JP3006110B2 - Brush charging device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a brush charger for charging an electrostatic latent image carrier in an image forming apparatus such as a copying machine or a printer.

[0002]

2. Description of the Related Art A brush charging device typically has a configuration shown in FIG.
As shown in FIG. 17, the fixed type charging brush B1 is brought into contact with the moving surface S of the electrostatic latent image carrier PC, or the charging brush roller B2 is brought into contact with the surface S as shown in FIG. It is charged to a potential.

The brush bristles F constituting the charging brush B1 and the brush roller B2 usually have a circular cross section.

[0004]

However, if the brush bristles have a circular cross section, the number of points at which the brush bristles come into contact with the electrostatic latent image carrier is very small, and it is difficult to stably obtain an effective conductive portion. For this reason, there is a problem that it is difficult to transfer charges smoothly from the brush hairs to the electrostatic latent image carrier, and it is difficult to stably and uniformly charge the surface of the carrier. Alternatively, there is a problem that the number of discharge points at which discharge occurs is small and sufficient charging is difficult to occur.

As a means for solving such a problem, Japanese Patent Application Laid-Open No. 62-134660 teaches that a large number of dotted conductive portions are formed by depositing carbon particles or the like on the surface of a charged brush bristle. However, there is a problem that such a conductive portion peels off with the elapse of time and cannot be stably charged for a long time. Also, Japanese Patent Application Laid-Open No. Hei.
No. 235 teaches that irregularities such as a star-shaped cross section are provided around the charge removing brush bristles. However, when such brush bristles are used for charging, the surface recesses may be left undeveloped or left undeveloped during development. Fine particles such as fragments of toner particles destroyed by the stress at the time of toner cleaning adhere thereto, thereby deteriorating the charging ability of the brush bristles, lowering the charging ability of the entire charging device, and reducing the charging ability of the fine powder adhering portion and the non-fine portion. There is a problem that streak-like image noise occurs due to the mixture.

Accordingly, the present invention provides an effective conductive portion in each brush bristle as compared with a conventional brush bristle having a circular cross section.
Further, it is an object of the present invention to provide a brush charging device which is maintained for a long period of time and hardly causes fine powder to adhere to brush bristles.

[0007]

According to the present invention, there is provided a brush charging device according to the above-mentioned object, wherein the brush bristles constituting the charging brush are made of fibers having a cross section of a convex polygon or a convex polygon. is there. The convex polygon is a polygon which does not have a concave portion and is formed only of a convex portion extending from inside to outside over the entire circumference. The number of convex portions of the convex polygon or convex polygon is not particularly limited, but is 1 to 10
About two pieces are appropriate, and more preferably about two to five pieces. If the number of projections exceeds 10, the shape becomes too polygonal and approaches a circle, making it difficult to expect the effect of increasing the number of charging points.

[0008] The material of the brush bristle is not particularly limited as long as it has appropriate conductivity. Such conductive materials include tungsten, stainless steel, gold,
Examples include metal wires such as platinum, iron, copper, and aluminum. In addition, as a conductive resin material, in a fiber such as rayon, nylon, acetate, cuprammonium, vinylidene, vinylon, ethylene fluoride, promix, benzoate, polyurethane, polyester, polyethylene, polyvinyl chloride, polyclar, polynosic, and polypropylene. A material in which a resistance adjuster such as carbon black, carbon fiber, metal powder, metal whisker, metal oxide, and semiconductor material is dispersed can be used. in this case,
A desired resistance value can be appropriately obtained by the amount of dispersion. Instead of dispersion, the fiber surface may be coated with a resistance adjusting material.

[0009]

According to the brush charging device of the present invention, the cross section of each bristle is formed as a convex polygon or a convex polygon, and each of the surrounding convex portions is formed in a case where the cross section of the brush bristle is a simple circle. Unlike each point on the circumference, the radius of curvature is very small, the electric charge is easily concentrated, and the charging ability in that part is improved. If the number of the projections is plural, the number of charging points increases accordingly. Then, the convex portion comes into contact with the electrostatic latent image carrier and charges it.

[0010]

Embodiments of the present invention will be described below with reference to the drawings. All of the embodiments described below are used by being incorporated in a printer whose configuration is schematically shown in FIG. First, the printer shown in FIG. 1 will be described. The printer shown in FIG. 1 includes a photosensitive drum 1 serving as an electrostatic latent image carrier at a central portion, and this drum is driven to rotate in a direction indicated by an arrow CW by driving means (not shown). Around the drum 1, a brush charging device 2, a developing device 3, a transfer charger 4, a cleaning device 5, and an eraser 6 are sequentially arranged.
The charging device 2 is a charging device according to the present invention.

An optical system 7 is disposed above the photosensitive drum 1. 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 reflection mirror. An exposure slit is formed on the floor of the housing 71, from which a charging device 2 and a developing device 3 are arranged.
The image can be exposed on the photosensitive drum 1 through the gap.

A pair of timing rollers 81, a pair of intermediate rollers 82 and a sheet cassette 83 are provided on the right side of the photosensitive drum 1 in the drawing.
Are sequentially arranged, and a paper feed roller 84 faces the paper feed cassette 83. A pair of fixing rollers 91 and a pair of discharge rollers 92 are sequentially arranged on the left side of the photosensitive drum 1 in the drawing, and a discharge tray 93 faces the pair of discharge rollers 92.

According to the printer, the surface of the photosensitive drum 1 is charged to a predetermined potential by the charging device 2, and the charged area is image-exposed from the optical system 7 to form an electrostatic latent image. The electrostatic latent image thus formed is developed by the developing device 3 to become a toner image, and moves to a transfer area facing the transfer charger 4. On the other hand, the paper feed rollers 84
As a result, the transfer paper 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 drum 1. Thus, in the transfer area, the toner image on the drum 1 is transferred onto the transfer paper by the action of the transfer charger 4, and the transfer paper reaches the fixing roller pair 91, where the toner image is fixed and then discharged by the discharge roller pair 92. The sheet is discharged to the paper tray 93.

After the toner image has been transferred to the transfer paper, the toner remaining on the photosensitive drum 1 is cleaned by a cleaning device 5, and the residual charge is erased by the emission of a lamp from an eraser 6. The system speed of the printer (the peripheral speed of the photosensitive drum 1) is 3.5 cm / sec, and the developing device 3 is a contact-type developing device using a one-component developer, and performs reversal development.

In the present embodiment, the photosensitive drum 1 is manufactured as described below, and is a negatively chargeable functionally separated organic photosensitive member having sensitivity to long wavelength light. First, 1 part by weight of τ-type metal-free phthalocyanine, polyvinyl butyral resin (acetylation degree 3 mol% or less, butylation degree 70 mol%,
Polymerization degree 1000) 2 parts by weight and tetrahydrofuran 1
00 parts by weight were placed in a ball mill pot and dispersed for 24 hours to obtain a photosensitive coating solution. This has an outer diameter of 30 mm and a length of 240
It was applied to the entire surface of a cylindrical aluminum substrate having a thickness of 2 mm using a dipping method and then dried to form a charge generation layer having a thickness of 0.4 μm.

Next, on this charge generation layer, the structural formula

[0017]

Embedded image

8 parts by weight of a hydrazone compound represented by the following formula, 0.1 parts by weight of an orange dye (Sumiplast Orange 12; manufactured by Sumitomo Chemical Co., Ltd.), and 10 parts by weight of a polycarbonate resin (Panlite L-1250; manufactured by Teijin Chemicals Ltd.) A coating solution dissolved in a solvent consisting of 180 parts by weight of tetrahydrofuran was applied by a dipping method, and then dried to form a charge transport layer having a thickness of 18 μm.

Here, the τ-type metal-free phthalocyanine is Cu
When using Kα ₁ / Ni X-ray of 1.541 ° wavelength,
Bragg angle (2θ ± 0.2 degrees) is 7.6, 9.2, 1
It has an X-ray diffraction pattern showing strong peaks at 6.8, 17.4, 20.4 and 20.9. In particular, 751 ± infrared absorption spectrum between 700～760Cm ^-1
The two absorption bands at 2 cm ⁻¹ are the strongest,
Almost absorption band of the same intensity of two between 0 cm ^-1, 328
It has a characteristic absorption at 8 ± 3 cm ⁻¹ .

The electrostatic latent image carrier to which the charging device of the present invention can be applied is not limited to the one described above. In an imaging system using a long-wavelength light source such as a laser optical system or an LED array, a photoconductor having a long-wavelength sensitivity as described above may be used, and a liquid crystal shutter array, a PLZT shutter array, etc. Imaging system, or a lens used in normal analog PPC,
In a visible light image forming system using a mirror optical system, a photoconductor having sensitivity in a relative visual range may be used.

The constitution is not limited at all, and the function-separated type photoreceptor or the single-layer type photoreceptor may be used. As the charge generation material and the charge transport material, all known materials can be used.
That is, hydrazone, an inorganic material such as zinc oxide, cadmium sulfide, selenium alloy, amorphous silicon, or phthalocyanine, an azo compound, etc.
An organic material using a styryl compound or the like as a charge transporting material can also be used.

Further, a surface protective layer may be provided on the outermost surface of the photoreceptor. Examples of such a material include a resin such as an ultraviolet curable resin, a room temperature curable resin, and a thermosetting resin. A resin in which a resistance-adjusting material is dispersed, a material in which metal oxides, metal sulfides, etc. are thinned in a vacuum by an evaporation method, an ion plating method, etc., and a plasma polymerization of a hydrocarbon-based gas An amorphous carbon film or the like can be used.

The material of the substrate is not particularly limited as long as it has conductivity, and the shape of the substrate depends on the imaging system.
It may be in the shape of a drum, a flat plate, or a belt.
If the light source used is coherent light, the substrate may be roughened or blackened to prevent the generation of a so-called interference pattern.

In this embodiment, the toner used in the developing device 3 is a negative charge type, 100 parts by weight of a bisphenol A type polyester resin, 5 parts by weight of carbon black MA # 8 (manufactured by Mitsubishi Kasei Kogyo Co., Ltd.), Bontron S-3
4 (manufactured by Orient Chemical Industry Co., Ltd.) and 3 parts by weight of Viscole TS-200 (manufactured by Sanyo Chemical Industry Co., Ltd.) 2.5
A composition consisting of parts by weight and kneaded by a known method,
Pulverized and classified to have an average particle size of 10 μm and a particle size of 7 to 13 μm
Was prepared, and 0.75% by weight of hydrophobic silica (Tanolux 500, manufactured by Talco) was added as a fluidizing agent to the toner particles.
The mixture was stirred with a homogenizer.

Such a toner is stored in the developing device 3 and is developed. Next, the basic configuration of the brush charging device 2 in the printer will be described. The charging device 2 is, for example, as shown in FIG.
Reference numeral 0 is made of a band-shaped pile cloth. The pile cloth can be obtained, for example, by weaving brush hairs 21 made of conductive fibers of 3 to 10 denier into a base cloth 22, and coating the back surface of the base cloth with a conductive adhesive.

The bristles can be woven in a V-shape as shown in FIG. 3 or a W-shape as shown in FIG. 4, for example, by bundling 50 to 100 bristles. The brush 20 is fixed to the back plate by the adhesive. Next, a specific example of the present invention will be described sequentially along with a comparative example. Before that, a method for evaluating streak-like image noise based on uneven charging on the surface of the photosensitive drum by the charging device 2 will be described.

Uneven charging occurs in a direction crossing the direction of travel of the surface of the photosensitive drum. Even after the image exposure, the charge unevenness remains as unevenness of the potential (V _i ) after the image exposure. That is, of the potential (V ₀ ) immediately after being charged by the charging device 2, a portion having a partially high potential also has a partially high potential (V _i ) after image exposure. When reversal development is performed in the printer, a portion with a lower potential (V _i ) is developed with a larger amount of toner. That is, the potential (V
_{The non-} uniformity of ( ₀ ) results in _non- uniformity of the potential (V _i ) and finally of the image. One of the performances of the charging device according to the present invention is how the image unevenness occurs. The degree of the image unevenness is determined by evaluating streak-like image noise.

Evaluation of image noise is performed as follows. Using the printer, after charging by the charging device 2, a repetition pattern of two dots on (lighting) and two dots off (light off) is written by a laser from the optical system 7 in the main scanning direction, and the same is applied in the sub scanning direction The laser lighting timing is adjusted so that a writing pattern of two dots on (lighting) and two dots off (light off) is obtained. Thereafter, through a reversal development, transfer and fixing processes, a print image as shown in FIG. 5 is obtained.

[0029] The main scanning direction of the maximum width of the fine black solid pattern consisting of 2 dots × 2 dots on the printed image and W _M. The standard deviation of W _M thirty minute black solid pattern that is continuous in the main scanning direction and sigma, to rank the streak image noise, such as: by this sigma. Standard deviation σ Evaluation symbol 0 μm ≦ σ <10 μm ◎ 10 μm ≦ σ <20 μm ○ 20 μm ≦ σ <40 μm △ 40 μm ≦ σ × When the standard deviation σ is large, the width of the fine black solid in the main scanning direction varies greatly in the main scanning direction. That means. When a dot pattern as described above is output, empirically, if σ is 40 μm or more, it is recognized as strong streak noise, which is not preferable. Therefore, preferably, the value of σ is 4
It is less than 0 μm, more preferably less than 20 μm. When the value of σ is less than 10 μm, it is more preferable because the noise cannot be recognized as streak noise.

In the above-mentioned image evaluation symbols, a mark ◎ indicates a preferable state in which streak-like image noise cannot be recognized, a mark ○ indicates a preferable state in which the noise can hardly be recognized, and a mark △ indicates that image noise is practically no problem. The crosses indicate the states where image noise poses a practical problem. Next, Examples and Comparative Examples will be sequentially described.

Example 1 As a bristle material, an electric resistivity of about 1 × 10 ⁵ Ω · c containing 12 wt% of conductive carbon powder with respect to the total weight.
m rayon fiber was adopted. As shown in FIG. 6, fifty of these fibers 21 are woven into a base cloth 22 having a thickness of 0.5 mm using a W weave as shown in FIG. = 240 mm, width W = 7 mm,
Height h1 = 7mm, fiber density 15,000 fibers / c at the center
An m ² charging brush 20 was formed, the back surface of the base cloth 22 was coated with a conductive adhesive, and the base cloth 22 was fixed to an aluminum back plate 23 having a thickness of t = 1 mm with the adhesive.

The rayon fibers were formed by spinning using a spinneret having the shape shown in FIG. The cross-sectional shape is substantially egg-shaped as shown in FIG. The diameter of an imaginary circle having the same area as the fiber cross-sectional area is 19 μm. Example 2 The rayon fiber in Example 1 was formed using a spinneret having the shape shown in FIG. 8A, and the cross-sectional shape was shown in FIG.
As shown in the figure, the shape was a flat ellipse, and two convex portions were provided. The diameter of the virtual circle having the same area as the fiber cross-sectional area is 21 μm. The rest is the same as in the first embodiment.

Example 3 The rayon fiber in Example 1 was formed by using a spinneret having a shape shown in FIG. 9A, and the cross-sectional shape was shown in FIG.
As shown in the figure, a triangular shape and three convex portions were used. The diameter of a virtual circle having the same area as the fiber cross-sectional area is 20 μm. The rest is the same as in the first embodiment.

Example 4 The rayon fiber in Example 1 was formed by using a spinneret having a shape shown in FIG. 10A, the cross section was made square as shown in FIG. 4 points were given. The diameter of an imaginary circle having the same area as the fiber cross-sectional area is 19 μm. The rest is the same as in the first embodiment.

Example 5 The rayon fiber in Example 1 was formed by using a spinneret having a shape shown in FIG. 11A, the cross section was made pentagonal as shown in FIG. 5 points. The diameter of a virtual circle having the same area as the fiber cross-sectional area is 20 μm. The rest is the same as in the first embodiment.

Example 6 The rayon fiber of Example 1 was formed using a spinneret having the shape shown in FIG. 12A, and the cross-sectional shape was made hexagonal as shown in FIG. Was given 6 points. The diameter of a virtual circle having the same area as the fiber cross-sectional area is 20 μm. The rest is the same as in the first embodiment.

Example 7 The diameter of an imaginary circle having the same area as the fiber cross-sectional area was 10 μm, and the cross-sectional shape of the fiber was similar to the rayon fiber cross-sectional shape of Example 2. The rest is the same as in the first embodiment. Example 8 The diameter of a virtual circle having the same area as the fiber cross-sectional area was 40 μm, and the cross-sectional shape of the fiber was similar to the rayon fiber cross-sectional shape of Example 2. The rest is the same as in the first embodiment.

Example 9 The diameter of an imaginary circle having the same area as the fiber cross-sectional area was 10 μm, and the cross-sectional shape of the fiber was similar to the rayon fiber cross-sectional shape of Example 6. The rest is the same as in the first embodiment. Example 10 The diameter of an imaginary circle having the same area as the fiber cross-sectional area was 40 μm, and the cross-sectional shape of the fiber was similar to the rayon fiber cross-sectional shape of Example 6. The rest is the same as in the first embodiment.

Comparative Example 1 The rayon fiber in Example 1 was formed with a spinneret shown in FIG. 13A, and the cross-sectional shape was made circular as shown in FIG. Its diameter is 20 μm. The rest is the same as in the first embodiment. Comparative Example 2 The rayon fiber in Example 1 was formed with the spinneret shown in FIG. 14A, and the cross-sectional shape was a star shape as shown in FIG. The diameter of an imaginary circle having the same area as the fiber cross section is 1
9 μm. The rest is the same as in the first embodiment.

Each of Examples 1 to 10 and Comparative Examples 1 and 2 described above was incorporated into the printer shown in FIG.
Level of DC voltage, the surface of the photosensitive drum 1 is averaged to −
It was charged to about 700 to -800 V. Then, printing was performed under a developing bias of -300 V, and image noise (streak noise) was evaluated by the above-described method at the beginning of printing and after 5,000 sheets, respectively. The results shown in Table 1 were obtained.

[0041]

[Table 1]

As can be seen from Table 1, in Examples 1 to 10, no image noise is recognized or a practical problem occurs after printing 5000 sheets as well as in the initial printing. This indicates that the brush bristles are formed in the shape of a convex polygon or a convex polygon, and the number of charging points is increased, so that uniform and stable uniform charging can be performed.

It can also be seen from Table 1 that charging is good when the diameter of the imaginary circle having the same area as the brush bristle cross-sectional area is at least in the range of 10 to 40 μm. On the other hand, in Comparative Example 1, since the brush bristle cross section is circular and the number of charging points is small, image noise occurs from the beginning of printing. In Comparative Example 2, the number of charging points was too large, so that the charging points did not act as if they were clearly formed, and fine powder gradually entered into the recesses on the circumferential surface of the brush hair, and after printing 5000 sheets, As a result, the charging ability is deteriorated and image noise appears.

It should be noted that the present invention is not limited to the above embodiment, but can be implemented in various other modes. For example, as shown in FIG.
Alternatively, the brush bristles 21 may be held by a holding member such as the above. The present invention can be applied not only to the above-mentioned fixed brush charging device but also to a rotary brush charging device as shown in FIG.

It is also conceivable to arrange a plurality of brush charging devices around the photosensitive drum 1 in FIG. 1. In this case, the present invention is applied to the charging device at the most upstream side in at least the drum rotation direction. It is desirable to apply.

[0046]

As described above, according to the present invention, each brush bristle has an effective conductive portion as compared with the conventional brush bristles having a circular cross section and is maintained for a long period of time. Is less likely to adhere to fine powder,
It is possible to provide a brush charging device capable of stably and uniformly charging for a long period of time.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of an example of a printer incorporating a charging device according to the present invention.

FIG. 2 is a perspective view illustrating a basic configuration of a charging brush in the charging device according to the embodiment of the present invention.

FIG. 3 is an explanatory diagram showing an example of a state in which brush hairs are planted on a base cloth.

FIG. 4 is an explanatory view showing another example of a state in which brush hairs are planted on a base cloth.

FIG. 5 is a diagram of a print image example for performing image noise evaluation.

FIG. 6 is a perspective view of one embodiment of the present invention.

FIG. 7 (A) is an explanatory view of a shape of a spinneret of rayon fiber which is a brush hair in one embodiment of the present invention, and FIG. 7 (B) is a cross-sectional view of a rayon fiber obtained by the spinneret.

FIG. 8 (A) is an explanatory view of a shape of a spinneret of rayon fiber which is a brush hair in another embodiment of the present invention, and FIG. 8 (B) is a cross-sectional view of a rayon fiber obtained by the spinneret.

FIG. 9 (A) is an explanatory view of a spinneret shape of rayon fiber which is a brush hair in still another embodiment of the present invention,
(B) is a sectional view of the rayon fiber obtained by the spinneret.

FIG. 10 (A) is an explanatory view of a spinneret shape of rayon fiber which is a brush hair in still another embodiment of the present invention,
(B) is a sectional view of the rayon fiber obtained by the spinneret.

FIG. 11 (A) is an explanatory view of a spinneret shape of rayon fiber which is a brush hair in still another embodiment of the present invention;
(B) is a sectional view of the rayon fiber obtained by the spinneret.

FIG. 12 (A) is an explanatory view of a spinneret shape of rayon fiber which is a brush hair in still another embodiment of the present invention,
(B) is a sectional view of the rayon fiber obtained by the spinneret.

13A is an explanatory view of a spinneret shape of rayon fiber which is a brush hair in Comparative Example 1, and FIG. 13B is a cross-sectional view of a rayon fiber obtained by the spinneret.

14A is an explanatory view of a spinneret shape of a rayon fiber as a brush hair in Comparative Example 2, and FIG. 14B is a cross-sectional view of a rayon fiber obtained by the spinneret.

FIG. 15 is a perspective view of another example of the charging brush according to the present invention.

FIG. 16 is an explanatory diagram of a conventional example.

FIG. 17 is an explanatory diagram of another conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Photoconductor drum 2 Brush charging device 20 Charging brush 21 Brush bristles 22 Base cloth 23 Back plate

Continuation of the front page (72) Inventor Issei Osawa 2-3-13 Azuchicho, Chuo-ku, Osaka-shi Osaka International Building Minolta Camera Co., Ltd. (56) References JP-A-61-168304 (JP, A) Opened 63-94452 (JP, U) Opened 61-96661 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) G03G 15/02

Claims (1)

(57) [Claims] 1. A brush charging device, wherein a brush bristle constituting a charging brush is formed of fibers having a cross-sectional shape of a convex polygon or a convex polygon.