
[0019]
According to a tenth aspect of the present invention, there is provided an image forming apparatus including the charging device according to any one of the first to ninth aspects, and an image carrier charged by the charging device.
[0020]
According to an eleventh aspect of the present invention, in the image forming apparatus of the tenth aspect, the charging roller is formed by the gap holding member in an image area of the image carrier, which is sandwiched between the circumferential grooves in the axial direction. The gap between the corresponding area and the image carrier is set to 100 μm or less.
[0021]
According to a twelfth aspect of the present invention, in the image forming apparatus according to the tenth or eleventh aspect, the image forming apparatus has a length in contact with at least the two gap holding members in the axial direction, and cleans the charging roller and the two gap holding members. A cleaning member that performs cleaning.
[0022]
According to a thirteenth aspect of the present invention, in the image forming apparatus according to any one of the tenth to twelfth aspects, at least the charging device and the image carrier are integrally detachable from the image forming device main body. There is a feature.
[0023]
【Example】
FIG. 1 schematically shows an image forming apparatus to which the present invention is applied. The image forming apparatus may be any known one such as a copying machine, a facsimile, and a printer, but the image forming apparatus in this embodiment is a printer. Although the image forming apparatus of this embodiment forms a full-color image, it may form a single-color image.
[0024]
The image forming apparatus 100 has a higher heat capacity than plain paper generally used for copying and the like, 90K paper such as OHP sheets, cards, and postcards, thick paper having a basis weight of about 100 g / m ² or more, and envelopes. Any of the large so-called special sheets can be used as a sheet-shaped recording medium for fixing a toner image. The size of the recording medium may be a size conforming to a general standard such as A4 size or A3 size, or may be a size out of the standard formed by cutting or the like.
[0025]
In the apparatus main body 1 of the image forming apparatus 100, four photoconductor units 2A, 2B, 2C and 2D as image carrier units are detachably mounted on the apparatus main body 1, respectively. At a substantially center of the apparatus main body 1, a transfer unit in which the transfer belt 3 is rotatably mounted in a direction indicated by an arrow A between a plurality of rollers including a paper suction roller 58 is disposed. Inside the transfer belt 3, four transfer brushes 57 are provided corresponding to the four photoconductors 5, respectively.
[0026]
The photoreceptor 5 as an image carrier provided in each of the photoreceptor units 2A, 2B, 2C, and 2D is disposed on the upper surface of the transfer belt 3 so as to be in contact with the photoreceptor unit. A charging device 30 is provided in each of the photoconductor units 5 in each of the photoconductor units 2A to 2D. Developing devices 10A to 10D that use different colors of toner are arranged corresponding to the photoconductor units 2A to 2D.
[0027]
The developing devices 10A to 10D have the same configuration, and are two-component developing type developing devices that differ only in the color of the toner used. The developing device 10A uses magenta toner, the developing device 10B uses cyan toner, the developing device 10C uses yellow toner, and the developing device 10D uses black toner. In each of the developing devices 10A to 10D, a developer including a toner and a carrier is stored.
[0028]
Each of the developing devices 10A to 10D includes a developing roller (not shown) facing the photoconductor 5, a screw for conveying and stirring the developer, a toner density sensor, and the like. The developing roller comprises an outer rotatable sleeve and a magnet fixed inside. The toner is supplied from the toner supply device in accordance with the output of the toner density sensor.
[0029]
The toner has a binder resin, a colorant, and a charge control agent as main components, and is further configured to include other additives as necessary. Specific examples of the binder resin include polystyrene, styrene-acrylate copolymer, polyester resin, and the like. 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.
[0030]
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.
[0031]
Examples of the fluidity-imparting agent include fine particles of metal oxides such as silica, titania, and alumina, and those obtained by subjecting these fine particles to surface treatment with a silane coupling agent, a titanate coupling agent, and the like, polystyrene, polymethyl methacrylate, and polyvinylidene fluoride. And the like. 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.
[0032]
As a method for producing a toner for a two-component developer, 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.
[0033]
As the carrier, a core material itself or a core material provided with a coating layer is generally used. Ferrite and magnetite can be used as the core material of the resin-coated carrier. The particle size of the core material is suitably about 20 to 60 μm. 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.
[0034]
A writing unit 6 is arranged above the photoreceptor units 2A to 2D, and a duplex unit 7 is arranged below the transfer belt 3. A waste toner storage unit 18 is located below the duplex unit 7. The image forming apparatus 100 has, on the left side of the apparatus main body 1, a reversing unit 8 for reversing and discharging a transfer sheet P as a recording medium after forming an image, or conveying the transfer sheet P to the duplex unit 7. .
[0035]
Although not shown in detail, the writing unit 6 includes four laser diode (LD) type light sources prepared for each color, a set of polygon scanners having six polygon mirrors and a polygon motor, and It has an fθ lens, a lens such as a long WTL, a mirror, and the like, which are arranged in the channel of the light source. The laser beam emitted from the laser diode is deflected and scanned by the polygon scanner and is irradiated on the photoconductor 5.
[0036]
The duplex unit 7 has a pair of transport guide plates 45a and 45b and a pair of transport rollers 46 in this embodiment, and a pair of transport rollers 46, and a duplex image forming mode for forming an image on both sides of the transfer paper P. Occasionally, the transfer paper P, on which an image is formed on one side and conveyed to the reversing conveyance path 54 of the reversing unit 8 and conveyed by switchback conveyance, is received and conveyed toward the paper feeding unit.
[0037]
The reversing unit 8 includes a plurality of paired transport rollers and a plurality of paired transport guide plates. The reversing unit 8 reverses the transfer paper P for forming a double-sided image as described above and carries out the reverse side to the double-sided unit 7. And discharges the transfer paper P after image formation to the outside of the image forming apparatus 100 in the same direction, or discharges the transfer paper P to the outside of the image forming apparatus 100 with the front and back reversed. Separating sheet feeding sections 55 and 56 for separating and feeding the transfer sheets P one by one are provided in the sheet feeding sections provided with the sheet feeding cassettes 11 and 12, respectively.
[0038]
Between the transfer belt 3 and the reversing unit 8, a fixing device 9 for fixing the image of the transfer paper P on which the image has been transferred is provided. On the downstream side of the fixing device 9 in the transfer paper transport direction, a reversing discharge path 20 is formed by branching, and the transfer paper P transported to the reversal discharge path 20 is discharged onto a discharge tray 26 by a pair of discharge rollers 25. Making it possible.
[0039]
At the lower portion of the apparatus main body 1, paper feed cassettes 11 and 12 capable of storing transfer papers P having different sizes in two upper and lower stages are provided. A manual tray 13 is provided on the right side of the apparatus main body 1 so as to be openable and closable in a direction indicated by an arrow B. By opening the manual tray 13, manual paper can be fed from the manual tray 13.
[0040]
The photoconductor units 2A to 2D are units having the same configuration, the photoconductor unit 2A forms an image corresponding to magenta, the photoconductor unit 2B forms an image corresponding to cyan, and the photoconductor unit 2B. 2C forms an image corresponding to the yellow color, and the photoconductor unit 2D forms an image corresponding to the black color.
[0041]
The operation of the image forming apparatus 100 when forming a full-color image will be described. When the image forming apparatus 100 receives full-color image data, each photoconductor 5 rotates clockwise in FIG. 1, and the surface of each photoconductor 5 is uniformly charged by the charging device 30. The writing unit 6 applies a laser beam corresponding to a magenta image to the photoconductor 5 of the photoconductor unit 2A, and a laser beam corresponding to a cyan image to the photoconductor 5 of the photoconductor unit 2B. The photoconductor 5 of the unit 2C is irradiated with laser light corresponding to a yellow image, and the photoconductor 5 of the photoconductor unit 2D is irradiated with laser light corresponding to a black image. An image is each formed. Each of the latent images reaches the positions of the developing devices 10A, 10B, 10C, and 10D by rotating the respective photoconductors 5, and is developed there by magenta, cyan, yellow, and black toners, and the four color toners are developed. It becomes an image.
[0042]
On the other hand, the transfer paper P is selectively fed from the paper feed cassettes 11 and 12 by the separation paper feed units 55 and 56, and is transferred onto the respective photoconductors 5 by a pair of registration rollers 59 provided immediately before the transfer belt 3. The sheet is conveyed at a timing coincident with the formed toner image. The transfer paper P is charged to a positive polarity by a paper suction roller 58 disposed near the entrance of the transfer belt 3, and is thereby electrostatically attracted to the surface of the transfer belt 3. While the transfer paper P is being conveyed while being attracted to the transfer belt 3, magenta, cyan, yellow, and black toner images are sequentially transferred, and a full-color toner image of four colors is formed. .
[0043]
The transfer paper P to which the toner image has been transferred is fused and fixed by the application of heat and pressure in the fixing device 9, and then passes through a paper discharge system according to the designated mode, and passes through the upper portion of the apparatus main body 1. When the double-sided image formation mode is selected, the sheet is inverted and discharged to the sheet discharge tray 26, the sheet is straight discharged from the fixing device 9 and straightly discharged through the inside of the reversing unit 8, or the inside of the reversing unit 8 is selected. After being fed into the reverse conveyance path, it is switched back and conveyed to the double-sided unit 7, where it is re-fed and the image forming unit provided with the photoreceptor units 2A to 2D. Is discharged. Thereafter, when an instruction to form two or more images is given, the above-described image forming process is repeated.
[0044]
The operation of the image forming apparatus 100 when forming a black and white image will be described. When the image forming apparatus 100 receives the black and white image data, the driven roller supporting the transfer belt 3 moves downward, and the transfer belt 3 separates from the magenta, cyan, and yellow photoconductors 5. The photoconductor 5 of the photoconductor unit 2D rotates clockwise in FIG. 1, and the surface of the photoconductor 5 of the photoconductor unit 2D is uniformly charged by the charging device 30.
[0045]
The photoconductor 5 of the photoconductor unit 2D is 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 device 10D, it 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.
[0046]
On the other hand, the transfer paper P is selectively fed from the paper feed cassettes 11 and 12 by the separation paper feed units 55 and 56, and is exposed to the photosensitive drum 2 </ b> D by the registration roller pair 59 provided immediately before the transfer belt 3. The sheet is conveyed at a timing coincident with the toner image formed on the body 5. The transfer paper P is charged by a paper suction roller 58 disposed near the entrance of the transfer belt 3, and is thereby electrostatically attracted to the surface of the transfer belt 3.
[0047]
Since the transfer paper P is conveyed while being attracted to the transfer belt 3, even if the transfer belt 3 is separated from the magenta, cyan, and yellow photoconductors 5, it is conveyed to the black photoconductor 5, and the black toner image is formed. Is transcribed. In order to stably transfer the transfer paper P by electrostatic attraction, the transfer belt 3 needs to have at least the surface layer made of a material having high resistance.
[0048]
The transfer paper P is fixed by the fixing device 9 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. As a material of the transfer belt 3, a resin material such as polyvinylidene fluoride, polyimide, polycarbonate, polyethylene terephthalate or the like 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.
[0049]
As shown in FIG. 2, each of the photoconductor units 2A to 2D includes a charging device 30, a photoconductor 5 on which an electrostatic latent image is formed, a brush roller 15 for cleaning the surface of the photoconductor 5, and a cleaning blade 47. are doing. The charging device 30 has a charging roller 14 and a gap holding member 103 engaged with the charging roller 14. A cleaning roller 49 for cleaning the roller surface is in contact with the charging roller 14 and the gap holding member 103.
[0050]
The brush roller 15 moves the toner scraped off by the cleaning blade 47 to the toner transport auger 48 side, and the collected waste toner is rotated by rotating the toner transport auger 48 to the waste toner storage section 18 shown in FIG. It is configured to be transported. In this embodiment, the diameter of the photoconductor 5 is φ30 mm, and each of the photoconductors 5 rotates in the direction of arrow C at 125 mm / sec. The brush roller 15 rotates clockwise in synchronization with the rotation of the photoconductor 5.
[0051]
The photoreceptor units 2A to 2D are provided with a positioning main reference portion 51 as a reference when the photoreceptor units 2A to 2D are attached to and detached from the apparatus main body 1, and a front side positioning sub reference portion 52 and a rear side positioning sub reference portion 53 are provided. When the photoreceptor units 2A to 2D are mounted on the apparatus main body 1, the photoreceptor units 2A to 2D can be reliably positioned at predetermined mounting positions by their reference portions. I have.
[0052]
Since the photoreceptor 5 and the charging device 30 are arranged in one unit, the configuration is such that the positional relationship between the photoreceptor 5 and the charging device 30 is determined in the unit, and the entire unit is replaced. Since the photoconductor 5 and the photoconductor 5 can be integrally attached to and detached from the apparatus main body 1, there is no need to adjust the gap, and the user can easily exchange the photoconductor. Here, the unit in which the photoconductor 5, the charging device 30, and the cleaning system, that is, the brush roller 15, the cleaning blade 47, and the cleaning roller 49 are integrated has been described. However, the cleaning system may have another unit configuration. The developing device 10 may be a unit integrated with the photoconductor 5 and the charging device 30.
[0053]
The photoreceptor 5 is formed by laminating an undercoat layer, a charge generation layer mainly composed of a charge generation material, and a charge transport layer mainly composed of a charge transport material on a conductive support.
As the conductive support, a support having a volume resistance of 10 ⁴ 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 is used.
[0054]
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, or 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.
[0055]
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.
[0056]
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.
[0057]
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. 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. A protective layer may be formed on the photoconductor 5 as a surface layer for the purpose of protecting the photosensitive layer and improving durability.
[0058]
FIG. 3 is a cross-sectional view of the charging roller 14 and the gap holding member 103 constituting the charging device 30. FIG. 3 shows one end of the charging roller 14 and the gap holding member 103 engaged with this end. The other end of the charging roller 14 has the same configuration. The gap holding member 103 is also engaged with the portion.
[0059]
The charging roller 14 is configured to charge the photoreceptor 5 and includes a cored bar 101 serving as a conductive support and a resin layer 102 serving as a charging member. Has a peripheral groove 105 in which a step 104 is formed and the gap holding member 103 is fitted therein. The gap holding member 103 is a member for forming a gap between the charging roller 14 and the photoconductor 5, and is a ring-shaped member.
[0060]
The metal core 101 is made of metal such as stainless steel. If the cored bar 101 is too thin, the influence of deflection when cutting or pressing the photoreceptor 5 cannot be ignored, and it is difficult to obtain the necessary gap accuracy. If the core metal 101 is too thick, there is a problem that the charging roller 14 becomes large or the mass becomes heavy. Therefore, the diameter of the core metal is preferably about 6 to 10 mm.
[0061]
The resin layer 102 of the charging roller 14 is preferably made of a material having a volume resistance of 10 ⁶ to 10 ⁹ Ωcm. If the resistance is too low, leakage of the charging bias tends to occur when there is a defect such as a pinhole in the photoreceptor, and if the resistance is too high, sufficient discharge does not occur and a uniform charging potential cannot be obtained. A desired volume resistance can be obtained by adding a conductive material to the resin serving as the base material, that is, by including the conductive material in the resin layer 102.
[0062]
As the base resin, resins such as polyethylene, polypropylene, polymethyl methacrylate, polystyrene, ABS (acrylonitrile-butadiene-styrene copolymer), and polycarbonate can be used. Since these base resins have good moldability, they can be easily formed.
[0063]
As the conductive material, an ion conductive material such as a polymer compound having a quaternary ammonium base is preferable. Examples of the polyolefin having a quaternary ammonium group include polyethylene, polypropylene, polybutene, polyisoprene, ethylene-ethyl acrylate copolymer, ethylene-methyl acrylate copolymer, ethylene-san vinyl acetate copolymer, ethylene-propylene Polyolefin such as copolymerization and ethylene-hexene copolymerization. In the present embodiment, a polyolefin having a quaternary ammonium base has been described as an example, but a high molecular compound other than a polyolefin having a quaternary ammonium group may be used as long as the object of the present invention is not contravened.
[0064]
The ionic conductive material is uniformly compounded and contained in the base resin by using means such as a biaxial kneader or a kneader. By subjecting the compounded material to injection molding or extrusion molding on the cored bar 101, it can be easily molded into a roller 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]
The thickness of the resin layer 102 of the charging roller 14 is desirably 1 to 3 mm. If the resin layer 102 is too thin, molding is difficult, and there is a problem in strength. If the resin layer 102 is too thick, the charging roller 14 becomes large, and the actual resistance of the resin layer 102 increases, so that the charging efficiency decreases. A protective layer to which toner or the like is unlikely to adhere can be formed on the resin layer 102 to a thickness of several tens of μm by coating or the like.
[0066]
When cutting the resin layer 102 to adjust the outer diameter, a step 104 for attaching the gap holding member 103 is formed at an end of the resin layer 102. As the gap holding member 103, a heat-shrinkable tube made of a fluororesin material such as PFA (tetrafluoroethylene-perfluoroalkylvinyl ether copolymer) or FEP (tetrafluoroethylene-hexafluoropropylene copolymer) can be used. Since these resins are excellent in releasability, toner sticking hardly occurs.
[0067]
Further, by using an insulating fluororesin, no discharge is generated at the position of the gap holding member 103, so that it is possible to prevent the toner from electrostatically adhering. The shape of the step 104 may be any of the shapes shown in FIGS. Each of the charging rollers 14 shown in FIGS. 3 and 4 has an image area of the photoconductor 5, that is, an area 14a corresponding to an area where a latent image and a toner image are formed. The maximum gap is set to 100 μm or less.
[0068]
The charging roller 14 shown in FIG. 3 includes a first region 14 a, which is an area corresponding to the image area of the photoconductor 5, sandwiched between the circumferential grooves 105 in the axial direction D, and a circumferential groove 105 in the axial direction D. And a second region 14b located closer to the end and corresponding to the non-image region of the photoconductor 5. The charging roller 14 shown in FIG. 4 has only the first area 14a. Since the peripheral groove 105 also corresponds to the non-image area of the photoconductor 5, the portion where the peripheral groove 105 is formed can be considered to be included in the second area 14b. For convenience of explanation, a region located on the end side of the circumferential groove 105 in the axial direction D and corresponding to the non-image region of the photoconductor 5 will be described as a second region 14b.
[0069]
The charging roller 14 shown in FIG. 3 has the second region, and the gap holding member 103 is prevented from shifting by attaching the heat-shrinkable gap holding member 103 to the concave peripheral groove 105. There is an advantage that the tube as the gap holding member 103 does not come off without using an adhesive or the like. Since the charging roller 14 shown in FIG. 4 does not have the second region and has the peripheral groove 105 at an end thereof, there is an advantage that the peripheral groove 105 can be easily formed. 3 and 4 show cross-sections including the rotation center axis O of the charging roller 14 indicated by a chain line in each drawing.
[0070]
If the depth of the peripheral groove 105 formed by the step 104 is small, the function as a stopper is insufficient, and if the depth of the peripheral groove 105 formed by the step 104 is too large, the thickness of the resin layer 102 is reduced as described above. However, there is a problem in terms of strength due to the limitation of charging performance. In addition, since the aim of the cap is determined by the charging performance, the step 104 needs to be increased in order to use a thick heat-shrinkable tube for the gap holding member 103. As long as the ratio between the thickness of the resin layer 102 and the thickness of the heat-shrinkable tube serving as the gap holding member 103 satisfies the relationship of 5 to 20, the function as a stopper and the strength of the resin layer 102 can be compatible. Therefore, the present embodiment satisfies this relationship.
[0071]
The gap holding member 103 is applied to the outside of the image area of the photoconductor 5, that is, the area outside the area where the latent image and the toner image are formed, so that the gap between the resin layer 102 of the charging roller 14 and the photoconductor 5 is formed. Form. The charging roller 14 is configured such that a gear (not shown) attached to an end of the cored bar 101 meshes with a gear (not shown) formed on a flange (not shown) of the photoconductor 5, and the photoconductor 5 is rotated by a photoconductor driving motor (not shown). The charging roller 14 also rotates at substantially the same speed as the photoconductor 5.
[0072]
Since the resin layer 102 does not come into contact with the photoconductor 5, even if a hard resin material is used for the charging roller 14 and an organic photoconductor is used for the photoconductor 5, the photoconductor 5 may be damaged. There is no. Further, if the gap is too wide, abnormal discharge occurs and charging cannot be performed uniformly. Therefore, the maximum gap needs to be suppressed to 100 μm or less. For this reason, both the photoconductor 5 and the charging roller 14 need to be configured with high precision, and the straightness needs to be 20 μm or less.
[0073]
Since a gap is provided between the charging roller 14 and the photoconductor 5 by the gap holding member 103, the load applied to the charging roller 14 is concentrated on the heat-shrinkable tube serving as the gap holding member 103. Is done. Since the durability of the heat-shrinkable tube is affected by both the width and the thickness, the larger the cross-sectional area, the better the durability.
[0074]
Further, in a general heat-shrinkable tube, there is a thickness deviation of about ± 10% of the thickness, so that the thicker the thickness, the larger the gap fluctuation. Therefore, thicker tubes cannot be used. Furthermore, if the width of the heat-shrinkable tube is increased, the length of the charging roller 14 is correspondingly increased, which leads to an increase in the size of the image forming apparatus 100.
[0075]
Considering these facts and various experimental results, the cross-sectional area of the gap holding member 103 in the cross section including the rotation center axis O of the charging roller 14 is 1.0 × in view of the durability and the gap accuracy of the heat-shrinkable tube. A range of 10 ^{−6 to} 3.0 × 10 ⁻⁶ m ² is appropriate. Note that the gap holding member 103 is attached to the circumferential groove 105 by being heated and thermally contracted, and is integrated with the charging roller 14. This cross-sectional area is the cross-sectional area after being integrated with the charging roller 14. . It is appropriate that the ratio of the width of the gap holding member 103 to the thickness of the gap holding member 103 is in the range of 25 to 100 from the viewpoint of miniaturization of the image forming apparatus 100 and gap accuracy. In this embodiment, all of these conditions are satisfied.
[0076]
When a gap is formed between the charging roller 14 and the photoconductor 5 in this manner, the gap always fluctuates within a certain range as the photoconductor 5 and the charging roller 14 rotate. In order to uniformly charge the photoconductor 5 in such a situation, the charging bias applied to the charging roller 14 should be equal to or more than twice the discharge starting voltage between the charging roller 14 and the photoconductor 5 in addition to the DC voltage. It is effective to superimpose an AC voltage having a peak-to-peak voltage. When the frequency of the applied AC voltage is low, stripe-shaped uneven charging is conspicuous. Therefore, it is desirable to set the frequency [Hz] to 7 times or more the linear velocity [mm / s] of the photoconductor 5. In this embodiment, a voltage that satisfies these conditions is applied to the resin layer 102 by a voltage applying unit (not shown).
[0077]
As a member for cleaning the charging roller 14, a cleaning brush 49 is disposed above the charging roller 14. The cleaning brush 49 is made by electrostatically implanting conductive fibers having a hair length of 2 mm on a core bar having a diameter of 4 mm. The cleaning brush 49 is rotatably abutted on the charging roller 14 by its own weight only, and cleans the surface of the charging roller 14 while rotating in the surrounding direction as the charging roller 14 rotates. Since the contact is made only by its own weight without using a pressurizing means such as a spring, even if the diameter of the cored bar 101 is small, deflection does not matter.
[0078]
Here, the length of the cleaning brush 49 in the axial direction D is made longer than the length of the charging roller 14 including the portion covered by the gap holding member 103, that is, the length of the portion covered by the resin layer 102. By contacting the entire portion covered by the, the surface of the gap holding member 103 can be simultaneously cleaned. Although there is a difference in the outer diameter of the charging roller 14 between the first region 14 a and the covering portion of the gap holding member 103, the charging roller 14 has a diameter of about several tens μm, at most 100 μm or less, which is sufficiently smaller than the bristle of the cleaning brush 49. Therefore, the cleaning performance of the first region 14a does not deteriorate.
[0079]
The length of the cleaning brush 49 is at least the length in contact with both the gap holding members 103, that is, one of the gaps, so that the charging roller 14 and both the gap holding members 103 disposed at both ends of the charging roller 14 can be simultaneously cleaned. The gap holding member 103 has a length from an end of the holding member 103 on the end side of the charging roller 14 to an end of the other gap holding member 103 on the end side of the charging roller 14, and is disposed so as to abut the gap holding members 103. And preferably has a length equal to or greater than the length of the portion of the charging roller 14 covered by the resin layer 102, and preferably the length of the portion covered by the resin layer 102. It is desirable that it is in contact with the whole.
[0080]
(Example)
The charging roller 14 was manufactured as follows. A resin composition (volume resistivity: 10 ⁶ Ωcm) obtained by blending 60 parts by weight of an ionic conductive agent with 100 parts by weight of an ABS resin as a resin layer 102 on a core metal 101 made of stainless steel and having a diameter of 8 mm is formed by injection molding. After that, the surface was cut to a diameter of 12 mm. Here, a peripheral groove 105 having a width of 8 mm was formed by forming steps 104 at both ends of the resin layer 102, and a 150 μm-thick PFA tube was cut into the peripheral groove 105 to have a width of 8 mm, and was attached as the gap holding member 103. The tube was shrunk by heating in an atmosphere at 120 ° C. for 20 minutes.
[0081]
When this charging roller 14 was set in the photoconductor unit of a color printer made by Ricoh Ipsiocolor 8000, the average gap in the image area between the photoconductor 5 and the charging roller 14 was about 45 μm. Was 65 μm and 25 μm, respectively. The measurement of the gap was performed using a laser scan micrometer LSM-600 manufactured by Mitutoyo. Details of the measurement method are described in the Japan Hardcopy 2001 Transactions. A paper passing test was performed at a linear speed of 125 mm / s of the photoreceptor 5 using the Epsio Color 8000. The charging bias was a DC component of -700 V, the AC component was a sine wave having a peak-to-peak voltage of 2.2 kV and a frequency of 900 Hz.
[0082]
When a 50,000-sheet passing test was performed under the above conditions, the image was good throughout the test, and the state of the heat-shrinkable tube as the gap holding member 103 was good even after 50,000 sheets were passed, and the gap was the same as the initial state. State was maintained. Also, the resin layer 102 of the charged portion was hardly stained.
[0083]
(Comparative Example 1)
A charging roller similar to that of the example was manufactured except that the depth of the groove of the resin layer 102 to which the heat shrink tube as the gap holding member was attached was 25 μm, and the thickness of the PFA tube was 75 μm. The charging roller was set on the photosensitive member unit of the Epsior Color 8000, and the gap between the photosensitive member 5 and the charging roller was measured. The average gap was about 45 μm, and the maximum and minimum values of the gap were 55 μm and 35 μm, respectively. Was.
[0084]
When a 50,000-sheet passing test was performed under the same conditions as in the example, the initial image was good, but fine dot-like stains appeared on a part of the image from around 30,000 sheets. Became. When the photoreceptor unit was checked, the heat-shrinkable tube as the gap holding member was elongated, and it protruded from the groove and climbed on the step 104, and the toner was clogged between the tube and the resin layer 102, so that the gap became too wide. Dirty dust had occurred.
[0085]
(Comparative Example 2)
A charging roller similar to that of the example was prepared except that the depth of the groove of the resin layer 102 to which the heat shrink tube as the gap holding member was attached was 400 μm, and the thickness of the PFA tube was 450 μm. When this charging roller was set on the photosensitive member unit of the Epsior Color 8000, and the gap between the photosensitive member 5 and the charging roller was measured, the average gap was about 45 μm, and the maximum value of the gap was 95 μm. The photoconductor 5 and the charging roller were in contact in the area.
[0086]
When a paper-passing test of 50,000 sheets was performed under the same conditions as in the example, the initial image was good, but the density unevenness of the charging roller cycle was found in a part of the halftone image from around 40,000 sheets. Began to occur. When the photoreceptor unit was checked, the condition of the heat-shrinkable tube as the gap holding member was good, but a part of the charging roller was very dirty with toner. It occurred near where it was.
[0087]
By configuring the charging device 30 as described above, when the image forming apparatus 100 having the charging device 30 forms an image as described above, whether the image is formed in a full-color image or a monochrome image. The surface of the photoconductor 5 is uniformly charged by the charging device 30 and is maintained over time, so that high-quality image formation is always performed.
[0088]
【The invention's effect】
The present invention is a charging roller having peripheral grooves at both ends for charging the image carrier, and a ring-shaped member engaged with each of the peripheral grooves, wherein the charging roller and the image carrier are In a charging apparatus having a gap holding member for forming a gap between the charging rollers, each of the gap holding members has an area in a cross section including a rotation center axis of the charging roller of 1.0 × 10 ^{−6 to} 3.0. × 10 ⁻⁶ m ² , the gap formed between the charging roller and the image carrier can prevent contamination of the charging roller, and the gap between the charging roller and the image carrier can be reduced at low cost. It is possible to provide a highly durable charging device that ensures both the durability of the member to be formed and the accuracy of the gap between the charging roller and the image carrier.
[0089]
Provided that the gap holding member is made of a heat-shrinkable material, the charging device can attach the gap holding member to the charging roller without using an adhesive and can prevent the gap holding member from coming off. can do.
[0090]
Assuming that the ratio of the width of the gap holding member in the axial direction of the charging roller to the thickness of the gap holding member is set to 25 to 100, the size of the entire charging device can be reduced by suppressing the size of the charging roller. It is possible to provide a charging device that can suppress the gap, improve the accuracy of the gap, and perform good charging.
[0091]
If the charging roller has a resin layer, it is possible to provide an inexpensive charging device that can be easily processed and has high accuracy, and can perform good charging.
[0092]
If the resin layer contains an ion conductive material, processing is easy, accuracy is easily obtained, good charging can be performed, and abnormal charging can be suppressed and good charging can be performed. A charging device can be provided.
[0093]
If the ratio of the thickness of the resin layer to the thickness of the gap holding member is set to 5 to 20, it is possible to suppress the enlargement of the charging roller and to suppress the enlargement of the entire apparatus, And a charging device capable of improving the gap accuracy and performing good charging.
[0094]
If the gap holding member is made of a fluorine-based resin, it is possible to provide a charging device which is excellent in releasability, hardly adheres dirt such as toner, and can perform good charging for a long period of time.
[0095]
If the fluororesin has an insulating property, it prevents electric leakage at a position where the gap holding member is in contact with the image carrier, and a discharge product generated by discharge at this contact position is applied to the image carrier. It is possible to provide a highly safe charging device capable of suppressing the amount of adhesion and preventing the entanglement of other members in contact with the image carrier caused by the increase in the friction coefficient of the image carrier.
[0096]
The charging roller is provided with voltage applying means for applying a voltage obtained by superimposing an AC voltage having a peak-to-peak voltage of at least twice the discharge start voltage between the charging roller and the image carrier on the DC voltage to the image carrier. If it is included, it is possible to provide a charging device that has high uniformity of charging potential and stability against environmental fluctuation even when the gap fluctuates, and can perform favorable charging.
[0097]
The present invention resides in an image forming apparatus having the charging device according to any one of claims 1 to 8 and an image carrier charged by the charging device. Accordingly, it is possible to provide an image forming apparatus that can perform favorable image formation over a long period at low cost.
[0098]
The gap between the first area corresponding to the image area of the image carrier, which is formed by the gap holding member and which is sandwiched between the circumferential grooves in the axial direction, and the image carrier is 100 μm or less. This makes it possible to provide an image forming apparatus in which abnormal discharge hardly occurs, the image carrier is uniformly charged, and good image formation can be performed.
[0099]
If the charging roller has a length in contact with at least both gap holding members in the axial direction and has a cleaning member for cleaning the charging roller and the two gap holding members, dirt such as toner may be present on the gap holding member. Prevents the gap from becoming unstable due to adhesion, prevents contamination of toner and the like on the surface of the charging roller from disturbing the charging potential, and performs good charging to perform good image formation. An image forming apparatus capable of performing the above can be provided.
[0100]
If at least the charging device and the image carrier can be integrally attached to and detached from the image forming apparatus main body, no adjustment is required even when a high-precision gap is required, and the user can easily replace the image forming device. Therefore, it is possible to provide an image forming apparatus which can perform good charging, perform good image formation, can be easily maintained, and is easy for the user to use.
[Brief description of the drawings]
FIG. 1 is a side view schematically showing a charging device to which the present invention is applied and an image forming apparatus having the same.
FIG. 2 is a side view showing the configuration around the image carrier, the charging device, and the image carrier shown in FIG.
FIG. 3 is a front sectional view of one end of the charging device shown in FIGS. 1 and 2;
FIG. 4 is a front sectional view of another configuration example of the charging device.
[Explanation of symbols]
5 Image Carrier 14 Charging Roller 14a Area 49 Corresponding to Image Area of Image Carrier Cleaning Member 100 Image Forming Apparatus 102 Resin Layer 103 Gap Type Holding Member 105 Circumferential Groove 105a First Groove 105b Second Groove D Charge roller Axial direction O Rotation center axis of charging roller

Claims (13)

A charging roller having a peripheral groove at both ends for charging the image carrier; and a ring-shaped member engaged with each of the peripheral grooves, wherein a gap is provided between the charging roller and the image carrier. In a charging device having a gap holding member for forming,
The charging device, wherein each of the gap holding members has an area of 1.0 × 10 ^{−6 to} 3.0 × 10 ⁻⁶ m ² in a cross section including a rotation center axis of the charging roller. 2. The charging device according to claim 1, wherein said gap holding member is made of a material having heat shrinkability. 3. The charging device according to claim 1, wherein a ratio of a width of the gap holding member in an axial direction of the charging roller to a thickness of the gap holding member is 25 to 100. The charging device according to any one of claims 1 to 3, wherein the charging roller has a resin layer. The charging device according to claim 4, wherein the resin layer contains an ion conductive material. 6. The charging device according to claim 4, wherein a ratio of a thickness of the resin layer to a thickness of the gap holding member is 5 to 20. The charging device according to any one of claims 1 to 6, wherein the gap holding member is made of a fluorine resin. 8. The charging device according to claim 7, wherein the fluororesin has an insulating property. 9. The charging device according to claim 1, wherein the charging roller applies an AC voltage having a peak-to-peak voltage that is at least twice as high as a discharge starting voltage between the charging roller and the image carrier. A charging device comprising: a voltage application unit for applying a voltage superimposed on a voltage to an image carrier. An image forming apparatus comprising: the charging device according to claim 1; and an image carrier charged by the charging device. 11. The image forming apparatus according to claim 10, wherein the charging roller is formed by the gap holding member, the area corresponding to the image area of the image carrier, sandwiched between the circumferential grooves in the axial direction, and the image carrier. An image forming apparatus, wherein a gap with a body is set to 100 μm or less. The image forming apparatus according to claim 10, further comprising a cleaning member that has a length that abuts at least the gap holding members in the axial direction, and that cleans the charging roller and the gap holding members. Image forming apparatus. 13. The image forming apparatus according to claim 10, wherein at least the charging device and the image bearing member are integrally detachable from an image forming apparatus main body. apparatus.

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