JPH086357A - Brush charging mechanism - Google Patents

Abstract

PURPOSE:To bring a charging brush into uniform contact with the surface of a photoreceptor for uniform electrification. CONSTITUTION:Many brush fibers 20 are provided on the surface of a l cylindrical core metal to form a charging brush. The tip of each brush fiber 20 is divided into multiple fine-diameter fibers 21. The divided fine-diameter fibers 21 are brought into contact with the surface of a photoreceptor to be charged for electrification. The brush fibers 20 are uniformly brought into contact with the surface of the photoreceptor. A charge injection layer is provided on the surface of the photoreceptor for electrification with low voltage.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a brush charging mechanism for charging a charged body such as a photoconductor mounted on an image forming apparatus such as a copying machine or a laser beam printer.

[0002]

2. Description of the Related Art Conventionally, in an electrophotographic image forming apparatus, a non-contact type is generally used as a charging device for an electrophotographic photosensitive member (hereinafter simply referred to as "photosensitive member") as an image bearing member (charged member). Corona chargers have been used. The corona charger has drawbacks such that a large amount of ozone is generated and a high voltage needs to be applied.

In recent years, in order to eliminate the drawbacks of the corona charger, a charging device designed for low ozone and low power consumption, that is, a contact charging device for charging by applying a voltage to a charging member in contact with a photosensitive member. Has been put to practical use. In particular, a roller charging type contact charging device using a conductive elastic roller (hereinafter referred to as “charging roller”) as a charging member is preferably used because it has excellent charging stability.

In roller charging, a charging roller is pressed against a photoconductor and a voltage is applied to the photoconductor to charge the photoconductor. The charging at this time utilizes a discharging phenomenon from the charging roller to the photosensitive member, and the charging is started by applying a voltage higher than a certain threshold voltage (charging start voltage) V _th . For example,
When a charging roller is pressed against an OPC photosensitive member having a thickness of 25 μm as a member to be charged to perform a charging process, the surface potential of the photosensitive member is reduced by applying a voltage of about 640 V or more to the charging roller. The rise starts and the surface potential after the rise starts increases linearly with a slope of 1 relative to the applied voltage. That is, in order to obtain a desired photoreceptor surface potential V _d , the charging roller is higher than the charging roller by V _th (V _d +
It is necessary to apply a DC voltage of V _th ). The contact charging method in which only the DC voltage is applied as described above is hereinafter referred to as "DC charging method".

However, in the DC charging method, the resistance value of the contact charging member fluctuates greatly due to environmental changes and the charging start voltage V _th fluctuates due to the change in the film thickness due to the abrasion of the surface of the photoconductor. Potential V of photoconductor surface
It was difficult to uniformly charge _d to a desired value.

Therefore, in order to further homogenize the charging, as disclosed in Japanese Patent Laid-Open No. 63-149669, a DC voltage corresponding to the desired V _d and a charging start voltage V _th of 2 are set. An "AC charging method" is used in which an oscillating voltage having an AC component having a peak-to-peak voltage that is more than double is applied to the contact charging member to charge the photoconductor. This utilizes the potential leveling effect of AC, and the potential of the photoconductor converges on V _d which is the center of the peak of the AC voltage, and is hardly affected by disturbance such as the environment.

For the above-mentioned DC charging and AC charging, there is a contact charging member using a brush-shaped charging brush in addition to the charging roller. Further, when a fixed brush is used as the charging brush, it is mechanically simple, and it is more advantageous in cost than the one using the charging roller. Therefore, it is being put to practical use.

By the way, also in the contact charging device using the charging roller and the charging brush described above, the essential charging mechanism is the same as in the non-contact charging system such as the corona charger, the discharge phenomenon from the charging member to the photosensitive member. Therefore, the charging start voltage V _{th of the} surface of the photoconductor is used as the voltage at the time of charging.
The above values are required, and a small amount of ozone is generated. AC
In addition to this, the charging method (especially, one using a charging roller) generates vibration noise (AC charging sound) between the charging member and the photoconductor due to a change in the direction of the electric field due to the AC voltage, and the surface of the charged object due to discharge Deterioration and the like became remarkable and became a new problem.

For this reason, there has been a demand for charging by directly injecting charges into the body to be charged.

As a method of directly injecting the charges,
For example, a charging method is known in which a voltage is applied to a charging brush as a contact charging member, and charges are injected into a trap level or the like on the surface of a photoconductor to perform contact injection charging.

[0011]

However, in the contact charging method using a charging brush, the method of injecting charges into the trap level or the like on the surface of the photoconductor has a poor injection efficiency and is still in practical use. Not in.

That is, in the charging by the charging brush, it is necessary to bring the brush bristles (brush fibers) into uniform contact with the surface of the photoreceptor, and a means for increasing the pile density of the pile or devising the shape of the fiber has been proposed. ing. Nevertheless, it was difficult to achieve uniform contact because there was a limit to the yarn diameter of the base fabric to increase the planting density, and there was a limit to how to devise the fiber shape.

From the standpoint of achieving this uniform contact, it is desirable to rotate and use a roller-shaped charging brush rather than a fixed charging brush. By rotating the roller-shaped charging brush to increase the peripheral speed difference with the photoconductor, the number of contact points can be substantially increased. However, from the viewpoint of preventing damage to the photoconductor and mechanical restrictions, there is a limit to the increase in the peripheral speed difference, and a practical charging property has not been obtained.

Therefore, according to the present invention, the brush charging mechanism is designed to improve the charge injection efficiency by increasing the contact points with the charged body (photoconductor) without increasing the peripheral speed difference with the charged body. It is intended to provide.

[0015]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, in which a charging member to which a charging voltage is applied is brought into contact with an object to be charged to charge the object. In the brush charging mechanism, the charging member includes a base to which a charging voltage is applied, and a large number of brush fibers whose base end is held by the base and whose tip is in contact with the surface of the body to be charged. It is characterized in that the tip of the brush fiber is divided into a plurality of small-diameter fibers that come into contact with the surface of the body to be charged.

Further, it is preferable that the member to be charged is a photoconductor having a photoinjection layer on the surface of a photoconductive layer having photoconductivity.

Further, a relative speed difference may be provided between the brush fibers of the charging member and the charge injection layer of the photoconductor.

[0018]

By virtue of the above construction, the tip end portion of the brush fiber of the charging member is divided into a plurality of small-diameter fibers, so that the number of contact points with the surface of the member to be charged can be increased and uniform contact can be improved.

Further, by providing the charge injection layer on the photosensitive layer having photoconductivity, the charge injection efficiency of contact injection charging at a low voltage is improved.

Further, by providing a relative speed difference between the brush fibers and the charge injection layer, it is possible to prevent the durability from being deteriorated due to the fatigue of the brush fibers.

[0021]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows a vertical cross section of a photosensitive member (object to be charged) 1 to be charged by the brush charging mechanism according to the present invention. The figure shows an enlarged vertical sectional view of the vicinity of the surface of the photosensitive member 1 formed in a drum shape.

The photoreceptor 1 comprises an aluminum cylinder 11, a conductive layer 12, an injection prevention layer 13, and a charge generation layer 1 in this order from the center side.
4, the charge transport layer 15, and the charge injection layer 16.

The aluminum cylinder 11 is a base body formed in a cylindrical shape and has a diameter of 30 mm. On its surface, a conductive layer 12 (hereinafter referred to as "UC layer") is an undercoat layer of about 20 μm. Is formed with a film thickness of.

The charge injection prevention layer (hereinafter referred to as “CP layer”) 13 is for preventing dark decay due to injection of holes from the aluminum cylinder 11. An electrically medium resistance material is used for this layer, and an insulating amylan resin is mixed with methoxymethylated nylon showing a certain degree of ionic conductivity and coated to a thickness of about 1 μm.

Charge generation layer (hereinafter referred to as "CG layer") 1
4 is a polyvinyl butyral resin as a binder and a disazo pigment as a charge generating material in a ratio of 1: 2.
Is applied in a layer thickness of about 1 μm.

Charge transport layer (hereinafter referred to as "CT layer") 1
5 is composed of a P-type semiconductor and has the above-mentioned CG.
Of the charge pairs generated in the layer 14, it plays a role of transporting only positive charges to the photoreceptor surface. Specifically, a polycarbonate resin in which hydrazone is dispersed at a weight ratio of 1: 1 is applied with a layer thickness of 20 μm.

At present, the OP of an ideal N-type semiconductor is used.
Although a C photoconductor has not been found, it is possible in principle to replace the P-type semiconductor having the above-described configuration with an N-type semiconductor and perform positive charging.

In the present invention, the charge injection layer 16 is provided on the CT layer 15 described above. This charge injection layer 16
This allows direct injection charging from a contact charging member (described later). The charge injection layer 16 is, for example, 70% by weight of SnO ₂ as a conductive filler 17 in a phosphazene resin.
((Weight of conductive filler / total weight of conductive filler and binder) × 100 [%]) to form a film having a thickness of 2 μm.

Regarding the dispersion amount of SnO ₂ at this time,
When the amount of dispersion is too large, the surface resistance value of the charge injection layer 16 becomes too low, and there is a possibility that lateral flow of latent image charges may occur after image exposure. Especially, in a high temperature and high humidity environment. This phenomenon becomes remarkable. On the other hand, if the amount of dispersion is too small, SnO ₂ does not sufficiently appear on the surface of the charge injection layer and charge is not sufficiently injected, resulting in partial charge failure. Specifically, a solid white image in the reversal development system causes black spots on the sandy surface and fogging on the entire surface, resulting in a defective image. In order to prevent these problems, the amount of SnO ₂ dispersed must be in the range of ₂ to 100 wt% as shown in Table 1.

[0031]

[Table 1] However, if the resistance charge injection layer 16 is simply formed on the surface of the photosensitive layer, the charge laterally flows through the surface, and the electrostatic latent image cannot be held. Therefore, the surface resistance is high, and the anisotropic conductivity is set so that the resistance value is small toward the inside of the photoconductor.

As an example of its constitution, it is possible to obtain the above-mentioned anisotropic conductive action by using an insulating binder in which an appropriate amount of conductive particles such as SnO ₂ having a light transmitting property are dispersed. .

Although it is possible to use other metal oxides, conductive carbon, etc. as the conductive filler, it is necessary that the light reaches the CG layer 14 at the time of image exposure. Good SnO ₂ particles are preferred. SnO
_When 70% by weight of ₂ was dispersed, the charge injection layer 16 alone showed a transmittance of 95% with respect to light of 730 nm, so that a latent image can be formed by image exposure at a level that poses no practical problem.

The same effect can be observed when TiO ₂ particles are dispersed as another conductive filler, but when TiO ₂ which is a white particle is dispersed in the charge injection layer 16, the light transmittance is reduced. When the light transmittance of the charge injection layer 16 is less than 50%,
Since a sufficient bright portion potential cannot be obtained, a good image cannot be obtained. If the exposure intensity is increased in order to prevent this, the light scattering phenomenon by the conductive particles of the charge injection layer 16 becomes remarkable, and the latent image bleeds and blurs, which is not preferable.

Actually, the principle of charge injection is described in detail in Japanese Patent Application No. 5-66150 filed by the present applicant.

An image was output by an electrophotographic printer using the photoconductor 1 and a charging brush described later.

FIG. 2 is a schematic diagram of a printer according to the present invention. This printer includes a primary charger (charging brush) 2,
The process cartridge 8 in which the developing unit 4, the cleaning unit (counter blade) 6 and the like are integrated is used.

In the figure, the photosensitive member 1 is a charging brush 2
After being uniformly charged by, the image is exposed by the laser beam 3 whose intensity is modulated according to the image signal, and that portion is discharged. In the developing unit 4, the one-component magnetic toner undergoes reversal development, and the exposed portion is visualized as a toner. Here, the jumping development method is used.

The toner image is transferred to the transfer material 9 in the next transfer section 5.

In the printer of this example, the transfer device is 3 kV.
The transfer roller to which the voltage of 1 was applied was used. After that, the toner image on the transfer material 9 is fixed by the heat fixing roller 7 and discharged to the outside of the machine.

On the other hand, the transfer residual toner remaining on the photosensitive member 1 is scraped off by a counter blade 6 made of urethane rubber to prepare for the next image formation.

The charging brush 2 used in the present invention is rotatably constituted by a cored bar 22 as a cylindrical substrate and a large number of semiconductive brush fibers 20 provided on the surface thereof. A voltage is applied to the charging brush 2 to rub against the photoconductor 1 to charge it. Semi-conductive brush fiber 20
Has a low volume efficiency of about 10 ² to 10 ⁷ Ω · cm. Specifically, SA-7 (Aryl series, Toray), Bertron (Nylon series, Kanebo), R
EC (Rayon system, Unitika), Robal (Polypropylene system, Mitsubishi Rayon), Cracabo (PET system,
Fibers having conductive carbon black dispersed therein such as Kuraray Co., Ltd. can be mentioned. These brush fibers 20 having a thickness of about 3 to 10 denier are easy to use in terms of conductivity and pile density.

Brush fibers 20 as shown in FIG. 7 (a)
Divides its tip into a plurality of thin fibers 21, as shown in FIG.

To divide the tip of the fiber brush 20,
For example, the metal roller 3 as shown in FIGS.
Several hundreds of jigs having thin blade-shaped notch 31 on the surface of
It is pressed against the surface of the charging roller 2 while being rotated by several thousand rotations. As an example, a stainless-steel roller 30 having a diameter of 10 cm was provided with thin blade-shaped cut grooves 31 having a depth of 250 μm and a pitch of 10 μm.

This roller 30 is rotated at 500 rpm, and in the opposite direction at 500 rpm, the thickness is 6 denier (fiber diameter is 35 μm) and the pile density is 100,000 pieces / inch.
^2. Fiber: By pressing the charging brush 2 of SA-7 while rotating, the tip portion was divided into a plurality of small diameter fibers.
The length of the thin fiber 21 was about 200 μm and the thickness was 3 to 6 μm. Outer diameter 14 mm, core metal diameter 8 m
The charging brush 2 having m and a resistance value of 1 × 10 ⁵ Ω (at the time of applying 250 V) was mounted on the process cartridge 8 shown in FIG.

The charging brush 2 has a nip width of about 7 m on the photoconductor 1.
process speed 25 mm / sec while rotating the same in the same direction as the photoconductor 1 so that the peripheral speed difference becomes 3 times.
It was charged with.

As a result, the surface potential of the photosensitive member 1 was -490V, which was almost equal to the applied voltage of -500V. The result of measuring the surface potential of the photoreceptor 1 at this time is shown in FIG.

It can be seen that the fluctuation range is smaller than the surface potential of the untreated (undivided) charging brush shown as a comparative example.

The rotating direction of the charging brush 2 may be opposite to that of the photosensitive member, but it is necessary to make the peripheral speed difference larger than that in the case of rotating in the same direction. In the opposite direction, if the peripheral speed difference is 0 when rotated at the same speed, the peripheral speed of the charging brush 2 must be doubled and rotated in order to obtain the same peripheral speed difference as described above.

Also, with the above printer, 32.5 ° C., 85
% RH high temperature and high humidity (hereinafter referred to as "H / H"), 23
Normal at 65 ° C and 65% RH (hereinafter referred to as "N / N"), 1
Image output was performed under each environment of low temperature and low humidity (hereinafter, “L / L”) of 5 ° C. and 10% RH, and a good image without defective charging, image blur, and flow could be obtained. In this example,
Since the charging method does not use electric discharge, ozone was not generated and the surface of the photoconductor 1 was not roughened due to electric discharge.

In order to obtain a similar image with a conventional photoconductor, it is necessary to apply a voltage in which an AC voltage of 2000 V (peak-to-peak voltage value) is superposed on a DC voltage of -500 V and to perform AC charging under these conditions. It was confirmed that the amount of ozone was about 0.01 ppm, the surface of the photoconductor 1 was roughened by the discharge, and the charging sound was generated by the oscillating electric field.

As a comparative example, when an image was formed using a conventional photoconductor under the bias conditions of this example, the photoconductor surface potential was almost 0 V, and charging was not performed.

As described above, by adopting the configuration of this embodiment, it becomes possible to carry out charging without a discharge by a low DC voltage, and to eliminate ozone generation and AC charging noise, which have been problems in the past. It has become possible.

Further, changes in the brush outer diameter and the charging nip width of the charging brush 2 when the number of prints increases are as shown in FIGS. 4 and 5, and the charging brush 2 of the present invention has a small settling amount. I understand. This is because the untreated (undivided) charging brush is liable to cause settling due to the contact pressure, whereas the charging brush 2 of the present invention absorbs the contact pressure moderately in the thin fiber portion at the tip, It is considered that this is because the portion with the original thickness is retained as it is.
As a result, there was little decrease in chargeability during durability, and after durability (5
000 sheets or later) The measured photoreceptor surface potential during charging is -4.
It was 70 V and had almost no effect on the image quality.

When an untreated (undivided) brush was used, the surface potential of the photosensitive member after running was -390 V, and fog occurred due to poor charging.

[0056]

As described above, according to the present invention,
By dividing the tip of the brush fiber of the charging brush into a plurality of small-diameter fibers, the brush fiber can be brought into uniform contact with the surface of the photoconductor, and the charging uniformity can be improved. It is possible to prevent the charging failure due to. In addition, since the change in the outer diameter of the charging brush is small and the change in the nip width is small even during durability, it is possible to effectively prevent the deterioration of the charging ability due to the fatigue of the brush fiber, and to perform stable charging without charging fog. it can.

[Brief description of drawings]

FIG. 1 is an enlarged vertical cross-sectional view showing the configuration near the surface of a photosensitive member to be charged in the present invention.

FIG. 2 is a schematic configuration diagram of an electrophotographic printer equipped with a charging brush.

FIG. 3 is a diagram showing the surface potential distribution in the circumferential direction of the photoconductor by a charging brush.

FIG. 4 is a view showing a change in brush outer diameter during durability.

FIG. 5 is a diagram showing a change in charging nip width during durability.

FIG. 6A is a front view of a jig for dividing the tip end portion of the brush fiber. (B) is a longitudinal sectional view of the same.

FIG. 7A is an enlarged view of a tip portion of a brush fiber before division. (B) is an enlarged view of the tip portion of the brush fiber after division.

[Explanation of symbols]

 1 Charged Member (Photosensitive Member) Photosensitive Drum 2 Charging Brush 3 Laser Light 4 Developing Unit 5 Transfer Roller 6 Cleaning Blade 7 Fixing Roller 8 Process Cartridge 9 Transfer Material 11 Aluminum Cylinder 12 Conductive Layer (Undercoat Layer, UC Layer) 13 Charge Injection prevention layer (CP layer) 14 Charge generation layer (CG layer) 15 Charge transport layer (CT layer) 16 Charge injection layer 17 Conductive filler 20 Brush fiber 21 Thin fiber 22 Substrate (core bar)

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tadashi Furuya 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc.

Claims (3)

[Claims] 1. A brush charging mechanism in which a charging member to which a charging voltage is applied is brought into contact with a member to be charged to charge the member to be charged, wherein the charging member is a substrate to which the charging voltage is applied, A plurality of brush fibers whose base end is held by the base body and whose tip is in contact with the surface of the body to be charged; and a plurality of brush fibers whose tip is in contact with the surface of the body to be charged. The brush charging mechanism is characterized in that it is divided into small diameter fibers. 2. The brush charging mechanism according to claim 1, wherein the member to be charged is a photoconductor having a charge injection layer on a surface of a photoconductive layer having photoconductivity. 3. The brush charging mechanism according to claim 2, wherein a relative speed difference is provided between the brush fiber of the charging member and the charge injection layer of the photoconductor.