JP2001109237A - Brush electrifying device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent dot state unevenness in density of an image when voltage between peaks of applied AC voltage is increased in a brush electrifying device. SOLUTION: The brush electrifying device is provided with an electrifying brush 2 consisting of a shaft 2a that is installed in contact with a surface of an electrostatic latent image carrier and rotated, that is provided with conductivity and a brush 2 that is provided to be radial on the shaft 2a and provided with conductivity and uniformly electrifying a surface of a photoreceptor 1 to a specified potential and an electrifying bias feeding power source 27 that is electrically connected to the electrifying brush 2 and applying superposed voltage consisting of AC voltage and DC voltage to the electrifying brush 2. In this case, the superposed voltage provided with a relationship of Vp<2×|Vc| is applied when the DC voltage applied to the electrifying brush 2 is Vc (V) and the voltage between the peaks of the AC voltage is Vp (V).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is used for an image forming apparatus such as an electrophotographic apparatus and an electrostatic recording apparatus, and uniformly covers the surface of a photosensitive member as an electrostatic latent image carrier with a conductive charging brush. The present invention relates to a charging device for charging a brush.

[0002]

2. Description of the Related Art In image forming apparatuses, equipment using dry toner occupies the mainstream, and many copiers, laser printers,
It has been put to practical use as plain paper facsimile, etc., and has achieved remarkable development. This image forming apparatus is an apparatus to which an electrophotographic process technology is applied, and visualizes an electrostatic latent image formed on a photoconductor as an electrostatic latent image carrier by toner particles.

In such an image forming apparatus, as a means for uniformly charging the surface of the photosensitive member, a corona charging device including a wire electrode and a shield electrode has been generally used. However, due to problems such as application of a high voltage, low charging efficiency, generation of ozone, and uneven charging due to wire contamination, the use of a conductive brush charging device that is advantageous for cost reduction has recently been increasing.

Hereinafter, the structure and operation of an image forming apparatus using a brush charging device will be described.

FIG. 4 is a schematic view showing an image forming apparatus having a conventional brush charging device.

The illustrated image forming apparatus is an image forming apparatus for visualizing an electrostatic latent image formed on a photoconductor by electrophotographic process technology using toner particles, and a photoconductor 1 as an electrostatic latent image carrier. have. The photoconductor 1 rotates in the circumferential direction and conveys a sheet described later.

[0007] A charging brush 2 is provided in contact with the surface of the photoreceptor 1. The charging brush 2 is provided in parallel with the rotation axis of the photoconductor 1 and rotates with a rotating metal shaft 2a.
And a conductive brush radially implanted on the outer peripheral surface of the shaft 2a. The charging brush 2 is electrically connected to a charging bias supply power supply 27, and uniformly charges the surface of the photoconductor 1 by a DC bias voltage supplied from the charging bias supply power supply 27.
When the photoconductor 1 is irradiated with the exposure light beam 4 obtained from the exposure optical system 3, the photoconductor 1 is exposed to form a predetermined electrostatic latent image.

A toner supply roller 6 for supplying the toner 10 stirred and conveyed to the surface of the developing roller 5 by a toner stirring member 11 rotatably supported at both ends of the developing hopper 9 is provided. The toner supply roller 6 is made of a metal shaft 6a made of stainless steel or the like, and an elastic member such as urethane or silicon is formed in a layered manner around the shaft 6a. Reference numeral 26 is connected to apply a DC supply voltage or a toner supply bias voltage in which DC and AC are superimposed.

The developing roller 5 has a shaft 5a made of metal such as stainless steel as a base material and an elastic member such as urethane or silicon formed in a layer on the outer peripheral surface. A developing bias voltage supply power supply 12 which is a constant voltage power supply is connected to the shaft 5a of the developing roller 5.

The toner 10 is a non-magnetic one-component toner. For example, carbon, wax,
It is composed of a material in which a charge control agent and the like are uniformly dispersed.

The developing roller 5 and the toner supply roller 6 are arranged in contact with each other, and are rotatably supported at both ends of a developing hopper 9 by shafts 5a and 6a, respectively. The developing roller 5 and the photoreceptor 1 contact each other and rotate in opposite directions.
And the toner supply roller 6 contact each other and rotate in the same direction. The developing roller 5 is in contact with the photoreceptor 1, and the toner supply roller 6 applies toner to a portion of the photoreceptor 1 where an electrostatic latent image is formed by a bias voltage applied from a developing bias voltage power supply 12. When 10 is transferred and attached, the electrostatic latent image is visualized.

Incidentally, the toner stirring member 11 is connected to the developing hopper 9.
The toner 10 is prevented from aggregating, and the toner 10 is conveyed toward the toner supply roller 6.

A toner regulating blade 7 is provided in contact with the developing roller 5. This toner regulating blade 7
It comprises an elastic metal spring plate member 7a and a toner regulating member 7b which comes into contact with the developing roller 5. The toner regulating member 7b is formed by integrally forming an elastic member such as urethane rubber or silicon rubber at one end of the metal spring plate member 7a. Such a toner regulating blade 7 is screwed to a blade holder 8. This toner regulating blade 7
Is pressing the developing roller 5 with a predetermined linear pressure, and the toner 1 supplied from the toner supply roller 6 to the developing roller 5
0 is frictionally charged by the toner regulating blade 7, and a thin toner layer is formed on the outer peripheral surface of the developing roller 5.

Paper 15 is stored in a paper cassette 14 provided at the starting point of the transport path. The paper 15 is sent out from the paper cassette 14 to the transport roller 17 one by one by a paper feed roller 16. Then, the fed sheet 15 is sandwiched between a pair of transport rollers 17 and is moved by an arrow A.
Is transported in the direction of the photoconductor 1 indicated by.

In order to match the paper 15 with the toner image formed on the photoreceptor 1, on a transport path before reaching the photoreceptor 1, a registration roller 18 is brought into contact with a driven roller 19 and
Is provided. Further, a transfer roller 20 is provided so as to be rotatably supported in contact with the photoconductor 1.

When the toner image reaches the contact portion between the transfer roller 20 and the photosensitive member 1 as the photosensitive member 1 rotates, the paper 15 is also brought into contact with the toner image by the registration roller 18 in timing. To reach. At this time, when a high voltage from a transfer bias voltage supply power supply 24 is applied to the metal shaft 20a of the transfer roller 20 to apply a charge having a polarity opposite to that of the toner 10 to the back surface of the sheet 15, the toner image is transferred onto the sheet 15. Is done.

A fixing device 21 including a heat roller 22 having a heat source therein and a pressure roller 23 for sandwiching and conveying the sheet 15 together with the heat roller 22 is provided at a stage subsequent to the conveyance path. The paper 15 on which the toner image has been transferred is sent to the fixing device 21 where the toner image is fixed. On the other hand, the photoreceptor 1 after the toner image has been transferred onto the paper 15 has the transfer residual toner scraped off by the cleaning blade 25, and is irradiated with light by the charge eliminator 13 to be neutralized, thereby preparing for the next process.

[0018]

However, in such a conventional brush charging device, the charging of the surface of the photoreceptor becomes uneven due to the uneven contact of the brush with the photoreceptor, and the image density non-uniformity looks like a brush sweep. There is a problem that it is easy to occur.

As a measure for preventing the image density unevenness in the form of sweeping lines, a technique of applying a superimposed voltage of a DC voltage and an AC voltage to a brush charger is widely used. Then, in the technique of applying the superimposed voltage, as the peak-to-peak voltage of the AC voltage is increased, uneven charging on the surface of the photoconductor due to uneven contact of the brush is improved.

This is because, by generating an oscillating electric field between the brush charging device and the photosensitive member, the electric charges alternately move between the two members, and as the photosensitive member passes near the contact portion with the brush, the electric charges are transferred. Is gradually reduced and converges to a constant potential. Therefore, as the peak-to-peak voltage of the AC voltage increases, the amount of charge movement increases, and the photoconductor can be charged more uniformly.

However, according to the study of the present inventor, it has become clear that when the peak-to-peak voltage exceeds a certain value, spot-like density unevenness occurs in the image. This makes it impossible to substantially uniformly charge the photosensitive member.

Accordingly, it is an object of the present invention to provide a brush charging device which can prevent the occurrence of spot-like density unevenness of an image when the peak-to-peak voltage of an applied AC voltage is increased.

[0023]

In order to solve this problem, a brush charging device according to the present invention is arranged so as to be in contact with the surface of an electrostatic latent image carrier, rotates, and has a conductive shaft and a conductive shaft. A charging brush made of a conductive brush provided radially to uniformly charge the surface of the electrostatic latent image carrier to a predetermined potential; a charging brush electrically connected to the charging brush; And a charging bias supply power source for applying a superimposed voltage consisting of a voltage and a DC voltage applied to the charging brush as Vc (V) and a peak-to-peak voltage of the AC voltage as Vp (V), where Vp <2 × | Vc |.

This makes it possible to prevent the occurrence of spot-like density unevenness in an image when the peak-to-peak voltage of the applied AC voltage is increased.

[0025]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The invention according to claim 1 of the present invention is directed to a shaft having a conductive property and being rotated while being in contact with the surface of an electrostatic latent image carrier, and a conductive shaft radially provided on the shaft. A charging brush made of a brush having a property and uniformly charging the surface of the electrostatic latent image carrier to a predetermined potential; and a superimposed voltage comprising a DC voltage and an AC voltage electrically connected to the charging brush. And a charging bias supply power supply for applying a DC voltage to the charging brush.
c (V), where Vp (V) is the peak-to-peak voltage of the AC voltage, the brush charging device has a relationship of Vp <2 × | Vc |, and has a polarity opposite to the charging polarity of the electrostatic latent image carrier. Is no longer applied to the brush, so that it is possible to prevent the occurrence of spot-like density unevenness in an image when the peak-to-peak voltage of the applied AC voltage is increased.

According to a second aspect of the present invention, in the first aspect of the invention, a temperature and humidity detecting means for detecting the temperature and humidity in the image forming apparatus, and a printed number detecting means for detecting the number of printed sheets of paper. Charging potential detecting means for detecting a charging potential on the surface of the electrostatic latent image carrier; image density detecting means for detecting the density of an image printed on paper; temperature and humidity detecting means; A control unit for changing a value of a peak-to-peak voltage of an AC voltage in accordance with a change in a DC voltage applied to the charging brush based on signals from the potential detection unit and the image density detection unit. Even if the value of 変 化 changes, the voltage of the polarity opposite to the charging polarity of the electrostatic latent image carrier is not applied to the brush,
This has the effect that it is possible to prevent the occurrence of spot-like density unevenness in an image when the peak-to-peak voltage of the applied AC voltage is increased. In addition, since the peak-to-peak voltage of the AC voltage can always be set to be large, it has an effect that it is possible to prevent the occurrence of the density unevenness in the sweep pattern of the image.

According to a third aspect of the present invention, in the second aspect, the DC voltage applied to the charging brush is Vc (V), and the peak-to-peak voltage of the AC voltage is Vp (Vp).
(V), where T is a constant, the brush charging device has a relationship of Vp = 2 × | Vc | −T, and has a polarity opposite to the charging polarity of the electrostatic latent image carrier even when the value of the DC voltage changes. Since the voltage is not applied to the brush, it has an effect that it is possible to prevent spot-like density unevenness of an image from occurring when the peak-to-peak voltage of the applied AC voltage is increased. In addition, since the peak-to-peak voltage of the AC voltage can always be set to be large, it has an effect that it is possible to prevent the occurrence of the density unevenness in the sweep pattern of the image.

According to a fourth aspect of the present invention, there is provided the brush charging device according to the third aspect, wherein the constant T is 0 ≦ T ≦ 200. Since a voltage having a polarity opposite to the charging polarity of the latent image carrier is no longer applied to the brush, it is possible to prevent the occurrence of spot-like density unevenness of an image when the voltage between the peaks of the applied AC voltage is increased. It has the effect that it becomes possible. In addition, since the peak-to-peak voltage of the AC voltage can always be set to be large, it has an effect that it is possible to prevent the occurrence of the density unevenness in the sweep pattern of the image.

According to a fifth aspect of the present invention, in the first or second aspect, the frequency of the AC voltage applied to the charging brush is f (Hz), and the conductive brush and the electrostatic latent image carrier A brush charging device having a relationship of f> v / l, where l (mm) is a contact width with the body, and v (mm / s) is a relative speed at a contact portion between the brush and the electrostatic latent image carrier. Since the AC voltage is applied to the conductive brush for one or more cycles while the electrostatic latent image carrier passes through the contact portion with the brush, the period of the surface of the electrostatic latent image carrier caused by the AC voltage is increased. This has the effect that it is possible to prevent the electrification unevenness.

An embodiment of the present invention will be described below with reference to FIGS. In these drawings, the same members are denoted by the same reference numerals, and duplicate description is omitted.

FIG. 1 is a schematic diagram showing the configuration of an image forming apparatus using a brush charging device according to an embodiment of the present invention. FIG. 2 is a diagram showing the charging bias voltage of a charging bias supply power supply in the image forming apparatus of FIG. FIG. 3 is an explanatory diagram showing an image evaluation result when a peak-to-peak voltage of a DC voltage and an AC voltage is changed. FIG. 3 is a schematic diagram showing a configuration of an image forming apparatus using a brush charging device according to another embodiment of the present invention. FIG.

The image forming apparatus shown in FIG. 1 is an image forming apparatus for visualizing an electrostatic latent image formed on a photosensitive member (electrostatic latent image carrier) by electrophotographic process technology using toner particles. A metal drum of aluminum or the like is used as a base material, an alumite layer as an insulator is provided on the outer peripheral surface thereof, and selenium (Se) or an organic photoconductor (hereinafter, referred to as an organic photoconductor)
It is called “OPC”. ), Etc., is provided with a negatively charged photosensitive member 1 formed by applying a photosensitive receiving layer such as a thin film. The photoreceptor 1 rotates in the circumferential direction (in the present embodiment, the clockwise arrow D direction) and conveys a sheet described later.

Here, the alumite layer is formed to protect the photosensitive layer from electrical breakdown. The photosensitive receiving layer has a laminated structure of a charge generating layer in which a charge generating substance is dispersed and contained in a binder resin and a charge transporting layer in which a charge transporting substance is contained. In the present embodiment, the charge transport layer is laminated on the charge generation layer, and the thickness of these photosensitive receiving layers is 25 μm.

A charging brush 2 is provided in contact with the surface of a photosensitive member 1 serving as an electrostatic latent image carrier. The charging brush 2 includes a conductive shaft 2a made of metal, which is provided in parallel with the rotation axis of the photoconductor 1 and rotates.
And a brush having conductivity that is radially implanted from the brush. Then, in the present embodiment, the charging brush 2 rotates clockwise in the direction of arrow E.

Here, the brush is made of rayon, acrylic, polypropylene, polyethylene, nylon, ETF
E and the like are used, and these are subjected to conductive treatment with carbon, metal or the like. In the present embodiment, conductive rayon fibers having a thickness of 6 denier and a carbon density of 100,000 fibers / inch ² and an outer diameter of 6 are used.
mm is implanted uniformly on a metal shaft 2a having an outer diameter of 18 mm.
It is a 5 mm brush. The brush has a contact width of 3 m instead of the photoreceptor 1 as in actual use conditions.
The value is 10 ⁵ Ω as determined from the value of the current flowing when a voltage of 100 V is applied when the aluminum drum is abutted at m.

Such a charging brush 2 includes a charging bias supply power source 2 for applying a superimposed voltage of a DC voltage and an AC voltage.
7 is electrically connected to the charging bias supply power supply 2
The surface of the photoreceptor 1 is uniformly charged by the power supply from.

When the photosensitive member 1 is irradiated with an exposure light beam 4 obtained from an exposure optical system 3 by modulating the image signal with light intensity modulation or pulse width by a laser driving circuit (not shown), the photosensitive member 1 Upon exposure, a predetermined electrostatic latent image is formed.

The toner 10 stirred and conveyed by a toner stirring member 11 rotatably supported at both ends by a developing hopper 9 is supplied to the surface of the developing roller 5 as a toner carrier, and remains without being developed. Toner 1 on developing roller 5
In order to scrape 0, a toner supply roller 6 is provided. The toner supply roller 6 is formed by forming a conductive foam on an outer peripheral surface of a shaft 6a made of a metal such as stainless steel, and has a resistance value of 10 ⁶ Ω · cm. A toner supply bias voltage supply power supply 26, which is a constant voltage power supply, is connected to the shaft 6a of the toner supply roller 6, and a toner supply bias voltage is applied.
In the present embodiment, the nip width between the toner supply roller 6 and the developing roller 5 is 2 mm. In the present embodiment, both the developing roller 5 and the toner supply roller 6 rotate in the directions of arrow B and arrow C, which are counterclockwise.

The developing roller 5 is intended a metal shaft 5a of stainless steel or the like of the single-layer silicon rubber was formed is a conductive elastic member on its outer circumferential surface as a base material, the resistance value, for example 10 ⁶ Ω · cm. A developing bias voltage supply power supply 12 which is a constant voltage power supply is connected to the shaft 5a of the developing roller 5.

Here, the rubber hardness of the developing roller 5 is preferably in the range of 30 to 60 degrees from the viewpoint of prevention of creep and dents, and the higher the surface roughness is, the thinner the toner layer is. Since uniformity can be achieved in the formation of
7 μmRz is preferred. The developing roller 5 in the present embodiment has a rubber hardness of 60 degrees and a surface roughness of 2 μmR.
z.

The toner 10 is a non-magnetic one-component toner. For example, carbon, wax,
It is composed of a material in which a charge control agent and the like are uniformly dispersed.

The developing roller 5 and the toner supply roller 6 are arranged in contact with each other, and are rotatably supported by shafts 5a and 6a at both ends of the developing hopper 9, respectively. As shown, the developing roller 5 and the photoconductor 1
And the developing roller 5 and the toner supply roller 6 come into contact with each other and rotate in the same direction (in the counterclockwise direction indicated by an arrow C). The rotation direction of the photoconductor 1 indicated by an arrow D that is clockwise with respect to the rotation direction of the developing roller 5 and the rotation direction of the toner supply roller 6 indicated by an arrow B). Therefore, the developing roller 5 and the toner supply roller 6 are in frictional contact.

The developing roller 5 is brought into contact with or in proximity to the photoconductor 1, and a developing bias voltage power supply 12
When the toner 10 is transferred and adhered by the toner supply roller 6 to the portion where the electrostatic latent image is formed on the photosensitive member 1 by the applied developing bias voltage, the electrostatic latent image is visualized.

The toner agitating member 11 draws a circular locus with the rotation of the toner supply roller 6 to prevent the toner 10 contained in the developing hopper 9 from aggregating and transport the toner 10 to the toner supply roller 6. I do.

A toner regulating blade 7 is provided in contact with the developing roller 5. This toner regulating blade 7
An elastic metal spring plate member 7a such as a stainless steel plate or a phosphor bronze plate, and a toner regulating member 7b that comes into contact with the developing roller 5 are provided. The toner regulating member 7b is formed by integrally forming an elastic member such as urethane rubber having a rubber hardness of 60 degrees at one end of the metal spring plate member 7a. Such a toner regulating blade 7 is screwed to a blade holder 8. The toner regulating blade 7 presses the developing roller 5 at a linear pressure of 80 g / cm, and the toner 10 supplied from the toner supply roller 6 to the developing roller 5
Is frictionally charged by the toner regulating blade 7 and the developing roller 5
, A thin toner layer is formed on the outer peripheral surface. In addition,
In the non-magnetic one-component contact developing system as in the present embodiment, the toner layer on the developing roller 5 is 0.4 to 0.6 mg.
/ Cm ² is preferred.

The photosensitive member 1, the developing roller 5, the toner supply roller 6, and the toner regulating blade 7 are disposed so as to be in constant contact with each other at their contact portions.

Paper 15 is stored in a paper cassette 14 provided at the starting point of the transport path. The paper 15 is fed to a paper cassette 14 by a half-moon shaped paper feed roller 16.
Are fed out to the transport roller 17 one by one. Then, the fed recording sheet 15 is nipped by a pair of transport rollers 17 and transported in the direction of the photoconductor 1 indicated by an arrow A.

The paper 15 is temporarily stopped and waited, and the paper 1 is stopped.
In order to make the toner image 5 and the toner image formed on the photoconductor 1 coincide with each other, a driven roller 1
9 is provided with a registration roller 18.
Further, a transfer roller 20 is provided so as to be rotatably supported in contact with the photoconductor 1. The transfer roller 20 is formed by forming a conductive foam around a metal shaft 20a made of stainless steel or the like, and has a resistance value of 10 ⁷ Ω · cm. A transfer bias voltage supply power supply 24, which is a constant current power supply, is connected to the shaft 20a.

When the toner image reaches the contact portion between the transfer roller 20 and the photosensitive member 1 with the rotation of the photosensitive member 1, the paper 15 is also brought into contact with the toner image by the registration roller 18 in timing. To reach. At this time, when a high voltage from the transfer bias voltage supply power supply 24 is applied to the metal shaft 20a of the transfer roller 20 to apply a charge having a polarity opposite to that of the toner 10 to the back surface of the sheet 15, the toner image on the photoconductor 1 becomes The image is transferred onto the paper 15.

At the subsequent stage of the transport path, there is provided a fixing device 21 composed of a heat roller 22 having a heat source therein, and a pressure roller 23 for sandwiching and transporting the sheet 15 together with the heat roller 22. Accordingly, the paper 15 on which the toner image has been transferred is sent to the fixing device 21, where the toner image is fixed by pressure and heat by the sandwiching rotation of the heat roller 22 and the pressure roller 23. On the other hand, the photoreceptor 1 after the toner image has been transferred onto the paper 15 has the transfer residual toner scraped off by the cleaning blade 25, and is irradiated with light by the charge eliminator 13 to be neutralized, thereby preparing for the next process.

The image forming apparatus shown in FIG. 3 has, in addition to the image forming apparatus shown in FIG. 1, a temperature / humidity detecting means 28 for detecting the temperature and humidity in the image forming apparatus, and detects the number of sheets printed on the paper 15. Sheet number detecting means 29, charging potential detecting means 30 for detecting the charging potential on the surface of photoreceptor 1, paper 1
5, an image density detecting means 31 for detecting the density of an image printed on the image 5, and these detecting means 28, 29, 30, 31
, The charging bias voltage for the charging brush 2 by the charging bias supply power supply 27, the developing bias voltage for the developing roller 5 by the developing bias voltage supply power supply 12, and the transfer bias voltage for the transfer roller 20 by the transfer bias voltage supply power supply 24 are changed. A CPU (control means) 32 for correcting the image by the operation is provided.

[0052]

Next, an embodiment of the present invention using the above-described image forming apparatus shown in FIGS. 1 and 3 will be described.

(Embodiment 1) In an electrophotographic apparatus using the brush charging device shown in FIG. 1, the DC voltage Vc of the charging bias voltage and the peak-to-peak voltage Vp of the AC voltage in the charging bias supply power supply 27 are changed. Image evaluation was performed.

Here, the frequency f of the AC voltage of the charging bias voltage is 800 Hz, the process speed as the peripheral speed of the photosensitive member 1 is 124 mm / sec, and the peripheral speed of the charging brush 2 is 1
61 mm / sec, peripheral speed of developing roller 5 is 217 mm
/ Sec, the peripheral speed of the toner supply roller 6 is 10 ⁸ mm /
sec.

FIG. 2 shows image evaluation results when the DC voltage Vc of the charging bias voltage and the peak-to-peak voltage Vp of the AC voltage are changed. In FIG. 2, the horizontal axis represents the peak-to-peak voltage Vp of the AC voltage of the charging bias voltage, and the vertical axis represents the DC voltage Vc of the charging bias voltage. Further, “◎” indicates an image of good image quality, “△” indicates an image in which spot-like density unevenness has occurred slightly, and “×” indicates an image in which spot-like density unevenness has occurred significantly over the entire image. The symbol “○” indicates an image in which the brush-like density unevenness has slightly occurred, and the symbol “□” indicates an image in which the brush-like density unevenness has significantly occurred over the entire image.

As is apparent from FIG. 2, when the peak-to-peak voltage Vp of the AC voltage exceeds twice the DC voltage Vc, spot-like density unevenness occurs in the image. When the peak-to-peak voltage Vp of the AC voltage exceeds twice the DC voltage Vc, the voltage applied to the charging brush 2 instantaneously becomes positive. At this time, the surface of the negatively charged photoconductor 1 becomes positive. Be charged. As a result, it is considered that electric charge between the photoreceptor 1 and the charging brush 2 due to the AC voltage is not evenly transferred, and a spot-shaped density unevenness occurs because the charging potential becomes locally non-uniform.

Further, the brush-like density unevenness of the brush is caused by the peak-to-peak voltage Vp of the AC voltage regardless of the value of the DC voltage Vc.
Occur at 1.0 kV or less. This is because when the peak-to-peak voltage Vp of the AC voltage is 1.0 kV or less, the potential difference between the photosensitive member 1 and the charging brush 2 cannot satisfy the discharge starting voltage according to Paschen's discharge theory, and the charge alternately moves between the two members. Is not performed.

As described above, the superimposed voltage of the DC voltage and the AC voltage is applied to the charging brush 2 which is arranged in contact with the photosensitive member 1, and the DC voltage is Vc (V), and the peak-to-peak voltage of the AC voltage is Vp (V). Then, by having a relationship of Vp <2 × | Vc |, it is possible to prevent spot-like density unevenness of an image.

(Embodiment 2) In an image forming apparatus, image density and gradation are generally largely changed by aging or environmental fluctuation.

Therefore, as shown in FIG. 3, the temperature and humidity detecting means 28, the number of printed sheets detecting means 29, the charged potential detecting means 3
0, the charging bias voltage, the developing bias voltage, and the transfer bias voltage can be changed based on the signal of the image density detecting means 31. That is, in the brush charging device, if the DC voltage Vc is changed, the charging potential of the photoconductor 1 can be corrected, and the image density can be corrected.

However, for example, a uniform charging state in the initial state is caused by a change in the resistance value of the charging brush 2 due to the attachment of foreign matter and a decrease in the thickness of the photosensitive layer of the photosensitive member 1 due to abrasion. This is because even the obtained peak-to-peak voltage Vp may cause charging unevenness after a lapse of time.

Here, the charging bias voltage was controlled by the charging potential detecting means 30 so that the charging potential of the photosensitive member 1 was always constant, and a durability test of 20,000 sheets was performed. The frequency f of the AC voltage and the peripheral speed of each member are the same as in the first embodiment.

Hereinafter, the evaluation results are shown in Table 1 and Table 2.
Shown in Table 1 shows the case where the peak-to-peak voltage Vp is constant and only the DC voltage Vc is changed, and Table 2 shows the case where the peak-to-peak voltage Vp is changed.
And the evaluation results when the DC voltage Vc is changed. In Tables 1 and 2, “◎” indicates an image of good image quality, “○” indicates an image in which some unevenness of the brush sweep density occurred, and “□” indicates the brush sweep density. 5 shows an image in which unevenness has significantly occurred.

[0064]

[Table 1]

[0065]

[Table 2]

As is clear from Tables 1 and 2, when the value of the DC voltage Vc changes by changing the value of the peak-to-peak voltage of the AC voltage Vp according to the change of the DC voltage Vc. However, it is possible to prevent the occurrence of brush-like density unevenness of the brush.

In the present embodiment, the control for the fluctuation in the charging potential of the photosensitive member 1 is performed. However, in the case of the control for the fluctuation in the charging potential, the DC voltage Vc
Is reduced so that the peak-to-peak voltage Vp
It may exceed twice c. In such a case,
By changing the value of the peak-to-peak voltage Vp according to the change of the DC voltage Vc, it is possible to prevent spot-like density unevenness.

In Table 2, a value obtained by subtracting a constant of 100 from twice the DC voltage Vc was used as the AC voltage Vp. As described above, if a relationship of Vp = 2 × | Vc | −T (T is a constant) is satisfied, it is possible to easily prevent the brush-like density unevenness and the spot-like density unevenness of the brush.

When the value of the constant T is too large, the discharge starting voltage of Paschen discharge theory cannot be satisfied.
It is preferably 200 or less. When the constant T is a negative value, the AC voltage Vp exceeds twice the DC voltage Vc, so that 0 ≦ T ≦
It suffices to have 200 relationships.

(Embodiment 3) Next, in the image forming apparatus shown in FIG.
And the peripheral speed of the charging brush 2 was changed to evaluate the image.

Here, the contact width between the photosensitive member 1 and the charging brush 2 is 3 mm, and the DC voltage Vc of the charging bias voltage is −60.
0 V, and the peak-to-peak voltage Vp of the AC voltage was set to 1.1 kV. The peripheral speed of the photoconductor 1, the peripheral speed of the developing roller 5, and the peripheral speed of the toner supply roller 6 are the same as those in the first embodiment.

The evaluation results are shown in Table 3 below. In Table 3, “◎” indicates an image with good image quality, “△” indicates an image with some periodic density unevenness, and “x” indicates an image with periodic density unevenness. .

[0073]

[Table 3]

From the results shown in Table 3, when the peripheral speed of the charging brush 2 is 161 mm / sec, the periodic density unevenness is not noticeable at f = 95 Hz, and does not occur at f = 100 Hz at all. The peripheral speed of the charging brush 2 is 2
In the case of 51 mm / sec, the periodic density unevenness became inconspicuous at f = 125 Hz, and did not occur at f = 130 Hz at all. Thus, the photosensitive member 1 and the charging brush 2
Since the appropriate value of the frequency f of the charging bias voltage differs depending on the difference in the relative speed v at the contact portion with the contact point, the following has been found.

That is, if the period of the AC voltage is not one or more while the photosensitive member 1 passes through the contact width 1 with the charging brush 2,
Periodic charging unevenness occurs on the surface of the photoconductor 1, and density unevenness occurs. Therefore, in order to prevent density unevenness from occurring, v / l <
It is necessary to satisfy the relationship of f. In the present embodiment, since the contact width between the photosensitive member 1 and the charging brush 2 is 3 mm, v
= 285 mm / sec, the appropriate value of the frequency f is 95
Hz or higher.

As described above, the frequency of the charging bias voltage is f (Hz), the relative speed at the contact portion between the photosensitive member 1 and the charging brush 2 is v (mm / sec), and the nip between the developing roller and the toner supply roller is If the width is l (mm), f>
By having the relationship of v / l, it is possible to prevent periodic density unevenness due to the frequency of the AC voltage.

[0077]

As described above, according to the present invention, a voltage having a polarity opposite to the charging polarity of the electrostatic latent image carrier is not applied to the brush. In this case, it is possible to prevent the occurrence of spot-like density unevenness of an image when the value is increased.

Further, if the value of the peak-to-peak voltage of the AC voltage is changed according to the change of the DC voltage applied to the charging brush, the peak-to-peak voltage of the AC voltage can always be set large, so that the image is swept. An effective effect of being able to prevent the occurrence of eye-like density unevenness is obtained.

If the AC voltage is applied to the conductive brush for one or more cycles while the electrostatic latent image carrier passes through the contact portion with the brush, the surface of the electrostatic latent image carrier caused by the AC voltage An effective effect of being able to prevent the periodic charging unevenness is obtained.

[Brief description of the drawings]

FIG. 1 is a schematic diagram illustrating a configuration of an image forming apparatus using a brush charging device according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram showing an image evaluation result when changing a peak-to-peak voltage of a charging bias voltage of a charging bias supply power supply and an AC voltage in the image forming apparatus of FIG. 1;

FIG. 3 is a schematic diagram illustrating a configuration of an image forming apparatus using a brush charging device according to another embodiment of the present invention.

FIG. 4 is a schematic view showing an image forming apparatus having a conventional brush charging device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Photoconductor (electrostatic latent image carrier) 2 Charging brush 2a Shaft 28 Temperature and humidity detecting means 29 Number of printed sheets detecting means 30 Charge potential detecting means 31 Image density detecting means 32 CPU (control means)

Claims (5)

[Claims] An electrostatic latent image carrier comprising: a conductive shaft rotatably disposed in contact with a surface of an electrostatic latent image carrier, and a conductive brush radially provided on the shaft. A charging brush that uniformly charges the surface to a predetermined potential, and a charging bias supply power source that is electrically connected to the charging brush and applies a superimposed voltage including a DC voltage and an AC voltage to the charging brush. Assuming that the DC voltage applied to the charging brush is Vc (V) and the peak-to-peak voltage of the AC voltage is Vp (V), Vp <2
A brush charging device having a relationship of × | Vc |. A temperature and humidity detecting means for detecting the temperature and humidity in the image forming apparatus; a print number detecting means for detecting the number of printed sheets; and a charging means for detecting a charged potential on the surface of the electrostatic latent image carrier. Potential detecting means, image density detecting means for detecting the density of an image printed on the paper, and temperature and humidity detecting means, the number of printed sheets detecting means, based on signals from the charged potential detecting means and the image density detecting means. 2. The brush charging device according to claim 1, further comprising control means for changing a value of a peak-to-peak voltage of the AC voltage in accordance with a change in the DC voltage applied to the charging brush. 3. A DC voltage applied to the charging brush is V
3. The brush charging device according to claim 2, wherein, when c (V) and a peak-to-peak voltage of the AC voltage are Vp (V) and a constant T, a relationship of Vp = 2 × | Vc | −T is satisfied. 4. The brush charging device according to claim 3, wherein said constant T satisfies 0 ≦ T ≦ 200. 5. The method according to claim 1, wherein the frequency of the AC voltage applied to the charging brush is f (Hz), the contact width between the conductive brush and the electrostatic latent image carrier is 1 (mm), The relative speed at the contact portion with the latent image carrier is v (mm / s)
3. The brush charging device according to claim 1, wherein f> v / l.