JP3304482B2 - Contact charging device and image forming device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to an image bearing member,
The present invention relates to an improvement in a contact charging device applied to an image carrier.

[0002]

2. Description of the Related Art As a brush charging device, there are a rotary brush type and a fixed brush type. For example, a rotating brush type brush charging device is configured such that a conductive roller is formed by forming a thin fibrous wire into a brush shape, and a brush is applied in a state where a DC voltage of 500 to 2 KV is applied to the conductive brush. Touch the tip to the photoconductor surface,
It rotates in a fixed direction and charges uniformly (Shinji Tetsuya “Contact charging technology without using a corona charger”, Journal of the Institute of Electrophotography 27, 4,573 (1988), Wano, Kimura, Nakajima “Conductive brush” Photoreceptor Charging Characteristics of Charging ", Journal of the Society of Electrophotography, 1987, PP97, 99, etc., and the basics and applications of electrophotographic technology (edited by the Electrophotographic Society), Corona P217. In addition, there is a fixed brush type brush charging device in which a conductive brush is used in a stationary state in a rod shape. The thickness of these brush fibers is
The diameter is 10 μm to several tens μm as standard values, and the resistivity of the brush is 10 ^3. Ω · cm-10 ⁵ Ω · cm.

[0003]

The conventional brush charging device has been cited as a major problem of uneven charging in both the rotating brush type and the fixed brush type. In the case of a rotating brush, there are the following types of uneven charging.

First, since the rotating brush is formed by winding a sheet-shaped conductive brush in a spiral manner around a roll core, the rotating brush is uniformly formed on the drum due to insufficient fiber density and uneven fiber direction at each sheet boundary. The fiber tip does not touch the
As a result, charging is not sufficiently performed, and spiral charging unevenness occurs.

Secondly, after leaving the drum in contact with the drum for a long period of time, the fibers at the contact portion lie down, causing breakage or bending. For this reason, uneven charging occurs due to insufficient contact with the drum.

Third, since a peripheral speed difference from the drum is required,
Driving in the direction opposite to the drum rotation direction is required. For this reason, a special driving device is required, and there are problems such as an increase in torque. Fourth, the cost is about three times or more that of the conventional corona charging method. On the other hand, although the fixed brush is more advantageous in cost than the rotating brush, the following problems are pointed out.

[0007] First, there is minute charging unevenness due to a decrease in the probability of contact with the drum, which is caused by the flocking density of the brush. There are restrictions on manufacturing to increase the brush flocking density, so measures such as widening the brush width are taken.However, increasing the contact probability per unit time to the rotating brush depends on the installation space etc. Have difficulty.

Secondly, it is easy to catch extraneous matter on the surface of the drum, such as fine toner after cleaning, and the extraneous matter at the electrostatic boundary part of the drum (a place corresponding to the rear end of the paper after transfer). May be discharged onto the surface of the drum again and adhered. These appear as stains on the output image. The problems of the rotating and fixed brushes have been described above. Problems common to the rotating and fixed brushes will be described.

The first is the detachment of the fibers from the base fabric. These include bristles in the process of manufacturing, breakage or detachment of fibers due to mechanical or electrostatic causes during operation. The detached fibers are mixed in other image forming processes such as a developing device and a transfer device, and cause various problems such as leaks and clogging of minute gaps.

Secondly, chemical fibers such as rayon in which carbon is dispersed in a brush charging device are usually used, and the fiber thickness is about 6D (φ30 μm). Since these rigid contacts based on the fiber length are in contact with the drum, the surface of the drum is scraped by friction at the sharp edge of the fiber tip drum contact portion. The abraded drum causes various problems such as a reduction in the charging potential due to a decrease in the film thickness or an insufficient cleaning due to local abrasion, which significantly reduces the life of the drum. In addition, the scraped drum surface sometimes adhered to the fiber tip and hindered uniform charging.

Thirdly, in the brush charging device, the amount of bite of the drum at the tip of the fiber is proportional to the charging potential. For this reason, in order to obtain a constant charging potential, a uniform bite amount is required over the entire length. However, it is difficult to perform uniform cutting to a degree that does not affect the charging potential in a predetermined fiber length cutting, and uneven charging occurs until the image quality is affected if the accuracy of attachment to the drum or bending of the fiber is included. .

The present invention has been made in view of the above circumstances, and an object of the present invention is to uniformly contact an image carrier, prevent charging unevenness, increase mechanical strength, and improve the image carrier. In the rubbing of the fiber, the occurrence of fiber breakage, dropout, etc. is prevented,
An object of the present invention is to provide an inexpensive contact charging device and an image forming apparatus that prevent generation of dirt in an output image.

[0013]

Means for Solving the Problems] contact charging device of the present invention, in the contact charging device for charging the photoreceptor in contact with the image bearing member, a core material having elasticity, wound on the core member
Conductive non-woven fabric obtained by polymerizing conductive polymer
The core made of electrically conductive non-woven fabric is removed using the elastic force of the core.
Part of the conductive non-woven fabric fits into the image bearing
A conductive holder for holding the body in surface contact
Voltage applying means for applying a voltage to the conductive nonwoven fabric via an electrically conductive holder .

An image forming apparatus according to the present invention comprises a charging unit for charging an image carrier, an exposure unit for forming a predetermined latent image on the image carrier charged by the charging unit, and a latent image for the latent image. Developing means for forming a visible image on the image carrier by adsorbing a developer onto the image carrier on which the image has been formed; and transferring the developed image on the image carrier developed by the developing means onto a transfer medium And a fixing unit for fixing the visual image transferred by the transfer unit onto a transfer medium, the charging unit includes an elastic core material,
Conductive non-woven fabric polymerized conductive polymer to be wound
And the core material wrapped with this conductive non-woven fabric, the elastic force of the core material
Utilizing it from the outside using a part of the conductive non-woven fabric
Conductive holder for holding the image carrier in surface contact
And voltage applying means for applying a voltage to the conductive nonwoven fabric via the conductive holder .

[0015]

When a voltage is applied to the conductive non-woven fabric which is in surface contact with the image carrier, the image carrier is charged. In this case, since the conductive non-woven fabric is in surface contact with the image carrier, charging unevenness is prevented and charging is performed uniformly. On a charged image carrier, a predetermined latent image is formed by exposure means, and on the image carrier on which the latent image is formed,
The developer is adsorbed by the developing means to form a visible image on the image carrier, and the visible image on the image carrier developed by the developing means is transferred onto a transfer medium by the transfer means. The developed image is fixed on the transfer medium by the fixing transfer means.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an image forming apparatus and a contact charging device according to the present invention will be described with reference to the drawings. FIG. 1 shows an image forming apparatus, which includes a drum photoconductor 202. The photoconductor 202 is, for example, a photoconductor as an image carrier used in a laser printer or the like. This photoconductor is φ3
It has a negative charge polarity in which a phthalocyanine-based charge generation layer having a thickness of about 0.05 μm and a charge transport layer of a hydrazone compound and polycarbonate having a thickness of about 18 μm are formed on a 0 mm aluminum tube. This photoconductor 20
2, a static eliminator 301 for uniformly exposing the surface of the photoconductor 202, a contact charging device 204 for uniformly charging the surface of the photoconductor 202, and scanning exposure of a laser beam onto the photoconductor 202 to form an image. A laser exposure unit 500 that forms an electrostatic latent image corresponding to a signal, a developing device 208 that visualizes the electrostatic latent image formed on the photoconductor 202 as a toner image, and a developing device 208 that converts the visualized toner image to a predetermined image. And an image transfer unit 209 for transferring the image to the image transfer medium (paper P). Further, a pair of aligning rollers 406 and a paper guide 420 are provided on a path for feeding the paper P from the paper cassette 400 containing the paper P to be transferred and the manual feed guide 404 to the image transfer unit 209. A conveyance guide 416 and a paper conveyance path 410 are provided at the subsequent stage of the image transfer unit 209, and communicate with the fixing device 350. Fixing device 35
0 is a heat roller 35 with a built-in heater lamp 351
2 and a pressure roller 353 pressed against the heat roller 352, and a paper P is provided between the rollers 352 and 353.
The toner image is fused and fixed on the sheet P by passing through the sheet P. The heat roller 352 and the pressure roller 353 are surrounded by a lower casing 354 and an upper casing 356, and have a structure in which heat is prevented from escaping to the outside as much as possible so as to secure a favorable temperature atmosphere required for fixing. The heat roller 352 is in a state in which a cleaner 358 is in contact with the heat roller 352, and is in a clean state so that good fixing can always be performed. In addition, the surface temperature of the heat roller 352 is detected by the thermistor 360 to perform fixing. The temperature is controlled so as to maintain the required temperature. At the subsequent stage of the fixing device 350, a paper discharge roller pair 408 and a paper discharge tray 14 are provided. Further, a drum cleaner 21 including an elastic blade member 232 that mechanically scrapes residual toner remaining on the photoconductor 202 from the photoconductor 202 is provided around the photoconductor 202.
0 is provided.

FIG. 2 is an enlarged view of the contact charging device 204 disposed around the photosensitive member 202. The contact charging device 204 includes a polyurethane foam core material 103 (thickness: 10 mm, width of a photosensitive member facing surface: 16 mm, hardness: 5 °, AS:
The conductive nonwoven fabric 100 is wound around the outer periphery of KER-C). The conductive nonwoven fabric 100 of this embodiment has a thickness of 0.4 mm.
Volume resistivity of about 10 ⁴ -10 ⁵ Ω · cm, surface resistivity 10 ⁵ -10 ⁶ Ω / □. A first example of the material is a conductive nonwoven fabric obtained by polymerizing polypyrrole, which is one of the π-conjugated conductive polymers, into a nonwoven fabric of polyester and nylon (trade name: ST Poly conductive nonwoven fabric NEA003 manufactured by Achilles Corporation). ) Is used. The fiber thickness of the conductive nonwoven fabric 100 is about 6 μm. In the first example, since a conductive polymer is polymerized as the conductive nonwoven fabric, there is no need to include a conductive material such as carbon, and the variation in electric resistance due to the dispersibility of carbon or the like is small.

Further, a metal conductive holder 102 made of U-shaped aluminum, stainless steel or the like for applying a voltage to and supporting the conductive non-woven fabric 100 is placed on the conductive non-woven fabric 100 by utilizing the elastic force of the core material 103. And is configured as a contact charging device.

The metal conductive holder 102 is electrically connected to a DC constant voltage power supply 104 as a voltage applying means, and is connected to a conductive non-woven fabric 100 as a contact through the metal conductive holder 102 through a predetermined position. Voltage (-4 in absolute value)
00V or more) is applied. The conductive nonwoven fabric 100 is 0.5 to 1.5 m from the surface of the photoconductor 202.
It is set to the biting amount of about m and is in light surface contact.

FIG. 3A is a schematic view of a surface (A surface) of the conductive nonwoven fabric 100 according to the present invention viewed from the drum photoreceptor side at a microscope level. Conductive nonwoven fabric 1 according to the present invention
No. 00 has a non-uniform fiber direction and many fibers are intricately entangled. Therefore, the fiber tip hardly protrudes from the surface, and the fiber surface mostly contacts the photoconductor 202. For reference, FIG. 3B is a schematic diagram of a microscope of the conventional brush charging device on the A surface.
Each fiber comes into contact with the photoconductor 202 in a bent state.

The nonwoven fabric used in this embodiment is ASTM
"A cloth-like substance having a web or mat-like structure in which fibers are joined together by a joining substance" as defined in, and is a cloth-like or sheet-like fiber material manufactured without using a spinning machine, loom, or knitting machine If so, chemical fibers such as acrylic and rayon may be used in addition to nylon and polyester. These are classified as dry nonwoven fabrics, but in the present invention, wet nonwoven fabrics typified by paper may be further subjected to a conductive treatment and used.

In the first example of this embodiment, a conductive non-woven fabric obtained by polymerizing polypyrrole, a conductive polymer (trade name, manufactured by Achilles Co., Ltd .; ST poly conductive non-woven fabric NEA0)
03) was used as a contact in surface contact with the photoreceptor, but other conductive non-woven fabrics may be used.

As a second example, there is a nonwoven fabric obtained by dispersing and blending carbon black or metal powder with a resin such as rayon, nylon, polyester or the like, and conducting a conductive treatment on the fiber itself.

As a third example, a non-woven fabric such as polyester or nylon is impregnated with a thermoplastic polyester in a solvent such as carbon and toluene to coat the surface of the insulating non-woven fabric. As a fourth example, a nonwoven fabric such as rayon may be composed of synthetic fibers carbonized under low pressure.

In this embodiment, the voltage applying means 104 is a DC constant voltage power supply as a first example. This is because the stability of the charging potential in the longitudinal direction of the photosensitive member 202 is good when printing small-size paper. Is selected from In the case of a constant current power supply, the transfer device 3 is located upstream of the photoconductor 202 in the rotation direction.
00, a positive transfer charge is applied to the surface of the photoconductor 202 via the paper. At this time, in the case of small-size paper, a portion where a positive charge is directly applied to the surface of the photoconductor 202 also occurs, so that it is impossible to absorb this potential difference during charging.

As a second example of the voltage applying means 104, there is one which applies an AC voltage. For example, frequency 1K
HZ, peak-to-peak AC voltage of 1.2KV -1.0
By superimposing a DC voltage of KV, stable charging characteristics with very little charging unevenness can be obtained.

The present inventor examined the charging characteristics of the contact charging device provided with the conductive nonwoven fabric according to the present invention with respect to the photoreceptor, and the results are shown in FIG. As can be seen from FIG. 4, it has been confirmed that the contact charging device of the present invention has the same function as the conventional brush charging device when the applied voltage rises from about -400 V and rises.

The present inventor examined the optical density of the output image at an arbitrary width of the contact charging device provided with the conductive nonwoven fabric according to the present invention in order to confirm the potential unevenness in the longitudinal direction of the photosensitive member 202. . That is, in the image forming apparatus shown in FIG. 1, the halftone image was output by increasing the developing bias potential applied to the developing device 208 from -400 V to a value closer to the charging potential -600 V. The result is shown in FIG. From FIG. 5, it has been confirmed that the contact charging device of the present invention greatly reduces charging unevenness compared to the brush charging device. Next, an image forming operation using this embodiment will be described.

As the drum photosensitive member 202 is rotated, the charge removing device 301 exposes the surface of the photosensitive member 202 uniformly. Next, in the contact charging device according to the present invention, a voltage of about -1.1 KV is applied to the conductive nonwoven fabric 100 via the metal conductive holder 102 by the voltage application means indicated by 104 in FIG. The contact charging device 204 uniformly applies
The photosensitive member 202 is charged to 600 V and is scanned and exposed to a laser beam on the photosensitive member 202 by using a laser exposure unit 500 to form an electrostatic latent image corresponding to an image signal. This photoconductor 202
The upper electrostatic latent image is developed by a developing device 208 using a two-component developer composed of toner t, visualized as a toner image, and sent to an image transfer unit 209.

On the other hand, paper taken out of the paper cassette 400 or manually fed from the manual feed guide 404 in synchronization with the toner image forming operation is transferred to the image transfer unit via the aligning roller pair 406 and the paper guide 420. 20
9, the toner image previously formed on the photoconductor 202 is transferred onto the sheet P by the operation of the transfer device 300. Next, the paper P passes through the paper transport path 410 under the guidance of the transport guide 416, is sent to the fixing device 350, and the toner image is fused and fixed to the paper P. Thereafter, the sheet is discharged to the sheet discharge tray 14 via the sheet discharge roller pair 408.

After the toner image is transferred onto the paper P,
The residual toner remaining on the photoconductor 202 is mechanically scraped off from the photoconductor 202 by a drum cleaner 210 including an elastic blade member 232.

The fixing device 350 includes a heater lamp 3
51, and a pressure roller 353 pressed against the heat roller 352 so that the toner image is melted and fixed on the sheet P when the paper P passes between the rollers 352 and 353. Has become.
The heat roller 352 and the pressure roller 353 are surrounded by a lower casing 354 and an upper casing 356, and have a structure in which heat is prevented from escaping to the outside as much as possible so as to secure a favorable temperature atmosphere required for fixing. The heat roller 352 is in a state in which a cleaner 358 is in contact with the heat roller 352, and is in a clean state so that good fixing can always be performed. In addition, the surface temperature of the heat roller 352 is detected by the thermistor 360 to perform fixing. The temperature is controlled so as to maintain the required temperature.

A paper guide 364 is arranged in the upper casing 356 and near the upstream side of the contact portion 362 between the heat roller 352 and the pressure roller 353. The guide is securely guided between the heat roller 352 and the pressure roller 353. A sheet guide 366 is provided on the sheet exit side of the fixing device 350, and guides the fixed sheet P to the sheet discharge roller pair 408.

[0034]

According to the contact charging device and the image forming apparatus provided with the conductive non-woven fabric according to the present invention, first, the conductive non-woven fabric is formed by directly joining fibers without using spinning, weaving and knitting steps. Since it is a certain type, it is possible to use a fiber having a non-uniform fiber orientation and a fine thickness as described above. From this, macroscopically as an aggregate of fibers,
Uniform contact is made to the photoreceptor. That is, in the conventional brush charging device in which the directionality of the fibers is constant, the charging unevenness occurs unless all the fibers are in the same direction over the entire length of the photoreceptor, whereas the fiber direction is uneven and the probability of contact with the photoreceptor is high. In the conductive nonwoven fabric of the present invention, uneven charging due to this directionality does not occur.

Second, since the fibers are intricately entangled and bonded, the fibers have excellent mechanical strength. Therefore, it is difficult for the fibers to be cut or slipped off when rubbed with the photoreceptor. Even if the fibers are slipped, the fibers are extremely thin, so that they do not affect other image forming processes. Third, since there are many paths of the charging current to the photoreceptor, which is the member to be charged, charging unevenness due to a difference in electric resistance between fibers does not occur.

Fourth, unlike a brush or the like, since the fibers are densely packed, it is difficult to capture the fine toner after cleaning, and even if it is captured, it does not discharge onto the photoreceptor. Therefore, it does not occur as a stain in the output image. Fifth, since the structure is simple and the conductive nonwoven fabric used as the contact does not include many steps in production, it is very inexpensive as a contact charging device.

[Brief description of the drawings]

FIG. 1 is a schematic explanatory view showing an example of an image forming apparatus of the present invention.

FIG. 2 is a sectional view showing an example of the contact charging device of the present invention.

3A is a schematic diagram of a contact surface of a contact charging device according to the present invention with a photoconductor, and FIG. 3B is a schematic diagram of a contact surface of a conventional contact charging device with a photoconductor.

FIG. 4 is a diagram showing a change in a charging potential of a photoconductor according to an applied voltage of a contact charging device according to the present invention, together with a case of a conventional contact charging device.

FIG. 5 is a diagram showing an optical density in a longitudinal direction of a photoconductor of a contact charging device according to the present invention, together with a case of a conventional contact charging device.

[Explanation of symbols]

14: paper discharge tray, 100: conductive non-woven fabric, 102: metal conductive holder, 103: core material, 104: voltage applying means, 202: drum photosensitive member, 204: contact charging device,
208: developing device, 209: image transfer unit, 210: drum cleaner device, 232: elastic blade member, 301 ...
Static eliminator, 400: paper cassette, 404: manual guide, 406: aligning roller pair, 410: paper transport path, 416: transport guide, 420: paper guide, 350
... fixing device, 351 ... heater lamp, 352 ... heat roller, 353 ... pressure roller, 354 ... lower casing,
356: Upper casing, 358: Cleaner, 360 ...
Thermistor, 408: paper discharge roller pair, 500: laser exposure unit.

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Masato Ogasawara 70, Yanagicho, Saiwai-ku, Kawasaki-shi, Kanagawa Prefecture Inside the Toshiba Yanagimachi Plant (56) References JP-A-4-51168 (JP, A) JP-A Sho56 -126861 (JP, A) Actual opening 57-94713 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) G03G 15/02 G03G 21/06

Claims (2)

(57) [Claims] 1. A contact charging device for charging a photoreceptor by contacting an image carrier, wherein a conductive material obtained by polymerizing an elastic core material and a conductive polymer wound on the core material.
And sex nonwoven core material wound with conductive nonwoven, utilizing the elastic force of the core member
And fitted from the outside, a part of the conductive non-woven fabric
A contact charging device, comprising: a conductive holder that holds the image bearing member in surface contact; and voltage applying means that applies a voltage to the conductive nonwoven fabric via the conductive holder . 2. A charging device for charging an image carrier, an exposure device for forming a predetermined latent image on the image carrier charged by the charging device, and an image carrier on which a latent image is formed by the exposure device. Developing means for adsorbing a developer on the body to form a visible image on the image carrier; transfer means for transferring the visible image on the image carrier developed by the developing means onto a transfer medium; An image forming apparatus comprising: a fixing unit that fixes a visual image transferred by a transfer unit onto a transfer medium; wherein the charging unit includes an elastic core material, and a conductive polymer wound around the core material. Polymerized conductive
And sex nonwoven core material wound with conductive nonwoven, utilizing the elastic force of the core member
And fitted from the outside, a part of the conductive non-woven fabric
An image forming apparatus, comprising: a conductive holder that holds the image bearing member so as to be in surface contact with the image carrier; and voltage applying means that applies a voltage to the conductive nonwoven fabric via the conductive holder .