JPH0225856A - Development method - Google Patents

Abstract

PURPOSE:To prepare an image excellent in evenness by superimposing a electric field to weaken the intensity of an electric field in either period of one part of the period to impress the electric field in a direction to cause a toner grain to transit or one part of the period to impress the electric field in the direction to drum the toner grain. CONSTITUTION:In at least either period of the period to impress the electric field to cause a toner 37 to transit from a developing sleeve 22 to a photosensitive body drum 1 or the period to impress the electric field in the direction to separate the toner 37 from the photosensitive body drum 1 to the contrary to the transition, the electric field to weaken the intensity of the electric field is superimposed. Thus, the image can be prepared which is rich in a gradation, in which a base fogging is small, in which the emphasis of an edge is properly executed, in which a density change in a half tone does not exist and which is excellent in the evenness.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a method for developing an electrostatic latent image formed by electrophotography, electrostatic recording, etc. The present invention relates to a developing method in which an alternating electric field is applied between electrostatic latent image carriers and a two-component developer is used, and the developing method is particularly suitable for recording image display devices, copying machines, printers, facsimile machines, etc. Regarding the method.

(Prior Art) Conventionally, a dry developer consisting of toner particles as a developing agent and a magnetic carrier is supported on the surface of a developer carrier and transported, and this developer is transferred to an electrostatic process carrying an electrostatic latent image. The developer is conveyed and supplied near the surface of the electrostatic latent image carrier to form a magnetic brush on the developer carrier, and while an alternating electric field is applied between the electrostatic latent image carrier and the developer carrier, the electrostatic developer is Developing methods for developing electrostatic latent images are known. This developing method is often commonly referred to as magnetic brush developing method.

The developer carrier described above is generally used as a developing sleeve of a developing device, so in the following explanation, the developing sleeve will be referred to generically, and the electrostatic latent image carrier is generally used as a photoreceptor drum in many cases. Therefore, in the following description, they will be collectively referred to as photosensitive drums.

Conventionally, this developing method uses a developer consisting of two components (carrier particles and toner particles) to form a magnetic brush on the surface of a developing sleeve with magnets arranged inside to maintain a minute development gap. By rubbing this magnetic brush against or bringing it close to the opposing photoreceptor drum and continuously applying an alternating electric field between the developing sleeve and the photoreceptor drum, the toner particles are transferred from the developing sleeve side to the photoreceptor drum side. So-called magnetic brush development is known in which development is carried out by repeatedly performing reverse displacement in the opposite direction (Japanese Patent Application Laid-Open No. 55-3).
No. 2060, No. 59-165082, etc.), and a non-contact alternating electric field development method using a two-component developer for the purpose of simple color development and multiple development is also known (Japanese Patent Laid-Open No.
No. 8-14268, No. 58-68051, No. 5B-1
No. 44452, No. 59-181362, No. 60-17
No. 8069).

(Problems to be Solved by the Invention) In the above-mentioned conventional magnetic brush development method in which alternating electric fields are applied, the effect of the electric field of the electrostatic latent image formed on the photoreceptor drum and the alternating electric field applied Since the method uses a development method that increases the development density and removes fog, there are problems such as difficulty in increasing the sharpness of the image edges of the resulting developed image.

Several methods can be considered to solve this problem, such as increasing the frequency of the alternating electric field applied between the photoreceptor drum and the developing sleeve to increase the density and eliminate fog. However, with this method, the image itself becomes high-contrast, and toner adhesion not only in non-image areas but also in image areas close to the potential of these non-image areas (so-called highlight areas) decreases, resulting in poor reproducibility. Another problem arises in that the amount of water tends to decrease.

This can be explained as a characteristic of image density for electrostatic latent images. Generally, the gradation of an image can be determined by the slope γ of the curve that indicates this characteristic, but in the developing method in which the frequency of the alternating electric field is increased, this slope γ is extremely steep, resulting in an image that lacks gradation. This is because as the frequency of the alternating electric field increases, the toner particles attached to the carrier particles and the toner particles on the developing sleeve cannot sufficiently follow the movement of the electric field, and after a certain threshold, the toner particles adhere to the photoreceptor drum. This is thought to be because the latent image tends to exhibit a binary development phenomenon of flying or not flying.

On the other hand, in contrast to the above, if the frequency of the alternating electric field is lowered (for example, to about several hundred Hz) in order to reduce the gradient γ, the toner particles will perform development while reciprocating between the photoreceptor drum and the developing sleeve. As a result, an image with good gradation can be obtained, but on the other hand, problems such as deterioration of fog and the possibility of the carrier adhering to the photoreceptor drum arise.

This is because by lowering the frequency, toner particles and carrier particles can better follow the movement of the electric field, but the toner particles and carrier particles that fly toward the non-image area on the photoreceptor drum are Due to the extended application time (because the frequency is low) of the electric field that causes transposition to the photosensitive drum side, it is trapped on the photosensitive drum, and even if the electric field for reverse transposition due to the alternating electric field acts, it cannot be completely eliminated. This is thought to be because it becomes difficult to remove.

In this way, in the method of developing with an alternating electric field using a conventional two-component developer, it is necessary to reduce fog and carrier adhesion and to make the obtained microscopic image excellent in gradation. There was a problem in that it was difficult to simultaneously satisfy the following.

The present invention solves the conventional problems in the so-called magnetic brush development method in which development is performed while applying an alternating electric field using a two-component developer as described above, and achieves high tonality, high tonality, and less blurring. It is an object of the present invention to provide a developing method capable of forming an image with excellent resolution and uniformity with little change in density in halftones.

Still another object of the present invention is to provide a developing method that can reduce transfer of excess toner, reduce the burden of further transferring a developed image onto transfer paper, and obtain high density with low consumption. It's there to provide.

(Means for Solving the Problems) The present invention has been made to achieve the above objects, and uses a two-component developer consisting of toner particles and carrier particles as a developed image, which is a feature of the developing method of the present invention. Surface &: A developing sleeve (developer carrier) to be carried and conveyed and a photosensitive drum (electrostatic latent image carrier) are arranged in a moving relationship while maintaining a small gap. A magnetic brush of the developer is formed on the developing sleeve in this gap, and an electric field is applied between the developing sleeve and the photosensitive drum in the direction of transferring toner particles from the developing sleeve to the photosensitive drum. In a developing method in which development is performed while alternately and repeatedly applying an electric field in a direction in which the toner particles are applied and a period in which the electric field is applied in a direction in which the toner particles are detached from the photoreceptor drum in the opposite direction to the transfer, the above-mentioned tree particles are During at least one of a part of the period in which the electric field is applied in the direction of transferring the toner particles and a part of the period in which the electric field is applied in the direction of drumming the toner particles, the electric field is weakened by 1! This is what I tried to do to make it public.

As described above, the method of the present invention includes a period in which an electric field is applied in the direction of transferring the toner from the developing sleeve to the photoreceptor drum, and a period in which the electric field is applied in the direction in which the toner is transferred from the photoreceptor drum to the photoreceptor drum in the opposite direction. It is sufficient that an electric field that weakens the electric field is superimposed during at least part of the period in which the electric field is applied in the direction of separation, but the effects of the present invention are more preferably realized when these are applied simultaneously. .

The method of the present invention can be applied to the so-called magnetic brush development method using the above-mentioned two-component developer.

In the configuration of the present invention, the alternating electric field between the photoreceptor drum and the developing sleeve can be generated by applying an alternating current voltage or by applying a rectangular pulse voltage for both the basic alternating electric field and the superimposed electric field. In addition, it may be a triangular wave, a sawtooth wave, or an asymmetric wave, and is not particularly limited.

Further, in the above configuration, a period in which an electric field is applied in a direction in which toner is transferred from a developing sleeve to a photoconductor drum (this is a period in which an electric field is applied in a direction in which an image area of the photoconductor drum is mainly developed; Toner is transferred to the non-image area to some extent due to the relationship with the potential of the image area).To superimpose the electric field that surrounds the electric field in a part of the area means to use a pulse synthesizer, etc., for example, to create one basic alternating electric field. as, 300
H2~2k)! This can be done by using an electric field in z and superimposing it with other short pulses that are in opposite phase during the transition.

Also, a period in which an electric field is applied in a direction to reversely transfer the toner from the photoreceptor drum to the developing sleeve (mainly a period in which an electric field is applied in a direction to peel off 11 (reverse transfer) the toner on the non-image area of the photoreceptor drum). The idea of superimposing an electric field that weakens the electric field on a part of the image area (the toner of the image area also undergoes a slight reverse transition in relation to the image area potential of the photoreceptor drum) is similar to the above, for example, as a basic idea. By superimposing one alternating electric field with another short pulse that has an opposite phase during the transition period, an electric field is created that does not have the strength to transfer toner between it and the non-image area (i.e., it is applied to the sleeve). The voltage may be a DC component having a value between the potential of the image area and the non-image area of the photoreceptor, and closer to the potential of the non-image area than the center between the two.

For example, when the electric field is weakened during a part of the period during which toner is transferred from the developing sleeve to the photoreceptor drum, the period during which the electric field is adjusted to weaken is the beginning, middle,
They may be provided at any end or in multiples. The same applies to the case where the above adjustment period is provided when the toner is reversely transferred from the photosensitive drum to the developing sleeve. Weakening the electric field generally refers to the potential between the image area potential and the non-image area potential of the photoreceptor drum, especially the potential of the DC component that is applied superimposed with the alternating electric field (midpoint potential between the upper and lower peaks of the alternating electric field). For example, in a normal analog copying machine using electrophotography, it is preferable to shift the applied voltage to or near the above potential. In many cases, in digital copying machines (for example, laser beam printers) used as printers for computer equipment, the image area potential is formed as a roughly constant potential in order to weaken the electric field during the period of toner transfer. In many cases, it is preferable to shift the image potential to or near that image potential.

The two-component developer used in the method of the present invention includes carrier particles, which are magnetic particles whose surfaces are coated with a resin, such as magnetic particles such as ferrite, and non-magnetic particles, which are made by bonding a charge control agent, an external additive, etc. with a resin. Examples include combinations of toner particles, but the invention is not particularly limited thereto, and any two-component developer used in so-called magnetic brush development can be used.

In the developing method to which the method of the present invention is applied, a two-component developer is typically conveyed on the surface of a rotating sleeve equipped with a fixed magnet for generating a magnetic field inside the developing sleeve, and this developing sleeve is used as a latent image carrier. A magnetic brush of developer is formed on the developing sleeve by an internal magnetic pole at the surface facing the photoreceptor drum with a small gap, and this magnetic brush is brought into contact with the surface of the photoreceptor drum. Should I rub it?
This method refers to a method in which toner particles are caused to adhere to a photoreceptor drum by driving them while bringing them close to each other, but the method is not particularly limited to this method. The method is not limited to the common name "magnetic brush development" as long as it is a method of non-contact development and can perform effective development by applying an alternating electric field.

Furthermore, applying a superimposed electric field to weaken the electric field is substantially the same even if the basic electric field is set low and an electric field that partially strengthens it is superimposed. ``overlapping'' shall include both of the above cases.

(Function) With the above-described configuration, the developing method of the present invention weakens the electric field during a part of the period in which the electric field is applied in the direction of transferring the toner from the developing sleeve to the photoreceptor drum. It is possible to control excessive supply of toner to the image area and reduce the tendency of toner to adhere to non-image areas.

In addition, by weakening the electric field during a part of the period in which the electric field is applied in the direction of reverse transfer from the photoreceptor drum toward the developing sleeve, it is possible to achieve rich gradation, less ground blur, and moderate edge emphasis. It is possible to form images with excellent uniformity without density changes in intermediate tones.

(Example) The present invention will be explained below based on specific examples.

Example 1 FIG. 1 is a sectional view of a developing device according to an embodiment of the present invention.

1 in this figure is an insulated drum for electrostatic recording or a-
Photoreceptor drum (or photoreceptor belt) with a layer of photoconductive insulating material such as 5e, Cds, ZnO, OPC, a-3I
It is. This photosensitive drum 1 is rotated in the direction of arrow a by a drive device (not shown). A developing sleeve 22 is located close to the photosensitive drum 1 and is made of a non-magnetic material such as aluminum or 5O5318.

The developing sleeve 22 has its left approximately half circumferential surface thrust into the container 36 from a horizontally long opening formed in the container longitudinal direction (the depth direction in the figure) at the lower left wall of the developing container 36 in the figure. is exposed outside the container and rotatably mounted on a bearing, and is rotatably installed horizontally, and is driven to rotate in the direction of the arrow.

Reference numeral 23 denotes a fixed permanent magnet (magnet) as a fixed magnetic field generating means, which is positioned inside the developing sleeve 22 in the position and orientation shown in the figure. It is held fixed in the same position and posture. This magnet 23 in this example has a north magnetic pole 23a, a south magnetic pole 23b, and a north magnetic pole 23c, 361! Has poles. Note that the magnet 23 may be an electromagnet instead of a permanent magnet. In this example, the maximum value of the vertical component of the surface magnetic flux density of the magnet 23 is approximately 700 Gauss for the poles 23a and 23c, and 850 Gauss for the pole 23b.

24 is a non-magnetic blade, and the developing sleeve 22
The base portion is fixed to the side wall of the container on the lower edge side of the opening of the developer supply device in which the developer supply device is disposed, and the tip side is arranged along the longitudinal length of the lower edge of the opening so as to protrude outward from the container 36 than the longitudinal length of the lower edge of the opening. It constitutes a developer regulating member. This non-magnetic blade 24 is
For example, it is made by bending 5uS316 into a ``H'' shape when viewed from a cross section.

27 is a carrier particle which is one component of a two-component developer, and is generally a ferrite particle (with a particle size of 20 to 100 μm, preferably 30 to 80 μm, and a resistance value of 107 Ωca or more, preferably XO'Ωc 111 or more). Maximum magnetization 3
0 to xooemu/g) is often used, and in this example, as will be described later, a resin coating was used.

37 indicates a non-magnetic toner which is another component of the two-component developer.

62 is a toner concentration detection sensor;
The toner auxiliary roller 63 repeatedly rotates (rotates in the direction of arrow C) and stops in accordance with the output of step 2, and the toner...
We are making it possible to supply the following.

A stirring member 66 rotates in the direction of arrow d, and mixes and stirs the developer peeled off from the sleeve 22 by the scraper 67 and the replenishment toner.

38 is a toner storage container.

In the above configuration, the developer regulated by the non-magnetic blade 24 is further regulated by an auxiliary regulation plate (not shown) and transported to the development area. After development, the toner concentration in the developer is detected by a toner concentration detection sensor 62. If the toner concentration is low, the replenishment roller 63
starts rotating and supplies toner.

The blade 24 is made of non-magnetic stainless steel with a thickness of 1.5 mm, and the pole 23 is made of stainless steel with a thickness of 1.5 mm.
It was installed on the lower side of a.

As carrier particles, ferrite particles with a particle size of 70 to 90μ coated with a mixed resin of acrylic and fluorine on the surface (maximum magnetization ~56 ea+u/g s resistance value 10' to 10'Ω) are used.
cm) was used.

As the non-magnetic toner, a [.-toner powder with an average particle diameter of 13 microns was used, which was mainly composed of 90 parts of a steel T/N resin, a polypropylene part, and 4 parts of carbon black.

Furthermore, the gap between the photosensitive drum 1 and the sleeve 22 should be approximately ! m
The developing device was constructed with a distance of 0.8 mm between the sleeve 22 and the blade 24.

Using the above developing device, the latent image potential of the photosensitive drum was set to -650V in the image area and -150V in the non-image area as the development conditions, and the developing bias was set to -200V DC voltage.
Development was carried out by superimposing the pulse waveform shown in the figure (that is, a pulse waveform in which an electric field that weakens the electric field is superimposed on a part of the basic electric field that simply reciprocates). Here, t1-1. Good images were obtained when the lengths were the same and each ranged from 60 .mu.Sec to 250 .mu.sec. In other words, 1
Good images were obtained when the cycle time (T, = "z t,) was in the range of Is+ 500 μsec to .3 n+sec. In the configuration of this example, T of 1 cycle.

If it is shorter than 500 μSeC, the image tends to be high contrast and γ tends to rise, similar to the case where a simple alternating electric field is applied in the conventional example described above. On the other hand, when T is longer than 3 m5ec, the toner and carrier can sufficiently follow the changes in the pulse, and as a result, toner and carrier fly to the photoreceptor drum and do not return, resulting in fogging and carrier adhesion. There is a tendency for this to occur.

Here, the difference between the case where pulses of an alternating electric field are simply applied and the case where a weakening electric field is superimposed on the pulses of the present invention will be explained using this example.

The voltage of multiple pulse waveforms giving an alternating electric field is set at 60 μs.
When applied at a short period of c~250 μsec, a high frequency electric field is applied to the developer. Here, since the carrier and toner are charged with opposite polarities, the carrier and toner repeatedly vibrate in opposite directions at the above-mentioned high frequency and give each other electric charges.Here, the carrier is restrained by the magnetic force of the magnet on the developing sleeve side. Furthermore, since the volume and specific gravity of the carrier are considerably larger than that of the toner, toner particles surround the carrier in a cloud-like state.

On the other hand, if the frequency is raised to the above range in conventional development by applying a simple alternating electric field, the toner tends to either fly or not fly in a binary manner after reaching a certain threshold.
The result is a high-contrast image with a strong γ. On the other hand, in this embodiment, as described above, the electric field is weakened during a part of the period in which toner is transferred from the developer carrier side to the latent image carrier and in a part of the period in which the toner is reversely transferred. A cloud occurs between the developing sleeve and the photoreceptor drum, and a state similar to soft touch or loud development is repeated.

Moreover, as mentioned above, the toner is more firmly charged by the carrier by increasing the number of times of friction between the toner and the carrier using high-frequency pulses, so fogging does not occur.Also, since the toner is given a flying signal with short pulses, the carrier is Compared to the case where a pulse is applied at a low frequency, the time required for receiving the flying force is shortened, and the tendency to excessively displace to the drum side is suppressed, and the adhesion of carriers is also eliminated.

As explained above, this embodiment makes it possible to obtain high-quality images with gradation, no fog, and no carrier adhesion. As an example, FIG. 9 shows the conventional bias (first
0) and the bias (Fig. 11) of this example. Due to the above-mentioned effects of this example, it was possible to obtain an image with a flat gradation of γ. I understand.

Embodiment 2 FIG. 3 shows a sectional view of a developing device according to another embodiment of the present invention. The apparatus of the example shown in FIG. 3 is different from the apparatus of Embodiment 1 shown in FIG. 1, and is a developing apparatus of a type in which magnetic particles and toner particles are mixed and stirred on a developing sleeve.

A case in which the present invention is applied to this device will be described below. 101 in this figure is an insulated drum for electrostatic recording or a
The photosensitive drum 101, which is a photosensitive drum (or photosensitive belt) having a photoconductive insulating layer such as -5o, Cds, ZnO, OPC, a-51, is rotated in the direction of arrow a by a drive device (not shown). be done. A developing sleeve 122 is located close to the photosensitive drum 101 and is made of a non-magnetic material such as aluminum or 5O5318. This developing sleeve 122 is connected to a developing container 136.
In the longitudinal direction of the container (in the depth direction of the figure) at the lower left wall in the figure.
The right half-circumferential surface is inserted into the container 136 through the horizontally elongated opening formed in the container 136, and the left half-circumferential surface is exposed to the outside of the container. be done.

Reference numeral 123 denotes a fixed permanent magnet (magnet) as a fixed magnetic field generating means, which is positioned and housed in the developing sleeve 122 in the illustrated position and orientation. This example magnet 123, which is held fixed in its position and orientation, has four magnetic poles: an N-pole magnetic pole 123a, an S-pole magnetic pole 123b, an N-pole magnetic pole 123c, and an S-pole magnetic pole 123d. Note that the magnet 123 may be an electromagnet instead of a permanent magnet.

124 is a non-magnetic blade, which is attached to the developing sleeve 1
The base portion is fixed to the side wall of the container on the upper edge side of the opening of the developer supply device in which the developer supply device 22 is disposed, and the tip side is lower than the upper edge position of the opening.
A developer regulating member is arranged along the longitudinal direction of the upper edge of the opening. This non-magnetic blade 124 is made by bending, for example, 5uS31B into a "F" shape when viewed from a cross section.

Reference numeral 126 denotes a magnetic particle limiting member whose upper surface is in contact with the lower surface side of the non-magnetic blade 124 and whose front end surface is a developer guiding surface 126a.

I27 is a carrier particle constituting one component of the two-component developing agent, and in this example, the particle size is 30 to 100 μm, preferably 40 to 70 μm, and the resistance value is 107 Ωcm or more, preferably 0°ΩCff1 or more. Ferrite particles (maximum magnetization a o emu/g) coated with a resin can be preferably used.

137 indicates a non-magnetic developer toner which is another component of the two-component developer.

131 is a developing container 13 in which a developing sleeve 122 is arranged.
In order to prevent carrier particles 12''l or non-magnetic toner particles 131 from leaking from the lower part of the image container 6, it is a magnetic material placed on the inner surface of the lower part of the image container facing the developing sleeve 122. It is formed by what has been applied.

As a result, a sealing effect is obtained in which the carrier particles 127 are recovered and prevented from sagging by the magnetic field between the magnetic body 131 and the S-polarity magnet i 123d.

Reference numeral 139 denotes a toner supply member that supplies toner to the brush portion of the carrier particles formed by the fixed magnetic pole 123 in the developing sleeve 122, and is made by pasting a rubber sheet on a rotatably bearing plate. The toner is conveyed as if sweeping the bottom surface of the developer container. Toner is supplied to the toner supply member 139 by a toner transport member (not shown) C in the toner storage device 138.

138 and 135 are a toner storage container and a magnetic particle storage container, respectively.

140 is the lower part of the developer container 136! =? : A sealing member that seals the accumulated toner, has elasticity, is bent toward the rotational direction of the developing sleeve 122, and elastically presses the surface of the developing sleeve 122. This sealing member 140 has an end on the downstream side in the rotational direction of the developing sleeve in a contact area with the developing sleeve so as to allow the developer to enter the inside of the container.

Reference numeral 13G denotes a scattering prevention electrode plate that applies a voltage of the same polarity as the developer to the floating developer generated in the developing process to stick it to the photoreceptor drum side and prevent it from scattering.

Further, the S magnetic pole 123d is a magnetic field generating means for magnetic sealing to form a magnetic field from one side to the other between the S magnetic pole 123d and the magnetic member 131, and a part thereof faces the magnetic member 131. The magnetic member 131 constitutes a substantial end of the developer accommodating portion of the developer-side container, and is located below the developing device. Toner particles located in the lower part of the container are incorporated into the developer on the surface of the sleeve. Therefore, stable recovery of carrier particles has the effect of stabilizing the developing ability.
The effectiveness of the method of the present invention can also be expected in this respect.

This magnetic member 131 may have a "<" or r L J shape, and may be made of a magnetic material that is not permanently magnetized, such as iron, or that is made weakly magnetic by deforming a non-magnetic material. .

In other words, the magnetic member 131 restrains the carrier particles, prevents the loss of the carrier particles, and facilitates recovery of the carrier particles, so that the toner particles in the developer container can be prevented from leaking from inside the container.

In the above configuration, by arranging the magnetic pole 123d as described above, a particularly favorable effect can be obtained in relation to the magnetic pole 123a. That is, due to the above relationship between the bottom of the container 136 and the magnetic pole 123d, the magnetic brush
Since the toner particles are not formed in a coarse state (compared to a merely stagnant state) within the carrier particles, an effect is obtained in which the amount of toner particles taken into the carrier particles does not become excessive. Excessive uptake results in insufficient charging of the toner, causing fogging.

Note that this configuration is also effective when carrier particles and nonmagnetic or weakly magnetic toner coexist in the developer container.

According to experiments, the developing sleeve 122 and the magnetic member 131
At a distance of 1112.5 am, the carrier particles are completely recovered and no leakage of toner particles is observed, indicating that stable development can be achieved.

The distance *d2 between the end of the non-magnetic blade 124 and the surface of the developing sleeve 122 is 50 to 800 μm, preferably 150 to 500 μm. If this distance is smaller than 50 μm, carrier particles tend to clog between the gaps, causing unevenness in the developer layer, and the developer necessary for good development cannot be applied, resulting in a developed image with a low density and a lot of unevenness. There are drawbacks that cannot be avoided. If the diameter is larger than 800 μm, the amount of developer applied onto the developing sleeve 122 increases, making it impossible to regulate the thickness of the developer layer to a predetermined value, increasing the amount of carrier particles attached to the photoreceptor drum, and increasing the circulation of the developer. The limiting member 126 weakens the development regulation, and there is a drawback that toner triboelectricity is insufficient and capping is likely to occur.

The fixedly placed magnetic poles 123a reposition the bucking carrier particles along the magnetic field lines.

The backing state in this space is unstable with respect to tribo-imposition, and a constant backing state is always required to stabilize it.

This is because a magnetic brush is formed by applying a force perpendicular to the direction of the carrier particles conveyed on the developing sleeve 122 in a substantially tangential direction, which not only has a stirring effect on the carrier particles but also has a peeling effect. The uniformity and stabilization of the tribo-imparting to the toner and the application of the carrier particle layer are further promoted. At this time, if the concentrated developer remains under great pressure due to the surrounding structure, there is a problem that the developer will become clogged. By,
It is believed that excessive pressure concentration in the regulated area can be prevented, and developer concentration and stable high-density magnetic particle existence ratio can be maintained.

Due to the above-mentioned restricted area, a stable amount of carrier particles and sufficiently charged toner particles can be formed as a thin layer of developer on the surface of the developer sleeve. Therefore, the development effect in the development area is stable.The toner particles carried on the surface of the development sleeve 122 are transferred to the photoreceptor drum 101 even if the developer conveyed to the development section does not fall within the range of 0 or more. Furthermore, by applying the alternating electric field shown in FIG. 4 to the developing section, good development can be performed. In the configuration of this example, the latent image conditions were the same as in Example 1, and when the same pulse bias as in Example was applied except for the alternating electric field and the waveform shown in Figure 4, a very good image was obtained. It was done.

Note that the configuration in FIG. 3 is shown in the case where the magnetic body 150 is installed on the non-magnetic blade 124 side of the developer limiting member 126, but in this case, it is preferable that the magnetic body 150 is installed at a position facing the magnetic pole 123a. do not have. This is because if they face each other, a strong concentrated magnetic field will be generated between them and the magnetic pole 123a, reducing the effect of stirring and loosening the carrier particles by the magnetic pole 123a. However, it is effective to provide a magnetic material in the regulating portion to magnetically regulate the carrier particles between the developing sleeve internal magnet 123 and the gap tolerance between the regulating member and the sleeve is increased. In addition, not only the tolerance but also the length of the chain between the regulating member and the sleeve itself can be expanded, which is 70 to 100μ compared to the case of only non-magnetic blades.
The degree can be expanded. Also, when comparing the toner deposited on the carrier particles or the developing sleeve 122,
The amount of charge on the toner deposited on the developer sleeve 122 is smaller than that on the carrier particles. The reason for this is that the carrier particles are also transported along with the six movements of the developing sleeve 122, so there is less chance that the toner on the developing sleeve 122 will be rubbed by the carrier particles. In order to lift the toner on the developing sleeve 122 to a predetermined value, it is necessary to actively rub the toner on the developing sleeve 122. That is, it is necessary to have carrier particles near the surface of the developing sleeve that cause a shift in relative velocity against the movement of the developing sleeve.

However, it is impossible to simply reduce the transportability of carrier particles, considering the aforementioned toner uptake effect. In addition, as described above, a magnetic material may be disposed in the regulating portion facing the magnetic pole 123a in the sleeve to generate a concentrated magnetic field and improve the sliding force of the carrier particles on the developing sleeve. The effect of arranging the maximum magnetic force generating portion of the magnetic pole in the space created by the circulation regulating member 26 is reduced.

Therefore, in this embodiment, the magnetic body 150 is provided downstream of the magnetic pole 123a in the rotational direction of the developing sleeve, so that the lines of magnetic force on the blade side of the magnetic pole 123a are concentrated approximately in the tangential direction of the surface of the developing sleeve. As a result, the carrier particles only near the surface of the developing sleeve form a magnetic brush along the surface of the developing sleeve and rub the toner on the developing sleeve, thereby increasing the triboelectricity of the toner on the developing sleeve.

Such a configuration, in combination with the effect of applying superimposed alternating electric fields in the method of the present invention, contributes to the formation of even better images.

The magnetic flux density of the magnetic pole 123a is preferably 600 G or more, preferably 700 G or more.
This is because the higher the magnetic flux density of the magnetic pole, the more stable it tends to be. In particular, in a developing device that does not have an automatic toner replenishment device to maintain toner content, it is preferable that the magnetic flux density be 800 G or more.

In Figure 3, the 1ift pole 123c is a developing magnetic pole, which is located in the developing area and has a magnetic flux density of 800 G or more to prevent magnetic particles from adhering to the latent image. is often preferable.

Example 3 Using a developing device shown in FIG. 5, which has roughly the same configuration as that in FIG. The developer contains (non-magnetic) toner particles with an average particle size of 8 μm and (magnetic) toner particles. A mixture of carrier was used, and the concentration ratio of toner particles was set to 30 wt%. In addition,
The content of magnetic powder in the carrier particles was 70 wt%, and particles with an average particle size of 50 μm were used. Furthermore, the magnetic poles are arranged so that the magnetic poles face the drum as shown in Figure 5, and the magnetic field strength of the magnetic poles N and S is such that the vertical magnetic field component is 700.
It was set to be Gaussian. Further, the strength of the horizontal magnetic field between the magnetic poles at this time was 610 Gauss.

Under this condition, the latent image potential of the image area is 1800V.

When the non-image area potential was OV, positively charged particles were used as the non-magnetic toner, and a pulse bias having the waveform shown in FIG. 6 was applied as the developing bias voltage, and a good image was obtained. Note that in this example, the pulse width and value were set as in Example 1.
, 2 is set larger than the case of contact development shown in 2.

This is to increase the development efficiency since this example uses non-contact development.

On each side explained above, the pulse width of the superimposed electric field to weaken the superimposed electric field in the middle of each period of dislocation and reverse transposition is also an important factor in design, but the method of the present invention One of the features is that a development state close to cloud development is created by alternating electric fields, and the period T, = Σt, of one cycle of the above elements or alternating electric fields.

Direct ml may be determined by design within a necessary range. Generally, one cycle is in the range of 500 μsec to 3 m5ec, and in the pulse voltage application method, it is preferable that the superimposed electric field that weakens the electric field be one or more pulses in each period of transposition and reversal, but any number of pulses may be used. . It goes without saying that all the potential values within one cycle may be different, and a construction method waveform or the like may be used.

FIGS. 7 and 8 show examples of usable modified waveforms.

It goes without saying that the present invention includes any combination of the above-mentioned configurations.

Further, the present invention can be applied not only to a toner in which the toner transferred to the photoconductor is reversely transferred onto the sleeve, but also to a device in which the toner is separated from the photoconductor and does not reach the sleeve.

[Effects of the Invention] As explained above, the developing method of the present invention is a developing method using a two-component developer, in which an alternating electric field is applied between the developing sleeve and the photoreceptor drum to remove the photoreceptor from the developing sleeve. These toner dislocations provide for toner dislocation onto the drum and toner reverse translocation in the opposite direction;
A superimposed electric field is applied to weaken the electric field during a part of the period of the reversal value, and this results in a favorable reciprocating movement of the toner, resulting in no fogging or carrier adhesion, and excellent gradation. This has the effect that an image can be obtained.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of Example 1 showing an outline of the developing device used to carry out the method of the present invention, FIG. 2 is an explanatory diagram of Example 1, FIG. Waveform explanatory diagrams. Figures 3 and 5 are explanatory diagrams showing the outline of the developing device used in the implementation of Example 2.3. Figures 7 and 8 rItJ are other examples of alternating electric fields used in the method of the present invention. Figure 9 showing
The diagram shows D-D with the conventional bias and the bias of the first embodiment.
The diagrams showing the curves, FIG. 10 and FIG. 11 are diagrams showing the bias of the conventional method and the first embodiment, respectively. It is. 1... Photosensitive drum, 22... Developing sleeve, 23
...Magnet, 27-...Carrier particle, 37.
...Toner particles, 36...Developer container. Fig. 1 s Exploration Fig. 3 -rs -TS s Fig. 9 Large signal 11 degrees -by) ■/10 Fig. 10 Fig. 11

Claims (1)

[Scope of Claims] 1. A developer carrier carrying and transporting a two-component developer consisting of toner particles and carrier particles as a developing agent on its surface and an electrostatic latent image carrier are separated by a minute gap. The magnetic brush of the developer is formed on the developer carrier in this gap, and the developer carrier is placed between the developer carrier and the electrostatic latent image carrier. A period in which an electric field is applied in a direction in which toner particles are transferred from the electrostatic latent image bearing member to the electrostatic latent image bearing member, and a period in which an electric field is applied in a direction in which the toner particles are separated from the electrostatic latent image bearing member in the opposite direction to the transfer are alternately applied. In a developing method in which development is performed while repeatedly applying an electric field, a part of the period during which the electric field is applied in the direction to transfer the toner particles, and a period during which the electric field is applied in the direction to separate the toner particles from the electrostatic image bearing member. A developing method characterized by superimposing an electric field that weakens the electric field in at least one period on a part of the electric field.