JPS63293571A - Carrier recovering device - Google Patents

Abstract

PURPOSE:To protect and electrostatic latent image carrier even if a spark is generated between a carrier recovering member and an electrostatic latent image carrier by impressing a bias having polarity capable of attracting a carrier through a protection resistor to the carrier recovering member arranged adjacently to the surface of the carrier set up on the downstream side of a developing area. CONSTITUTION:At the time of developing an electrostatic latent image in a developing area A, the slight quantity of magnetic carrier in developer De is stuck to the surface of a photosensitive drum 1. The stuck carrier is attracted and recovered to the outer periphery of a carrier recovery sleeve 14 by the magnetic force of a magnetic roll 15 and a bias impressed to bias power supplies E2, E3 in a carrier removing area B. Since the protection resistor R is arranged between the power supplies E2, E3 and the sleeve 14 even if a spark is generated between the drum 1 and the sleeve 14 due to a potential difference between the drum 1 and the sleeve 14, a current value flowing into the drum 1 is small and a photosensitive layer formed on the surface of the drum 1 is not damaged.

Description

Detailed Description of the Invention Field of Application The present invention uses a carrier recovery device, specifically a two-component developer consisting of a mixture of carrier and toner, to carry on the surface of an electrostatic latent image carrier. The present invention relates to a carrier recovery device attached to a developing device that develops an electrostatic latent image.

Prior art and its problems In general, the developing device includes a developing sleeve provided facing the surface of an electrostatic latent image carrier, and an N and S pole magnetized sequentially in the circumferential direction on the outer periphery of the developing sleeve. A well-known device is equipped with a magnetic roller provided at the top. In this developing device, the developer consisting of a mixture of carrier and toner is attracted like a magnetic brush onto the outer circumferential surface of the developing sleeve by the magnetic action of the magnetic roller, and based on the rotation of the developing sleeve and/or the magnetic roller. The image is transported along the outer circumferential surface of the developing sleeve to the developing area, that is, the area where the surface of the electrostatic latent image carrier and the outer circumferential surface of the developing sleeve closely face each other, where it is carried on the surface of the electrostatic latent image carrier. Develop the electrostatic latent image. At this time, the toner in the developer that has been conveyed to the development area has already retained an electric charge on the friction band 1 with the polarity opposite to that of the electrostatic latent image area due to friction with the carrier. The electrostatic latent image is electrostatically attracted to the image area. On the other hand, since the carrier in the developer is magnetically attracted to the outer peripheral surface of the developing sleeve by the magnetic action of the magnetic roller, it does not adhere to the electrostatic latent image carrier.

However, as a practical matter, it has been experienced that a small amount of carrier adheres to the electrostatic latent image carrier during development, resulting in problems such as carrier leakage outside the developing device and image unevenness due to a decrease in developer. is occurring. Additionally, it has been experienced that such carrier adhesion is more likely to occur when a carrier with a small particle size or weak magnetism is used, such as a carrier with magnetic fine powder dispersed in a resin. .

Therefore, the present applicant has conventionally proposed Japanese Patent Application Laid-Open No. 58-176
No. 661 and Japanese Unexamined Patent Publication No. 61-200561,
It has been proposed that a carrier collection member equipped with a magnetic roller is provided facing the surface of the electrostatic latent image carrier. It is disclosed that carrier recovery ability is improved.

However, in the case of reversal development, such as in laser printers, in which toner is transferred to the image area where the charge has disappeared,
Carrier adhesion occurs based on the difference between the back shadow potential of the electrostatic latent image and the bias potential to the developing sleeve, and in order to re-adhere this carrier to the collection member, it is necessary to It is necessary to apply a high-voltage DC bias to the collection member so that an electric field greater than the electric field generated by the potential difference between them acts.

Therefore, if there is a defect such as a pinhole on the surface of the electrostatic latent image carrier, there is a risk that sparks will occur between the pinhole and the carrier collection member, causing a large current to flow through the electrostatic latent image carrier and damaging it. The problem was that the cost was extremely high. especially,
Amorphous-silicon photoreceptors have many pinholes, which increases the degree of damage.

Means for Solving the Problems Therefore, the carrier recovery device according to the present invention includes a carrier recovery member made of a conductive material installed close to the surface of the electrostatic latent image carrier on the downstream side of the development area, and a carrier recovery member made of a conductive material. The device is composed of a power supply means for applying a voltage, and a resistor interposed between the carrier recovery member and the power supply means.

That is, even if a spark occurs between the carrier collection member and the electrostatic latent image carrier, a large current will not flow between the carrier collection member and the electrostatic latent image carrier.

X effort Hereinafter, one embodiment of the present invention will be described with reference to the accompanying drawings.

FIG. 1 shows a magnetic brush developing device (MD) equipped with a carrier recovery device according to the present invention, in which the photosensitive drum (+) is 17
It is rotated in the direction of arrow (a) at a circumferential speed of 6 mm/sec, and as it rotates, an electrostatic latent image is formed on the surface by a well-known image forming process (not shown).

The developing device (MD) generally includes a developing sleeve (3) provided in a developing tank (2) at opposing positions on the surface of the photoreceptor drum (1), and a developing sleeve (3) provided inside the developing sleeve (3). It consists of a magnetic roller (4) provided therein, and a bucket roller (5) installed with its lower half almost buried in the developer (De) housed inside the developer tank (2). .

The developing sleeve (3) is formed into a cylindrical shape with an outer diameter of 31 mm from a non-magnetic conductive material (for example, non-magnetic stainless steel), and is adapted to be applied with a DC voltage by a developing bias power source (El). . Further, the developing sleeve (3) is 0.0000 0.00000 with respect to the surface of the photoreceptor drum (1) in the development area (A).
, 7 m1% gap is maintained, and during development, it is rotationally driven in the direction of arrow (b) at a rotational speed of 3 Orpm by a drive source (not shown). The magnetic roller (4) has S on its outer periphery.
, 10 N poles are sequentially magnetized in the circumferential direction, and the arrow (b
) direction at a rotation speed of 120 Orpm.

Further, the magnetic force of the magnetic roller (4) is set so that a magnetic field of 1000 Gauss is formed on the outer peripheral surface of the developing sleeve (3). Therefore, the developer (De) supplied to the outer peripheral surface of the developing sleeve (3) is
It is attracted like a magnetic brush on the outer peripheral surface of the
) direction.

The developing agent (De) contained in the developer tank (2) is made of a mixture of a magnetic carrier and an insulating toner, and is frictionally charged to have different polarities by the friction of rain particles. Note that specific examples of the developer will be described later.

The packet roller (5) is provided with a plurality of packets around its periphery, and is driven to rotate in the direction of arrow (d) during development, and transfers the developer (De) scooped up by the packets to the outer periphery of the developing sleeve (3). supply to.

Further, a scraper plate (6) and a cleaning plate (7) made of a flexible non-magnetic material such as a resin film or a thin metal plate are attached to the outer peripheral surface located below the developing sleeve (3). Rotation direction of the developing sleeve (3) [arrow (b)
)] is attached to the support (8) so as to be in pressure contact in the following reverse direction and in the opposing forward direction, respectively.

On the other hand, above the developing sleeve (3) there is an upper casing (
9) is installed. The inner circumferential surface of the upper casing (9) is rubbed by the developer (De) conveyed on the outer circumferential surface of the developing sleeve (3).
) is considered to be a concentric arc surface. At the end of the upper casing (9) on the side of the photoreceptor drum (1), on the extension line of the circular arc surface, there is provided a flexible insulating seal plate (10) whose tip is connected to the photoreceptor drum. It is attached so that it comes into pressure contact with the surface of (1).

Further, a developer transport blade (12) is installed in the developer tank (2) below the scraper plate (6) so as to be rotatably driven in the direction of arrow (e).

Furthermore, the developing tank (3) is located below the developing sleeve (3).
) A carrier recovery device (11) is installed at the open end of the carrier. In this carrier recovery device (11), the carrier recovery sleeve (14) is made of a non-magnetic conductive material (for example, non-magnetic stainless steel) and has a cylindrical shape with an outer diameter of 16 mm. It is installed in area (B) with a gap of 0.5 mm to the surface of the photoreceptor drum (1), and is connected to a DC bias power source (E, ) and an AC bias power source (E3) via a protective resistor (R). is connected to apply a bias for carrier recovery.

Also, the developer tank (2) of this carrier collection sleeve (14)
) side is in pressure contact with the tip of a scraper plate (16) rising from the inner surface of the developer tank (2), and the magnetic roller (15) is magnetized with S and N poles in the circumferential direction on the outer circumference. The magnetic force is 7 on the outer peripheral surface of the sleeve (14).
The setting is such that a magnetic field of 0.00 Gauss is generated. Further, this magnetic roller (15) is rotatable and receives the action of the magnetic field of a magnetic roller (4) built in the developing sleeve (3), and follows the rotation of the magnetic roller (4) in the direction of arrow (b). and is driven to rotate at 300 rpm in the direction of arrow (f). Note that the DC bias from the DC bias power source (E) has a polarity that allows carriers to be attracted to the carrier recovery sleeve (14).

Here, the developer will be explained in detail.

The developer consists of a mixture of a magnetic carrier and an insulating toner, and the magnetic carrier can be triboelectrified with the toner, has a high resistance value of I01'Ωcm or more, and has a particle size of 5 to 6.
0 μm (average particle diameter: 40 μm), and is made by dispersing magnetic fine powder in a resin, and the proportion of the magnetic fine powder in the total particles is 50 to 75 wt%. More specifically, the magnetic carrier is manufactured by, for example, melting and mixing an insulating resin and a magnetic fine powder, cooling and pulverizing the mixture, and selecting the particles to have an average particle size of 40 μm. As an insulating resin,
Polyethylene, polyacrylic acid ester, polymethyl methacrylate, polystyrene, styrene acrylic polymer, epoxy resin, coumaron resin.

Malenic acid resin 1 Carbonic acid resin, fluoric acid resin, etc. can be used. Further, as the magnetic fine powder, Fe70t is used.

FeO4, ferrite, magnetite, etc. may be selected as appropriate. On the other hand, as the insulating toner, conventionally known ones can be used, and the particle size thereof is 5 to 30 μm (average particle size 10
-15 μm), and the volume resistivity is approximately 10 14 Ωam or more.

In the above configuration, the current 11t! (2) Developer (D
e) is scooped up by the packet as the packet roller (5) rotates in the direction of arrow (d), and is conveyed to a position where the magnetic force of the magnetic roller (4) is applied, and the outer peripheral surface of the developing sleeve (3) It is attracted like a magnetic brush. and,
Arrow (b) of developing sleeve (3) and magnetic roller (4)
As the developing sleeve (3) is rotated in the direction shown in FIG. reach. In this development area (A), the photoreceptor drum (1
) is rubbed by the developer (De), and the electrostatic latent image carried on the surface is developed. after that,
The developer (De) is scraped off from the outer peripheral surface of the developing sleeve (3) by a scraper plate (6) and returned into the developing tank (2).

By the way, when the electrostatic latent image is developed in the surface development area (A), some amount of the magnetic carrier in the developer (De) may adhere to the surface of the photoreceptor drum (1). The surface of the photosensitive drum (1) to which the magnetic carrier is attached is a developing area (
A) and moves in the direction of arrow (a) to reach the carrier removal area (B) where the carrier recovery sleeve (14) closely faces the surface of the photoreceptor drum (1).

In this carrier removal area (B), the carrier attached to the surface of the photoreceptor drum (1) in the development area (A) is removed by the magnetic force of the magnetic roller (I5) and the bias power source (E).

The carrier is attracted to the outer peripheral surface of the carrier recovery sleeve (14) by the DC bias and AC bias applied at (E,). The carriers attracted to the outer circumferential surface of the sleeve (14) are conveyed on the outer circumferential surface of the sleeve (14) in the direction opposite to the arrow (f) as the magnetic roller (15) rotates in the direction of the arrow (f). The developer is scraped off into the developer tank (2) by the scraper plate (16), and returned to the developer (De) in the developer tank (2). In addition, the powder smoke toner leaking to the outside from the carrier removal area (B) also adheres to the outer circumferential surface of the carrier recovery sleeve (14) together with the carrier, and is returned into the developer tank (2).

In addition, a photoreceptor drum (1) and a carrier collection sleeve (1) are also included.
4), even if a spark occurs between them, the power source (Et), (E3) and the carrier collection roller (1)
4), the current value flowing through the photoreceptor drum (1) is small and does not damage the surface photoreceptor layer.

By the way, the reason why an alternating current bias is superimposed and applied to the carrier recovery sleeve (14) in addition to a direct current bias is as follows.

First, a DC bias with a polarity capable of attracting carriers is applied to the carrier recovery sleeve (14), but in the carrier removal region (B), an alternating magnetic field based on the rotation of the magnetic roller (4) is applied to the carrier recovery sleeve (14). An electric field is also formed by the AC bias applied to the photoreceptor drum (I4), and the carriers attached to the surface of the photoreceptor drum (1) are disturbed and vibrated by the action of these alternating magnetic fields and alternating electric fields, causing the photoreceptor drum (1) to vibrate. This is because it becomes easier to separate from the surface of 1).

Here, the voltage values of the development bias, the carrier recovery bias, and the resistance of the protective resistor are determined separately for regular development (positive-positive development) and reversal development (negative-positive development).

Specific examples of values are shown in the table below.

As is clear from the table above, in regular development, the polarity of the potential of the non-image area of the electrostatic latent image and the polarity of the charge on the carrier are the same.
It is considered that the adsorption force of the carrier to the photoreceptor drum (1) is relatively small. On the other hand, in the reversal phenomenon, since the two polarities are different, the adsorption force of the carrier to the surface of the photoreceptor drum (1) is large. Therefore, in reversal development, it is important to generate a larger carrier suction force by superimposing an alternating current bias on the carrier collection sleeve (14) than in regular development.

In the reversal development, it is desirable that the voltage value of the carrier recovery DC bias be higher than the voltage value of the non-image area of the electrostatic latent image. In addition, it is desirable that the voltage value of the carrier recovery AC bias is as high as possible, but 500 V (
rms) was also effective.

By the way, the carrier collection sleeve (14) is indicated by the arrow (
It may be rotated (up to about 60 rpm) in the opposite direction to f).

Effect of Moxibustion As is clear from the above explanation, in the carrier recovery device of the present invention, the carrier recovery member installed close to the surface of the electrostatic latent image carrier on the downstream side of the development area collects carriers via a protective resistor. It is designed to apply a bias with a polarity that allows it to be attracted.

Therefore, even if a spark occurs between the electrostatic latent image carrier and the carrier collection member based on the potential difference between the two, only a small current flows through the electrostatic latent image carrier, and the electrostatic latent image Does not damage the carrier.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a developing device equipped with a first embodiment of the present invention. (A)...Development area, (B)...Carrier removal area, (MD)...Development device, (De)...Developer,
(R)...protective resistor, (E,)...DC bias power supply, (E3)...AC bias power supply, (14)...carrier collection sleeve, (15)...magnetic roller.

Claims (1)

[Claims] 1. A carrier attached to a developing device that develops an electrostatic latent image carried on the surface of an electrostatic latent image carrier using a two-component developer consisting of a mixture of carrier and toner. A recovery device includes a carrier recovery member made of a conductive material installed close to the surface of the electrostatic latent image carrier on the downstream side of a developing area, a power supply means for applying a voltage to the carrier recovery member, and the carrier recovery member and the power supply means. A carrier recovery device comprising: a resistor interposed between the carrier recovery device and the carrier recovery device.