JPH07287433A - Electrifier - Google Patents

Abstract

PURPOSE:To provide a high reliable electrifier capable of stably and excellently electrifying over a long period by eliminating electrification unevenness due to the fluctuation of a gap in a very small gap electrifier and a defect and soiling on the surfaces of an electrifying member and a body to be electrified. CONSTITUTION:In the electrifier 2 provided with the electrifying member 22 on which a discharge surface 23 is provided to face the surface of a photoreceptor 1 with a very small gap (g) and a power source 24 impressing a voltage between the electrifying member 22 and the photoreceptor 1 to charge the body to be electrified, the surface roughness of the discharge surface 23 of the electrifying member 22 is 5mum-100mum in 10-piece average roughness Rz.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a charging device for charging an object to be charged. In particular, the present invention relates to a charging device that is incorporated in an image forming apparatus such as an electrophotographic copying machine or a printer and that charges a surface of an electrostatic latent image carrier as a charged body.

[0002]

2. Description of the Related Art Conventionally, in an image forming apparatus such as an electrophotographic copying machine or a printer, a charging device has been used to charge an electrostatic latent image carrier such as a photosensitive drum. The surface of the charged electrostatic latent image carrier is irradiated with light according to the original image to form a latent image, and a toner image is formed according to the latent image, and the toner image is transferred to a transfer material. To be done.

Although various types of charging devices have been proposed and put into practical use, contact charging devices or minute gap charging devices, which generate almost no ozone, have been attracting attention due to environmental protection problems in recent years. There is.

The former is one in which a member to be charged and a charging electrode are in contact with each other, and a brush, a roller, a blade or the like is used as the charging electrode.

On the other hand, in the latter, as shown in FIG. 4, a semiconductive charging member 42 as a charging electrode is arranged on the surface of the photosensitive member 1 at a gap g of several tens μm to several hundreds μm (hereinafter referred to as a gap).
This charging member 4 is of a non-contact type that is brought close to
2 is adhered to the conductive support 41 by an adhesive having conductivity. Reference numeral 43 in the figure denotes a power source for charging the electrostatic latent image carrier 1 by applying a voltage to the charging member 42 to cause discharge between the photoconductor 1 and the charging member 42. In this minute gap charging device 2, there is a curve a shown in FIG. 5 between the applied voltage at the start of discharge and the gap g.
, Which follows a “Paschen curve” generally indicated by the curve d. Regarding the uniformity and stability of the discharge, if the gap g is less than about 100 μm, uniform and stable discharge is likely to occur and uniform charging is possible, but if the gap g exceeds about 100 μm, the uneven streamer is generated. -Like discharge and dot-like non-uniform charging.

[0006]

However, in the former charging device, since the charging electrode is in contact with the surface of the photosensitive member,
Creep deformation strain remains in the contact area of the charging electrode, which causes charging failure. In addition, stains such as toner and paper powder easily adhere to the charging electrode, which causes uneven charging, which in turn causes image unevenness.

On the other hand, in the latter charging device 2, the gap g between the photosensitive member 1 and the charging member 42 needs to be extremely small, less than about 100 μm, in order to obtain good charging.
This is because the dimensions are approximately the same as the dimensional tolerances of the components of the charging device 2. Therefore, even if a gap holding member such as a spacer is provided, the gap g varies due to the dimensional error of the spacer itself. It is known that the discharge between the member to be charged and the charging device depends on the gap g and the potential difference between the two, and if the gap g fluctuates, the charging potential of the photoconductor 1 becomes uniform. However, it has a problem of causing image noise.

[0008]

In view of the above problems, it is an object of the present invention to provide a charging device capable of uniformly charging an object to be charged even if the gap is increased. More specifically, it solves the uneven charging due to the fluctuation of the gap in the conventional minute gap charging device and the uneven charging due to the defects and the stains on the surface of the charging member and the body to be charged, and the stable and good charging is prolonged. An object is to provide a highly reliable charging device that can be obtained over a period of time.

[0009]

In order to solve the above-mentioned problems, the present invention is characterized in that the surface roughness of the discharge surface of a charging member is 5 μm to 100 μm in terms of ten-point average roughness Rz. Is.

[0010]

According to the present invention, stable discharge is performed from the roughened discharge surface. For example, when the surface of the charging member is made into a fine rough surface shape of 12 μm with a ten-point average roughness Rz defined in JIS-B-0601 by a general buffing treatment, the applied voltage at the start of discharge of the charger and the gap The relationship is as shown by the curve c in FIG. 5 when the curve b and Rz are 21 μm, and the discharge starts at a lower voltage than in the case where the surface is not roughened. In other words, if the applied voltage is the same, the upper limit value of the gap with which a stable discharge can be obtained becomes large by making the surface rough.

The suitable range of roughening is 10 μm to 100 μm, preferably 10 μm to 50 μm in terms of ten-point average roughness Rz. When Rz is 5 μm or less, no effect is seen, and when Rz is 100 μm or more, stable discharge cannot be obtained and image defects such as white spots due to nonuniform charging occur.

[0012]

Embodiments of the present invention will be described below with reference to the drawings. Hereinafter, an example in which the invention of the present application is applied to an electrophotographic printer will be described, but the invention of the present application is not limited to this, and can be applied to all charging devices that charge a body to be charged.

FIG. 1 is a front sectional view showing a schematic structure of an electrophotographic printer to which the present invention is applied. The printer 100 is provided with a drum-shaped photoconductor 1 which is an electrostatic latent image carrier serving as a member to be charged in a substantially central portion.
Is rotationally driven in the direction of arrow a by a driving means such as a motor (not shown). A charging device 2, a developing device 3, a transfer charger 4, and a cleaning device 5 are sequentially arranged around the photoconductor 1.

An optical system 7 is arranged above the photoconductor 1, and this optical system is provided in a housing 71 with a semiconductor laser generator, a polygon mirror, a toroidal lens, a half mirror, a spherical mirror, a folding mirror and a reflecting mirror. Etc. are arranged, and the exposure slit 7 is provided on the floor of the housing 71.
2 is formed, from which the photosensitive drum 1 can be imagewise exposed through a space between the charging device 2 and the developing device 3.

A timing roller pair 81, an intermediate roller pair 82, and a sheet feeding cassette 83 are sequentially arranged on the right side of the photosensitive member 1 in the figure, and a sheet feeding roller 84 faces the sheet feeding cassette 83. Further, a fixing roller pair 91 and a paper discharge roller pair 92 are sequentially arranged on the left side of the photosensitive drum 1 in the figure,
The paper discharge tray 93 faces the paper discharge roller pair 92. According to this printer 100, the surface of the photoreceptor 1 is the charging device 2
Are uniformly charged to a predetermined potential by the optical system 7 in the charged area.
Is imagewise exposed to form an electrostatic latent image. The electrostatic latent image thus formed is developed by the developing device 3 into a toner image, and the toner image is transferred to the transfer area facing the transfer charger 4.

On the other hand, from the paper feed cassette 83 to the paper feed roller 8
4, the transfer sheet is pulled out, reaches the timing roller pair 81 via the intermediate roller pair 82, and is fed to the transfer area in synchronization with the toner image on the photoconductor 1. Thus, in the transfer area, the photoreceptor 1 is acted upon by the action of the transfer charger 4.
The upper toner image is transferred onto the transfer paper, the transfer paper reaches the fixing roller pair 91, where the toner image is fixed, and then the paper is discharged to the paper discharge tray 93 by the paper discharge roller pair 92.

After the toner image is transferred onto the transfer paper, the toner remaining on the photoconductor 1 is cleaned by the cleaning device 5. The system speed of the printer 100 (peripheral speed of the photosensitive drum 1) is 3.5 cm / sec, and the developing device 3 is a one-component contact developing device for performing reversal development.

The photosensitive member 1 is a function-separated type organic photosensitive member for negative charging which is sensitive to long-wavelength light. For the charge generation layer, a mixture of τ-type metal-free phthalocyanine and polyvinyl butyral resin was formed on the aluminum drum of the substrate to a thickness of about 0.4 μm. Next, as a charge transport layer, a mixture containing a hydrazone compound and a polycarbonate resin as main components was formed to a thickness of about 18 μm. The member to be charged applicable to the present invention is not limited to the photoconductor 1 described above.

In this embodiment, the toner used in the developing device 3 is of a negative charging type, and a mixture containing a bisphenol A type polyester resin and carbon black as main components is kneaded, pulverized and classified by a known method to obtain an average particle size. Diameter is 1
The one having a diameter of 0 μm was used. Such toner was stored in the developing device 3 and development was performed under a developing bias of -300V.

Next, a schematic structure of the charging device 2 according to the present invention will be described with reference to FIG. The charging device 2 is a conductive support 2
The charging member 22 is adhered to the surface of No. 1 with an electrically conductive adhesive. An aluminum support plate having a thickness of 8 mm, a width of 10 mm, and a length of 240 mm was used as the conductive support 21 of this example. The conductive support 21 is not limited to the one made of aluminum, but may be made of iron, SUS, or the like.
A metal material such as steel, copper, chrome, or titanium, or a resin material or fiber material that has been subjected to a conductive treatment can be used. The surface of the charging member 22 facing the photoconductor 1, that is, the discharge surface 23 is roughened to a predetermined roughness as described later. The charging device 2 is arranged so that its discharge surface 23 approaches the charging surface of the photoconductor 1 in parallel with a predetermined gap g. Further, a power source 24 for applying a negative charging voltage is connected to the support plate 21. The applied voltage for charging may be an alternating voltage, or may be a superimposed direct voltage and an alternating voltage.

The charging device 2 shown in FIG.
The second discharge surface 23 is adhered to the conductive support 21 so that the discharge surface 23 has a substantially flat shape, but the shape is not limited to this and may be, for example, a cylindrical shape. In addition, the charging member 22
It is also possible to form a film without adhering to the conductive support 21. Further, a spacer or the like may be provided to secure a gap g between the discharge surface 23 and the photoconductor 1.

Materials for the charging member 22 include polyethylene, polypropylene, ionomer, polyvinyl alcohol, polyvinyl acetate, ethylene vinyl acetate copolymer, poly-4-methylpentene-1, polymethyl methacrylate, polycarbonate, polystyrene, acrylonitrile acryl. Methyl acid copolymer, acrylonitrile butadiene styrene copolymer, polyterephthalate ethylene, polyurethane elastomer, cellulose nitrate, cellulose acetate, cellulose triacetate, cellulose propionate, cellulose acetate butyrate, ethyl cellulose, regenerated cellulose, nylon 6, nylon 66, Nylon 11, Nylon 12, Polyimide, Polysulfone, Polyethersulfone, Polyvinyl chloride, Vinyl chloride vinyl acetate copolymer, Polyvinylidene chloride, Vinylidene chloride copolymer, a vinyl nitrile rubber alloy, polytetrafluoroethylene, polychlorotrifluoroethylene, polyvinyl fluoride, polyvinylidene fluoride, in a plastic material such as polyethylene tetrafluoroethylene copolymer,
Conductive carbon in powder form, fiber form, etc., metal such as iron, aluminum, copper, chromium, titanium, tin, zinc, gold, silver, cobalt, lead, platinum, antimony oxide, indium oxide, molybdenum oxide, It is possible to use a sheet or film that has been subjected to a conductive treatment by dispersing a metal oxide such as the above, a conductive polymer such as polyacetylene, polypyrrole, polythiophene, or the like. The material may be composed of two or more materials, or may be composed of two or more layers. In addition, such a film can be produced by a usual method of film molding such as a casting method, an extrusion method and a stretching method.

The electrical resistivity of the charging member 22 is preferably 10 11 Ωcm or less in order to prevent a voltage drop.
Further, in order to prevent the occurrence of spot-like discharge due to overcurrent, it is desirable to set it to 10 3 Ωcm or more. Further, the thickness thereof is not particularly limited as long as the strength is within a range that does not cause a problem in practical handling and durability, but generally about 15 to 500 μm can be considered.

As a method for roughening the discharge surface 23, for example, natural fibers (wool, deer hair, animal hair such as rabbit hair, cotton, linen, etc.), chemical fibers (rayon, acetate, nylon, polypropylene, acrylic, Polyester etc.), glass fiber or stainless steel fiber etc. are hardened with resin,
Alternatively, mechanical polishing means (buff polishing, brush polishing, etc.) in which sheet-like felt or cloth made of those fibers is entangled three-dimensionally by the action of moisture, heat, and pressure to rub it by rubbing it against a brush. Can be mentioned. When such a mechanical polishing means is used, an abrasive (particles made of resin or inorganic material) and water, a surface active agent, cutting oil or the like may be interposed between the rubbing member and the charging member. You don't have to. When using an abrasive, a felt, cloth, or brush in which abrasive particles are embedded or bonded may be used. The surface roughness is the type, size, thickness or density of the fiber, or when using abrasive particles, the type of abrasive particles, the shape of the particles, the particle size, the particle size distribution, the amount, and the pressing force of the polishing machine. It can be adjusted by the rubbing force. Further, as another method for roughening the discharge surface, a sand blast method or the like in which abrasive particles are struck on the surface of the charging member can be used.

Next, specific examples of the charging device 2 according to the present invention will be sequentially described together with comparative examples. Before that, measurement of potential unevenness on the surface of the photosensitive member 1 due to charging of the charging device 2 and image noise The evaluation method will be explained.

1. Measurement and evaluation method of surface potential and potential unevenness of photoreceptor 1 Surface potential meter at development position (manufactured by Trek, model 360)
Then, the surface potential (Vo) of the photoconductor 1 and the fluctuation range (ΔVo) of the surface potential were measured. Then, the fluctuation range (ΔVo) of the surface potential was evaluated as follows.
In addition, about the evaluation symbol ○, it is a preferable state, and the evaluation symbol Δ
The mark indicates that the potential unevenness is a little worrisome but can be put to practical use, and the evaluation symbol x indicates that it is a problem in practical use. Surface potential fluctuation range (ΔVo) Evaluation symbol 100 V or less ○ 100 V to 300 V Δ 350 V or more × 2. Image noise evaluation method Sakura densitometer (model PDA- manufactured by Konica Corporation)
65) was used to print a dot image of 1 dot / 4 dots, the width of fluctuation in image density after printing 500 sheets was measured in the width direction, and the width of fluctuation in image density was evaluated as follows. still,
For the evaluation symbol ○ mark, a preferable state where image noise is hardly noticed, for the evaluation symbol Δ mark, image noise is a little worrisome but practically tolerable, and for the evaluation symbol × mark, there is a practical problem. It shows the state of the extent. Nylon-based (Example 1, Example 4, Comparative Example 2), polyimide-based (Example 2, Comparative Example 1), and polyethylene-based (Example 3) semi-conductive films were used as charging members in Table 1 and their The evaluation results when various charging devices 2 each having a surface roughened by buffing or sandblasting and used with a gap of 100, 300, 500, or 1000 μm are shown.

[0027]

[Table 1]

From the results shown in Table 1, when the surface of the charging member is smooth (Rz 2 μm: Comparative Example 1), the gap is 100 μm.
However, the surface of the charging member has a ten-point average roughness Rz of 5 μm to 100 μm.
The surface roughness of 10 μm to 50 μ is preferable, and 100 μ which cannot be achieved by the conventional minute gap charging device.
It can be seen that a uniform charging potential can be obtained over the entire surface of the member to be charged in a wide gap g of m to 1 mm, and a high-quality image with less noise and unevenness can be obtained. Rz
Is less than 5 μm, no effect is seen and Rz is 100
When the thickness is more than μm, stable discharge cannot be obtained and image defects such as white spots due to nonuniform charging occur.

The discharge characteristics of Example 1 and Example 2 in Table 1 are shown in FIG. In the figure, b is the characteristic of the first embodiment, and c
Is the characteristic of the second embodiment. From this figure, it can be seen that the charging device of this embodiment starts discharging at a lower voltage than the charging device a whose discharge surface is not roughened. In other words, when the same voltage is applied, the charging device of this embodiment can make the gap larger.

Further, as can be understood from the data of Table 1, particularly preferable results are obtained when the gap g is 100 to 300 μm.

[0031]

As is apparent from the above description, according to the charging device of the present invention, stable discharge is performed from the roughened discharge surface, and therefore, the upper limit of the gap between the discharge surface and the body to be charged. The value can be increased. By increasing the upper limit of the gap, the dimensional variation of the charging device components does not affect the discharge, a uniform charging potential is obtained over the entire surface of the charged object, and high-quality images with less noise and unevenness can be obtained. Obtainable.

[Brief description of drawings]

FIG. 1 is a front sectional view showing a schematic configuration of a copying machine to which a charging device of the present invention is applied.

FIG. 2 is a cross-sectional view showing a schematic configuration of a charging device according to the present invention.

FIG. 3 is a perspective view of a charging device according to the present invention.

FIG. 4 is a sectional view showing a schematic configuration of a conventional charging device.

FIG. 5 is a graph showing the relationship between the voltage applied to start discharge and the gap between the member to be charged and the charging member.

[Explanation of symbols]

 1: Photoconductor 2: Charging device 21: Conductive support 22: Charging member 23: Power supply g: Gap between photoconductor drum and charging member

Front page continuation (72) Keiko Nagayasu Keiko Nagaan 2-3-13 Azuchi-cho, Chuo-ku, Osaka City Osaka International Building Minolta Camera Co., Ltd. (72) Masafumi Yamamoto 2-3-13 Azuchi-cho, Chuo-ku, Osaka Osaka International Building Minolta Camera Co., Ltd.

Claims (1)

[Claims] 1. A charging device having a charging member, the discharge surface of which is provided so as to face a member to be charged with a minute gap, and the surface roughness of the discharge surface of the charging member is a ten-point average roughness Rz. A charging device having a thickness of 5 μm to 100 μm.