JPH01193771A - Electrophotographic developing device - Google Patents

Abstract

PURPOSE:To form a distinct image and to improve development efficiency by providing a fixed electrode consisting of a conductive non-magnetic member in the state of non-contact with an image carrier in the vicinity of a developing gap between an electrostatic latent image carrier and a toner carrier, and forming an electric field where a magnetic toner can be transferred to the image carrier side, between the fixed electrode and the image carrier. CONSTITUTION:A fixed electrode 3 consisting of a conductive non-magnetic member is provided by maintaining the state of non-contact with an electrostatic latent image carrier 1 in the vicinity of a developing gap between the image carrier 1 and a high resistance magnetic toner carrier 2. Subsequently, the fixed electrode 3 is applied to a ground or a prescribed bias voltage, and between the fixed electrode 3 and the image carrier 1, an electric field where a magnetic toner 10 can be transferred to the image carrier 1 side. In such a way, even when recording speed becomes high, the distinct image is formed and the development efficiency can be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an electrophotographic developing device using high-resistance magnetic toner, and more specifically relates to an image carrier that holds an electrostatic latent image and a toner carrier. The present invention relates to an electrophotographic development method in which toner is transferred to the surface of the image carrier by an electric field effect applied near the development gap between the two phases and arranged opposite to each other.

"Prior Art" Conventionally, as an electrophotographic developing device using high-resistance magnetic toner, a magnet body is included in a toner carrier near the closest gap (hereinafter referred to as the developing gap) between the two carriers arranged facing each other. While the toner spikes formed by the above are rubbed on the image bearing surface, charges are injected into the toner by the electrostatic latent image held on the image carrier, and the charged toner at the tip of the toner spikes is transferred to the image on the surface of the image carrier. A magnetic brush development method in which the toner layer is selectively transferred to the toner portion, and the toner layer is image-bearing by arranging the above-mentioned carriers facing each other while maintaining a development gap larger than the thickness of the toner layer supported on the toner carrier. There is a development method called flying development in which toner that has been previously charged is selectively ejected on the flow side of the development gap by the charge of an electrostatic latent image without making rectangular contact with the body surface.

These development methods include a forward development method in which a latent image is formed in the image area and toner with the opposite polarity to the latent image is transferred to the image area, and a toner with the same polarity as the latent image is transferred to the image area. Although there are reversal development systems, all of them have a structure in which the toner is transferred to the image area by an electric field effect. In other words, the transfer of the toner to the image area depends on the electric field.

On the other hand, the development of printers using the electrophotographic technology described above is active, but printers need to be made faster by matching the processing speed of the computer itself, and for this reason, it is necessary to increase the processing speed per unit time compared to conventional printers. In order to increase the amount of toner transfer, research has been conducted to apply a higher electric field to the development gap.

For example, it is possible to raise the potential of the electrostatic latent image formed on the image carrier to increase the electric field strength, but if such a method is adopted, the photoelectric properties of the image carrier will deteriorate in a short period of time.
There is a problem with durability.

``Problems to be Solved by the Invention'' Therefore, in order to increase the electric field strength, it is preferable to narrow the developing gap, but in the case of so-called flying development, the toner layer thickness must be increased in response to the narrowing. The film must be made thinner, and it is quite difficult to make the film thinner without waviness or fluctuations in film thickness.

In both cases of magnetic brush development and flying development, the image carrier is generally constructed as a photoreceptor drum, and the image carrier is often constructed as a developing sleeve, but such rotating cylindrical bodies are susceptible to center runout and In addition to axis misalignment, assembly errors are likely to occur, and the narrower the gap is, the more even a slight misalignment in precision will greatly affect uneven development, and there is a limit to how narrow the gap can be. Furthermore, when the width of the rotating bodies is narrowed, a so-called blocking phenomenon occurs in which toner is compressed and solidified in the narrowed development gap, and from this point of view as well, there is a limit to narrowing the width.

In view of the shortcomings of the prior art, the present invention provides a method for obtaining the same electric field strength as the width of the development gap between the image carrier and the toner carrier without narrowing it. It is an object of the present invention to provide a developing method that can form a clear image and improve development efficiency even when the recording speed is increased while increasing the amount of transfer.

Another object of the present invention is to provide a developing device for electrophotography which has a simple structure and can always provide stable image quality.

"Means for Solving the Problems" In order to achieve the above technical problems, the present invention provides an arrangement in which an image carrier that holds an electrostatic latent image and a toner carrier that carries high-resistance magnetic toner are arranged facing each other. In an electrophotographic developing device, (1) a fixed electrode made of a conductive non-magnetic material is placed facing the image carrier in the vicinity of the development gap between both carriers, or in other words, maintains at least a non-contact state with the image carrier; The point set.

In this case, the shape of the fixed electrode is not particularly limited, such as a wire, a band-shaped member, etc., but it is placed near the developing gap and
must be configured to meet the requirements of

The same applies to the arrangement gap between the fixed electrodes, and as long as they do not contact the image carrier, there is no limitation on whether or not they contact the toner carrier, and it is also possible to integrate the fixed electrode and the toner carrier. be. For example, when a fixed sleeve that does not rotate is used for the toner carrier, the positioning of the fixed electrode may be easier if the fixed electrode and the fixed sleeve are integrated.

(2) The fixed electrode is grounded or a predetermined bias voltage is applied to form an electric field between the fixed electrode and the image carrier that can transfer the magnetic toner toward the image carrier. In the case of reversal development, by applying a bias voltage Vi smaller than the latent image potential Vd on the image carrier side to the magnetic body or grounding it, an electric field that can transfer the magnetic toner to the image carrier side can be formed. .

In this case, on the toner carrier side, a bias voltage Vx equal to or lower than the human insulating pressure Vi may be applied, or it may be grounded, but in any case, the potential difference between the image carrier and the magnetic member Unless the potential difference between the magnetic member and the toner carrier is greater than the potential difference between the magnetic member and the toner carrier, an electric field that allows the magnetic toner to be transferred to the image carrier cannot be formed.

(2) Preferably, at least a part of the magnetic toner carried on the toner carrier is configured to be transferable to the image carrier side by the electric field while passing between the fixed electrode and the image carrier. Shape of fixed electrode and arrangement δ between both supports
This can be easily achieved by appropriately setting a gap and, in particular, by forming a toner spike on the upstream side of the fixed electrode.

Therefore, the toner carrier used in the present invention generally includes a magnet for forming the toner ears, but the magnet may be either a fixed magnet or a rotating magnet.

"Operation" When the present invention is applied to, for example, a magnetic brush development method, as shown in FIG. The toner brush 10a is formed on the entrance side of the fixed electrode 3 by the developing magnetic pole 40.
, and at least a portion of the toner spike 10a passes between the fixed electrode 3 and the image carrier 1 while its tip is in contact with the image carrier l side.

At this time, since an electric field is formed between the fixed electrode 3 and the image carrier 1, charges are injected into the toner 10 by the electric field, and the toner 10 is brought into contact with the image carrier 1 on the electrode 3. The charged toner at the tip of the toner spike 10a is selectively transferred to the image area on the surface of the image carrier 1, forming a desired toner image.

The same applies to the flying development method, in which the toner 10 that has been charged in advance on the upstream side of the fixed electrode 3 is partially (tip) formed by forming a toner stay on the toner spike 10a or on the artificial side of the fixed electrode 3. The charged toner 10 is caused to ride on the fixed electrode 3 and face the image carrier 1, and the charged toner 10 is selectively flown by the action of the electric field formed between the electrode 3 and the image carrier 1, and the charged toner 10 is caused to fly onto the surface of the image carrier 1. A desired toner image is formed on the image area.

Therefore, according to this technical means, the toner transport function and the electric field forming function in the toner carrier 2 in the prior art are substantially separated, the toner carrier 2 mainly carries out toner transport, and the toner 10 is image-bearing by forming an electric field. The structure is such that the transfer to the body 1 side is mainly performed by the fixed electrode 3.

For this reason, even if the gap between the image carrier 1 and the toner carrier 2 is widened, the electric field strength can be increased by narrowing the gap s1 between the fixed electrode 3 and the image carrier 1, thereby increasing the amount of toner transfer. It is possible to form a clear image and improve development efficiency even when the recording speed is increased while increasing the recording speed.

As a result, the gap between the image carrier 1 and the toner carrier 2 can be widened, and even if there is some accuracy error, the image will not be adversely affected, which is extremely advantageous in terms of assembly, processing, and maintenance. be.

In addition, since the fixed electrode 3 only needs to be positioned and fixed near the developing gap, there is no room for core runout or misalignment, unlike with a rotating sleeve, and as a result, high assembly accuracy can be achieved, and the developing unit and image carrier It is also possible to integrate it with the l unit, which makes it easier to achieve even higher accuracy.

Furthermore, since the fixed electrode 3 extends in a direction that blocks the toner 10 from the conveying direction, toner 10 and stagnation tend to occur on the inlet side of the fixed electrode 3, which hinders development. Efficiency is further improved.

Note that the fixed electrode 3 can be placed apart from the toner carrier 2 in a non-contact state, or in contact with it, but if it is in contact with it, it cannot be formed at the same potential as the toner carrier 2. , reverse transfer from the fixed electrode 3 to the toner carrier 2 side can be completely prevented.

As a technique similar to the present invention, a technique is disclosed in which a grounded frictional charging member 101 is provided at the development position on the sleeve 2 and between the magnetic toner 10 and the image carrier l, as shown in FIG. (Japanese Patent Publication No. 59-21035), this technique is certainly effective in that the triboelectric charging member 101 is grounded, is located at the developing position, and can maintain a non-contact state with the image carrier 1. - similar in appearance to the present invention;

However, in the prior art, the magnetic toner 10 before development is positively charged by friction to stabilize the development.
It is an essential requirement to be located between the two.

On the other hand, in the present invention, the toner carrier 2 mainly transports the toner, and the transfer of the toner lO to the image carrier l side by forming an electric field is mainly performed by the fixed electrode 3. It is assumed that at least a part of the supported magnetic toner IO passes between the fixed electrode 3 and the image carrier 1, and the fixed electrode 3 is positioned between the magnetic toner IO and the image carrier 1 as in the prior art. If this is done, the effects of the present invention cannot be achieved at all.

Further, the grounding of the triboelectric charging member 101 is simply to release the electric charge accumulated in the triboelectric charging member, and the magnetic toner 10 can be transferred to the image carrier 1 between the fixed electrode 3 and the image carrier 1. It is not grounded to form an electric field.

"Embodiments" Hereinafter, preferred embodiments of the present invention will be described in detail by way of example with reference to the drawings. However, the dimensions, materials, shapes, relative arrangements, etc. of the components described in this example are not intended to limit the scope of the invention, unless otherwise specified, and are not intended to be a comprehensive explanation. Just an example.

FIGS. 1 to 4 all show a reversal development type developing device using a high-resistance magnetic toner 10 according to an embodiment of the present invention.

In FIG. 1, reference numeral 1 denotes a photosensitive drum on which a photoconductive insulating layer 1a carrying a latent image is formed, and is configured to be positively charged. Various process equipment are located there.

Reference numeral 2 denotes a non-magnetic sleeve arranged to face the photosensitive drum l and configured to be rotatable in the direction of the arrow. By enclosing the fixed magnet assembly 4 in the sleeve, the high-resistance magnetic toner 10 in the toner container 5 is A thin film-like toner layer whose thickness is regulated by a layer thickness regulating member 6 without being carried on the circumferential surface thereof can be transported to the developing position side where the photosensitive drum 1 is disposed opposite to it. Further, the fixed magnet assembly 4 has a developing magnetic pole 40 located closest to the photosensitive drum 1, in other words, slightly upstream of the developing gap.

A developing gap w located downstream of the developing magnetic pole 40
Nearby, a non-magnetic conductive fixed electrode 3 made of a wire-like, for example, aluminum wire is stretched in the axial direction of the photoreceptor drum l, at least in a non-contact state with the photoreceptor drum l, and the fixed electrode 3 and the non-magnetic sleeve 2 are connected to a bias generation circuit 7 that generates a switching pulse bias.

As shown in the first figure, for example, the fixed electrode 3 is attached by fitting the rotating shaft 20 of the non-magnetic sleeve 2 to the shaft portion 41 of the fixed magnet assembly 4 through a built-in bearing.
The wire-shaped fixed electrode 3 may be stretched between a mounting plate 32 which fixes the ring-shaped support 31 in a circular manner and extends from the support 31 to the developing gap.
It is easy to set the angular interval in the circumferential direction with respect to 0. still,
In the figure, 35 is a sleeve driving gear.

Next, the operation of this embodiment will be explained based on FIG. After the thickness is regulated, it is transported to the developing position formed by the photosensitive drum 1 and the sleeve 2.

The toner 10 conveyed to the vicinity of the development position first forms a brush-like toner ear 10a by the developing magnetic pole 40, the tip of which is brought into contact with the surface of the photoreceptor drum 1, and then at least a part of the toner ear 10a is brought into contact with the fixed electrode. 3, the toner IO is injected with charge by the electric field formed between the fixed electrode 3 and the photoconductor drum 1, and the photoconductor is transferred onto the electrode 3. The charged toner 10 at the tip of the toner spike 10a in contact with the photosensitive drum 1 is selectively transferred to the image area on the surface of the photosensitive drum 1, forming a desired toner image.

The switching pulse-like bias voltage applied to the sleeve 2 and the fixed electrode 3 may have a maximum pulse voltage that is smaller than the latent image potential Vd on the image carrier l side, for example, if the latent image potential Vd is 0V-30 for 500V
By applying a bias voltage of 0 V, it is possible to form an electric field that allows the magnetic toner lO, which has moved over the fixed electrode 3 to the position facing the photoreceptor drum 1, to be transferred to the image carrier 1 side.

In this case, since the nonmagnetic sleeve 2 and the fixed electrode 3 are at the same potential, no reverse transition occurs.

In addition, as shown in FIG. 2, for example, by grounding the fixed electrode 3,
If the configuration is such that a bias voltage of 0V to 120V is applied to the sleeve side, the potential difference between the drum l and the electrode 3 (50
0V) is the potential difference between electrode 3 and sleeve (OV-120V)
), and in this case also, the magnetic toner lO can be smoothly transferred to the image carrier l side.

As shown in FIG. 2, the fixed electrode 3A can also be formed by a band-like member whose short side is arranged along the tangential direction of the photosensitive drum 1, or by fixing and enclosing the non-magnetic sleeve 2. In a mechanism for transporting the magnetic toner IO carried on the non-magnetic sleeve 2 while rotating the magnet assembly 4, the fixed electrode 3B may be formed integrally with the non-magnetic sleeve 2B.

Fig. 3 shows such a modification, in which a short rectangular fixed electrode can be formed through a slit gap 34 in which ribs 33 are provided at predetermined intervals. According to this embodiment, even if bias is not applied to both the fixed electrode 3B and the non-magnetic sleeve 2B, it is possible to naturally form them at the same potential by applying bias only to one side, and at the same time, toner can be applied to the inlet side of the fixed electrode 3B. Carrier 2
The toner lO that has been conveyed on B is likely to accumulate, and more of the toner lO that has been conveyed on B is more likely to cross over the fixed electrode 2B, so that the developing efficiency is improved.

In addition, using the apparatus shown in FIG. 2, the aluminum fixed electrode 3A of @G: 1.5mm, wall thickness t: 0.08s + porcelain, and the gap Sl with the photoreceptor drum 1 were set to 0.25. The developing gap between the photoreceptor drum 1 and the non-magnetic sleeve 2 is 0.35, 0.40, and 0.45.
When the distances were sequentially increased to 0.50 mm, no decrease in image density was observed up to 0.50 s+m, and naturally no background fogging due to reverse transition was observed.

"Effects of the Invention" As described above, according to the present invention, it is possible to obtain the same electric field strength without narrowing the development gap between the image carrier and the toner carrier, and without narrowing the development gap. Thereby, it is possible to provide a developing method that can increase the amount of toner transfer while also forming a clear image and improving development efficiency even when the recording speed is increased.

Further, the present invention has a simple structure because it simply provides a fixed electrode made of a conductive non-magnetic material near the development gap without contacting the image carrier, and is fixedly arranged with the electrode. Because of this, it has various advantages such as always being able to obtain stable image quality.

[Brief explanation of the drawing]

1 to 4 each show a reversal development type developing device according to an embodiment of the present invention, and FIG. 1 is an overall schematic diagram, and FIG.
The figure is an enlarged view of the main part, and FIGS. 3 and 4 are perspective views showing how the fixed electrode is attached. FIG. 5 is a schematic diagram showing a developing device according to the prior art.

Claims (1)

[Scope of Claims] 1) In an electrophotographic developing device in which an image carrier holding an electrostatic latent image and a toner carrier carrying a high-resistance magnetic toner are disposed facing each other, a developing gap between the two carriers is provided. A fixed electrode made of a conductive non-magnetic material is provided in the vicinity of the image carrier in a non-contact state, and grounding or a predetermined bias voltage is applied to the fixed electrode to create a magnetic field between the fixed electrode and the image carrier. An electrophotographic developing device characterized in that an electric field is formed in which the toner can be transferred to the image carrier side.2) At least a part of the magnetic toner carried on the toner carrier passes between the fixed electrode and the image carrier. The electrophotographic developing device according to claim 1, wherein the electrophotographic developing device is configured to be able to transfer to the image carrier side by the electric field.