JPH0460675A - Method and device for electrophotographic development - Google Patents

Abstract

PURPOSE:To obtain a copy picture which is free from photographic fog and is superior in vividness by supplying toner to an image carrier under the alternating electric field applied between the image carrier and a sleeve and the alternating magnetic field due to a magnet roll to perform development. CONSTITUTION:Magnetic toner 4 is moved in the same direction as rotation of a sleeve 7 and is supplied to an image carrier 1 under the alternating electric field, which is applied between the image carrier 1 and the sleeve 7 by an AC power source 9, and the alternating magnetic field due to a magnet roll 6 to perform development. That is, toner 4 on the sleeve 7 is oscillated by the action of the alternating electric field and the alternating magnetic field, and toner 4 is repeatedly moved back and forth (oscillated) between th image carrier 1 and the surface of the sleeve 7 by a toner brush brought into contact with the surface of the sleeve 7 and the image carrier 1. At this time, toner 4 is stuck to only a part corresponding to an electrostatic image on the carrier 1 by the Coulomb's force because the electrostatic latent image potential exists on the surface of the image carrier 1. Thus, magnetic toner 4 stuck to the electrostatic latent image potential part forms a vivid copy image free from photographic fog.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an electrophotographic developing method and an apparatus thereof, and in particular, to an electrophotographic developing method and an apparatus thereof, and in particular to a method for obtaining clear and fog-free copied images using high-resistance magnetic toner. This article relates to a magnetic brush development method that can be used.

[Prior Art] Conventionally, as a magnetic brush developing method, a one-component method using a -component developer and a two-component method using a two-component developer are known. The -component type method has the advantage that the structure of the developing device is simple and maintenance is easy.In particular, in the so-called jumping development method and selective development method using -component magnetic toner,
It has the advantage of being inexpensive and producing very clear copy images. On the other hand, however, in implementing such conventional methods, very strict mechanical precision is required, for example, the gap between the image carrier and the sleeve (or the surface of the developer layer) must be precisely maintained at a predetermined value over the entire length of the sleeve. Therefore, it is quite difficult to implement this method in an electrophotographic apparatus that forms large-sized copy images such as AO size, which requires a considerably long sleeve length, and it has not been implemented to date. It has not been. On the other hand, although the two-component method can solve the drawbacks of the one-component method, it is necessary to control the mixing ratio of toner and carrier so that it is always within a predetermined range, and due to carrier fatigue, The disadvantage is that the entire developer must be replaced. Furthermore, a developing method using a developer made of a mixture of minute magnetic carriers and non-magnetic toner is known (for example, Japanese Patent Publication No. Sho δ9-24416). The method disclosed in this publication consists of approximately 5 to 3
A developer brush is formed by a magnetic developer consisting of a mixture of an insulating magnetic carrier having a particle size of 0 um and an insulating non-magnetic toner, and this developer brush is applied to the electrostatic image carrier under the action of an alternating magnetic field. Develop by rubbing the surface.

[Problem M to be solved by the invention] Although the method using the above-mentioned microcarriers provides a very high-quality developed image without fog and can solve some of the above-mentioned problems, it still However, there remains a problem in controlling the toner concentration, in which the mixing ratio of toner must be controlled within the range of 6 to 35 wt%.

The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide an electrophotographic developing method capable of obtaining copied images that are free from fog, have excellent image clarity, and are rich in gradation.

[! ! Means for Solving the Problem] In order to solve the above problems y and The magnetic roll and sleeve are rotated in the opposite direction to the rotation direction of the image carrier to move the toner in the same direction as the rotation direction of the sleeve, and the toner is transferred between the image carrier and the sleeve. In particular, the image carrier is provided with an alternating electric field and an alternating magnetic field by the magnet roll to perform development. (2) the frequency of the alternating magnetic field is a frequency that acts at least once while the same portion of the toner brush is in contact with the image carrier;
Furthermore, (3) the most suitable effect can be obtained by setting the alternating electric field to a frequency that does not cause a beat with the alternating magnetic field.

An apparatus embodying this method includes a casing containing high-resistance magnetic toner, which is disposed adjacent to a rotating drum-shaped image carrier, and a casing having magnetic poles of different polarities alternately in the circumferential direction, a magnet roll that rotates in a direction opposite to the rotational direction of the carrier; a sleeve that includes the magnet roll therein and rotates in the same direction as the magnet roll independently of the magnet roll; and the image carrier and the sleeve. and a device for applying an alternating electric field between the two.

[Operation] According to this means, the magnetic toner on the sleeve is vibrated by the action of the alternating electric field and the alternating magnetic field, and the toner is reciprocated between the image carrier and the sleeve surface in the toner brush that contacts the image carrier from the sleeve surface. Repeat motion (vibration). At this time, since there is an electrostatic latent image potential on the surface of the image carrier, the toner adheres only to the portion of the carrier corresponding to the electrostatic image due to the cloner. In this way, compared to the conventional developing method using a constant magnetic field or constant potential, the magnetic toner that is attracted to the electrostatic latent image potential area by applying a vibrating force due to the synergistic effect of an alternating electric field and an alternating magnetic field is produced with a clear fog-free image. Form a duplicate image.

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

In the figure, l is an image carrier formed by forming a photoreceptor such as Se on the circumferential surface of a cylindrical drum. During this rotation, an electrostatic image is formed on the surface of the image carrier by a suitable electrostatic image forming means. As the image carrier and the electrostatic image forming means, those having a well-known structure such as those used in xerography, for example, can be used.

A developing device 2 is disposed adjacent to the image carrier 1, and a magnetic toner 4 is housed in a casing 3 of the developing device 2.

The magnetic toner has an electrical resistance value of 1016 Ωcm or more,
It contains ferrite powder of 25% or more, preferably 25 to 60%, and has an average particle size of 16 microns.

If the particle size is too small, blurring will occur in the copied image, and if it is too large, the sharpness of the characters will deteriorate.

On the side of the image carrier 1 inside the casing 3, a magnet roll 6- is provided adjacent to and extending parallel to the image carrier 1.
It is arranged. The magnet roll 6 has magnetic poles (S, N) of different polarities alternately at approximately equal intervals in the circumferential direction, and rotates in the opposite direction to the rotation direction of the image carrier l, that is, in the counterclockwise direction (indicated by arrow B). It is arranged to rotate. A nonmagnetic cylindrical sleeve 7 that extends parallel to the magnet roll 6 and encloses the magnet roll 6 is provided so as to rotate in the same direction as the magnet roll 6 and independently of the magnet roll 6. The magnetic toner on the sleeve 7 is moved in the direction opposite to the direction of rotation of the sleeve 7 by the magnetic field of the magnet roll 6, but the sleeve 7 resists the movement by the magnet roll 6 and moves the toner onto the sleeve. Rotate at a sufficient speed to convey in the direction of 70 rotations. That is, when the magnet roll 6 is rotated in the direction of arrow B, the toner on the sleeve 7 rotates on the surface of the sleeve 7 due to the action of the magnetic field of the magnet roll 6, and tries to move in the opposite direction to the rotation direction of the magnet roll 6. be done. However, by rotating the sleeve 7 in the direction of arrow C at a speed higher than this moving speed of the toner, the magnetic toner on the sleeve moves in the direction of rotation of the sleeve 7 against the action of the magnet roll 60. The moving speed of the magnetic toner is preferably approximately the same as the circumferential speed of the image carrier 1, and the soft brush portion of the toner brush is in contact with the surface of the image carrier 1 or is close to the surface with a slight gap. It is transported like this. In this contact or proximity state, the magnetic toner is transferred to the magnet roll 6
The surface of the image carrier l and the surface of the sleeve 70 are reciprocated (
(vibration) and a puff (puff) is applied to the electrostatic latent image area of the image carrier 1.
or transferred to obtain a clear copy image. still,
In order to improve the toner conveying force of the sleeve 7, the surface of the sleeve 17 is preferably treated with particles having a particle size smaller than 250 mesh by shot blasting or the like.

The rotational speed of the magnet roll 6 is preferably such that an alternating magnetic field acts at least once on the toner in the same portion of the toner brush while the same portion of the toner brush is in contact with the image carrier 1. For example, the number of magnetic ladders of the magnet roll 6 is l
OExtremely, when the circumferential speed of the image carrier 1 is 12011ta/Sec, 120am (peripheral speed of the image carrier I)/approximately 5Sm()
An alternating magnetic field of 24 Hz or higher is preferable. At this time, the rotational speed of the sleeve 7 is such that the magnetic toner on the sleeve 7 is transferred to the image carrier 1 as described above.
It corresponds to a speed that is approximately the same as the zero circumferential speed. still,
If the moving speed of the toner on the sleeve 7 is slower than the circumferential speed of the image carrier 1, the toner tends to scatter on the front side of the solid image of the copy, and when it is slower, the toner tends to scatter on the rear side. Furthermore, in the case of line images, the resolution of horizontal lines in particular tends to be poor in any case.

In this case, a round image may be copied into an ellipse.
The difference in the moving speed of the magnetic toner with respect to the circumferential speed of the image carrier 1 is within ±50%, but it is desirable that the speed be approximately equal.The surface magnetic flux on the sleeve 7 of the alternating magnetic field is 5%.
00 Gauss or more is preferable.

A doctor blade 8 regulates the thickness of the toner brush, and is made of a non-magnetic material. For example, when the distance between the image carrier 1 and the sleeve 7 is set to 0.71, the distance between the tip of the doctor blade 8 and the sleeve 7 is preferably set to about 0.2IIll.

Reference numeral 9 denotes an alternating current power source, which applies an alternating electric field between the sleeve 7 and the image carrier l. The frequency of the alternating electric field is determined in correlation to the number of rotations of the magnet roll 6, and is set to a frequency that does not cause a beat (resonance) phenomenon with the alternating magnetic field by the magnet roll 6. Note that the alternating electric field may be one in which an alternating current bias is superimposed on a direct current bias.

Support 1I Using an image carrier on which a SeTe photoconductor was deposited, the dark area potential was 650 V and the light area potential was 100 V according to the xerography method while moving the image carrier at a circumferential speed of 140 am/Sec.
An electrostatic latent image of v was formed. Sleeve 7 is 401+1ff
250 on the surface of the sleeve made of 5US304 with a diameter of lφ
Beads with a mesh particle size were shot blasted for about 5 minutes, and as the magnet roll 6, a magnet with 12 poles and a length of about 934 mm was used so that the surface magnetic velocity on the sleeve was about 500 Gauss. A roll was used to supply magnetic toner to form a toner brush, and the electrostatic latent image was developed.

The distance between the sleeve 7 and the tip of the doctor blade 8 is Q,
3 m, and the distance between the image carrier 1 and the sleeve 7 is 0°6 m.
+i. Sleeve 7 has a DC voltage of 100 to 200
A bias multiplied by an AC voltage having a frequency selected from a range of 0 Hz is applied. The sleeve 7 and the magnet roll 6 are rotated in the opposite direction to the rotation direction of the image carrier l, and the magnetic toner on the sleeve 7 is 12.5 InI11 per rotation of the magnet roll while rotating in the opposite direction to the rotation direction of the magnet roll 6.
is actuated to move at a speed of The sleeve 7 is rotated in the same direction as the rotational direction of the magnet roll 6 at least at a faster speed than the moving speed of the sleeve. For example, when the magnet roll 6 is rotated at 600 rpm+, the distance is 125 m.
The sleeve 7 is rotated at a speed of m/sec or higher. Although a reasonably good copy image can be obtained under these conditions, to obtain the best copy image, the rotational peripheral speed of the image carrier 1 and the moving speed of the magnetic toner should be approximately the same.

In experiments, it has been found that one of the important conditions for obtaining clear copied images is that the speed difference is within the range of 50% to 150% of the peripheral speed of the drum. At speeds other than this, the copied image of the round solid original image will be developed into a vertically long ellipse.
In addition, the resolution decreases, causing problems. The optimum frequency of the AC voltage is determined by the magnetization radius of the magnet roll 60, the number of poles, the rotation speed, and the circumferential speed of the image carrier l. It is important to select a frequency that does not cause the beat phenomenon. Under the above conditions, the developing bias AC voltage 9
50 V, frequency 1 kHz, DC voltage 150 V, magnet roll 6 rotation speed 500 rpm, three 17 rotation speed 12 Orpm, and as a result, a clear high-resolution copy image could be obtained. The toner used at this time was a magnetic toner containing an acrylic resin, approximately 45% ferrite powder, and a pigment as its main components and having an electrical resistance of 1015 Ωcll. Incidentally, when a magnetic toner having a resistance of 1015 ΩcI11 or less was used, background fogging occurred.

[Effects of the Invention] According to the developing method according to the present invention, the advantages of the one-component method using high-resistance magnetic toner are maintained, and the problems thereof are solved.There is no background fog and the image is clear. Copy images with excellent accuracy and rich tonality can be obtained without strict mechanical precision or the trouble of controlling toner density.

[Brief explanation of the drawing]

The figure is a schematic side view for explaining the electrophotographic developing method according to the present invention. 1... Image carrier, 2... Developing device, 3... Casing, 6... Magnet roll, 7... Sleeve,
9...AC power supply, 8...Doctor blade.

Claims (6)

[Claims] (1) High-resistance magnetic toner is attracted to the outer circumferential surface of a sleeve that has a magnet roll in which magnetic poles of different polarities are arranged alternately, and the magnet roll and sleeve are each rotated in a direction opposite to the rotational direction of the image carrier. The magnetic toner is rotated to move the magnetic toner in the same direction as the rotational direction of the sleeve, and the toner is provided to the image carrier under an alternating electric field applied between the image carrier and the sleeve and an alternating magnetic field by the magnet roll. An electrophotographic development method characterized by performing development. (2) The electrophotographic developing method according to claim 1, wherein the development is performed while moving the magnetic toner on the sleeve at substantially the same speed as the moving speed of the image carrier. (3) The electrophotographic development according to claim 1 or 2, wherein the frequency of the alternating magnetic field is a frequency that acts at least once while the same portion of the magnetic brush is in contact with the image carrier. Method. (4) The electrophotographic developing method according to any one of claims 1 to 3, wherein the alternating electric field has a frequency that does not cause a beat with the alternating magnetic field. (5) a casing disposed adjacent to a rotating drum-shaped image carrier and containing high-resistance magnetic toner therein; includes a magnet roll rotating in opposite directions, a sleeve having the magnet roll inside and rotating in the same direction as the magnet roll independently of the magnet roll, and applying an alternating electric field between the image carrier and the sleeve. An electrophotographic developing device comprising: (6) The electrophotographic developing device according to claim 5, wherein the surface of the sleeve is shot blasted with beads having a particle size smaller than 250 mesh.