JP2510247B2 - Development method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for developing an electrostatic latent image formed by an electrophotographic method, an electrostatic recording method, or the like, and more specifically, a developer carrier and a static latent image. The present invention relates to a developing method in which an alternating electric field is applied between electrostatic latent image carriers to perform development using a two-component developer, and particularly to a developing method suitable for a recording image display device, a copying machine, a printer, a facsimile, and the like.

(Prior Art) Conventionally, a dry developer consisting of toner particles as a developer and a magnetic carrier is carried on the surface of a developer carrying member and conveyed, and the developer is carried by an electrostatic latent image carrying electrostatic latent image. A magnetic brush of this developer is formed on the developing carrier by being fed near the surface of the latent image carrier and the electrostatic brush is applied while applying an alternating electric field between the electrostatic latent image carrier and the developer carrier. A developing method for developing an electrostatic latent image by visual development is known. This developing method is often called a magnetic brush developing method.

Since the developer bearing member is generally used as a developing sleeve of a developing device, the developing sleeve is generically referred to in the following description, and the electrostatic latent image bearing member is often used as a photosensitive drum. Therefore, in the following description, the term "photosensitive drum" is also used.

Conventionally, as a developing method, a magnetic brush is formed on the surface of a developing sleeve having a magnet inside by a developer composed of a two-component composition (carrier particles and toner particles), and a small developing gap is maintained to face each other. The magnetic brush is rubbed or brought close to the photoconductor drum, and an alternating electric field is continuously applied between the developing sleeve and the photoconductor drum to displace the toner particles from the developing sleeve side to the photoconductor drum side. A so-called magnetic brush development is known in which development is performed by repeatedly performing reverse rotation in the opposite direction (Japanese Patent Laid-Open No. 55-32).
No. 060, No. 59-165082, etc.), and a non-contact type alternating electric field development method using a two-component developer for the purpose of simple color development and multiple development is also known (JP-A-56-14268). ,
58-68051, 56-144452, 59-181362, 6
0-176069).

(Problems to be Solved by the Invention) In the conventional magnetic brush developing method of applying an alternating electric field, the action of the electric field of the electrostatic latent image formed on the photosensitive drum and the alternating electric field to be applied is used. There is a problem that it is difficult to increase the sharpness at the image edge portion of the obtained visible image because the development method is to increase the development density and remove the fog.

Several methods are conceivable as a method for solving such a problem. For example, a method of increasing the frequency of an alternating electric field applied between the photosensitive drum and the developing sleeve to increase the density and remove the fog may be adopted. It is conceivable that in such a method, the image itself becomes a high contrast image, and the adhesion of toner is reduced not only in the non-image portion but also in the image portion (so-called highlight portion) close to the potential of the non-image portion,
Another problem is that the reproducibility is likely to deteriorate.

This is explained as a characteristic of the image density with respect to the electrostatic latent image. Generally, the gradation of the image can be judged by the gradient γ of the curve showing this characteristic, but in the development of the method in which the frequency of the alternating electric field is increased, the gradation γ stands extremely and the image lacks the gradation. easy. This is because the toner particles attached to the carrier particles and the toner particles on the developing sleeve are
When the frequency of the alternating electric field increases, it becomes impossible to sufficiently follow the movement of the electric field, and there is a marked tendency to show a binary development phenomenon with respect to a latent image whether or not to fly on the photosensitive drum, with a certain threshold as a boundary. It is thought to be because.

On the other hand, contrary to the above, when the frequency of the alternating electric field is lowered to reduce the gradient γ (for example, about several hundred Hz), the toner particles reciprocate between the photosensitive drum and the developing sleeve to perform development. Thus, an image with good gradation can be obtained, but on the other hand, problems such as deterioration of fog and adhesion of the carrier to the photosensitive drum also occur.
This is because lowering the frequency improves the trackability of the electric field of the toner particles and carrier particles, but the toner particles and carrier particles flying toward the non-image area on the photosensitive drum are It is trapped on the photoconductor drum due to the extension of the application time of the electric field to be displaced to the drum side (since the frequency is low), and even if the electric field for inversion due to the alternating electric field acts, it is completely removed. It is thought that it becomes difficult.

As described above, in the conventional method of developing using a two-component developer by an alternating electric field, the resulting visible image should have less fog and carrier adhesion and be excellent in gradation. There was a problem that it was difficult to satisfy both at the same time.

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 the above-mentioned two-component developer, and it is rich in gradation and less in background fog It is an object of the present invention to provide a developing method capable of forming an image with excellent resolution and resolution with little change in density in a halftone.

Still another object of the present invention is to provide a developing method capable of reducing the transfer of extra toner, reducing the burden of further transferring a visible image onto a transfer paper, and obtaining a high density with less consumption. It is in the place of providing.

(Means for Solving the Problems) The present invention has been made in order to achieve the above object, and a characteristic of the developing method of the present invention is that a two-component developer having toner particles and carrier particles is carried and conveyed. In a developing method of developing by forming an alternating electric field between a developer carrier having a developing magnetic pole for forming a magnetic brush in the developing section and an electrostatic image carrier carrying an electrostatic agent, The electric field in the direction of moving the carrier particles toward the electrostatic image bearing member is weakened during a part of the period in which the electric field is applied.

The method of the present invention weakens the electric field in the period in which the electric field is applied in the direction in which the toner is transferred from the developing sleeve to the photosensitive drum as described above. Specifically, for example, an electric field for weakening the electric field is applied. It can be realized by overlapping.

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

In the configuration of the present invention, the alternating electric field between the photosensitive drum and the developing sleeve is a system by applying an AC voltage for both the basic alternating electric field and the overlapping electric field.
In addition to the method of applying a rectangular wave pulse voltage, a triangular wave, a sawtooth wave, or an asymmetry may be used, and the method is not particularly limited.

Further, in the above structure, a period in which an electric field is applied in a direction in which toner is transferred from the developing sleeve to the photoconductor drum (a period in which the electric field is mainly applied in a direction in which the image portion of the photoconductor drum is developed, and In order to superimpose an electric field that weakens the electric field in a part of (the toner slightly transfers to the non-image part in relation to the image part potential), for example, a pulse synthesizer is used, and 300 Hz as one basic alternating electric field is used.
This can be done by using an electric field of ~ 2kHz and superimposing another short pulse on the electric field that is out of phase during the transition period.

In addition to the above configuration, during the period in which an electric field is applied in a direction in which toner is reversely transferred from the photosensitive drum to the developing sleeve (mainly in a direction in which toner on the non-image portion of the photosensitive drum is peeled (reverse transfer)). It is a period for applying an electric field, and the electric field for weakening the electric field is superposed on a part of (the toner of the image section is slightly reverse-transferred in relation to the image section potential of the photosensitive drum), for example, in the same manner as described above. For example, by superimposing another short pulse having an opposite phase in the transition period on one basic alternating electric field, an electric field having no strength for transferring the toner to the non-image portion is formed (that is, , The voltage applied to the sleeve is a DC component having a value between the image part and the non-image part potential of the photoconductor and a value closer to the non-image part potential than the center between them). be able to.

When the electric field is weakened in a part of the period for adjusting the electric field to be weakened, that is, a part of the period in which the toner is transferred from the developing sleeve to the photosensitive drum, at any of the beginning, the middle, and the end, or a plurality of these, It may be provided. The same applies to the case where the above-described adjustment period is provided when the toner is reversely transferred from the photosensitive drum to the developing sleeve in addition to the above configuration. To weaken the electric field generally means between the image part potential and the non-image part potential of the photoconductor drum, and especially to the potential of the direct current component (the intermediate potential of the upper and lower peaks of the alternating electric field) which is applied together with the alternating electric field. The case where the applied voltage is shifted can be exemplified, but the invention is not particularly limited thereto. For example, in an ordinary analog copying machine using electrophotography, it is often preferable to shift the potential to or near the above potential, but in a digital copying machine (for example, a laser beam printer) used as a printer for computer equipment or the like. In order to weaken the electric field during the transfer of the toner, it is often preferable to shift to the image potential or its vicinity because the potential of the image portion is formed as a substantially constant potential.

The two-component developer used in the method of the present invention is, for example, carrier particles, which are magnetic particles obtained by coating the surface of magnetic particles such as ferrite with resin, and non-magnetic particles obtained by binding a charge control agent, an external additive and the like with a resin. The combination of the toner particles can be exemplified, but the invention is not particularly limited thereto, and any two-component developer used in the so-called magnetic brush developing method can be used.

In the developing method to which the method of the present invention is applied, typically, a two-component developer is conveyed on the surface of a rotary sleeve having a fixed magnet for generating a magnetic field inside the developing sleeve, and the developing sleeve is a latent image carrier. A magnetic brush (spike) of the developer is formed on the developing sleeve by the internal magnetic pole at the surface portion facing the photosensitive drum with a small gap, and the magnetic brush is brought into contact with the surface of the photosensitive drum. This is a method of adhering toner particles to a photosensitive drum by moving them while rubbing or bringing them close to each other. However, the method is not particularly limited to this and two-component development of toner particles and carrier particles is performed. A method of performing contact or non-contact development using an agent, which is capable of effective development by applying an alternating electric field, is not limited to a magnetic brush development method. Nor shall.

In addition, applying a superimposed electric field to weaken the electric field
Even if the basic electric field is set low and an electric field that partially strengthens the electric field is superposed, it is substantially the same. Therefore, in the present invention, "superimposing an electric field that weakens the electric field" includes both cases described above. I shall.

(Operation) The developing method of the present invention has the above-mentioned structure.
By weakening the electric field in a part of the period in which the electric field is applied in the direction in which the toner is transferred from the developing sleeve to the photosensitive drum, the excessive supply of toner to the image area is adjusted, and the toner adheres to the non-image area. The tendency can be weakened.

(Examples) The present invention will be described below based on specific examples.

Embodiment 1 FIG. 1 is a sectional view of a developing device according to an embodiment of the present invention. In the figure, reference numeral 1 is an electrostatic recording insulating drum or a photosensitive drum (or photosensitive belt) having a photoconductive insulating material layer such as α-Se, Cds, ZnO, OPC, α-Si. The photosensitive drum 1 is rotated in the direction of arrow a by a driving device (not shown). Reference numeral 22 is a developing sleeve which is located close to the photosensitive drum 1, and is made of a non-magnetic material such as aluminum or SUS316. This developing sleeve 22 is
At the position of the lower left wall of the developing container 36 in the drawing, a substantially semi-peripheral surface of the right side is formed from the horizontally long opening formed in the container longitudinal direction (depth direction in the drawing).
It is inserted inward, the left substantially semi-peripheral surface is exposed to the outside of the container, and is rotatably borne so as to be rotatably provided laterally and is rotationally driven in the direction of arrow b.

Reference numeral 23 denotes a fixed permanent magnet (magnet) as a fixed magnetic field generating means which is positioned and installed in the developing sleeve 22 in the position and orientation shown in the drawing. Even when the developing sleeve 22 is rotationally driven, this magnet 23 is not shown. It is fixed and held as it is in the position and orientation. This magnet 23 of the present example is an N pole magnetic pole 23a, S
It has three magnetic poles, a magnetic pole 23b having a pole and a magnetic pole 23c having an N pole. The magnet 23 may be replaced with a permanent magnet and an electromagnet may be provided. In this example, the maximum value of the vertical component of the surface magnetic flux density of the magnet 23 was set to about 700 gauss for the 23a and 23c poles and 850 gauss for the 23b pole.

Reference numeral 24 denotes a non-magnetic blade, the base portion of which is fixed to the side wall of the container on the lower edge side of the developer supply device in which the developing sleeve 22 is arranged, and the tip side of the blade protrudes to the outside of the container 36 from the lower edge position of the opening. Thus, a developer regulating member is arranged along the lower edge of the opening. This non-magnetic blade 24, for example
The SuS316 is bent into a V-shape when viewed from the cross section.

27 is a carrier particle which is one component of a two-component developer, and generally has a particle size of 20 to 100 μm, preferably 30 to 8 μm.
In many cases, resin particles coated with ferrite particles (maximum magnetization of 30 to 100 emu / g) having a resistance value of 0 μm and a resistance value of 10 ⁷ Ωcm or more, preferably 10 ⁸ Ωcm or more are used. I used the one.

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

62 is a toner concentration detection sensor, and this sensor 62
Rotation of the 63 toner auxiliary rollers (arrow c
The toner can be supplied by repeating (rotating in the direction) and stopping.

Reference numeral 66 denotes a stirring member which rotates in the direction of arrow d, and mixes and stirs the developer and the replenishment toner separated from the sleeve 22 by the scraper 67.

 38 is a toner storage container.

In the above configuration, the developer regulated by the non-magnetic blade 24 is further regulated by the auxiliary regulation plate (not shown) and conveyed to the developing area. For the developer after development, the toner concentration detection sensor 62 detects the toner concentration in the developer. When the toner concentration is low, the supply roller 63 starts rotating and supplies toner.

The blade 24 is made of non-magnetic stainless steel having a thickness of 1.5 mm and is provided on the downstream side of the pole 23a with respect to the sleeve rotation direction b.

As the carrier particles, ferrite having a particle size of 70 to 90 μ (maximum magnetization of 56 emu / g, resistance value of 10 ⁷ to 10 ⁸ Ωcm) coated with a mixed resin of acrylic and fluorine was used.

As the non-magnetic toner, a toner powder having an average particle diameter of 13 μ, which mainly comprises 7 parts of polypropylene and 4 parts of carbon black in 90 parts of styrene resin was used.

Furthermore, the gap between the photosensitive drum 1 and the sleeve 22 is about 1 mm,
The developing device was configured so that the distance between the sleeve 22 and the blade 24 was 0.8 mm.

Using the above developing device, as a developing condition, the latent image potential of the photosensitive drum is set to an image portion −650 V and a non-image portion −150 V,
Development was performed by superposing the pulse waveform shown in FIG. 2 (that is, a pulse waveform obtained by superposing an electric field weakening electric field on a part of the basic electric field) shown in FIG. 2 on a DC voltage of -200 V as a developing bias. Here, good images were obtained when the lengths of t ₁ to t ₈ were set to be the same and were set in the range of 60 μsec to 250 μsec. In other words, one cycle time A good image was obtained in the range of 500 μsec to 3 msec. In the configuration of this example, if the T _{S of} one cycle is shorter than 500 μsec, the image tends to have a high contrast and γ tends to rise, similar to the application of the simple alternating electric field of the conventional example described above. Conversely, T _S
When the time is 3 msec or more, the toner and carrier can sufficiently follow the change of the pulse, and as a result of the toner and carrier that fly to the photoconductor drum and do not return, fog and carrier adhesion tend to occur. .

Here, the difference between the case of simply applying a pulse of an alternating electric field that reciprocates and the case of the developing method of the present invention in which a weakening electric field is superposed on this pulse will be promoted and explained in this example.

The voltage of multiple pulse waveforms that give an alternating electric field is 60 μsec.
When applied in a short cycle of up to 250 μsec, a high frequency electric field is added to the degree of development. Here, since the carrier and the toner are charged with opposite polarities, the carrier and the toner repeatedly vibrate in the opposite directions at the above high frequency to give electric charges to each other. Here, the carrier is constrained by the magnetic force of the magnet on the side of the developing sleeve, and has a volume and specific gravity considerably larger than that of the toner, so that the toner particles are covered in a cloud shape around the carrier.

On the other hand, when the frequency is raised to the above range by the conventional development in which a simple alternating electric field is applied, the toner tends to fly binaryly at a certain threshold or does not move, and as a result, γ The resulting image is stiff and tough. On the other hand, in the present embodiment, as described above, the electric field is weakened from the developer carrying member side to the latent image carrying member for a part of the period of toner transfer to the latent image carrying member and a part of the inversion period. Cloud occurs between the developing sleeve and the photoconductor drum, and the state close to soft touch cloud developing is repeated. In addition, as described above, the toner increases the number of times of friction between the toner and the carrier due to the high frequency pulse and is firmly charged by the carrier, so that the fog does not occur. In addition, since a signal that flies with a short pulse is given, the carrier receives a flying force for a shorter time than when a pulse is applied at a low frequency, and the tendency to extremely shift to the drum side is suppressed. It is also possible to obtain the effect of eliminating the adherence of.

As described above, this embodiment has gradation
A high-quality image free from fogging of the carrier can be obtained. As an example, FIG. 9 shows a conventional bias (see
(FIG. 10) and the DD curve in the bias (FIG. 11) of the present embodiment, the above-described effects of the present embodiment have made it possible to obtain an image with a gradation of γ. I understand.

Second Embodiment FIG. 3 is a sectional view of a developing device according to another embodiment of the present invention. The apparatus shown in FIG. 3 is different from the apparatus shown in Embodiment 1 shown in FIG. 1 in that the magnetic particles and the toner particles are mixed and agitated on the developing sleeve.

Hereinafter, a case where the present invention is applied to this device will be described.
101 in this figure is an electrostatic recording insulating drum or α
A photosensitive drum (or photosensitive belt) having a photoconductive insulating material layer such as —Se, Cds, ZnO, OPC, α-Si. The photosensitive drum 101 is rotated in the direction of arrow a by a driving device (not shown). Reference numeral 122 denotes a developing sleeve which is located close to the photosensitive drum 101 and is made of a non-magnetic material such as aluminum or SUS316. This developing sleeve 122
Is a right half-peripheral surface projected into the container 136 through a horizontally long opening formed in the longitudinal direction (depth direction of the drawing) at the position of the lower left wall of the developing container 136, and the left substantially semi-peripheral surface is exposed outside the container. It is rotatably supported and rotatably provided laterally, and is rotationally driven in the direction of arrow b.

Reference numeral 123 denotes a fixed permanent magnet (magnet) as a fixed magnetic field generating means which is positioned and installed in the developing sleeve 122 in the position and orientation shown in the drawing. Even if the developing sleeve 122 is driven to rotate, the magnet 123 is not shown. It is fixed and held as it is in the position and orientation. This magnet 123 of this example has a magnetic pole of N pole 1
23a, S pole magnetic pole 123b, N pole magnetic pole 123c, S pole magnetic pole 123
It has 4 magnetic poles of d. The magnet 123 may be an electromagnet instead of the permanent magnet.

Reference numeral 124 denotes a non-magnetic blade, which is the developing sleeve 122.
The base portion is fixed to the side wall of the container on the upper edge side of the developer supply device provided with, and the tip end side is protruded to the outside of the container 136 from the upper edge position of the opening and arranged along the length of the upper edge of the opening. It constitutes a developer regulating member. This non-magnetic blade 124 is
For example, SuS316 is bent into a "V" shape when viewed from the cross section.

Reference numeral 126 is 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 the developer guide surface 126a.

127 is a carrier particle which constitutes one component of a two-component developer, and in this example, the particle size is 30 to 100 μm, preferably 40 to 70 μm and the resistance value is 10 ⁷ Ωcm or more, preferably 10 ⁸ Ω.
Resin-coated ferrite particles having a size of cm or more (maximum magnetization of 60 emu / g) can be preferably used.

Reference numeral 137 denotes a non-magnetic developer toner which is another component of the two-component developer.

131 is a developing sleeve on the inner surface of the lower part of the developing container in order to prevent leakage of carrier particles 127 or non-magnetic toner particles 137 from the lower part of the developing container 136 in which the developing sleeve 122 is arranged.
The magnetic substance is disposed so as to face 122, and is formed of, for example, an iron plate plated. This makes the magnetic material 13
A magnetic field between the 1 and S poles 123d provides a sealing effect to achieve recovery and leakage prevention of carrier particles 127.

139 is a toner supply member for supplying toner to the brush portion of the carrier particles formed by the fixed magnetic pole 123 in the developing sleeve 122, and a rubber sheet is attached to a sheet metal rotatably bearing to sweep the lower surface of the developing container. To transport. Toner is supplied to the toner supply member 139 by a toner conveying member (not shown) in the toner storage container 138.

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

Reference numeral 140 denotes a seal member that seals toner accumulated in the lower portion of the developing container 136, has elasticity and is bent in the rotation direction of the developing sleeve 122, and elastically presses the surface of the developing sleeve 122. . The sealing member 140 has an end portion on the downstream side in the rotation direction of the developing sleeve in the contact area with the developing sleeve so as to allow the developer to enter the inside of the container.

Reference numeral 130 denotes a scattering prevention electrode plate that applies a voltage having the same polarity as that of the developer to the floating developer generated in the developing process to adhere to the photosensitive drum side to prevent scattering.

The S magnetic pole 123d is a magnetic field for magnetic sealing for forming a magnetic field from one side to the other with the magnetic member 131, and a part thereof faces the magnetic member 131. Magnetic member 1
31 is a substantial end of the developer container of the developer container,
It is located below the developing device, and around this area, the toner particles located below the container are taken into the developer on the surface of the developing sleeve along with the movement of the collected (magnetic) carrier particles. Therefore, the stable recovery of carrier particles brings about the effect of stabilizing the developing ability, and the effectiveness of the method of the present invention can be expected also in this respect.

As the magnetic member 131, it is possible to apply a member having a “U” shape or an “L” shape and having a weak magnetism by deforming a magnetic material or a non-magnetic material that is not permanently magnetized such as iron. .

That is, since the magnetic member 131 restrains the carrier particles and prevents the loss of the carrier particles and facilitates the recovery of the carrier particles, the toner particles in the developer container can be prevented from leaking from the container.

In the above structure, by arranging the magnetic pole 123d as described above, a particularly preferable effect is obtained in relation to the magnetic pole 123a. That is, the bottom of the container 136 and the magnetic pole 123d.
Due to the above relationship with, the magnetic brush is not formed in a rough state (compared to a stagnant state) in 121, so that the amount of toner particles taken into the carrier particles does not become excessive. Is obtained. Excessive incorporation causes insufficient charging of the toner and causes fogging.

This structure is also effective when carrier particles and non-magnetic or weakly magnetic toner are mixed in the developer container.

Experiments show that carrier particles are completely collected at a distance of 2.5 mm between the developing sleeve 122 and the magnetic member 131, leakage of toner particles is not seen at all, and stable development can be achieved.

The distance d ₂ 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 less than 50 μm, carrier particles are clogged between them and the developer layer is liable to be uneven, and the developer necessary for good development cannot be applied, and only a developed image with a thin density and a lot of unevenness is obtained. There are drawbacks that cannot be avoided.
On the other hand, if it is larger than 800 μm, the amount of developer applied onto the developing sleeve 122 increases, and the predetermined developer layer thickness cannot be regulated.
There is a drawback that carrier particles adhere to the photoconductor drum more often, the developer circulates, the development regulation becomes weaker than that of the developer limiting member 126, the toner tribo becomes insufficient, and fogging easily occurs.

The fixedly arranged magnetic pole 123a rearranges the packed carrier particles along the magnetic field lines. The packing state in the space is unstable with respect to tribo application, and a constant packing state is always required for stabilization. This forms the magnetic brush with the carrier particles conveyed on the developing sleeve 122 in the substantially connecting direction by the force orthogonal to the direction, so that not only the stirring effect on the carrier particles but also the loosening effect works, and Further, tribo-imparting to the carrier and uniformization / stabilization of coating of the carrier particle layer are further promoted. At this time, if the concentrated developer due to the peripheral configuration is still under a great pressure, there is a problem that the developer gets too clogged, but the portion of the magnetic pole 123a that generates the maximum magnetic force faces the guide surface 126a. Therefore, it is considered that excessive pressure concentration in the regulated region can be prevented, and the concentration of the developer and the stable existence ratio of the magnetic particles with high density can be maintained.

Due to the above restriction region, a stable amount of carrier particles and sufficiently charged toner particles can be formed as a thin developer layer on the surface of the developing sleeve. Therefore, the developing effect in the developing area becomes stable. In order to transfer at least the toner particles carried on the surface of the developing sleeve 122 among the developers conveyed to the developing section to the photosensitive drum 101, the alternating electric field shown in FIG. 4 is applied to the developing section. As a result, good development can be performed. In the configuration of this example, the latent image conditions were the same as in Example 1, and the same pulse bias as in Example was applied as the alternating electric field except that the waveform shown in FIG. Was given.

Although the configuration of FIG. 3 is shown as a case where the magnetic body 150 is installed on the non-magnetic blade 124 side of the developer limiting member 126, in this case, it is preferable to provide the magnetic body 150 at a position facing the magnetic pole 123a. Absent. Because if they are facing each other,
A strong concentrated magnetic field is generated between the magnetic pole 123a and the magnetic pole 123a.
This reduces the stirring and loosening effect of the carrier particles. However, magnetic regulation of the carrier particles with the developing sleeve internal magnet 123 by providing a magnetic body in the regulation portion increases the gap tolerance between the regulation member and the sleeve,
It is effective. Further, not only the tolerance, but also the gap length of the restricting member and the sleeve itself can be expanded, and it can be expanded by about 70 to 100 μm as compared with the case of only the non-magnetic blade.
Further, when comparing the toner particles attached to the carrier particles or the developing sleeve 122, the amount of charge of the toner particles attached to the developing sleeve 122 is smaller than that of the toner particles attached to the carrier particles. The reason for this is that as the developing sleeve 122 moves,
This is because the carrier particles are also conveyed, so that the toner on the developing sleeve 122 is less likely to be rubbed by the carrier particles. To raise the toner on the developing sleeve 122 to a predetermined value, the developing sleeve
It is necessary to positively rub the toner on 122. That is, it is necessary to have carrier particles in the vicinity of the surface of the developing sleeve, which cause a relative velocity deviation against the movement of the developing sleeve.

However, simply lowering the transportability of carrier particles is impossible in view of the above-mentioned toner intake action. Further, as described above, a magnetic member is arranged in the restricting portion so as to face the in-sleeve magnetic pole 123a, and a concentrated magnetic field is generated to improve the rubbing force of carrier particles on the developing sleeve. The effect of arranging the maximum magnetic force generating portion of the magnetic pole in the space formed by the circulation restricting member 26 is reduced.

Therefore, in this embodiment, the magnetic body 150 is provided on the downstream side of the magnetic pole 123a in the rotating direction of the developing sleeve.
The magnetic lines of force on the blade side of a are concentrated almost in the tangential direction of the developing sleeve surface. 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 the toner on the developing sleeve is rubbed with the toner particles, whereby tribo-imparting of the toner on the developing sleeve can be enhanced.

Such a structure contributes to the formation of a more excellent image in combination with the effect of the application of the alternating electric field with which the method of the present invention is superimposed.

The magnetic flux density of the magnetic pole 123a is 600 G or more, preferably 700 G
The above is preferable. This is because the application state of the developer tends to be more stable with respect to the change in the toner content of the magnetic particle layer as the magnetic flux density of the cut magnetic pole increases. In particular, in a developing device that does not have an automatic toner replenishing device for maintaining toner content, it is preferable that the magnetic flux density is 800 G or more.

In FIG. 3, the magnetic pole 123c is a developing magnetic pole, but this developing magnetic pole is located almost at the developing portion and preferably has a magnetic flux density of 800 G or more in order to prevent magnetic particles from adhering to the latent image. In many cases.

Third Embodiment A developing device having a configuration similar to that of FIG. 1 shown in FIG. 5 is used, and the distance between the photosensitive drum 201 and the developing sleeve 222 is 50.
The thickness of the developer layer was set to 0 μm, and the thickness of the developer layer was regulated by the nonmagnetic blade 224 so as to be 400 μm at the position closest to the photosensitive drum 201 (in this example, non-contact development is performed). As the developer, a mixture of (non-magnetic) toner particles having an average particle diameter of 8 μm and (magnetic) carrier was used, and the concentration ratio of the toner particles was set to 30 wt%. The content of the magnetic powder in the carrier particles was 70 wt%, and particles having an average particle size of 50 μm were used. Further, the magnetic poles were arranged such that the magnetic poles faced the drum as shown in FIG. 5, and the magnetic field strengths of the magnetic poles N ₁ and S ₁ were set so that the vertical magnetic field component was 700 gauss. The strength of the horizontal magnetic field between the magnetic poles at this time was 610 gauss.

Under these conditions, when the latent image potential of the image area is -600 V and the non-image area potential is 0 V, positively charged particles are used as the non-magnetic toner, and the pulse of the waveform shown in FIG. 6 is used as the developing bias voltage. A good image was obtained when a bias was applied.
In this embodiment, the pulse width and value are set to be larger than those in the contact development shown in the first and second embodiments. This is because the developing efficiency is increased in response to the non-contact development in this example.

In each of the examples described above, the pulse width of the superimposed electric field for weakening the electric field superimposed in the middle of each period of dislocation and reverse transition is also one of the important factors in terms of design, but the method of the present invention One of the features is that a developing state close to cloud development is created by an alternating electric field, and the cycle of one cycle of the above elements or the alternating electric field. Can be determined by design within the necessary range. Generally, one cycle is set in the range of 500 μsec to 3 msec, and in the pulse voltage application method, the superimposed electric field that weakens the electric field may be set to 1 pulse or more in each period of dislocation and inversion, but any number of pulses may be used. The potential values may all be different in the range of one cycle. Of course, it does not matter, and a normal waveform or the like may be used.

FIG. 7 and FIG. 8 show examples of usable waveforms of the modification.

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

Further, the present invention can be applied not only to the case where the toner transferred to the photoreceptor is reversely transferred onto the sleeve, but also to the case where the toner is separated from the photoreceptor and does not reach the sleeve.

As described above, in the developing method of the present invention, in the developing method using the two-component developer, an alternating electric field is applied between the developing sleeve and the photoconductor drum to remove the photoconductor from the developing sleeve. When the toner dislocation to the drum can be given, the electric field is weakened during a part of the dislocation of the toner, whereby the preferable reciprocating behavior of the toner appears, and as a result, fog or carrier adhesion is prevented. Without
Moreover, there is an effect that an image excellent in gradation is obtained.

[Brief description of drawings]

FIG. 1 is an explanatory view of Embodiment 1 showing an outline of a developing device used for carrying out the method of the present invention, FIG. 2 is FIG. 4 and FIG. 6 is a pulse voltage of each Embodiment 1, 2, 3 Waveform explanatory diagrams, FIGS. 3 and 5 are explanatory diagrams showing an outline of the developing device used for carrying out Examples 2 and 3, and FIGS. 7 and 8 are other examples of the alternating electric field used in the method of the present invention. FIG. 9 is a diagram showing an example, FIG. 9 is a diagram showing a DD curve with a conventional bias and a bias of the first embodiment, and FIGS. 10 and 11 are conventional and first, respectively.
It is a figure which shows the bias of an Example. Is. 1 ... Photosensitive drum, 22 ... Development sleeve, 23 ... Magnet, 27 ... Carrier particles, 37 ... Toner particles, 36 ... Development container.

Front page continuation (72) Inventor Takahiro Kubo 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (56) Reference JP-A-60-134262 (JP, A) JP-A-55-53371 ( JP, A)

Claims (1)

(57) [Claims] 1. A toner comprising toner particles and carrier particles.
An alternating electric field is formed between a developer carrier having a developing magnetic pole for carrying and carrying the component developer and forming a magnetic brush in the developing section, and an electrostatic image carrier carrying an electrostatic image. In the developing method of developing, the electric field in the direction in which the carrier particles are directed toward the electrostatic image bearing member is weakened during a part of the period in which the electric field is applied.