JPH0136102B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a developing method using a one-component magnetic developer;
and devices.

A method in which magnetic toner is used to form a thin layer of toner on a sleeve using a specific application method, and this is developed by facing the latent image forming body with a gap equal to or larger than the toner layer, is a method that reduces fogging. It's a great way to give clear images. However, this method has the drawback that the following development is likely to occur.

That is, (1) the lines of electric force in the peripheral area of the latent image cannot reach the sleeve surface, and therefore there is a problem in the reproducibility of the peripheral area of the line.

(2) When a highly cohesive toner is used, toner transfer from the sleeve surface to the latent image forming body is less likely to occur.

(3) Low gradation.

SUMMARY OF THE INVENTION An object of the present invention is to provide a developing method and apparatus which improves the above-mentioned drawbacks, has excellent line reproducibility, facilitates toner transfer (thus ensuring high density), and has high gradation. .

The conditions considered necessary in the present invention to achieve this purpose are: (1) Formation of a repelling magnetic field in the developing section.

(2) Applying an alternating electric field in the development gap.

It is. DESCRIPTION OF THE PREFERRED EMBODIMENTS Details of embodiments of the developing method and apparatus according to the present invention will be explained below with reference to the drawings.

FIG. 1 shows the magnetic lines of force in the developing section and the state of the toner. As shown in the figure, in the region where a repulsive magnetic field is formed by arranging the same polarity adjacently, the toner chains 5 arranged in a spike shape along the lines of magnetic force are in a fully elongated state, and the non-magnetic sleeve 3 As the latent image forming member 1 moves, it moves from position A to position B in the figure while remaining extended in the direction of the latent image forming surface of the latent image forming member 1. Therefore, in this region, the toner density is low, the adhesion between the particles and between the particles and the sleeve is weak, and the toner is easily transferred to the latent image forming member.
Furthermore, since the toner chains are stretched, they are easily felt in the lines of electric force in the peripheral area 4a of the latent image forming body 4, resulting in excellent reproducibility of fine lines. Furthermore, an image with high gradation can be obtained, probably because the toner moves from position A to position B at high speed.

However, on the other hand, it is difficult to obtain a dense image, probably because the toner density is low. Further, there is a problem in that the toner chains tend to extend significantly, and the tips of the chains tend to come into contact with the latent image forming surface, which tends to cause fogging and staining in non-image areas. Here, if an alternating electric field is applied between the back electrode 2 and the sleeve 3, the above-mentioned defects are improved, as described in Japanese Patent Application No. 53-92108, etc., and the reproducibility and gradation of fine lines are improved. It has become clear that rich, detailed, and high-quality images can be obtained. The effect of an alternating electric field is explained as follows.

While passing through the developing section, an alternating electric field causes the toner to reciprocate between the latent image forming surfaces of the sleeve. As a result, the toner that has once been transferred to the latent image surface in a chain state is loosened as it moves back and forth between the toner and the sleeve, and is uniformly rearranged on the image surface. Furthermore, the effect of the electric field allows toner in a wide area on the sleeve to contribute to development. These effects make it possible to obtain detailed images. In addition, fogging in non-image areas that may occur due to the friction of toner chains can also be avoided.
It becomes possible to remove it when the alternating electric field is in opposite phase.

In order to achieve these effects, it has been found that the frequency of the alternating electric field should be set to a value sufficiently low to allow the toner to reciprocate between the sleeve surface and the latent image forming surface, preferably 1 KHz or less. Below, this point is shown in Figure 2A.
This will be explained with reference to the experimental results shown in B. Figure 2 A and B are image reflection density D versus electrostatic latent image potential.
The figure shows a plot of the experimental results. Hereinafter, this curve will be referred to as a V-D curve. The experiment was conducted under the following configuration. A positive electrostatic latent image is formed on the cylindrical electrostatic imaging surface. A magnetic toner (30% magnetite content), which will be described later, is used as the toner, and is applied onto the magnetic sleeve to a layer thickness of approximately 60 μm, and the friction between the toner and the sleeve surface imparts a negative charge to the toner. . The results obtained when the minimum development gap between the electrostatic image forming surface and the magnetic sleeve was maintained at 100μ are shown in FIG. 2A, and the results obtained when the minimum development gap was maintained at 300μ are shown in FIG. 2B. The magnetic flux density in the developing section due to the magnet contained in the sleeve is approximately 700 Gauss. The cylindrical electrostatic imaging surface and the sleeve rotate at approximately the same speed, approximately 110 mm/sec. Therefore, the electrostatic image forming surface gradually moves away from the toner carrier after passing through the minimum gap in the developing section. The alternating electric field applied to this sleeve is a sine wave with an amplitude of 400V (800V peak-to-peak) and a DC voltage of +200V superimposed on it. Figure 3 A, B
In the case shown in , the alternating frequency of this applied voltage is 100
V-D for Hz, 400Hz, 800Hz, 1KHz, 2KHz
3A and 3B, and a V-D curve when the back electrode of the electrostatic image forming surface and the sleeve are electrically connected without applying an external electric field.

These results show that when no external electric field is applied, the slope of the V-D curve, the so-called γ value, is very large, but by changing the alternating low-frequency electric field,
It can be seen that 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.When the gap is 100μ, the effect becomes extremely weak when the frequency exceeds 1KHz, and when the gap is 300μ, the effect becomes extremely weak.
In the case of , the effect decreases when the frequency becomes around 800Hz, and becomes extremely weak when the frequency exceeds 1KHz. The reason for this is thought to be as follows. During the development process when an alternating electric field is applied, when toner repeatedly adheres and detaches between the sleeve surface and the latent image forming surface,
A finite amount of time is required to reliably perform the reciprocating motion. In particular, toner that transfers when subjected to a weak electric field requires a long time to ensure the transfer. On the other hand, in order to reproduce halftone density, it is necessary that toner subjected to an electric field of a certain threshold value or more, even if the electric field is weak, is transferred reliably within a half cycle of the alternating electric field. For this purpose, it is advantageous to have a low frequency alternating electric field, and therefore, as shown in the experimental results, particularly good gradation can be obtained with a low frequency alternating electric field. The validity of this argument can be obtained from a comparison of the experimental results shown in Figure 2 A and B. The results shown in FIG. 2B were conducted under the same conditions as the experiment shown in FIG. 2A, except that the gap between the electrostatic image forming surface and the sleeve surface was increased to 300 μm. When the gap is widened, the electric field strength to which the toner is exposed decreases, and therefore the toner transfer speed decreases. Furthermore, since the flight distance becomes longer, the transfer time becomes longer. Actually the second
As is clear from Figure B, the γ value becomes considerably large at about 800 Hz, and when it exceeds 1 KHz, it becomes almost the same as the γ value when no alternating voltage is applied. Therefore, in order to produce the same effect as when the gap is narrow in terms of improving gradation, it is preferable to further lower the frequency or increase the intensity of the alternating voltage.

On the other hand, 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 uneven development will likely occur in the image due to the alternating voltage. As a result of the above experiment, the frequency is 40Hz.
Up to this point, generally good images were obtained, but below that point, unevenness occurred in the visible images. It has been found that the lower limit of the frequency for preventing unevenness in the developed image is particularly dependent on the development conditions, particularly the development speed (also referred to as process or speed, VPmm/sec). In this experiment, the moving speed of the electrostatic image forming surface was 110 mm/sec, so the lower limit of frequency was 40/100×Vp0.3×Vp. It has been confirmed that any waveform of the applied alternating electric field, such as a sine wave, a rectangular wave, a sawtooth wave, or an asymmetric wave thereof, is effective.

In this way, applying an alternating bias has a remarkable effect on improving gradation.

Embodiments according to the present invention will be described below.

Embodiment 1 In FIG. 3, 1 is a latent image forming body having an insulating layer on the surface of a CdS photoreceptor, 2 is a back electrode thereof, 3 is a non-magnetic sleeve, 6 is a fixed permanent magnet roll enclosed by the sleeve, 6a is a magnetic pole that forms a repulsive magnetic field, and 7 is a magnetic toner, which is obtained by kneading and pulverizing 75% styrene/maleic acid resin, 20% ferrite, 3% carbon black, and 2% charge control agent. 8 is a toner container, 9 is a magnetic material (iron)
It is a blade and is disposed on the fixed magnet roll with one main pole 6b (at a position facing the sleeve surface magnetic flux 850G (Gauss) with a gap of 240μ from the sleeve surface.As the sleeve rotates, The thickness of the magnetic toner is regulated by magnetic force by the magnetic blade 9, applied onto the sleeve, and conveyed to the development position A. In the case of this embodiment, the thickness of the applied toner is about 100μ on average, and the repulsion At position A where the magnetic field is formed, it extends to a height of approximately 200μ.The minimum gap between the latent image forming body 1 and the sleeve 3 is maintained at 300μ.The sleeve surface magnetic flux density near the repulsion pole is N ₁ −800G, N ₂ −780G, N ₁
The lowest magnetic flux density between N2 and _N2 is 40G.

10 is a power supply for applying an alternating electric field at position A, and the back electrode 2 is set to ground potential;
The voltage is applied to the sleeve 3 and the magnetic blade 8.

The potential of the latent image on the latent image forming body 1 is approximately
500V, non-image area approximately 0V, applied voltage is frequency
It is a sine wave of 300Hz, maximum value 670V, minimum value -230V. The latent image holder 1 rotates at a circumferential speed of 110 mm/sec, and the sleeve 3 rotates at substantially the same speed and in the same direction.

Good microscopic images were obtained under the above settings.

Embodiment 2 In FIG. 4, 1 is an Se photoreceptor, 11 is a toner carrier made of conductive rubber, 20 is a toner coating layer thickness regulating member made of chloroprene rubber, and magnet rule 13 is
facing one main pole 13b (magnetic flux density 1000G),
It is pressed against the toner carrier 11. Toner 14
is a product obtained by kneading and pulverizing 65% styrene resin, 32% magnetite, and 3% charge control agent. The average thickness of the toner layer is approximately 80 μm, and in the developing section it is extended to a maximum of approximately 160 μm due to the repelling magnetic pole 13a.
The gap between the toner immediate support member 11 and the latent image forming member 1 is maintained at approximately 200 μm in the developing section. The magnetic flux density of the repelling magnetic pole 13a in the developing section is N ₁ -1000G,
N ₂ −960G, and 600G at the lowest magnetic flux density part between N ₁ and N ₂ . The latent image potential was +600V in the image area and +50V in the non-image area. The applied alternating voltage is a rectangular wave with a frequency of 400 Hz and a maximum value of -300 V from the power supply 10. The photoreceptor 1 rotates at a peripheral speed of 200 mm/sec, and the toner carrier 11 rotates in the same direction as the photoreceptor 1 at a peripheral speed of 193 mm/sec. Good images were obtained with the above settings.

The effects of the above example can be summarized as follows (1)
~(4).

(1) The magnetic toner can be easily separated from the toner carrier by the repelling magnetic field, and the alternating bias electric field acts on this toner, so it is difficult to move the toner, especially between the latent image carrier and the toner carrier. The movement of reciprocating through the gap is further promoted.

(2) As a result, the toner tends to adhere to non-images of the latent image, making it possible to improve the gradation of the image.

(3) On the other hand, since the toner adhering to the non-image area is removed when the alternating bias is in opposite phase, background fog does not substantially occur.

(4) A kind of cloud-like situation occurs when the repulsive magnetic field and the positive phase of the alternating bias combine, and the edge phenomenon at the image edges of the latent image can emphasize the visualization of the edges, resulting in a clear line image. A microscopic image can be obtained.

In particular, by making the magnetic poles of the magnetic N ₁ and N ₂ on the upstream side relative to the moving direction of the toner carrier 11 have a larger magnetic flux density than the magnetic poles on the downstream side, the toner carrier can supply the toner. It is possible to more reliably separate the entire magnetic toner from the toner carrier, thereby increasing the supply of the magnetic toner to the developing section. Furthermore, on the downstream side, the dominance of the alternating electric field is relatively increased in the balance between the reciprocating motion of the toner due to the magnetic poles and the alternating electric field, so excess magnetic toner can be reliably removed from the photoconductor surface while further increasing the development density. The image quality will be clear.
In any case, development with extremely high development efficiency can be achieved for a small development area, exceeding the limits of development that can be achieved by alternating electric field frequencies and potential differences (a much higher level of development than development using a simple development magnetic field). Needless to say, it is possible to achieve ideal development at high speed, high density, and high image quality.

On the other hand, the conventional jumping of insulating non-magnetic toner by alternating electric fields (British Patent No. 1458766)
In this case, since there is no magnetic constraint condition, the toner separated from the donor is controlled only by the electric field, but since the electric field required for separation is extremely strong, the toner itself floating in the space is affected by the developing area. It has a problem with flying off. However, according to this embodiment, since the toner that is about to scatter can be restrained by the magnetic force between the magnetic poles of the same polarity in cooperation with the alternating electric field, there is no problem of scattering as in the conventional toner. still,
The scattered toner not only contaminates the outside of the device, but also adheres to unpredictable areas as the photoreceptor moves, causing the inconvenience of forming unnecessary images. The present invention can solve these inconveniences.

As explained above, in the present invention, the action of an alternating electric field and a repulsion magnetic field caused by magnetic poles of the same polarity is applied to the behavior of magnetic toner on the developing section, so that between the same poles, toner particles move horizontally. The synergistic effect of the magnetic force and the electric field force in the forward and backward directions of the alternating electric field allows the magnetic toner particles to be loosened efficiently and fine development of the ideal latent image of toner particles to be performed.
It is possible to obtain precise development and high-quality images. Furthermore, on the development start side, the magnetic poles forming the repulsion magnetic field assist the detachment of the magnetic toner from the non-magnetic rotating body by the toner forward movement component toward the latent image forming body due to the alternating electric field, and develop the entire supplied magnetic toner. At the end of development, the toner is returned to the non-magnetic rotating body side due to the alternating electric field, which assists in the collection of magnetic toner that is unnecessary for the latent image, thereby preventing background fog. The effect can be ensured.

Therefore, according to the present invention, a compact, high-speed
A developing method and apparatus that can achieve high-quality image development can be provided.

[Brief explanation of drawings]

Figure 1 is an explanatory diagram explaining the principle of the present invention, Figure 2
Figures A and B are characteristic diagrams showing the relationship between electrostatic latent image potential and image density depending on the applied alternating bias, and Figures 3 and 4 are sectional views of embodiments according to the present invention. DESCRIPTION OF SYMBOLS 1...Latent image holding member, 3, 11... Toner carrying member, 6a, 13a... Repulsion magnetic pole, 10... Alternating bias source, 7, 14... Magnetic toner.

Claims (1)

[Claims] 1. A magnetic toner layer is formed on a non-magnetic rotating body, and a magnetic field of a magnet included in the non-magnetic rotating body is generated at an opposing portion where the rotating body and the latent image forming body face each other with a gap maintained. In the developing method, a repulsive magnetic field is formed in the opposing portion by adjacent magnetic poles of the same polarity, and the minimum gap between the non-magnetic rotating body and the latent image forming body is larger than the thickness of the magnetic toner layer at this position. A developing method characterized in that a large alternating electric field is formed in the gap to repeatedly attach and detach magnetic toner from a latent image forming body. 2. A developing device comprising a movable non-magnetic rotating body on which a magnetic toner layer is formed, and fixed magnetic field generating means for applying a magnetic field to a developing section where the non-magnetic rotating body faces the latent image forming body with a gap therebetween. , the fixed magnetic field generating means has adjacent magnetic poles of the same polarity facing the developing section, the gap is larger than the layer thickness of the magnetic toner formed by the magnetic field generating means, and the gap is larger than the layer thickness of the magnetic toner formed by the magnetic field generating means; A developing device comprising means for forming an alternating electric field to repeatedly attach and detach magnetic toner from a latent image forming body.