JP2505800B2 - Development device - Google Patents

Description

TECHNICAL FIELD The present invention relates to a two-component developing type developing device that performs development using magnetic carrier particles and toner particles.

The present invention is a developing device applicable to various types of display devices for image recording, printers, and facsimile electrophotographic devices.

(Background Art) The applicant of the present application has previously provided an apparatus that performs development by supplying only one-component toner to the developing section with two components in the developing container, unlike the conventional two-component developing method.

This is because magnetic particles are first charged into the developer supply container, and the toner is adsorbed and held as a magnetic particle layer (first layer) on the inner surface of the developer supply container of the developing sleeve that is rotationally driven, and then the toner is retained. It was put in and stored outside the above-mentioned magnetic particle layer (second layer) to carry out development (JP-A-59-59).
No. 204866, JP-A-59-204867).

These hold magnetic particles in the developing container and circulate a part of the bound magnetic particles as the developing sleeve rotates. By this circulation, replenishment toner is taken into the magnetic particles and a thin layer of toner is placed on the sleeve. It was to form a layer. This also discloses the basic constitution of mixing and stirring magnetic particles and toner on the sleeve, which is extremely important, and the effect was remarkably superior to an apparatus which does not adopt this basic constitution. Especially in terms of simplifying and downsizing the device, it was unique. However, even if a uniform thin toner layer can be formed on the sleeve by this circulation action, when developing for a long period of time,
It was confirmed that when some impact is applied when the developing position is made detachable from the main body of the image recording apparatus, the circulation action becomes unstable and image deterioration occurs. However, such an inconvenience was also a minor defect in view of the many unique features and advantages as described above.

The applicant has been able to solve these inconveniences through many experiments, and has developed a developing device which produces a great effect in a two-component developing device which positively supplies magnetic carrier particles to the developing section, in Japanese Patent Application No. 60-204605. (September 17, 1960 application) etc.

According to these proposals, the developer forms a substantial packing state in the developer application amount regulation section.
By stabilizing this packing state, the toner with insufficient tribo is removed, the charge on the toner is improved, and the toner tribo is made uniform. Can be transported.

As described above, the packing state of the developer in the developer coating amount regulating portion is the key to controlling the charging of the toner, and stable maintenance of this packing state maintains a good image for a long period of time. Is equivalent to that. The following are the main constituent elements for forming this packing state. That is, the magnetic field acting on the gear gap between the developer application amount regulating member (blade) and the developer carrying member (developing sleeve) (hereinafter abbreviated as SB gear gap) and the regulating portion. Specifically, the relative position of the developer coating amount regulating member and the cutting pole, such as the strength of the cutting pole, the half width, and the magnetic flux density distribution. (An angle formed by the tip of the regulating member and the peak position of the cutting pole) and the shape of the magnetic particle limiting member.
Various other factors affect the packing state, but the above-mentioned four points are dominant in the structure of the developing device. By optimizing the settings of these four points, a stable packing state can be maintained and a stable image can be obtained for a long period of time.

(Problems to be Solved by the Invention) As described above, according to these proposals, a developing device which does not have an automatic toner replenishing device for maintaining toner content, which cannot be obtained by the conventional developing method and device, is provided. It has become possible to make a disposable type small-sized one, but the main point is the stabilization of the packing state of the regulation portion, and the optimization of the above-mentioned four constituent elements. With the recent downsizing of the apparatus, downsizing of the developing apparatus and downsizing of the developing sleeve will be inevitable in the future, and it becomes difficult to maintain the above-mentioned packing state with downsizing of the developing sleeve. That is, as the diameter of the developing sleeve becomes smaller, the diameter of the magnet arranged in the developing sleeve must be made smaller, and it becomes difficult to obtain a predetermined strength of the cut pole. This results in narrowing the latitude of the magnetic field acting on the above-mentioned restriction portion. Further, as the diameter of the developing sleeve becomes smaller, the setting of the angle between the regulating blade and the cutting pole becomes more severe.

In addition, the smaller the diameter of the developing sleeve, the smaller the area where toner particles can contact the sleeve, and the smaller the diameter of the magnet, the absolute amount of magnetic particles that can be held in the developing container by the magnetic force of the magnet. Has decreased,
Since the surface area of the magnetic particles with which the toner particles can come into contact also decreases, the ability of the developing device to impart tribo to the toner particles decreases, making it more difficult to maintain a stable packing state.

(Summary of the Invention) The present invention, which solves the above-mentioned problems, is directed to a developer carrying member which faces a electrostatic image carrying member and carries a developer having magnetic particles and toner particles, and a developer on the developer carrying member. A developer in which a magnetic field is formed in a regulating member that regulates the amount and a regulating portion that is provided inside the developer carrier and that has a magnetic flux density peak position on the upstream side of the regulating portion in the moving direction of the developer carrier. In the developing device having a coating magnetic pole, the magnetic flux density distribution curve formed by the developer coating magnetic pole is characterized in that the downstream side is gentler than the upstream side in the moving direction of the developer carrying member.

(Embodiment) FIG. 2 is a sectional view of a developing device according to an embodiment of the present invention. The latent image carrier 1 is an insulating drum for electrostatic recording or α-
It is a photosensitive drum or photosensitive belt having a photoconductive insulating material layer such as Se, CdS, ZnO ₂ , OPC, α-Si. The latent image carrier 1 is rotated in the direction of arrow a by a driving device (not shown).
Reference numeral 22 denotes a developing sleeve which is in proximity to or in contact with the latent image carrier 1, and is made of a non-magnetic material such as aluminum or SUS316. The developing sleeve 22 has a laterally long opening formed in the lower left wall of the developing container 36 in a longitudinal direction of the container so that a substantially right half peripheral surface projects into the container 36, and a substantially left half peripheral surface is exposed outside the container and rotatably supported. It is installed horizontally and is driven to rotate in the direction of arrow b.

Reference numeral 23 is a fixed permanent magnet (magnet) as a fixed magnetic field generating means which is inserted into the developing sleeve 22 and is positioned and held in the position and orientation shown in the drawing. Even when the developing sleeve 22 is rotationally driven, the magnet 23 is at the position shown in the drawing. It is fixedly held as it is. The magnet 23 has four magnetic poles, an N-pole magnetic pole 23a, an S-pole magnetic pole 23b, an N-pole magnetic pole 23c, and an S-pole magnetic pole 23d. The magnet 23 may be an electromagnet instead of the permanent magnet.

Reference numeral 24 designates a base portion fixed to the side wall of the container on the upper edge side of the developer supply device in which the developing sleeve 22 is disposed, and the tip end side is projected to the outside of the container 36 more than the upper edge position of the opening and extends along the length of the upper edge of the opening. With a non-magnetic blade as a developer control member,
For example, SuS316 is bent into a cross-section road shape.

Reference numeral 26 is a magnetic particle limiting member whose upper surface is in contact with the lower surface side of the non-magnetic blade 24 and whose front end surface is the developer guide surface 261.

27 is a magnetic particle having a particle size of 30 to 100 μm, preferably 40
A resin coated ferrite particle (maximum magnetization of 60 emu / g) having a resistance of 10 ⁷ Ωcm or more, preferably 10 ⁸ Ωcm or more at ˜80 μm can be used.

 37 is a non-magnetic developer toner.

Reference numeral 31 is a magnetic material disposed on the inner surface of the lower portion of the developing container so as to face the developing sleeve 22 in order to prevent leakage of the magnetic particles 27 or the non-magnetic toner particles 37 from the lower portion of the developing container 36 in which the developing sleeve 22 is disposed. There is, for example, an iron plate to which plating is applied. A magnetic field between the magnetic body 31 and the S-polarity magnetic pole 23d provides a sealing effect of recovering the magnetic particles 27 and preventing leakage.

Reference numeral 39 denotes a toner supply member for supplying toner to the brush portion of the magnetic particles formed by the fixed magnetic poles 23 in the developing sleeve 22.A rubber sheet is attached to a rotatably bearing sheet metal, and the toner is swept down the lower surface of the developing container. Transport. The toner is supplied to the toner supply member 39 by a toner conveying member in a toner storage container 38 (not shown).

38 and 35 are a toner storage container and a magnetic particle storage container, respectively.

Reference numeral 40 denotes a seal member for sealing the toner accumulated in the lower portion of the developing container 36, which has elasticity and is bent in the rotation direction of the sleeve 22, and elastically presses the surface side of the sleeve 22.
The seal member 40 has an end portion on the downstream side in the sleeve rotation direction in the contact area with the sleeve so as to allow the developer to enter the inside of the container.

Reference numeral 30 denotes an anti-scattering electrode plate for applying a voltage of the same polarity as that of the floating developer generated in the developing step to adhere to the photoreceptor side to prevent scattering.

Further, the S magnetic pole 23d is a magnetic field for magnetic sealing for forming a magnetic field from one side to the other with the magnetic member 31, and one part faces the magnetic member 31. Magnetic member 31
Is located below the developing device at the substantial end of the developer accommodating portion of the developer container. At the periphery of the container, the movement of the collected magnetic carrier particles causes the developer on the sleeve surface to move downward into the developer. Take in the toner particles located at Therefore, stable recovery of magnetic particles has the effect of stabilizing the developing ability.

The magnetic member 31 has a V shape or an “L” shape, and a member having weak magnetism can be applied by deforming a magnetic material or a non-magnetic material such as iron which is not permanently magnetized. When a magnet is used as the magnetic member 31, the flat surface 66
Must have an N-polarity that is different from the magnetism S of the magnet S.

That is, since the magnetic member 31 prevents the loss of the magnetic particles while restraining the magnetic particles and facilitates the collection of the magnetic particles, it is possible to prevent the toner particles in the developer container from leaking from the container.

Further, by disposing the magnetic pole 23d as described above, another preferable effect can be obtained in relation to the magnetic pole 23a.
That is, due to the above-mentioned relationship between the bottom of the container 36 and the magnetic pole 23d, the magnetic brush is not formed in a coarse state (compared to a stagnant state) inside the toner particle 36, so that the toner particles in the magnetic particles are not formed. Does not become excessive.
Excessive incorporation leads to insufficient charging of the toner and causes fogging.

This configuration is also effective when magnetic particles and non-magnetic or weakly magnetic toner are mixed in the developing container.

According to the experiment, the distance between the developing sleeve and the magnetic member 31 2.
At 5 mm, the magnetic carrier particles were completely recovered, no leakage of toner particles was observed, and stable development was achieved.
The presence of the surface 66 in this region means that the magnetic force of the magnetic pole 23d is
It is considered that the magnetic field sealing effect is increased because 6 is appropriately dispersed and the magnetic force in this region can be substantially increased.

The distance d ₂ between the end of the non-magnetic blade 24 and the surface of the developing sleeve 22 is 50 to 800 μm, preferably 150 to 500 μm.
If this distance is less than 50 μm, the magnetic particles described later are clogged in the meantime, and the developer layer tends to be uneven, and the developer required for good development cannot be applied, and the density of the developed image is low and uneven. There is a disadvantage that can only be obtained.
On the other hand, if it is larger than 800 μm, the amount of the developer applied onto the developing sleeve 22 increases and the predetermined developer layer thickness cannot be regulated.
There is a drawback that magnetic particles adhere to the latent image carrier more and circulation of a developer, which will be described later, and development restriction by the developer limiting member 26 are weakened, toner tribo becomes insufficient, and fogging easily occurs.

Even if the sleeve 22 is rotationally driven in the direction of arrow b, the magnetic particle layer slows its movement as it moves away from the sleeve surface due to the balance between the magnetic force, the constraint force based on gravity and the conveying force in the moving direction of the sleeve 22. In the upper part of the magnetic particle layer, a static layer that can move to some extent but is almost immobile is formed. Of course, some fall under the influence of gravity.

Therefore, by appropriately selecting the arrangement positions of the magnetic poles 23a and 23d and the fluidity and magnetic characteristics of the magnetic particles 27, the magnetic particle layer is transported toward the magnetic pole 23a toward the sleeve to form a moving layer. The movement of the magnetic particles causes the magnetic particle layer (first layer) to take in the toner from the toner layer (second layer), and the toner is frictionally charged by the rubbing of the magnetic particles or the sleeve, and the toner is developed as the sleeve 22 rotates. It is transported to the area and provided for development.

The movement of the magnetic particle layer is determined by the fluidity and magnetic force of the developer, and when the toner content in the magnetic particles is low, the stationary layer becomes small, and most of the magnetic particle layer moves quickly, and the toner is removed from the toner layer. take in. Further, when the toner content is high, the stationary layer becomes large, and the moving layer of the magnetic particle layer cannot contact the toner layer covered with the stationary layer, and hardly takes in the toner. Therefore, a certain amount of toner content is naturally maintained.

Next, the magnetic particle layers in the vicinity of the non-magnetic blade 24, which is a developer application amount regulating member, and in the vicinity of the limiting member 26 will be described. The limiting member does not only mechanically prevent unnecessary entry of the replenishment toner into the developer regulating portion. As described above, the magnetic pole is provided in the regulation area surrounded by the sleeve for the member 26.
The magnetic particles conveyed by the rotation of the sleeve by the N ₁ pole are packed along the guide surface 261 of the limiting member 26 to increase the density. In this area, the exchange of magnetic particles that are conveyed and invaded with the magnetic particles that flow out from the blade occurs dynamically, so that the magnetic particles collide with each other and are in a blunt state. It is in a practical packing state. For this reason, tribo is imparted to the toner from the magnetic particles or the sleeve, and the toner having a small tribo imparted by being attached to the magnetic particles or the sleeve with a weak force is conveyed away from the magnetic particles or the sleeve. That is, toner selection and charging improvement are performed. Therefore, the toner to which tribo is sufficiently imparted can be used for development. Further, the non-uniform state during the transportation of the magnetic particles is leveled in the space, and the coating of the magnetic particle layer is made uniform and stable. Therefore, the limiting member 26 requires the guide surface 261, and the inclination of the slope and the volume of the space have a great influence on the packing state of the magnetic particles in the space.

On the other hand, magnetic poles fixedly arranged in this area
23a rearranges the magnetic particles in the packing state along the magnetic lines of force. The packing state in the space is unstable for tribo application, and a constant packing state is always required for stabilization. And This forms a magnetic brush with the force of magnetic particles conveyed almost tangentially on the sleeve in a direction direct to the direction, so that not only the stirring effect on the magnetic particles but also the loosening effect is exerted, and Of tribo and the homogenization and stabilization of the coating of the magnetic particle layer are further promoted. At this time, if the developer concentrated by the peripheral configuration is subjected to a large pressure, there is a problem that the developer is clogged too much.
It is considered that the maximum magnetic force of the magnetic field is generated so as to face the guide surface 261 to prevent excessive pressure concentration in the regulated region, and to maintain the concentration of the developer and the stable high-density magnetic particle existence ratio. To be

Due to the above-mentioned restriction region, a stable amount of magnetic 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 102 becomes stable. Further, there is provided an alternating electric field forming means for forming in the developing section an alternating electric field for transferring at least the toner particles carried on the surface of the developing carrying member among the developers conveyed to the developing section to the electrostatic latent image carrier. Then, in the developing unit, the volume ratio of the magnetic particles of the developer conveyed to the developing unit to the volume of the space formed by the electrostatic latent image carrier and the developer carrying member is
It was confirmed that a great effect was obtained for the developing method and the apparatus of 1.5% to 30%.

FIG. 2 shows a case where the magnetic body 50 is installed on the non-magnetic blade side of the developer limiting member 26. In this case, it is not preferable to provide the magnetic body 50 at a position facing the magnetic pole 23a. This is because they are opposed to each other, and a strong concentrated magnetic field is generated between the magnetic poles 23a and the magnetic particles agitation and loosening effects of the magnetic poles 23a are reduced. However, it is effective to provide a magnetic body in the restricting portion to magnetically restrict the magnetic particles between the restricting portion and the magnet 23 inside the sleeve, because the gap tolerance between the restricting member and the sleeve is increased. Also, when comparing the magnetic particles or the toner adhered on the sleeve, the charge amount of the toner adhered on the sleeve is smaller than that charged on the magnetic particles. This is because the magnetic particles are also conveyed along with the movement of the sleeve, so that the toner on the sleeve is less likely to be rubbed by the magnetic particles. In order to raise the toner on the sleeve to a predetermined value, it is necessary to actively rub the toner on the sleeve. That is, it is necessary to have magnetic particles in the vicinity of the sleeve surface that cause a relative velocity shift against the movement of the sleeve.

However, simply lowering the transportability of the magnetic particles is impossible in view of the above-mentioned toner intake action. In addition, as described above, it is also possible to arrange the magnetic body in the restriction portion so as to face the in-sleeve magnetic pole 23a to improve the rubbing force of the magnetic particles that generate the concentrated magnetic field onto the sleeve, as described above. The effect of arranging the maximum magnetic force generating portion in the magnetic pole in the space formed by the regulating member 26 is reduced.

Therefore, in this embodiment, the magnetic body 50 is provided on the downstream side of the magnetic pole 23a in the sleeve rotation direction so that the magnetic lines of force on the blade side of the magnetic pole 23a are substantially concentrated in the tangential direction of the sleeve surface. As a result, the magnetic particles only near the surface of the sleeve formed a magnetic brush along the surface of the sleeve and rubbed the toner on the sleeve to enhance tribo-impartment of the toner on the sleeve.

Here, the magnetic flux density distribution of the magnetic pole 23a will be described. The maximum magnetic flux density of the magnetic pole 23a stabilizes the applied state of the developer against the change of the toner content of the magnetic particle layer in the developing device of the present invention which does not have an automatic toner replenishing device for maintaining the toner content. In order to increase the mechanical accuracy tolerance of the gap between the blade tip and the sleeve, the magnetic flux density at the point facing the tip of the blade 24 should be 800 G or more, and the packing state of the magnetic particles in the restricted area should be increased. 600G or more is desirable to stabilize the temperature. However, the magnetic flux density peaked at 800 G as the magnet diameter decreased.
There is a limit to securing a wide magnetizing width of magnetic flux density of 600 G or more if the above, when the cut pole 23a is symmetrical,
If the magnetic flux density at the point corresponding to the tip of the blade 24 is 600 G or more, the angle θ formed by L ₁ and L ₂ must be narrowed, and the effect of the magnetic body 50 and the guide surface 261 of the limiting member 26 described above. Will be reduced. Further, it is preferable that α ₂ is small.

When α ₂ is large, the magnetic brush of the magnetic particle layer on the sleeve becomes large, and the toner is excessively taken in from the gap between the brushes, and the toner concentration in the magnetic particle layer rises too much, causing fog on the ground. FIG. 1 is a diagram showing the magnetic flux density distribution of the magnet 23 in the embodiment of the present invention when a small-diameter sleeve having a diameter of 16 mm is used. As shown in FIG. 1, the maximum magnetic force of the magnet center and the maximum magnetic force of the magnetic pole 23a are shown. With the straight line connecting the generation point as a reference, the angles formed by the straight lines connecting the center of the magnet and the magnetic flux density 600G on the upstream and downstream sides of the magnetic pole 23a in the blade rotation direction are α ₂ and α ₁ , respectively, and α ₁ ≧ θ, α ₁ ＞
It is desirable to be α ₂ .

That is, without slowing down the effect of the magnetic body 50 and the guide surface 261 by slowly decreasing the magnetic flux density on the downstream side in the moving direction of the developing sleeve, the magnetic flux density at the point facing the tip of the blade 24 is set to 600 G or more, and the magnetic pole 23a. It is possible to effectively utilize the ability of.

In FIG. 1, the magnetic pole 23c is a developing magnetic pole, but the 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.

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

In any case, the present invention can provide a high image quality which cannot be obtained by the conventional developing method and apparatus, and has an excellent effect that the developing apparatus can be made a small disposable type.

The toner supply member is located inside the developing container 36 and is close to or in contact with the magnetic particle layer, and is driven to rotate in the direction of arrow d so that the toner
Are supplied to the magnetic particle layer.

A toner storage container 38 for storing toner is arranged adjacent to the developing container 36 in a substantially horizontal direction. Inside the toner storage container, a toner conveying member for feeding toner into the developing container 36 is provided.

The S magnetic pole 23b is a carrier magnetic pole provided to prevent the developing layer applied uniformly on the nonmagnetic blade 24 from being disturbed because the distance between the cutting magnetic pole 23a and the developing magnetic pole 23c is large. Since the S magnetic pole 23b does not disturb the developer layer, the strength of the magnetic pole is approximately equal to or slightly lower than that of the developing magnetic pole 23c.
When using a developing sleeve of 16φ, if the distance between the cutting magnetic pole and the developing magnetic pole is within 100 ° at the sleeve center angle, the disturbance of the developer layer on the sleeve is small. Disturbance of the layer is large and it is preferable to provide a carrier pole in the middle.

The S magnetic pole 23d is a recovery magnetic pole that collects the developer after development, and is arranged on the upstream side in the moving direction of the developing sleeve 22 with respect to the tip of the magnetic seal 31. When the magnetic pole 23d is arranged on the downstream side of the tip of the magnetic seal 31, a magnetic particle spike is formed by the magnetic pole 23d in the vicinity of the toner intake port in the lower part of the developing container 36, and it becomes extremely easy to take in the toner and the frictional charging is sufficiently performed. Not performed, it is easy to cause fog.

Here, the volume ratio of the magnetic particles in the developing section will be described. "Developing section" means sleeve 22 to photosensitive drum 1
Where toner is transferred or supplied. The "volume ratio" is the percentage of the volume occupied by the magnetic particles present therein relative to the volume of the developing section. In the above-mentioned developing device, it is extremely preferable that this volume ratio has an important influence, and that it is 1.5 to 30%, particularly 2.6 to 26%.

If it is less than 1.5%, a decrease in the density of the developed image is observed, a sleeve ghost is generated, a remarkable density difference occurs between a portion where the spike 51 is present and a portion where the spike 51 is not formed, and the density is formed on the surface of the sleeve 22. It is not preferable in that the thickness of the developer layer to be formed becomes non-uniform as a whole.

When it exceeds 30%, the degree to which the sleeve surface is closed increases, and fogging occurs, which is not preferable.

In particular, for the present invention, the above-mentioned conditions listed as the preferred developing method are not limited to the image quality that monotonically deteriorates or increases as the volume ratio increases or decreases, but 1.5 to 30
%, A sufficient image density can be obtained, and even if less than 1.5%, it is 30
This is based on the fact that the image quality is deteriorated even when the ratio exceeds%, and neither sleeve ghost nor fogging occurs in the range of the above numerical values where the image quality is sufficient. The former is considered to be due to the negative characteristics, and the latter is thought to be caused by the fact that the amount of magnetic particles becomes large and the surface of the sleeve 22 cannot be opened, and the amount of toner supplied from the surface of the sleeve 22 is greatly reduced. Can be

If it is less than 1.5%, the reproducibility of the line image is inferior and the image quality density is remarkably reduced. On the other hand, if it exceeds 30%, there are problems that the magnetic particles damage the surface of the photosensitive drum, and that transfer and fixing occur because they adhere as part of the image.

When the presence of magnetic particles is close to 1.5%, when reproducing a large-area uniform high-density image (solid black), "Arabi"
In some cases (particular environment or the like), there is a case where a partial development unevenness referred to as “development unevenness” occurs. This value is because the volume ratio of the magnetic particles to the developing portion is 2.6% or more, this range becomes a more preferable range, and when the presence of the magnetic particles is close to 30%, the spikes of the magnetic particles are There is a case where toner supply from the sleeve surface is delayed around the contacting portion (when the developing speed is high, etc.), and scaly density unevenness may occur during solid black reproduction. As a certain range for preventing this, the above volume ratio of the magnetic particles is more preferably 26% or less.

If the volume ratio is in the range of 1.5 to 30% (in the embodiment, 4%)
%), As shown in FIG. 3, the ears 51 are formed on the surface of the sleeve 22 in a sparse manner to a preferable degree, and the toner on both the sleeve 22 and the ears is sufficiently opened to the photosensitive drum 1. Since the toner 100 on the sleeve also fly-transfers due to the alternating electric field, almost all of the toner is in a state in which it can be consumed for development. Therefore, high developing efficiency (of toner that can be consumed for development among toner existing in the developing portion) Ratio)
And high image density can be obtained. Preferably, a small but intense spike vibration is caused, which loosens the magnetic particles and the toner 100 adhering to the sleeve 22. In any case, it is possible to prevent the generation of uneven sweep and ghost image as in the case of a magnetic brush. Further, the friction of the magnetic particles 27 and the toner 37 becomes active due to the vibration of the ears, so that the toner 37 is improved in triboelectrification and the occurrence of fogging can be prevented. The high developing efficiency is suitable for downsizing of the developing device.

The volume ratio of the magnetic particles 27 present in the developing section is (M /
h) × (1 / ρ) × [(C / (T + C)]], where M is the coating amount (g / cm ² ) of the developer (mixture ... non-peaking) per unit area of the sleeve. ), H is the height of the developing space (cm), ρ is the vacuum degree of the magnetic particles g / cm ³ , C / (T +
C) is the weight percentage of magnetic particles in the developer on the sleeve.

The ratio of the toner to the magnetic particles in the developing section defined above is preferably 4 to 40% by weight. When the alternating electric field is strong (the rate of change is large or Vpp is large) as in the above embodiment, the ears are separated from the sleeve 22 or the base thereof, and the separated magnetic particles 27 are separated between the sleeve 22 and the photosensitive drum 1. Reciprocates in the space. Since the energy of the reciprocating motion is large, the effect of the above-described vibration is further promoted.

The above behavior was confirmed by shooting 8000 frames / second with a high-speed camera (manufactured by Hitachi Ltd.). By reducing the gap between the surface of the photosensitive drum 1 and the surface of the sleeve 22, the photosensitive drum 1
Even if the contact pressure with the spikes is increased and the vibration is reduced,
Since the gap is large on the inlet side and the outlet side of the developing unit, sufficient vibration occurs and the above-mentioned effect is exhibited.

Conversely, it is preferable to increase the gap between the photosensitive drum 1 and the sleeve 22 so that the ears do not contact the photosensitive drum 1 in a state where no magnetic field is applied, but it is preferable that the ears be in contact with the photosensitive drum 1 when the magnetic field is applied.

In FIG. 2, the sleeve 22 is made of an aluminum sleeve having a diameter of 16 mm and the surface of which is subjected to unstable sandblasting with alundum abrasive grains, and the magnet 23 is magnetized by four poles so that N poles and S poles alternate. Was used. The maximum value of the surface magnetic flux density by the magnet 23 was about 800 gauss.

As the blade 24, 1.2 mm thick non-magnetic stainless steel was used, and the angle θ was set to 15 °. The angle α ₁ of the magnetic pole 23a is 15 ° and α ₂ is 10 °.

As magnetic particles, particle size 70 with silicone resin coating on the surface
~ 50μ (250/300 mesh) ferrite (maximum magnetization 60e
mu / g) was used.

As the non-magnetic toner, a blue toner obtained by externally adding 0.6% of colloidal silica to a toner powder having an average particle diameter of 10 μm, which is composed of 100 parts of styrene / butadiene copolymer resin and 5 parts of copper phthalocyanine pigment, is used. A toner coating layer having a coating thickness of about 10 to 30 μm was obtained thereon, and a magnetic particle layer of 200 to 300 μ was further obtained thereon. The toner adheres to the surface of each magnetic particle.

At this time, the total weight of the magnetic particles and all the toners on the sleeve 22 was about 2.43 × 10 ^-2 g / cm ² .

At this time, the weight ratio of the toner attached to the magnetic particles and the toner attached to the sleeve was about 2: 1.

The magnetic particles were spiked by the magnetic field by the magnetic pole 23b in the sleeve 22 at and near the developing section to form a spiked brush with a maximum length of about 1.2 mm.

When the charge amount was measured by the blow-off method, the triboelectric charge amount of the toner on the sleeve and the magnetic particles was +12 μC / g.

This developing device was installed in an FC-5 type copying machine manufactured by Canon Inc., and the photosensitive drum 3 (organic photosensitive material) and sleeve 22 were used.
The distance between the surface and the surface was 350 μm. When the volume ratio was determined under these conditions, it was about 10%. (H = 350 μm, M = 2.43 ×
10 ⁻² g / cm ² , ρ = 5.5 g / cm ³ , T / (T + C) = 20.4%).
Bias power supply 4 frequency 1800Hz, peak-to-peak value 1
When development was carried out using an alternating voltage of 200 V and a DC voltage of -270 V superimposed, a good blue image was obtained.

Further, when the solid black image was developed and the sleeve surface after the development was observed, the toner adhering to the magnetic particles and the toner on the sleeve were almost consumed, and the development was performed at a developing efficiency close to 100%.

As for the developing characteristics, there was no fog and good developing characteristics could be obtained.

Further, regarding the effect of the magnetic member 31, it was confirmed that good magnetic particles can be prevented from entering and leaking and good circulation can be achieved.

As described above, according to this embodiment, high image density,
With high development efficiency, it is possible to perform development without fog, ghost image, unevenness of sweep, and negative characteristics.

As the material of the sleeve 22, in addition to aluminum, a conductor such as brass or stainless steel, a paper cylinder, or a synthetic resin cylinder can be used. Also, the surface of these cylinders can be made to function as a developing electrode by conducting the surface treatment or by using a conductor. Furthermore, a conductive elastic body, for example, a conductive sponge may be wound around the peripheral surface using a core roll.

With respect to the magnetic pole 23b of the developing unit, the magnetic pole is arranged at the center of the developing unit in the embodiment, but may be shifted from the center, or the developing unit may be arranged between the magnetic poles.

Silica particles may be externally added to the toner in order to enhance fluidity, and abrasive particles or the like may be externally added for polishing the surface of the photosensitive drum 3 which is a latent image holding member in the transfer type image forming method. You may use what added a small amount of magnetic particles to the toner. That is, magnetic toners can be used as long as they are significantly weaker than magnetic particles and can be tribocharged.

In order to prevent the ghost image phenomenon, the developer layer remaining on the sleeve 22 that has not been used for development from the surface of the sleeve 22 that has returned to the inside of the container 21 and rotated, is scraped off once by a scraper means (not shown), and The scraped sleeve surface may be brought into contact with the magnetic particle layer to recoat the developer.

A mechanism for detecting the concentration of the magnetic particles and the toner and automatically replenishing the toner in accordance with the output may be provided.

The developing device of the present invention can be used as a single-use type developing device in which the container 21, the sleeve 22, the blade 24 and the like are integrated, or as a normal developing device fixed to the image forming apparatus.

(Embodiment 2) FIG. 4 shows another embodiment of the present invention. FIG. 4 shows a magnet 23 when a developing sleeve 22 having a diameter of 20 mm is used.
In the case of using a magnet having a slightly larger diameter, the magnetic flux at a point facing the blade 24 at the maximum magnetic flux density 800G or more of the magnetic pole 23a described in the previous embodiment is shown. For densities above 600G, the above angle α ₁ > α ₂
It can be achieved without. However, for example, when a magnet of α ₁ = α ₂ is used, it faces the blade 24 when the maximum magnetic force generation point deviates only a few degrees to the upstream side in the blaze rotation direction due to variations in assembling individual products in mass production. The magnetic flux density at the point is less than 600G. Therefore, by setting α ₁ > α _{2 as} described in the previous embodiment of the present invention, it is effective that the latitude is wide enough to be able to cope with the case where the angle θ varies in mass production.

(Effects of the Invention) As described above, by gently reducing the magnetic flux density on the downstream side in the rotation direction of the developing sleeve of the cutting pole, the magnetic field acting on the restricting portion is reduced by reducing the diameter of the magnet accompanying the decreasing diameter of the developing sleeve. It is possible to prevent the stacking of the latitude, effectively utilize the capability of the magnet, promote the stabilization of the packing state of the regulation portion, and supply the developing device having a good image property. It is especially effective for a system using a small-diameter sleeve with a diameter of 20 mm or less.

[Brief description of drawings]

FIG. 1 is a diagram showing a magnetic flux density distribution of a magnet according to the present invention, FIG. 2 is a schematic sectional view of a developing device according to the present invention, and FIG. 3 is a diagram showing a state of a developer in a developing section. FIG. 4 is a diagram showing a magnetic flux density distribution of a magnet which is another embodiment of the present invention. 1 is a latent image carrier 22 is a developing sleeve 23 is a magnet 27 is a magnetic particle 30 is a scattering prevention electrode plate 24 is a non-magnetic blade 35 is a magnetic particle storage container 37 is a toner particle 26 is a magnetic particle limiting member 38 is a toner particle storage container 39 is a toner supply member 31 is a magnetic seal 40 is a seal member 50 is a magnetic material 36 is a developing container

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Hiroshi Taka 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Atsushi Hosoi 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Incorporated (56) Reference JP 60-95573 (JP, A) JP 54-143237 (JP, A) JP 61-159664 (JP, A)

Claims (1)

(57) [Claims] 1. A developer carrying member facing a electrostatic image carrying member and carrying a developer having magnetic particles and toner particles, a regulating member for regulating the amount of the developer on the developer carrying body, and a developer. In a developing device having a magnetic field formed in a restriction portion provided by a restriction member provided inside the carrier, and a developer coating magnetic pole having a peak position of magnetic flux density that is upstream of the restriction portion in the moving direction of the developer carrier, The developing device is characterized in that the magnetic flux density distribution curve formed by the developer coating magnetic pole is gentler on the downstream side than the upstream side in the moving direction of the developer carrier.