JPH02191973A - Developing device - Google Patents

Abstract

PURPOSE:To improve the reproducibility of an image end part by alternately repeating the transfer stage and the reverse transfer stage of toner and changing the gap between a toner carrier and an electrostatic image holding body to control the intensity of electric field in the latter half of the development process. CONSTITUTION:An electrostatic image holding body 4 is moved in the direction of an arrow to reach an area (3) through development areas (1) and (2). The gap between the electrostatic image holding surface and a toner carrier 5 is gradually widened from the narrowest value in a development part, and electric fields of transfer from the image part of the electrostatic image holding body 4 in a transfer area and reverse transfer from the toner carrier 5 of the non-image part in a reverse transfer area as shown in the figure. The first process and the second process of development occur in areas (1) and (2) respectively, and in the case of the image part, transfer and reverse transfer of toner alternately occur in accordance with the phase of the alternating electric field in the area (1), and electric field of transfer and reverse transfer are weakened together because of extension of the development gap and transfer is possible but reverse transfer does not occur in the area (2), and transfer and reverse transfer do not occur to complete development in the area (3).

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for developing a single static image, and more specifically to a method for developing a single-component developer, in particular, it is capable of achieving nine gradations without blurring, image clarity, and immediate gradation. The present invention relates to an electrostatic image developing method and apparatus that make it possible to obtain a visible image rich in color.

Conventionally, as an electronic reproduction development method using a component latent developer, a powder cloud method using toner particles in a spray state, and a toner layer formed on a toner support member such as a web or sheet have been used. to the electrostatic image holding surface,
A contact development method in which development is performed, a jumping development method in which the toner layer is not brought into direct contact with the electrostatic image holding surface and the toner is selectively flown onto the holding surface by the electric field of the electrostatic image, and
Among the above-mentioned various component development methods, the powder cloud method, contact development method, and magneto-dry method use conductive magnetic toner. (should be)
, since the non-image area (area of the background to which toner should not originally adhere) was in contact without distinction, toner adhesion also occurred in the non-image area, and the occurrence of background fog could not be avoided. . However, in the jumping development method (for example, the method described in Japanese Patent Publication No. 41-94-&75), the toner layer and the electrostatic image holding surface are developed with force (non-contact, with a gap between them), so the background cover is However, the resulting visible images generally have the following drawbacks:

The first problem is that the sharpness decreases at the edges of the image area. The electric field of an electrostatic image at the edge of the image is as shown in FIG. 4a in the case of an electrostatic latent image formed on a three-electron photoreceptor. In other words, if a conductive member is used as the developer support near the center of the image area, the electric lines of force will emanate from the image area and reach the toner support, so the toner will be affected by this w1 force! The photoreceptor flies along the surface of the photoreceptor and is deposited on the surface of the photoreceptor for development. However, at the edge of the image area, the lines of electric force do not reach the toner support due to the electric charge induced in the non-image area, causing smearing, making the adhesion of the flying toner extremely uncertain. , some barely stick, and some don't stick at all. As a result, the resulting image lacks sharpness and is unclear at the edges of the image portion, and when developing line drawings, there is an inconvenience that υ appears thinner than the original image.

In order to avoid this in the normal jumping development method, the gap between the electrostatic image holding surface and the developer support surface must be made sufficiently small (for example, less than Zooμ), and in practice,
Accidents of pressure contact between the two surfaces with the developer or mixed foreign matter are likely to occur. Moreover, maintaining such a small gap often involves difficulties in device design.

The second problem is that images obtained by the jumping development method generally lack gradation. In jumping development, the toner only flies when the electric field of the electrostatic image overcomes the restraining force on the toner support.

The force that binds the toner to the toner support is due to van der Waalska between the toner and the toner support, adhesion between the toners, and the fact that the toner is electrically charged. This is the resultant force of the reflected force between the body and the body.

Therefore, only when the potential of the electrostatic image exceeds a certain value (hereinafter referred to as the toner transfer threshold)9 and the resulting electric field exceeds the toner binding force, toner flight occurs and the electrostatic Toner adhesion to the image bearing surface occurs.

However, the binding force of the above-mentioned toner to the support varies depending on the individual toner or the particle size of the toner, even if the toner is manufactured and mixed according to a certain recipe. is thought to be narrowly distributed around an approximately constant value, and correspondingly, the threshold value of the image surface potential also exists around a certain value, so that the threshold value can be set to a certain value. The result is that toner adhesion occurs in image areas with a surface potential exceeding the threshold value, but on the contrary, toner adhesion hardly occurs in image areas with a surface potential below the threshold value, and the so-called γ (gamma = electrostatic image potential Picture for *@ degree t
As a result, only the desired image can be obtained if the tonality is high (gradient of the magnetic curve).

The present invention has been made in order to eliminate the problems of each of the above-mentioned black-component developing methods, and its main purpose is to provide excellent reproducibility at the edge of the image, no blurring, and good gradation. An object of the present invention is to provide an electrostatic image developing method and an apparatus thereof that make it possible to obtain a visible image rich in color.Embodiments and examples according to the present invention will be described in detail below with reference to the drawings. .

The present invention will be described in detail using FIG. 1 as an example.

The voltage waveform applied to the toner carrier is shown in the lower row, and although it is a rectangular wave here, it is not limited to this as will be described later. At time interval t1, a bias voltage of magnitude Vmin is applied, and at time interval t, a bias voltage of magnitude Vm
A bias voltage of ax is applied. Vmin, Vm
The size of ax is determined by Vmin (when the image area charge formed on the image surface is positive and this is to be developed with negatively charged toner, the image area potential is VD and the non-image area potential is VL). Vy, (Vp (Vmax...)
・・・・・・・・・ Select to satisfy (1).

If selected in this way, at time interval t, the bias voltage Vm
i n acts on the tendency to promote development and is called the toner transfer stage.

Furthermore, during the time interval t, the bias voltage Vmax inhibits development, and acts to reverse the tendency of the toner transferred to the latent image surface during the time interval t1 to be returned to the toner carrier, which is referred to as a toner reverse transfer stage.

vth-f and Vthsr in FIG. 1 are the potential thresholds at which the toner is transferred from the toner carrier to the latent image surface and from the latent image surface to the toner carrier, respectively, and the curves shown in the figure The point with the largest slope of the rising edge is considered to be the potential value extrapolated using a straight line. The upper part of Figure 1 shows 1. The toner transfer amount at t and the toner reverse transfer degree at t are plotted as a model against the latent image potential.

The amount of toner transferred from the toner carrier to the electrostatic image holder in the toner transfer stage is represented by curve 1 shown by the broken line in FIG.
It will be like this. The slope of this curve is approximately equal to the slope of the curve when no alternating bias voltage is applied.

This slope is large and has a value between VL and VD,
The amount of toner transfer tends to be saturated, resulting in poor reproduction of halftone images and poor gradation.

The second broken line curve 2 shown in FIG. 1 represents the probability of toner defreezing.

One of the features of the developing method according to the present invention is that the toner transfer step and the toner reverse transfer step are alternately repeated. Towards the latter half of the process, the intensity of the electric field acting on the gap between the toner carrier and the electrostatic image holder, that is, the development gap, is changed in a unique manner by the method described below, in other words, the electric field intensity is adjusted. By tightening the toner, the toner transfer is controlled and the amount of toner transferred and attached to the surface of the electrostatic image holder and contributing to development is finally focused in accordance with the potential of the electrostatic image. It was possible to obtain a phenomenon in which the toner transfer amount is shown as curve 3 in FIG. 1, the slope is small, and the toner transfer amount changes almost in a negative manner from VL to VD. Therefore, in the non-image area, there is almost no toner adhesion in practical terms, and on the other hand, toner adhesion to the halftone image area is an excellent microscope image with extremely high gradation according to the surface potential. can get.

As a method of adjusting the electric field strength in the development gap, there is a method of gradually converging the applied alternating voltage to a suitable constant DC value, but the present invention proposes a method of increasing the development gap itself during the development process. We are hiring. below,
The method will be explained in detail.

An example of the developing process in this method is shown in FIG. Second
As shown in FIG. 8, 0, the electrostatic image holder 4 moves in the direction of the arrow, and during this period passes through the development areas (2) and (2), and reaches (2). 5 is a toner carrier. Therefore, the gap between the electrostatic image holder and the toner carrier gradually widens starting from the closest position in the developing section. FIG. 6 (6) shows the electric field of the image area of the electrostatic image carrier, and 1 line 0 shows the electric field of the transfer and countertransference from the toner carrier in the non-image area. Further, FIG. 6(c) shows the waveform of the alternating voltage applied to the toner carrier, and when the electrostatic image charge is positive, l Vmax - Vr.

1'> VL -Vmin l, l Vmax -V
n l (l VD -Vmin l...-(2)
is set. The solid line arrow in the waveform indicates an electric field that causes toner transfer, and the broken line arrow indicates an electric field that causes toner reverse transfer.

The first process in development occurs in area (2), and the second process occurs in area (2). In the case of the image area shown in FIG. 2 (5), in area
Both countertransferences take place alternately. Because the development gap is getting farther apart, in (2), both the transition and reverse transition electric fields become weak, and although toner transfer is possible, the reverse transition electric field is no longer strong enough (below the threshold value) for reverse transition a. In case (2), neither transfer nor countertransference occurs anymore, and development is completed.

In the case of the non-image area shown in FIG. 20, both toner transfer and counter transfer occur in area (3).

Therefore, in the area of , soil power pre-existing conditions are occurring. In case (2), both the transfer and reverse transition electric fields are weak (C), toner reverse transfer is possible, but the transition electric field (below the threshold) that causes the transition disappears. Therefore, the ground yellowtail will be removed in this area. In case (2), neither transfer nor countertransference occurs anymore, and development is completed. For halftones, the final amount of toner transfer to the latent image surface is determined by the amount of toner transfer and the amount of reverse transfer depending on the potential, and in the end, as shown in curve 3 in Figure 1, the slope is small, and therefore the gradation is Figure 3 shows the experimental results in which the effects of the present invention were clearly demonstrated.
5), shown in 0. This is a measurement of image reflection density 0 for static image potential bacteria, and the experimental results are plotted in the figure.

Hereinafter, this curve will be referred to as a V-D curve. 5j! The experiment was conducted under the following structure. A positive electrostatic latent image is formed on the cylindrical electrostatic imaging surface. A magnetic toner (30% magnetite content), which will be described later, was used as the toner, and a layer thickness of approximately 60 μm was applied to a non-magnetic sleeve containing a magnet.
The toner is applied to a certain extent, and friction between the toner and the sleeve surface imparts a negative charge to the toner. The results when the minimum development gap between the electrostatic image forming surface and the magnetic sleeve was maintained at 100μ are shown in FIG. 3(A), and the results when the same was maintained at 300μ are shown in FIG. The magnetic flux density at the developing area due to the magnet contained in the sleeve is about 700 Gauss. The cylindrical electrostatic imaging surface and the sleeve rotate at approximately the same speed, and the speed is approximately 110111117(5). Therefore, the electrostatic imaging surface passes through the minimum gap (peak-to-peak) in the developing section.
Peak goon) sine wave to DC 800 I-Iz, IAHz, L5 KH
z (Figure 3 (A) +7)) and the V-D curve when the back electrode of the electrostatic image forming surface and the sleeve are electrically connected without applying an external bias electric field. A curve is shown.

From these results, when no external electric field is applied,
It can be seen that although the slope of the V-D curve, the so-called γ value, is very large, by applying a low frequency alternating electric field, the γ value becomes smaller and the gradation becomes extremely high. As the frequency of the external electric field is increased, the γ value gradually increases, and the effect of tightening the gradation from high to high fades.If the gap is 100μ, the effect becomes extremely strong when the frequency exceeds I KHz under the above amplitude. When the gap is 300μ, the effect decreases when the frequency is about 800Hz, and becomes extremely weak when the frequency exceeds I KHz.

The reason for this is thought to be as follows. When the toner repeatedly adheres and detaches between the sleeve surface and the latent image forming surface during the developing process in which an alternating field is applied, a finite amount of time is required to reliably perform the reciprocating movement. Particularly when toner is transferred under a weak electric field, it takes a long time for the toner to transfer reliably. On the other hand, in order to reproduce half-tone density, it is necessary that toner subjected to an electric field of a certain threshold value or more is reliably transferred within a half period of the alternating electric field, even if the electric field is weak. For this purpose, it is advantageous if the frequency of the alternating electric field is low, and therefore, as shown by experimental results, particularly good gradation can be obtained with an alternating electric field of very low frequency. The validity of this argument can be obtained from the comparison of the experimental results shown in Figure 3 (5) and ■. The results shown in Figure 3 (■) are as shown in Figure 3 (■) except that the gap between the electrostatic image forming surface and the sleeve surface was increased to 300μ.
This experiment was conducted under the same conditions as the experiment shown in 5). When the gap is widened, the electric field strength to which the toner is exposed decreases, and thus the toner transfer speed decreases. Furthermore, since the flying board distance becomes longer, the transition time ends up becoming longer.

In fact, as is clear from FIG. 30, the γ value becomes considerably large at about 50 Hz, and when it exceeds I KHz f, it becomes equivalent to the γ value when almost no alternating voltage is applied.

Therefore, in order to achieve the same effect as when the gap is narrow in improving gradation, it is preferable to lower the frequency or increase the intensity of the alternating voltage.

-1. If the frequency is too low, the reciprocating motion of the toner will not be repeated sufficiently while the latent image forming surface passes through the developing section, and the image will be prone to development defects due to the alternating voltage. Become. As a result of the above experiment, a generally good image was obtained up to a frequency of +oHz, and when the frequency was lower than that, bugs appeared in the visible image.

The lower limit of the frequency for not causing bugs in such a microscopic image is:
It has been found that it depends particularly on the development conditions, especially on the development speed (or process, also referred to as speed, vp1!II). In this experiment, the moving speed of the electrostatic image forming surface was 1 anan.
Since o*m7(8), the lower limit of the same wave number is
Vp≧Q, 3×Vp. It has been confirmed that any waveform of the applied alternating voltage, such as a sine wave, a rectangular wave, a toothed wave, or an asymmetric wave thereof, is effective.

As described above, applying alternate biases has a remarkable effect on improving gradation, but the voltage value must be set appropriately. That is, if the alternating bias l Vmin l is set too large, the amount of toner adhering to the non-image area during the toner transfer stage is too large, and the toner is not sufficiently removed during the second development process.
Capri stains may appear on the image. Also, Vmax
If I is set too large, the toner will not be pulled back from the image area too much, resulting in so-called solid black.
=-・-(3) Vmin: Vt, -l vt
h@fl ------・-(4) It is appropriate to set it to 08 degrees. Vth-f and Vth-r are the potential threshold values already explained. If the voltage value of the alternating bias is selected in this way, an appropriate image can be obtained without excessive toner adhering to the non-image area during the toner transfer stage and without pulling back too much toner from the image area during the toner reverse transfer stage. As mentioned above, applying an external alternating voltage between the latent image forming surface and the toner carrier can significantly improve the gradation of the image and prevent fogging, but as described below, By using magnetic toner as a developer and a sleeve containing a permanent magnet as a developer carrier, and appropriately setting the external alternating voltage value, it is possible to simultaneously improve the reproducibility of line images.

Hereinafter, the description will be given assuming that the electrostatic image forming charge is positive, but the invention is not limited to this. In the so-called jumping development method, mtI
! It originates from the iigII end. Electric lines of force are shown in Figure 4 (6)
As shown in the figure, ink the back electrode on the latent image forming surface.
Therefore, the toner starting from the toner carrier is difficult to adhere to the edges of the image. Therefore, the resulting image has thin lines and poor edges. It tends to be.

Therefore, in this system, an alternating bias is applied and the V
If min is set sufficiently low, the lines of electric force in the developing section at the toner dislocation stage will become as shown in FIG. 40.

That is, the angle around the lines of electric force at the end of the electrostatic image is small, and a parallel electric field is formed. However, as already mentioned, if Vmin is set too low,
Fog stains occur in non-image areas.

In an embodiment of the present invention, magnetic toner is used as a developer,
The advantage of using a sleeve containing a permanent magnet as a developer carrier is mainly that it solves this problem. By appropriately setting the magnetic substance content in the developer and the magnetic field strength of the permanent magnet, the force of binding the toner onto the sleeve can be uniformly increased, and the value of vth-7 can therefore be made sufficiently large. Can be done. As a result, Vmin can be maintained while minimizing toner adhesion to non-image areas during the toner transfer stage.
could be set low.

In this way, by applying an alternating bias during jumping development using magnetic toner, it is possible to obtain images with high gradation, clear edges, and no fogging. Ta.

-1. Generally, in jumping development of high-resistance toner, transporting the developer to the developing section and imparting a charge are extremely difficult problems.0 Among these, using magnetic toner as the developer,
A method in which the toner is conveyed by a sleeve and a charge is applied by frictional charging between the sleeve surface or the application member and the toner is considered to be one of the extremely advantageous methods.

In addition, as a means of applying this magnetic toner onto the sleeve, there are two methods: pressing an elastic body onto the sleeve, or placing the magnetic body facing the magnetic pole position of the permanent cornerstone of the sleeve, keeping it out of contact with the sleeve surface, and applying the magnetic force. When controlling the coating thickness of magnetic toner, in normal jumping development, the condition of toner coating on the sleeve directly affects the image quality.
When applied using the former method, the applied state is relatively dense and the image quality is good. However, in this application method, the toner is strongly rubbed onto the sleeve surface, which causes the resin component of the toner to adhere to the sleeve surface, and as a result, the toner is significantly prevented from being charged.

On the other hand, if the latter method is used, the adhesion of toner to the sleeve surface can be suppressed to a minimum, but the state of toner application on the sleeve surface is rough with scattered toner particles, and after the formed image. The image quality directly reflects this state and becomes coarse as shown in FIG. 5 (6).

However, by applying the alternating bias described repeatedly in the present invention in the developing section, the toner particles perform reciprocating motion between the latent image and the sleeve surface, and in the process are loosened into individual particles. As shown in FIG. 5, the toner can be densely adhered to the image area of the electrostatic image plane.

Specific details will be shown below using examples.

Embodiment (1) FIG. 6 shows the configuration of an example of a developing device for carrying out the developing method according to the present invention.

11 is a photosensitive drum having an insulating layer on the CdS layer; 12
is a non-magnetic (stainless steel) sleeve, and both members 1
1 and 12 are 0 or 1. rotating in the same direction at a constant speed of peripheral speed 110 @i / Se[f. Photosensitive drum 11 Required leave 12
The diameter of each is 801111! , 311111m, both of which are maintained with a minimum gap of 200μ, and a developing section is formed in the vicinity thereof. Along with the rotation, both
Inevitably, the gap becomes larger after passing through the closest position.

13 is a permanent magnet fixed within the sleeve; 14 is a magnetic toner to be described later; and 15 is a magnetic (iron) blade for uniformly applying the toner onto the sleeve. The components of the magnetic toner used in this example are as follows.

Polystyrene 60wt% magnetite 35wt% carbon black 5wt% negative charge control agent (Subiron) 25E% colloidal silica (external addition) Weight ratio to toner 0.2% Grade 15 is magnet 1
It is installed at a position facing the magnetic pole No. 3 with a gap between its tip and the sleeve 120 maintained at 180μ. The magnetic field at the tip of member 15 is approximately 1 oooG. magnetic toner 14
The thickness of the fb sleeve 120 is regulated by the blade 15 to about 70 μm, and the fb sleeve 120 is charged with a negative charge by friction with the surface of the fb sleeve 120, and is conveyed to the developing section. The magnetic field at the development position is 750G. The sleeve 12 and the blade 15 are kept electrically conductive to prevent discharge between them, and are powered by a power source 16.
Alternate voltages are applied to the conductive support member of the photosensitive drum 11 . The frequency of the alternating voltage is 200Hz, and the amplitude is 4.
00 V (soo Vpp) o Sine wave D, M,
Flow! A pressure of +200 V is applied in the form of a weight. The electrostatic image potential is +500 V in the image area and Ov in the non-image area.

In addition, the member x7Fi is a plastic toner container. Based on the above structure, a clear image with high gradation and no capri can be obtained. Embodiment (2) Other developing method according to the present invention The seventh developer configuration is
As shown in the figure.

21 is a photosensitive drum having an insulating layer on a CdS layer;
Reference numeral 2 denotes an aluminum sleeve, and members 21 and 22 rotate in the same direction at substantially the same circumferential speed of 400 tm/height.

Further, a developing section is formed between the photosensitive drum 21 and the swivel, and in the vicinity thereof. As the two rotate, the gap between them inevitably becomes larger after passing the closest position023
is an symmetrical permanent magnet located within the sleeve and fixed, 24
is a magnetic toner to be described later. 2- is an iron blade for uniformly applying the toner onto the sleeve.

The components of the magnetic toner used in this example are as follows.

Grade 25 is installed at a position facing the magnetic pole of magnet 23, with the gap between its tip and sleeve 22 maintained at 250μ. The magnetic field at the tip of grade 25 is approximately 75
It is 0G. Magnetic toner 24 is opposed between the poles of a magnet in a reave of about 120 microns thick by grade 25.

27 is a toner container.

Sleeve 22 and blade 25 are kept in electrical continuity and powered by power source 26 to prevent electrical discharge between them.
Alternate voltages are applied to one conductive support member. The frequency of the alternating voltage is 400Hz, the amplitude is 600V
(12QOVpp) DC voltage +200 to cv sine wave
It is applied in the form of superimposing V. Further, the electrostatic image potential is +350V in the image area and -2oV in the non-image area.

Based on the above configuration, it was possible to obtain a clear left image with high gradation and no capri.

In the above description, the case where the image portion potential VD is positive has been described in detail, but the present invention is not limited to this case, and can also be applied when the image portion potential is negative. The same applies if the positive force is small and the negative force is large.

Therefore, if the image area charge is negative, the above-mentioned (1)
~(4)°C is expressed as the following (IY~(4Y).

Vmax > VL) VD” > Vmin
=--(IYVmin: VD -I Vth-
r l ・・−・−(37Vmax
s Vx, + l Vth@71 −
(47) As explained in detail above, the present invention has an electrostatic image carrier 1 having a back chamber and a pole, on which an electrostatic image is formed, and a magnet that supports a magnetic developer layer and is fixed therein. A low frequency,
In other words, the present invention provides a developing method that performs development while applying an alternating electric field with a frequency of I KHz or less, and an apparatus for carrying out the method. The transfer of the developer to the non-image area and the reverse transfer to the developer carrier are alternately and reliably repeated in the gap between the two, and this forward movement of the developer creates an image with extremely excellent gradation. A statue can be performed. Furthermore, since the magnetic developer layer is supported on a non-magnetic carrier containing a magnet, the magnetic developer uniformly increases the binding force of the developer on the carrier by the action of a magnetic field. As a result, the potential threshold values vth and -f for developer transfer can be set to sufficiently large values, so that the adhesion of developer to non-image areas can be kept to a small amount, making it possible to minimize soil pressure. .

In this way, the developing method using the magnetic developer according to the present invention to perform developer transfer and reverse transfer has high gradation by applying a low frequency alternating bias electric field.
A beautiful image with clear image edges and no fogging or staining could be obtained.

In an electrophotographic development method, an electrostatic image carrier and a toner carrier are made to face each other with a gap between them, and a constant extremely high-frequency pulse bias (frequency of 10 kilocycles/second to 3,000 kilocycles/second) is applied to this gap. A technique is known in which toner is applied to image areas but not toner is applied to non-image areas during the development process (for example, see US Pat. No. 1,890,929). In this known example, there is no technical idea of placing the magnetic developer under the action of a magnetic field and applying a low frequency alternating voltage to the development gap in order to improve gradation as in the present invention.
In fact, by adjusting and changing the applied electric field strength during the development process, the magnetic developer is transferred to the non-image area under the required magnetic restraint, and the development of low potential areas of the image is also emphasized, thereby eliminating the phenomenon of lack of development at the edges of the image. There is no description of the technical concept of reproducing faithful gradation.

The explanatory drawings, FIG. 5(5) and ■ are explanatory drawings for explaining the movement of the developer, and FIGS. 6 and 7 are explanatory drawings of each embodiment embodying the developing method according to the present invention.

@Electronic image holder...4, 10, 21 Developer carrier...5, 12, 22 specifications, 3893418 specification, etc.) Both of them use high-frequency pulses, and for the same reason as mentioned above, the technical idea is different from that of the present invention.

[Brief explanation of the drawing]

FIG. 1 shows a graph explaining the principle of the developing method according to the present invention and an example of the applied voltage waveform. A process explanatory diagram schematically showing the movement of the developer and the applied voltage waveform in the second process, the third stage, and ■ are the electrostatic image potential versus image in the case of applying a low frequency voltage in the developing method according to the present invention. A diagram showing the characteristics of concentration, Figure 4, ■ is a drawing of electric lines of force generated from an electrostatic image. Figure 3 (A) lo. ■■ No. 2

Claims (1)

[Scope of Claims] An image carrier; a toner carrier disposed with a development gap relative to the image carrier to carry magnetic toner; and a magnetic toner that supplies magnetic toner to the surface of the toner carrier. a supplying means; an elastic body pressed against the toner carrier to form a layer of magnetic toner supplied to the surface of the toner carrier into a thinner magnetic toner layer than the development gap; and an alternating electric field for forming an alternating electric field in the development gap. A developing device comprising: alternating electric field forming means;