JPS61200561A - Carrier recovering device - Google Patents

Abstract

PURPOSE:To recover securely carriers sticking on the surface of a photosensitive body by superposing an AC bias upon a DC bias which has such a polarity that carriers are attracted and applying the resulting bias to a carrier recovery member provided nearby the photosensitive body surface behind a development area. CONSTITUTION:A small amount of magnetic carriers in a developer De are stuck on the surface of the photosensitive drum 1 in the development area A. Then, the surface of the photosensitive drum 1 moves through the development area A as shown by an arrow (a) and the carrier recovery plate 13 reaches a carrier removal area B facing the photosensitive drum 1 closely. The magnetic carriers stuck on the surface of the drum 1 are attracted by a carrier recovery plate 13 with the DC and AC biases applied from bias power sources E2 and E3. The magnetic carriers stuck on the carrier recovery plate 13 move down along the operating carrier recovery plate 13 in the magnetic field of a magnetic roller 4 according to the rotation of the roller 4 shown by an arrow (b) and are returned into the developer De in a developer tank 2. Thus, the carriers stuck on the surface of the photosensitive body are removed securely.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention uses a carrier recovery device, specifically, a two-component developer consisting of a mixture of carrier and toner, to coat the surface of an electrostatic latent image carrier. The present invention relates to a carrier recovery device attached to a developing device that develops a carried 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 transported to the development area already holds a triboelectric charge of the same polarity as the polarity of the electrostatic latent image area due to friction with the carrier.
It is electrostatically attracted to the electrostatic latent image portion. On the other hand, the carrier in the developer is magnetically attracted to the outer circumferential surface of the developing sleeve by the magnetic action of the magnetic roller, so that 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 in which fine magnetic powder is dispersed in a resin. .

For this reason, it has been proposed in the past, for example, as described in Japanese Utility Model Publication No. 51-38363, in which a magnetic recovery device is mounted to face the photosensitive drum. However, this method has the problem of not being able to exhibit sufficient recovery ability because it attempts to recover carriers attached to the surface of the photoreceptor drum only using the static magnetic field of the magnetic recovery device. . In particular, copying machines with high process speeds, printers that reversely develop and visualize electrostatic latent images formed with light beams, etc., and binder-type or organic photoreceptors that tend to cause carrier adhesion are used. This is insufficient for the developing device of a copying machine.

On the other hand, the present applicant has proposed a carrier recovery member equipped with a magnetic roller as opposed to the surface of an electrostatic latent image carrier as JP-A-58-176661. It is disclosed that carrier recovery ability can be improved by applying a direct current bias to the member. However, DC voltage cannot be applied at a high voltage due to safety standards, and there is still a problem that improvement in recovery efficiency cannot be expected, especially in reverse development, etc., which requires a high voltage bias for carrier recovery. There is. That is, in the case of reversal development, 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. This is because it is necessary to apply a high voltage DC bias to the collecting member so that an electric field greater than the electric field generated by the potential difference acts between the collecting member and the electrostatic latent image carrier.

Means for Solving the Problems Therefore, the carrier recovery device according to the present invention includes a carrier recovery member made of a non-magnetic conductive material installed close to the surface of the electrostatic latent image carrier behind the development area, and the carrier recovery member. The present invention is characterized by comprising: a DC bias power supply that applies a DC bias with a polarity capable of attracting carriers; and an AC bias power supply that applies an AC bias to the carrier recovery member in a manner superimposed on the DC bias.

[First Embodiment, see FIG. 1] FIG. 1 shows a magnetic brush developing device (MD) equipped with a first embodiment of the carrier recovery device according to the present invention, in which the photoreceptor drum (1) is Arrow (a) at a circumferential speed of 176ml1/sec
With the rotation, an electrostatic latent image is formed on the surface by a well-known image forming device (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) and a packet roller (5) installed with its lower half almost buried in the developer (De) housed inside the developer tank (2). .

The developing sleeve (3) is made of a non-magnetic conductive material (for example, non-magnetic stainless steel) and is formed into a cylindrical shape with an outer diameter of 31 mm, and is adapted to be applied with a DC voltage by a developing bias power source (E). There is. 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).
, a gap of 7 mm is maintained, and during development, it is rotated at a rotation speed of 3 Orpm in the direction of arrow (b) by a drive source (not shown). The magnetic roller (4) has S and N on its outer periphery.
Ten poles are sequentially magnetized in the circumferential direction, and are rotated at a rotation speed of 120 Orpm in the direction of arrow (b). 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 attracted to the outer peripheral surface of the developing sleeve (3) like a magnetic brush, and is transported in the direction of arrow (c) during development. Ru.

The developer (De) contained in the developer tank (2) is made of a mixture of a magnetic carrier and an insulating toner, and is triboelectrically charged to have different polarities due to 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 circumference, and is rotated in the direction of arrow (a) during development, and the developer (De) scooped up by the packets is transferred to the outer peripheral surface 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 HI furnace casing 9) on the photoreceptor drum (+) side and on the extension line of the arcuate 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).

Also, the developer tank (2) is located below the developer sleeve (3).
A developer leakage prevention plate (11) is installed at the opening end of the developer. The leakage prevention plate (11) is made of a non-magnetic conductive material such as aluminum or stainless steel, and is adapted to be applied with a DC voltage having a polarity opposite to that of the toner.

Further, a developer tank (2) below the scraper plate (6)
A developer transporting blade (12) is installed inside the developer transporting blade (12) so as to be rotatable in the direction of arrow (e).

The carrier recovery device includes a carrier recovery plate (13), a DC bias power supply (E3) for applying a bias to the carrier recovery plate (13), and an AC bias power supply (E3) for superimposing an AC bias on the carrier recovery plate (13). ). The carrier recovery plate (13) is made of a non-magnetic conductive material such as aluminum or stainless steel, and is located between the outer circumferential surface of the developing sleeve (3) and the developer leakage prevention plate (11), and its tip is located in the developing area (A). ) is installed at a position close to the surface of the photoreceptor drum (1) immediately after the photoreceptor drum (1), and the knife-shaped tip surface is substantially along the surface of the photoreceptor drum (1). The DC bias from the DC bias power source (E) has a polarity that can attract carriers to the carrier collection plate (13).

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 101'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, melt-mixing an insulating resin and magnetic fine powder and cooling the mixture. Polyethylene is used as an insulating resin. 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, Fetus is used.

Fed, ferrite, magnetite, etc. may be selected as appropriate. On the other hand, as the insulating toner, conventionally known ones can be used, and the average particle size thereof is 5 to 50 .mu.m and the volume resistivity is about to'' Ωcm or more.

In the above configuration, the developer (De) in the developer tank (2)
is scooped up by the packet as the packet roller (5) rotates in the direction of arrow (d), and is scooped up by the magnetic roller (5).
The developing sleeve (
3) Be attracted to the outer peripheral surface like a magnetic brush. Then, as the developing sleeve (3) and the magnetic roller (4) are rotated in the direction of arrow (b), the developing sleeve (3) is transported along the outer circumferential surface of the sleeve (3) in the direction of arrow (C). based on the rotation of the magnetic roller (4)], the development area (A) is reached. In this development area (A), the surface of the photoreceptor drum (1) is rubbed by the developer (De), and the electrostatic latent image carried on the surface is developed. Thereafter, the developer (De) is scraped off from the outer shoulder of the developing sleeve (3) by a scraper plate (6) and returned to the developer tank (2).

By the way, when the electrostatic latent image is developed in the 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 the arrow (a) to reach the carrier removal area (B) where the carrier recovery plate (13) closely opposes the surface of the photoreceptor drum (1). In this carrier removal region (B), the magnetic carriers attached to the surface of the photoreceptor drum (1) are removed by the bias power source (Et), (E
The carrier is adsorbed to the carrier recovery plate (13) by the DC bias and AC bias applied in step 3).

Therefore, in the development area (A), the photoreceptor drum (
The magnetic carrier attached to the surface of 1) is reliably removed from the surface of the photoreceptor drum (1) in this carrier removal area (B), and the photoreceptor drum after being developed by this developing device (MD). Substantially no carrier adhesion occurred on the surface of (1). Then, as the magnetic roller (4) rotates in the direction of arrow (b), the magnetic carrier attached to the carrier collection plate (13) moves downward along the carrier collection plate (13) due to the action of the magnetic field, and is moved downward into the developing tank. It is returned to the developer (De) in (2).

On the other hand, the toner that has turned into powder smoke in the development area (A) is prevented from leaking by the seal plate (lO) in the upper part, and the power source (1O) in the lower part.
El), the toner is adsorbed to the leakage prevention plate (II) to which a DC voltage of opposite polarity to the toner charging polarity is applied, and leakage to the outside is prevented.

By the way, the reason why an alternating current bias is superimposed and applied to the carrier recovery plate (13) 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 collection plate (13), but by superimposing an AC bias, it is possible to generate a stronger carrier attraction force.

In addition, in the carrier removal area (B), in addition to an alternating magnetic field based on the rotation of the magnetic roller (4), a carrier collection plate (13) is applied.
An electric field is also formed by an alternating current bias applied to the
Due to the action of these alternating magnetic fields and electric fields, the photoreceptor drum (1
This is because the carrier attached to the surface of the photoreceptor drum (1) is disturbed and vibrates, making it easier to separate from the surface of the photoreceptor drum (1).

Here, specific examples of voltage values such as the developing bias and the carrier recovery bias in the first embodiment are shown in the table below, divided into regular development (positive-positive development) and reversal development (negative-positive development).

As is clear from the above table, in regular development, the polarity of the potential of the non-image area of the electrostatic latent image and the charged polarity of 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 reversal development, 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 plate (summer 3) 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.

[Second Embodiment, see Figure 2] This second embodiment is equipped with a carrier recovery sleeve (14) containing a magnetic roller (15) as a carrier recovery device, and the magnetic brush developing device (MD) itself is the first
The configuration is similar to that of the embodiment.

That is, the carrier collection sleeve (14) is made of a non-magnetic conductive material (
For example, it is made of non-magnetic stainless steel (non-magnetic stainless steel) and is formed into a cylindrical shape with an outer diameter of 16n+m.
They were installed with a gap of 5 mm maintained, and a bias for carry and recovery was applied using the same DC bias power supply (E) and AC bias power supply (E3) as in the first embodiment. There is. Further, the outer peripheral surface of the carrier recovery sleeve (14) on the developer tank (2) side is provided with a
) is in pressure contact with the tip of the scraper plate (16) rising from the inner surface.

The magnetic roller (15) has S and N poles sequentially magnetized in the circumferential direction on its outer periphery, and its magnetic force is set so that a magnetic field of 700 Gauss is formed on the outer periphery of the sleeve (14). Further, this magnetic roller (15) is rotatable and is connected to a magnetic roller (4) built in the developing sleeve (3).
Under the action of the magnetic field, the magnetic roller (4) rotates in the direction of arrow (r) at 300 rpm following the rotation of the magnetic roller (4) in the direction of arrow (b).

In the above configuration, the photosensitive drum (
The carriers attached to the surface of 1) are removed from the carrier removal area (
B), the magnetic force of the magnetic roller (!5) and the bias power supply (
The carrier is attracted to the outer circumferential surface of the carrier recovery sleeve (14) by the DC bias and AC bias applied at steps Et) and (E3). The carrier attracted to the outer circumferential surface of the sleeve (14) moves along the arrow (
With the driven rotation in the direction f), the sleeve (14) is conveyed on the outer peripheral surface in the direction opposite to the arrow (f), and is scraped off into the developing tank (2) by the scraper plate (16). It exhibits the same effects as the first embodiment. 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).

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

Further, the voltage values of the bias power supplies (Et), (E3), etc. are the same as those in the table shown in the first embodiment.

Effects of the Invention As is clear from the above explanation, the present invention applies a direct current bias or an alternating current bias with a polarity capable of attracting carrier to a carrier recovery member installed close to the surface of the electrostatic latent image carrier at the rear of the developing area. By superimposing the applied voltages, the carrier adhering to the surface of the electrostatic latent image carrier in the developing area can be reliably adsorbed to the carrier collection member and removed from the surface of the electrostatic latent image carrier. There is no need to worry about various troubles caused by being transported to the transfer section or cleaning section, which are processes, or uneven images. Moreover, the carrier recovery efficiency is further improved by applying AC bias in a superimposed manner, which is particularly effective in reverse development where carrier adhesion is likely to occur. It is also possible to recover carrier reliably without increasing the voltage value of DC bias, making it safe. be.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a cross-sectional view of a developing device equipped with a first embodiment of the present invention, and FIG. 2 is a cross-sectional view of a developing device equipped with a second embodiment of the present invention. (A)...Development area, (B)...Carrier removal area, (MD)...Development device, (De)...Developer, (E,)...DC bias power supply, (E3 )・・
・AC bias power supply, (13)...Carrier recovery plate, (14)...Carrier recovery sleeve, (15)
...Magnetic roller.

Claims (1)

[Claims] 1. In 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, the electrostatic latent image carrier at the rear of the development area a carrier recovery member made of a non-magnetic conductive material installed close to the surface; a DC bias power source that applies a DC bias of a polarity capable of attracting carriers to the carrier recovery member; and an AC bias power source that applies an AC bias.