JP2002014519A - Image forming device and image carrier unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent an electrifying member such as an electrifying roller from coming into contact with the surface of an image carrier such as a photosensitive body in an image forming area. SOLUTION: Tape materials 18 and 18 are respectively wound in a peripheral direction and fixed at both ends of the conductive rubber roller part 17 of the electrifying roller 14, and a specified cavity C corresponding to the thickness of the tape material 18 is formed at a part in the image forming area Ac between the roller 14 and a photosensitive drum 5. Assuming that the straightness in the axial direction of the surface of the drum 5 is D and the straightness in the axial direction of the surface of the roller part 17 of the roller 14 is E, the cavity C holds relation D+E<C. Thus, the part in the area Ac of the roller 14 is prevented from coming into contact with the surface of the drum 5.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming area of a charging member, which is disposed close to a surface to be charged of an image bearing member so as to form a predetermined gap, and the charging member and the image bearing member are arranged. The present invention relates to an image forming apparatus provided with a charging device for charging the surface to be charged by applying a voltage between the image forming device and an image carrier unit mounted on the image forming device.

[0002]

2. Description of the Related Art Conventionally, an image forming area of a charging member is arranged close to the surface of a photoreceptor as an image bearing member, and a voltage is applied between the charging member and the photoreceptor to apply a voltage to the surface of the photoreceptor. There is a non-contact type charging device for charging a battery. In such a charging device, for example, a convex portion is formed on both ends of a roller portion formed of rubber of a charging roller serving as a charging member by winding a spacer or a tape around the outer periphery of the roller portion,
Thus, a non-contact charging device has been proposed in which a portion other than both ends of the charging roller is brought into non-contact with the surface of the photoreceptor and the photoreceptor is charged in that state ( For example, see JP-A-3-240076, JP-A-4-360167, JP-A-5-107871, and the like.

According to these non-contact charging devices, the portion of the charging roller corresponding to the image forming area does not come into contact with the photoreceptor, so that the adhered matter such as toner adhered to the surface of the photoreceptor does not transfer to the roller portion. You can do so.

[0004]

However, even if the charging roller is prevented from contacting the photosensitive member in the image forming area, the surface of the charging roller and the photosensitive member have minute irregularities, that is, their axial directions. Has a straightness that cannot be avoided in terms of machining accuracy (a value expressed by the height from the valley of the concave portion to the top of the peak of the convex portion, and when the object is flat, the flatness) Depending on the straightness (or flatness) of the surfaces of the charging roller and the photoconductor, they may come into contact with each other.

[0005] In this case, even if it is intended to be a non-contact charging device, when most of the surface of the charging roller comes into contact with the surface of the image bearing member, the surface of the image bearing member becomes inoperable. The dirt adhering to the surface of the charging roller is transferred to the surface of the charging roller, thereby deteriorating the charging performance.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and is intended to prevent a charging member such as a charging roller from coming into contact with a surface of an image carrier such as a photoreceptor in an image forming area. It is an object of the present invention to prevent dirt adhering to the surface of the carrier from transferring to the surface of the charging roller.

[0007]

According to the present invention, in order to achieve the above object, a charging member is arranged so that at least a portion of an image forming area forms a predetermined gap with respect to the surface of an image carrier. By applying a voltage between the charging member and the image carrier, in an image forming apparatus including a charging device configured to charge the surface of the image carrier, the flatness of the surface of the image carrier is A, When the flatness of the surface of the charging member facing the image carrier is B, and the predetermined gap is C, the following relationship is established. A + B <C

The predetermined gap is preferably formed by bringing a contact member provided outside the image forming area of the charging member into contact with the surface of the image carrier. Further, the predetermined gap is formed by an abutting member provided so as to be sandwiched between the charging member and the surface of the image carrier, so that the thickness of the abutting member becomes the predetermined gap C. You may.

Further, the roller-shaped charging member is brought into contact with the surface of the cylindrical image carrier via an abutting member provided outside the image forming area, thereby forming an image between the charging member and the image carrier. An image forming apparatus including a charging device configured to form a predetermined gap in the formation region and apply a voltage between the charging member and the image carrier to charge the surface of the image carrier, When the straightness in the axial direction of the surface of the image carrier is D, the straightness in the axial direction of the roller surface of the charging member is E, and the predetermined gap is C, the following relationship may be satisfied. D + E <C Further, there is provided an image carrier unit mounted on any one of the image forming apparatuses, wherein the image carrier and the charging member are integrally formed.

[0010]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic view showing a charging device and a photosensitive drum according to an embodiment of an image forming apparatus according to the present invention, and FIG. 2 is a seam of a tape material as an abutting member similarly wound around both ends of the charging roller. FIG. 3 is an overall configuration diagram showing a small-sized color printer which is an image forming apparatus having a plurality of charging devices and a plurality of photosensitive drums shown in FIG. 1 in order to explain the portions.

A color printer, which is an image forming apparatus shown in FIG. 3, is a four-drum full-color electrophotographic image forming apparatus. Units 2A, 2B, 2C and 2
D are detachably attached to the apparatus main body 1. In this small-sized printer, a transfer belt 3 is mounted at a substantially center in the apparatus main body 1 so as to be rotatable between a plurality of rollers in a direction indicated by an arrow A.

The photoreceptor drum 5 provided in each of the four photoreceptor units 2A, 2B, 2C and 2D contacts the upper surface of the transfer belt 3 in FIG. Units 2A to 2D are provided respectively. The developing device 1 uses a different toner color for each of the photoreceptor units 2A to 2D.
0A to 10D are provided.

A writing unit 6 is provided above the photosensitive units 2A to 2D, and a duplex unit 7 is provided below the photosensitive units 2A to 2D. Further, this small printer is equipped with a reversing unit 8 for reversing and discharging the transfer paper P after image formation and conveying it to the duplex unit 7 on the left side of the apparatus main body 1 in FIG.

Between the transfer belt 3 and the reversing unit 8, there is provided a fixing device 9 for fixing the image of the transfer paper on which the image has been transferred. On the downstream side of the fixing device 9 in the transfer paper transport direction, a reverse transport path 20 is formed by branching, and the transfer paper P transported there is allowed to be discharged onto a paper discharge tray 26 by a paper discharge roller pair 25. .

In a lower portion of the apparatus main body 1, a paper feed cassette 1 capable of storing transfer papers P having different sizes in two upper and lower stages is provided.
1 and 12 are provided respectively. Further, a manual tray 13 is provided on the right side of the apparatus main body 1 so as to be openable and closable in the direction of arrow B, and the manual tray 13 is opened so that manual paper can be fed therefrom.

The photoreceptor units 2A to 2D are units having the same configuration, the photoreceptor unit 2A forms an image corresponding to yellow, the photoreceptor unit 2B forms an image corresponding to magenta, The photoconductor unit 2C forms an image corresponding to cyan, and the photoconductor unit 2D
Forms an image corresponding to the black color. Then, they are arranged at intervals in the transport direction of the transfer paper.

As shown in FIG. 4, each of the photosensitive units 2A to 2D has a charging roller 14 of a charging device 4 and an OPC drum whose surface is charged by the charging roller 14 to form an electrostatic latent image by exposure. Drum 5, which is an image bearing member of a system, and a brush roller 15, which constitutes a cleaning device for cleaning the surface of the photosensitive drum 5, are formed as an integrated unit, and the unit 1 shown in FIG. It is made detachable with respect to.

As shown in FIG. 1, the charging device 4 includes a charging roller 14 serving as a charging member and a predetermined gap C between the image forming area Ac and the photosensitive drum 5 by a configuration described later.
And a voltage is applied between the charging roller 14 and the photosensitive drum 5 to charge the surface of the photosensitive drum 5 to be charged.

The charging roller 14 of the charging device 4 is, for example,
SUM-Ni plating (steel surface is nickel-plated
Both ends of the outer peripheral surface of the cored bar 16 which is the metal shaft formed by
Except for the parts excluding epichlorohydrin rubber
And the volume resistivity is 1 × 10 ³~ 1 × 10⁸Ω · cm
The conductive rubber roller portion 17 as an elastic portion was formed.
Things.

At both ends of the conductive rubber roller portion 17, an adhesive sheet having one surface formed of, for example, one of polyester, polyethylene terephthalate (PET), polypropylene (PP), and polyimide (PI) is formed on the adhesive surface. There is a tape material 1 which is an abutting member
8, 18 are wound in the circumferential direction with the adhesive surface inside. Here, in each of the tape materials 18, for example, a sheet layer is formed of polypropylene having a thickness of 40 μm, and an adhesive layer having a thickness of 20 μm is formed on an inner surface thereof to have a total thickness of 60 μm.

Then, each of the tape members 18, 18 on both sides thereof
As shown in FIG. 2, one side of the tape material 18 is shown, the edges 18a, 18b on both sides, which are both ends in the circumferential direction, do not overlap with each other, and the axial direction of the roller indicated by the arrow J is shown in all positions around the circumference. The adhesive surface side is fixed by sticking so that there is no portion where the tape material 18 does not exist. Therefore, as shown in the figure, both end portions of each tape material 18 are cut obliquely, and the cut edges 18
a and 18b are opposed to each other.

As shown in FIG. 1, in the charging device 4, the charging roller 14 is brought into contact with the tape material 18, 18 at both ends with the portion of the photosensitive drum 5 outside the image forming area Ac. By applying a voltage between the charging roller 14 and the photosensitive drum 5 from a power supply (not shown), the surface of the photosensitive drum 5 is charged.

The charging roller 14 slides at both ends of a core 16 by pressure springs 19, 19.
The photosensitive drum 5 is pressurized with a predetermined pressing force through the. The charging roller 14 is provided with a pressure spring 19
Alternatively, the tape members 18 at both ends may be brought into contact with the photosensitive drum 5 by its own weight without using.

A driving gear 40 is fixed to one end of the core 16 on the right side in FIG. 1, and a driving force from a motor (not shown) is transmitted to the driving gear 40 so that the charging roller 14 is connected to the same line as the photosensitive drum 5. It rotates at high speed. Charging roller 14
The voltage is applied to the core 16 by, for example, DC-7.
00V is applied under constant voltage control, and AC voltage is applied under constant current control.

The charging roller 14 has, for example, an outer diameter of the cored bar 16 of 9 mm and a conductive rubber roller portion 17 formed on the rubber layer of epichlorohydrin rubber having a wall pressure of 1.5 mm. Further, the conductive rubber roller portion 17
For example, rubber hardness is about 77 degrees in old JIS-A,
A rubber having a test piece hardness of 50 degrees or more is used.

The positions on the photosensitive drum 5 where the tape members 18, 18 on both sides of the charging roller 14 come into contact are:
This is the portion of the coating portion forming the photosensitive layer, and the coating portion is softer than the non-coating portion located outside the portion where the tape members 18 of the photosensitive drum 5 are in contact with each other. Made of material. Therefore, the tape material 1
The abrasion of the tape members 18, 18 can be reduced as compared with the case where the members 8, 18 contact the uncoated portion.

That is, Table 1 shows the case where the tape members 18 on both sides of the charging roller 14 are actually brought into contact with the coated portion on the photosensitive drum 5 and the case where they are brought into contact with the non-coated portion. This shows the results of experiments in which the degree of wear (tape scratches, turn-up, etc.) of the tape members 18 on both sides was confirmed. In each of the tape members 18 used here, the sheet layer was formed of a 40 μm thick polypropylene. Then, an adhesive layer having a thickness of 20 μm was formed on the inner surface thereof to obtain a total thickness of 60 μm. Then, continuous paper passing was performed up to 100,000 sheets, and the state of the tape material 18 was visually checked for each sheet shown in Table 1 in the middle. At that time, the tape materials 18 and 1 on both sides
8 was judged to be the one with the highest degree of wear. In the experiment, the tape 18 was brought into contact with the coated portion of the photosensitive drum 5 and the tape 18 was brought into contact with the non-coated portion, three times each.

According to the results of this experiment, the tape materials 18, 1
When the coating material 8 is brought into contact with the coated portion formed of a softer material than the non-coated portion, the tape 18 is clearly consumed better. In Table 1, ◎ indicates that there is no scratch on the surface of the tape material, ○ indicates that the surface of the tape material has rubbed marks but no problem, and △ indicates that the tape material is damaged and foreign matter is found at the cut. A state in which the tape material has swelled up (a state in which an abnormal image is obtained) is shown. A mark indicates a state in which the end of the tape material has been peeled off, and a mark X indicates a state in which the tape material has been completely peeled off.

[0029]

[Table 1]

The photosensitive drum 5 shown in FIG. 4 is rotationally driven in the direction of arrow C by a motor which is rotationally driven through a drum driving timing belt, a drum driving pulley (both not shown) and the like. An example of forming the photosensitive drum 5 will be described below. In addition, the photoconductor drum 5 is not limited to only the creation example described here. [Photoreceptor Preparation Example 1] A coating liquid for an undercoat layer, a coating liquid for a charge generation layer, a coating liquid for a charge transport, and a coating liquid for a protective layer are sequentially coated and dried on an aluminum drum having a diameter of 30 mm. To form a 3.5 μm undercoat layer, a 0.2 μm charge generation layer, a 20 μm charge transport layer, and a 5 μm protective layer in a laminated state, for yellow, magenta, cyan, and black. Photosensitive drums 5 were obtained.

The undercoat layer, the charge generation layer and the charge transport layer were formed by dip coating, and the protective layer was formed by spraying. The undercoat layer coating liquid is formed by combining the following. Alkyd resin (Veccosol 1307-60-EL:
6 parts by weight melamine resin (Super Beckamine G-821-6)
0): Dainippon Ink and Chemicals, Inc.) 4 parts by weight Titanium oxide (CR-EL: Ishihara Sangyo Co., Ltd.) 40 parts by weight Methyl ethyl kent 200 parts by weight

Next, the coating liquid for the charge generation layer is formed by combining the following. Charge generating substance having the structure shown in Chemical formula 1 3 parts by weight Polyvinyl atar (ESLEC BX-1: manufactured by Sekisui Chemical Co., Ltd.) 1 part by weight Methyl ethyl kent 100 parts by weight

[0033]

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The coating solution for charge transport is formed by combining the following. Z-type polycarbonate (Teijin Chemical: Panlite TS-2)
050) 1 part by weight Low molecular charge transporting material having the structure shown in Chemical formula 2 8 parts by weight Tetrahydrofuran 100 parts by weight Silicone oil (KF50-100CS: manufactured by Shin-Etsu Chemical Co., Ltd.) 1 part by weight

[0035]

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Next, the coating liquid for the protective layer is formed by combining the following. Z-type polycarbonate (Teijin Chemical: Panlite TS-2)
050) 10 parts by weight Low molecular charge transporting material having the structure shown in Chemical formula 3 7 parts by weight Tetrahydrofuran 100 parts by weight Cyclohexanone 400 parts by weight α-alumina (Sumicorundum AA-03: manufactured by Sumitomo Chemical Co., Ltd.) 5 parts by weight Part Specific resistance lowering material (BYK-P104: manufactured by BYK-Chemie) 0.05 parts by weight

[0037]

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[Photoreceptor Preparation Example 2] The same configuration as in Photoreceptor Preparation Example 1 was used, except that the coating liquid for the protective layer in Photoreceptor Preparation Example 1 was changed to the following. In this example, titanium oxide is used instead of α-alumina. The coating liquid for the protective layer is formed by combining the following. Z-type polycarbonate (Teijin Chemical: Panlite TS-2)
050) 10 parts by weight Low molecular charge transporting material having the structure shown in Chemical formula 4 7 parts by weight Tetrahydrofuran 100 parts by weight Cyclohexanone 400 parts by weight Titanium oxide (manufactured by Ishihara Sangyo) 5 parts by weight Specific resistance lowering material (BYK-P104) : Big Chemie) 0.05 parts by weight

[0039]

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[Photoreceptor Preparation Example 3] The same configuration as in Photoreceptor Preparation Example 1 was used except that the coating liquid for the protective layer in Photoreceptor Preparation Example 1 was changed to the following. In this example, silica is used in place of α-alumina. The coating liquid for the protective layer is formed by combining the following. Z-type polycarbonate (Teijin Chemical: Panlite TS-2)
050) 10 parts by weight Low molecular charge transporting material having the structure shown in Chemical formula 5 7 parts by weight Tetrahydrofuran 100 parts by weight Cyclohexanone 400 parts by weight Silica (manufactured by Shin-Etsu Silicone Co., Ltd.) 5 parts by weight Specific resistance lowering material (BYK-P104) : Big Chemie) 0.05 parts by weight

[0041]

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[Photoreceptor Preparation Example 4] The same configuration as in Photoreceptor Preparation Example 1 was used, except that the coating liquid for the protective layer in Photoreceptor Preparation Example 1 was changed to the following. In this example, Z-type polycarbonate is not used, and silica is used instead of α-alumina instead of low molecular charge transport substance and α-alumina. The coating liquid for the protective layer is formed by combining the following. Low molecular charge transporting material having the structure shown in Chemical formula 6: 18 parts by weight Tetrahydrofuran: 100 parts by weight Cyclohexanone: 400 parts by weight Silica (manufactured by Shin-Etsu Silicone Co., Ltd.): 5 parts by weight Specific resistance lowering material (BYK-P104: manufactured by BYK Chemie) 0.05 parts by weight

[0043]

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[Photoreceptor Preparation Example 5] The same configuration as in Photoreceptor Preparation Example 1 was adopted except that the thickness of the charge transport layer in Photoreceptor Preparation Example 1 was 25 μm and no protective layer was provided. Each of the photoreceptor units 2A to 2D shown in FIG.
A cleaning blade 47 having a leading end slidably in contact with the surface of the cleaning roller 47 to scrape off the transfer residual toner and the like adhering to the surface.
In 5, the waste toner is moved to the toner transport auger 48 side, and the waste toner collected by rotating the toner transport auger 48 is transported to a predetermined waste toner storage unit.

The photosensitive units 2A to 2D are
Also on the surface of the conductive rubber roller portion 17 of the charging roller 14,
For example, when a charging roller cleaner 49 made of a sponge is brought into contact with the conductive rubber roller 17, even if toner, dust, or the like floating in the apparatus adheres to the surface of the conductive rubber roller 17, it can be cleaned. Note that this photoconductor unit 2
In A to 2D, a positioning main reference portion 51 is provided as a reference for attaching and detaching the device to and from the apparatus main body 1 (see FIG. 3), and a front positioning reference portion 52 and a rear positioning reference portion 53 are provided. Are provided integrally with the bracket 50, and when the photoconductor units 2A to 2D are mounted on the apparatus main body 1, the photoconductor units 2A
2D can be reliably positioned at a predetermined mounting position.

Each of the photosensitive drums 5 of the photosensitive units 2A to 2D rotates in the direction of arrow C as described above, and their linear speeds are monochrome speed priority mode, monochrome image quality priority mode, and color speed priority. 185mm / sec, 125mm / sec depending on several modes such as mode, color image quality priority mode, thick paper / OHP passing mode
c, it can be adjusted in three stages of 62.5 mm / sec. In addition, this photoconductor unit
The brush roller 15 may be removed from the configuration, and the charging roller 14 and the photosensitive drum 5 may be configured as an integrated unit.

The developing devices 10A to 10D shown in FIG.
The configurations are all the same, and they differ only in the color of the toner used. The developing device 10A uses a yellow toner, the developing device 10B uses a magenta toner, the developing device 10C uses a cyan toner, and the developing device 10D uses a black toner. . The writing unit 6 shown in FIG. 5 is a laser diode (LD) type one-color, monochromatic two-beam writing unit of one polygon motor having two six-sided rotating polygon mirrors 22a and 22b. The writing unit 6 includes yellow scanning light and magenta scanning light and cyan scanning light by rotating polygon mirrors 22 a and 22 b emitted from a laser diode (not shown) serving as a light source and rotated by a polygon motor 21. And the scanning light for black are reflected right and left separately.

The scanning light for yellow and the scanning light for magenta pass through the two-layer fθ lens 23, respectively, and the scanning light for yellow is reflected by the mirror 27 to form a long WTL 24.
Through the mirror unit 28 via the mirrors 28 and 29
A is irradiated on the photosensitive drum 5 of A. The scanning light for magenta is reflected by the mirror 31, passes through the long WTL 32, and passes through the mirrors 33 and 34 to the photosensitive unit 2 </ b> B.
Is irradiated on the photosensitive drum 5. Further, the scanning light for cyan and the scanning light for black pass through the two-layer fθ lens 35.
, The cyan scanning light is reflected by the mirror 36, passes through the long WTL 37, and is irradiated onto the photosensitive drum 5 of the photosensitive unit 2C via the mirrors 38 and 39. The scanning light for black is reflected by the mirror 41, passes through the long WTL 42, and is irradiated onto the photosensitive drum 5 of the photosensitive unit 2D via the mirrors 43 and 44.

The duplex unit 7 shown in FIG. 3 comprises a pair of transport guide plates 45a and 45b and a plurality (four in this example) of transport rollers 46 forming a pair, and forms images on both sides of the transfer paper. In the double-sided image forming mode, 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 is received, and the photoconductor units 2A to 2D are provided. Is re-conveyed to the current image forming unit. The reversing unit 8 is composed of a plurality of transport rollers forming a pair and a plurality of transport guide plates forming a pair. The reversing unit 8 reverses the transfer paper P when forming a double-sided image as described above and carries out the transfer paper P to the duplex unit 7. And discharges the transfer paper P after image formation to the outside of the apparatus in the same direction, or discharges the transfer paper P to the outside of the apparatus by turning over. Separating sheet feeding sections 55 and 56 for separating and feeding the transfer sheets P one by one are provided in the sheet feeding section provided with the sheet feeding cassettes 11 and 12, respectively.

This small printer employs a roller curvature separation system using the transfer belt 3.
Inside, are provided four transfer brushes 57 corresponding to the four photosensitive drums 5, respectively. In this small printer, when the image forming operation is started, each photosensitive drum 5 rotates clockwise in FIG. Then, the surface of each photosensitive drum 5 is uniformly charged by applying a voltage between the photosensitive drum 5 and the charging roller 14 of each charging device. Then, the writing unit 6 irradiates the charged surface of the photosensitive drum 5 of the photosensitive unit 2A with a laser beam corresponding to a yellow image.

The writing unit 6 applies a laser beam corresponding to a cyan image to the charged surface of the photosensitive drum 5 of the photosensitive unit 2B, and a magenta laser to the charged surface of the photosensitive drum 5 of the photosensitive unit 2C. A laser beam corresponding to the color image is irradiated on the charged surface of the photoconductor drum 5 of the photoconductor unit 2D, and a laser beam corresponding to the black image is irradiated thereon, and a latent image corresponding to each color is formed thereon. Is done. Then, when the respective latent images reach the positions of the developing devices 10A, 10B, 10C and 10D by the rotation of the photosensitive drum 5, the latent images there are yellow, magenta,
The toner images are developed with cyan and black toners to form four color toner images.

On the other hand, the transfer paper P is fed from the selected paper feed stage in the paper feed cassette 11 or 12 by the separation paper feed unit 55 or 56, and is fed to the photosensitive unit 2A.
The registration roller pair 59 provided immediately before
At an accurate timing coincident with the toner image formed on each photoconductor drum 5, it is conveyed between the photoconductor drum 5 of the photoconductor unit 2 </ b> A and the transfer belt 3. At this time, the transfer paper P is charged to a positive polarity by the paper suction roller 58 disposed near the entrance of the transfer belt 3, and thereby is electrostatically attracted to the surface of the transfer belt 3. Then, while the transfer paper P is attracted to the transfer belt 3 and conveyed in the same direction by the rotation of the transfer belt 3 in the direction of arrow A, yellow, magenta, cyan, and cyan Each black toner image is sequentially transferred, and when the black toner image passes through the photoreceptor unit 2D, 4
A full-color toner image of color superposition is formed.

The transfer paper P is melted and fixed by applying heat and pressure to the transfer paper P in the fixing device 9, and thereafter passes through a paper discharge system according to a designated mode, and is discharged to the upper part of the apparatus main body. The sheet is inverted and discharged to the paper tray 26, or is straightly discharged from the fixing device 9 and passes through the inside of the reversing unit 8. Alternatively, when the double-sided image forming mode is selected, the sheet is fed back to the reversing conveyance path 54 in the reversing unit 8, is switched back, is conveyed to the double-sided unit 7, is re-fed from there, and is In the image forming unit provided with 2A to 2D, the image is discharged after an image is formed on the back surface. Thereafter, when an instruction to form two or more images is given, the above-described image forming process is repeated.

In this small printer, a predetermined gap C is formed in the image forming area Ac between the charging roller 14 and the photosensitive drum 5 as described with reference to FIG. Between a pair of tapes 18, 1
8, the gap C
Is a dimension such that when the straightness in the axial direction of the surface of the photosensitive drum 5 is D and the straightness in the axial direction of the surface of the conductive rubber roller portion 17 of the charging roller 14 is E, the relationship of D + E <C is established. I manage it.

That is, all parts have fine irregularities on the surface which cannot be avoided in manufacturing. Therefore, as shown in FIG. 6, a cross-sectional shape of one of the photosensitive drums 5 in the axial direction is enlarged, and the valleys 5 formed on the surface of the photosensitive drum 5 are enlarged.
a, the straightness D (= H ₁ ) in the axial direction of the photosensitive drum 5 obtained at the height H ₁ from the height a to the highest peak 5 b;
The highest peak portion 17b to a height of straightness E in the axial direction of the charging roller 14 obtained with H ₂ from the valley portion 17a which is formed on the surface of the conductive rubber roller portion 17 of the charging roller 14 as shown in FIG. 7 (= H ₂ ), the gap C shown in FIG. 1 is made larger.

The gap C maintaining the above relationship is determined by the thickness of the tape members 18 wound around the outer peripheral surfaces of both ends of the conductive rubber roller portion 17 of the charging roller 14. In this way, even if the peak 5b of the photosensitive drum 5 and the peak 17b of the conductive rubber roller 17 of the charging roller 14 face each other as shown in FIG.
Are in a relationship of D + E <C, the peak 5b of the photosensitive drum 5 does not contact the peak 17b of the conductive rubber roller 17 of the charging roller 14.

Therefore, according to this image forming apparatus,
Even when an adhered substance such as untransferred toner adheres to the surface of the photosensitive drum 5, since the charging roller 14 does not contact the surface of the photosensitive drum 5, the adhered substance is transferred to the surface of the charging roller 14. Nothing to do. Therefore, good charging performance is obtained, and a high-quality image is obtained. If the gap C is too large, the charging performance is degraded. For example, the gap C is preferably set to 100 μm or less. Further, the straightness D in the axial direction of the photosensitive drum 5 is D.
Is the maximum straightness in the axial direction at each of a plurality of different positions in the circumferential direction of the surface of the photosensitive drum 5, and D is the maximum straightness in the circumferential direction of the conductive rubber roller portion 17 of the charging roller 14. Assuming that the maximum straightness in the axial direction at each position is E, the peak 5b of the photosensitive drum 5 and the peak 17b of the conductive rubber roller 17 of the charging roller 14 are formed over the entire circumference. The probability of contact almost disappears.

However, the straightness D is determined only by the straightness of the surface of the photosensitive drum 5 in one axial direction, and the charging roller 1
Even if the straightness E is determined only by the straightness in one axial direction of the surface of the conductive rubber roller portion 17 of No. 4, each straightness of the conductive rubber roller portion 17 generally differs greatly from the straightness at other positions in the circumferential direction. There is no problem. By doing so, the peak 5b of the photosensitive drum 5 is
And the peak portion 17 of the conductive rubber roller portion 17 of the charging roller 14
Even if b may momentarily come into contact at a certain point in time, it does not matter since they do not always contact.

FIG. 9 is a schematic diagram showing the vicinity of an image forming section of an image forming apparatus in which the image carrier is a belt-shaped photosensitive belt. The image forming apparatus according to this embodiment is provided with a belt-shaped photoreceptor belt 75 which is an image carrier which is stretched between a plurality of rollers in an image forming unit and rotates in the direction of arrow G. The surface of the photoreceptor belt 75 is charged by a charging roller 14 of a charging device, and the charged surface is exposed by an optical system 81 including a light source, an illumination mirror, a projection lens, a projection mirror, and the like, and a latent image is formed thereon. Is done. The latent image is rotated by the rotation of the photoreceptor belt 75 in the direction of arrow G to form
When it moves to the position 2, it is developed by the developing device 72 and becomes a visible image (toner image).

Further, the visible image is transferred to a transfer sheet P by a transfer section 73, and the toner image is heated and fixed by a fixing device 74 and discharged to a discharge tray (not shown).
Then, the transfer residual toner remaining on the surface of the photoreceptor belt 75 is cleaned by the cleaning device 76, and the next image forming operation is repeatedly performed. Also in this image forming apparatus, the charging roller 14 has both ends of the conductive rubber roller portion 17 on the image forming area portion (see the image forming area Ac described in FIG. 1) on the surface of the photoreceptor belt 75 as an image carrier. Tape material 1 wrapped around the part and fixed
By bringing the portions 8 and 18 into contact, a predetermined gap C corresponding to the plate thickness is formed in the image forming area. A is the flatness of the surface of the photoreceptor belt 75, and B is the straightness of the surface of the charging roller 14 facing the photoreceptor belt 75 (or flatness if the charging member has a flat surface like a blade). Then, the relationship of A + B <C is established.

That is, the flatness B on the surface of the photoreceptor belt 75, which is determined from the height from the valley of the fine unevenness formed on the surface of the photoreceptor belt 75 to the highest peak, and the The gap C is larger than the value obtained by adding the straightness (flatness) A of the charging roller 14 obtained from the height from the trough formed on the surface of the conductive rubber roller portion 17 to the highest peak. Like that. With this configuration, the peaks of the photoreceptor belt 75 and the peaks of the conductive rubber roller 17 of the charging roller 14 do not come into contact with each other, so that the image forming apparatus described with reference to FIGS. Similarly to the above, it is possible to prevent the attached matter such as untransferred toner remaining on the surface of the photoreceptor belt 75 from being transferred to the charging roller 14.

FIG. 10 is a front view showing the charging roller and the photosensitive drum of the embodiment in which the abutting member is a roller. In this embodiment, the abutting member is a charging roller 14 '.
Rollers 82, 8 attached to both ends of the cored bar 16 formed of the metal shaft outside the image forming area Ac, respectively.
The rollers 82 are in contact with both ends of the photosensitive drum 5. Its roller 82, for example made of rubber, is formed to be larger than the outer diameter D ₁ of the conductive rubber roller portion 17 of the outer diameter D ₂ charging roller 14 ', the outer diameter D
Forming a predetermined gap C by the difference between the ₁ and D _2.

Also in this embodiment, the straightness D in the axial direction of the surface of the photosensitive drum 5 and the charging roller 14 'are also described.
The gap C is set to be larger than the value obtained by adding the straightness E in the axial direction of the surface of the conductive rubber roller portion 17 as described above. Even in this case, the conductive rubber roller portion 17 of the charging roller 14 ′ can be prevented from contacting the image forming area Ac on the surface of the photosensitive drum 5. Even if an adhered substance such as toner adheres, the adhered substance does not transfer to the surface of the charging roller 14 ', so that good charging performance can be obtained, and a high quality image can be obtained.

[0064]

As described above, according to the present invention, the following effects can be obtained. According to the image forming apparatus of the present invention, the surface of the charging member and the surface of the image carrier are larger than the value obtained by adding the flatness A of the surface of the image carrier and the flatness B of the surface of the charging member facing the image carrier. Is larger, the image forming area of the image carrier does not come into contact with the charging member. Therefore, even when dirt such as untransferred toner adheres to the surface of the image carrier, the dirt does not transfer to the charging member, so that a good charging performance can be obtained, and thereby a high quality image can be obtained. Is obtained.

According to the image forming apparatus of the present invention, the abutting members are rollers attached to both ends located outside the image forming area of the charging roller, and the rollers are brought into contact with both ends of the image carrier. Since the predetermined gap C can be formed, the charging member is a charging roller having a conductive rubber roller section, and a tape-shaped abutting member is wound around each end of the conductive rubber roller section to form the gap C. When the charging roller is pressed against the image carrier, the portion of the conductive rubber roller around which the abutting member is wound is elastically deformed, so that the gap C is narrowed, and the charging roller is moved to the surface of the image carrier. There is a risk of contact, but such a thing disappears.

According to the image forming apparatus of the present invention, the predetermined gap C is determined by the thickness of the abutting member provided outside the image forming area between the charging member and the surface of the image carrier. Even if the precision is not so severe, the gap C can be easily set to a target value only by controlling the thickness of the butting member.

According to the image forming apparatus of the present invention, even when the charging member has a roller shape and the image carrier has a cylindrical shape, the image forming area of the image carrier has a charging member. Good contact with the charging member, even when dirt such as untransferred toner adheres to the surface of the image carrier. Resulting in a high quality image.

According to the image carrier unit of the fifth aspect, since the image carrier is formed in the image carrier unit integrated with the charging member, the workability when replacing the image carrier and the charging member or performing maintenance. Can be improved.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a charging device and a photosensitive drum of an embodiment of an image forming apparatus according to the present invention.

FIG. 2 is a front view showing only one end side for explaining a seam portion of a tape material which is an abutting member wound around both end portions of the charging roller.

FIG. 3 is an overall configuration diagram showing a small color printer which is an image forming apparatus provided with a plurality of charging devices and photosensitive drums of FIG.

FIG. 4 is a configuration diagram showing a photosensitive unit provided in the small printer.

FIG. 5 is a configuration diagram showing a writing unit provided in the small printer of FIG. 3;

FIG. 6 is an explanatory diagram for explaining the straightness in the axial direction of the surface of the photosensitive drum.

FIG. 7 is an explanatory diagram for explaining the straightness in the axial direction of the surface of the conductive rubber roller portion of the charging roller.

FIG. 8 is a schematic diagram illustrating a state in which a peak of a photosensitive drum and a peak of a conductive rubber roller of a charging roller face each other.

FIG. 9 is a schematic configuration diagram illustrating the vicinity of an image forming unit of an image forming apparatus in which an image carrier is a belt-shaped photosensitive belt.

FIG. 10 is a front view showing the charging roller and the photosensitive drum of the embodiment in which the abutting member is a roller.

[Explanation of symbols]

2A, 2B, 2C, 2D: Photoconductor unit (image carrier unit) 4: Charging device 5: Photoconductor drum (image carrier) 14, 14 ': Charging roller (charging member) 18: Tape material (butting member) ) 82: Roller (butting member)

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Masumi Sato 1-3-6 Nakamagome, Ota-ku, Tokyo Inside Ricoh Company (72) Inventor Hitoshi Ishibashi 1-3-6 Nakamagome, Ota-ku, Tokyo Stock Ricoh Co., Ltd. (72) Inventor Hiroshi Yoshinaga 1-3-6 Nakamagome, Ota-ku, Tokyo Stock Company Ricoh Co., Ltd. (72) Inventor Iwa ▲ Saki ▼ Yukiko 1-3-6 Nakamagome, Ota-ku, Tokyo Stock Company F term in Ricoh Company (reference) 2H200 FA08 FA12 FA17 GA23 GA43 GB12 HA11 HB12 HB20 HB37 HB45 HB48 LA07 MA04 MC02 NA02 NA03

Claims (5)

[Claims] 1. A charging member is disposed such that at least a portion of an image forming area forms a predetermined gap with respect to the surface of an image carrier, and a voltage is applied between the charging member and the image carrier. Thereby, in the image forming apparatus provided with a charging device configured to charge the surface of the image carrier, the flatness of the surface of the image carrier is A, the surface of the charging member facing the image carrier is When the flatness is B and the predetermined gap is C, the following relationship is established. A + B <C 2. The image forming apparatus according to claim 1, wherein the predetermined gap is formed by bringing an abutting member provided outside the image forming area of the charging member into contact with the surface of the image carrier. Image forming apparatus. 3. The predetermined gap is formed by an abutting member provided so as to be sandwiched between the charging member and the surface of the image carrier, and the thickness of the abutting member is defined by the predetermined gap. 3. The image forming apparatus according to claim 1, wherein the image forming apparatus is C. 4. A roller-shaped charging member is brought into contact with the surface of a cylindrical image carrier via an abutting member provided outside the image forming area, so that a gap between the charging member and the image carrier is obtained. Forming a predetermined gap in the image forming area, and applying a voltage between the charging member and the image carrier to thereby charge a surface of the image carrier. In the apparatus, when the straightness in the axial direction of the surface of the image carrier is D, the straightness in the axial direction of the roller surface of the charging member is E, and the predetermined gap is C, the following relationship is established. An image forming apparatus comprising: D + E <C 5. An image carrier unit mounted on the image forming apparatus according to claim 1, wherein:
An image carrier unit in which the image carrier and the charging member are integrally formed.