JPH04350875A - Developing device - Google Patents

Abstract

PURPOSE:To develop an excellent toner image on the surface of a photosensitive body by forming a uniform thin layer of developer on the surface of a developing sleeve. CONSTITUTION:A notched groove 4a is provided on a part of a fixed magnetic roller 4 which is included in the developing sleeve 3, and the magnetic pole of N pole is formed on both sides which hold the notched groove 4a between them, then a repulsive magnetic pole is formed on the surface of the developing sleeve which rotates on the outside side of the roller 4. A cylindrical bar 5 is provided to be opposed to the notched groove 4a of the roller 4 and uniformly pressed in contact with the surface of the sleeve 3 through an elastic member 6. A napping peak formed of the developer D carried through the sleeve 3 with the repulsive magnetic pole is regulated by the curved surface with the specified curvature of the cylindrical bar 5 so as to form the uniform thin layer of the developer on the surface of the sleeve 3. Then, the excellent toner image is developed on the surface of the photosensitive body 16.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the structure of a developer layer forming means for regulating the developer conveyed by a developing sleeve provided in a magnetic brush developing device of an electrophotographic image forming apparatus.

0002

[Prior Art] Generally, in an electrophotographic image forming apparatus using a two-component developer, it is necessary to make the layer thickness of the developer on the developing sleeve thin and uniform in order to obtain a good toner image on the photoreceptor surface. It becomes.

[0003] Conventionally, the layer thickness has been regulated by a fixing regulating plate that has been used for a long time, but there is also a limit to the mechanical attachment accuracy between the developing sleeve and the fixing plate, and this method does not allow uniform and even unevenness. It was difficult to obtain thin layers.

[0004]Recently, as a countermeasure for such problems,
The means disclosed in Japanese Patent No. 0-22363 is well known. That is, this means provides a concave permanent magnet in the developing sleeve to form a repulsive magnetic field, and creates a magnetic field with a magnetic field strength distribution having two peaks on the surface of the developing sleeve in the direction of rotation thereof, thereby creating two peaks on the surface of the developing sleeve. The developer to be conveyed is regulated by forming spikes of developer that separate into spikes, and by providing a regulating plate with a predetermined gap between the spikes and the surface of the developing sleeve. In this way, the developer is stably transported and good development is performed.

[0005]

[Problems to be Solved by the Invention] However, in the above-mentioned Utility Model Publication No. 60-22363, the developer regulating means using a regulating plate and forming a repulsive magnetic field has the problem that both ends of the regulating plate facing the developing sleeve are edges. Since the developing sleeve is shaped like this, it is extremely sensitive to the installation position with respect to the developing sleeve, and the state of aggregation of the developer changes. For example, due to slight eccentricity of the developer sleeve, installation error or deformation of the regulating plate, the developer that remains between the developing sleeve and the regulating plate does not pass smoothly and forms a uniform thin layer. It has the disadvantage that it cannot be done.

SUMMARY OF THE INVENTION An object of the present invention is to provide a developing device in which the developer conveyed by the developing sleeve can form a uniform thin layer on the surface of the developing sleeve.

[0007]

[Means for solving the problem] This purpose is as follows:
, c, or d.

(a) 2 consisting of a magnetic carrier and a toner
In a developing device of an image forming apparatus using component developers,
A developing sleeve that magnetically holds and transports the developer has magnetic poles of the same polarity juxtaposed to form a repulsive magnetic field, and has a curvature at the tip facing the surface of the developing sleeve on which the repulsive magnetic field is formed. 1. A developing device comprising a developer layer forming means for regulating developer.

(b) The developing device according to item (a), wherein the developing layer forming means is provided in pressure contact with the surface of the developing sleeve.

(c) In (a), the developing layer forming means has a distance of 0.05 to 1.0 mm from the surface of the developing sleeve.
A developing device characterized in that the developing device is provided with an interval of .

(d) In (a), (b), and (c), when the peak interval of the magnetic force on the surface of the developing sleeve is d, the diameter φ of the tip of the developer layer forming means is 0. 5d
A developing device characterized in that the developing device is set within a range of ≦φ≦3d.

0012

[Example] The structure of the present invention and a side view showing a state in which the developer layer forming means (cylindrical rod) in FIG. The description will be given with reference to a side view showing a state in which the developing device is disposed with a gap in the developing sleeve, a diagram showing the magnetic field intensity distribution in FIG. 3, and a side sectional view showing the configuration of the developing device in FIG. 4. However, the present invention is not limited to this example.

In the present invention, a two-component developer mainly consisting of magnetic carrier particles and toner particles is supplied onto the surface of a developer transport carrier to form a thin developer layer. This is particularly effective in an apparatus in which a developer layer is placed under an oscillating electric field to thereby develop a latent image on the surface of an image carrier.

That is, the present invention makes it possible to use micronized magnetic carrier particles and toner particles without trouble by performing development under an oscillating electric field using magnetic carrier particles of a two-component developer. .

In general, when the average particle size of the magnetic carrier particles is large, (1) the condition of the ears of the magnetic brush formed on the developer transport carrier is rough, so that an electrostatic image is developed while being vibrated by an electric field; Also, unevenness tends to appear in the toner image, and the toner concentration in the ears becomes low, resulting in problems such as inability to perform high-density development. In order to solve this problem (2), the average particle size of the carrier particles can be reduced, and as a result of experiments, the effect starts to appear when the average particle size is 70 μm or less, especially 60 μm or less, and when the average particle size becomes 30 μm or less, it becomes substantially It was found that the problem (■) no longer occurs. In addition, the problem (2) can be solved by making the magnetic carrier finer particles, which increases the toner concentration in the ears and enables high-density development. However, if the carrier particles are too fine, (1) they will adhere to the surface of the image carrier together with toner particles, or (2) they will easily scatter. These phenomena are related to the strength of the magnetic field on which the carrier particles act, and therefore the strength of the magnetization of the carrier particles, but in general,
It appears when the average particle size of carrier particles becomes 15 μm or less. A portion of the carrier particles adhering to the surface of the image carrier is transferred onto the recording paper along with the toner, and the remaining portion is removed from the surface of the latent image carrier along with the residual toner by a cleaning device such as a blade or a fur brush.

However, basically, it is most important to minimize the amount of carrier adhesion to the surface of the image carrier. As a result of various studies by the inventors, the magnetization of the carrier is 10 to 60 emu/in the magnetic field on the developing sleeve.
Practically preferable results are obtained when g is 15 to 5
It has become clear that particularly good results are obtained when the concentration is 0 emu/g.

If the magnetization of the carrier particles is less than 10 emu/g, the adsorption force of the carrier to the developer transport carrier is insufficient, resulting in insufficient developer transport, and the effect of the repulsive magnetic field is insufficient, resulting in a thin layer Forming power decreases. Further, the carrier leaves the surface of the developer transporting carrier and tends to migrate and adhere to the surface of the image carrier, which is undesirable. On the other hand, magnetization is 60 emu
If it exceeds /g, the formed magnetic brush ears will become rough and the image will be rough, and since the ears are high, breakdown will easily occur through the ears, making it difficult to avoid high bias voltage. Problems include problems such as the adsorption force on the surface of the developer transport carrier being excessive and toner particles being strongly compressed between carrier particles, resulting in deterioration of the developer, and developer transport devices that use rotating magnets causing the carrier to easily scatter. This is not desirable in practice. Furthermore, the effect of the repulsive magnetic field is too strong, and the amount of developer passing through is too low.

The present invention is suitably used for small particle size carriers and small magnetization carriers as described above.

The average particle size of the magnetic carrier is preferably 60 μm or less and 15 μm or more.

[0020] Such magnetic carrier particles contain metals such as iron, chromium, nickel, cobalt, etc., or compounds or alloys thereof, such as triiron tetroxide, r. -ferric oxide,
Chromium dioxide, manganese oxide, ferrite, manganese
Particles of ferromagnetic substances such as copper alloys, or the surface of these magnetic particles are coated with styrene resin, vinyl resin, ethylene resin, rosin modified resin, acrylic resin, polyamide resin, epoxy resin, polyester resin. Particles obtained by coating them with resins such as balmitic acid, fatty acid waxes such as valmitic acid, stearic acid, etc., or by making particles of resins or fatty acid waxes containing dispersed magnetic particles are used as conventional average particle particles. It is obtained by sorting the particle size using a diameter-based means. Further, the carrier particles described above can also be made spherical by a known method. The spherical carrier has no directionality of magnetization, and a developer layer is formed uniformly. Carrier particles have no edges, and the electric field does not concentrate on the edges, so even if a high bias voltage is applied to the developer transport carrier, image distortion due to discharge and breakdown of the bias voltage are unlikely to occur, and development is possible. It has advantages such as improved fluidity of the agent. The fact that this high bias voltage can be applied means that when development under an oscillating electric field in the present invention is performed by applying an oscillating bias voltage, the effects described below can be fully exhibited. That's what I say.

[0021] Wax can also be used as carrier particles that produce the above-mentioned effects, but from the viewpoint of the durability of the carrier, it is preferable to use resins as described above. Furthermore, the resistance of the carrier particles is 108
It is preferable to form insulating magnetic particles so that the resistance is Ωcm or more, particularly 10 13 Ωcm or more. This resistivity is determined by placing the particles in a container with a cross-sectional area of 0.50 cm2 and tapping, then applying 1 kg/cm2 onto the packed particles.
Apply a load of 1000V/c between the load and the bottom electrode.
This value is obtained by reading the current value when applying a voltage that generates an electric field of As a result, carrier particles tend to adhere to the surface of the image carrier, or breakdown of the bias voltage tends to occur.

[0022] To summarize the above, the magnetic carrier particles used in the method of the present invention are spherical so that the ratio of the long axis to the short axis is 3 times or less, and there are no protrusions such as needle-shaped parts or edge parts. The resistivity is preferably 10 8 Ωcm or more, particularly preferably 10 13 Ωcm or more. For such magnetic carrier particles, magnetic powder consisting of particles as close to spherical as possible is selected and coated with resin, or fine magnetic powder is dispersed in resin, solidified, and pulverized into a spherical shape. Alternatively, it can be manufactured by using a spray drying method.

Next, regarding toner, as the average particle size of toner particles becomes smaller, the amount of charge qualitatively decreases in proportion to the square of the particle size, and the adhesion force such as van der Waals force decreases. As the toner particles become larger, it becomes difficult for the toner particles to separate from the carrier particles, and once the toner particles adhere to the non-image area of the image bearing surface, they cannot be easily removed by rubbing with a conventional magnetic brush and can cause fogging. It begins to give birth. In the conventional magnetic brush development method,
When the average particle size of toner particles was 10 μm or less, such problems became noticeable. The developing method of the present invention solves this problem by performing development using a developer layer, a so-called magnetic brush, under an oscillating electric field. That is,
The toner particles adhering to the developer layer are easily moved away from the developer layer and transferred to the image area and non-image area on the image carrier surface by the electrically applied vibrations, and are also easily separated from the developer layer. When the surface of the image carrier is rubbed with the developer layer, toner particles attached to the non-image area of the image carrier can be easily removed or moved to the image area, and the developer layer When the thickness is made thinner than the gap between the image carrier surface and the developer transport carrier surface, toner particles with a low charge amount hardly migrate to the image area or non-image area, and are also rubbed against the image carrier surface. Because of this, toner particles do not adhere to the image carrier due to frictional charging, and toner particles having a particle size of several μm can now be used. Therefore, it is possible to obtain a clear toner image with good reproducibility in which the electrostatic latent image is faithfully developed. Further, the oscillating electric field weakens the bond between toner particles and carrier particles, and the adhesion of carrier particles accompanying toner particles to the image bearing surface is also reduced. In particular, when the thickness of the developer layer is made thinner than the gap between the developer carrier surface and the developer transport carrier surface, toner particles with a large amount of charge vibrate under the oscillating electric field in the image area and non-image area. Depending on the strength of the electric field, the carrier particles also vibrate, allowing the toner particles to selectively migrate to the image area on the image carrier surface, which greatly reduces the adhesion of the carrier particles to the image carrier. Ru. Due to the electric field, toner particles in the non-image area may or may not reach the non-image area. The same applies to careers.

On the other hand, as the average particle size of the toner increases,
As mentioned earlier, image distortion becomes noticeable. Normally, toner with an average particle size of about 20 μm is not a problem in practice for developing fine lines arranged at a pitch of about 10 lines/mm with high resolution, but if fine particles with an average particle size of 10 μm or less are used, The resolution has been significantly improved, and it is now possible to produce clear, high-quality images that faithfully reproduce the differences in shading. For the above reasons, the appropriate condition for the particle size of the toner is that the average particle size is 20 μm or less, preferably 10 μm or less. In addition, in order for the toner particle size to follow the electric field, the charge amount of the toner particles should be greater than 1 to 3 μC/g (preferably 3 to 30 μC/g).
0 μC/g) is desirable. Particularly when the particle size is small, a high amount of charge is required.

[0025] Such toner can be obtained in the same manner as conventional toners. That is, it is possible to use a toner in which spherical or amorphous nonmagnetic or magnetic toner particles in conventional toners are sorted by an average particle size sorting means. Among these, it is preferable that the toner particles are magnetic particles containing magnetic particles, and it is particularly preferable that the amount of magnetic fine particles does not exceed 60 wt %. When the toner particles contain magnetic particles, the toner particles are influenced by the magnetic force of the magnet included in the developer transport carrier, which further improves the uniform formation of the magnetic brush. , fogging is prevented from occurring, and toner particle scattering is also less likely to occur. However, if the amount of magnetic material contained is too large, the magnetic force between the carrier particles and the carrier particles becomes too large, making it impossible to obtain a sufficient developing density. frictional electrification becomes difficult to control.
Toner particles may be easily damaged or agglomerated with carrier particles. Particularly when using color toners, clear colors cannot be obtained unless the amount of magnetic material is 30 wt% or less.

To summarize the above, a preferable toner in the developing method of the present invention uses a resin as described above for the carrier and fine particles of a magnetic material, and also contains a coloring component such as carbon and, if necessary, a charge control agent. In addition, the particles have an average particle diameter of 20 μm or less, particularly preferably 10 μm or less, which can be produced by a method similar to a conventionally known method for producing toner fine particles. Furthermore, spherical toner brings about favorable results in improved fluidity, developer stirring, and transport charging.

In the developing method of the present invention, a developer in which the above-mentioned spherical carrier particles and toner particles are mixed in the same ratio as in a conventional two-component developer is preferably used. Further, if necessary, a fluidizing agent for improving the fluidity and sliding of the particles, a cleaning agent for cleaning the surface of the image carrier, and the like are mixed. As the fluidizing agent, colloidal silica, silicone varnish, metal soap, or nonionic surfactant can be used, and as the cleaning agent, fatty acid metal salt, organic group-substituted silicone, fluorine, etc. can be used as a surfactant. Can be done.

The above are the conditions for the developer, and next, the conditions for the developer transport carrier which forms a developer layer with such developer and develops the electrostatic image on the image carrier will be described.

The thickness of the developer layer formed on the developer transport carrier is preferably such that the adhered developer is sufficiently scraped off by the thickness regulating blade to form a uniform layer. The gap between the developer transport carrier and the image carrier is preferably several tens to 1000 μm. If the surface gap between the developer transport carrier and the image carrier becomes narrower than several tens of micrometers, it will be difficult to form magnetic brush ears that will uniformly develop the gap, and it will also be difficult to develop enough toner particles. If the gap greatly exceeds 1000 .mu.m, the opposing electrode effect decreases, making it impossible to obtain a sufficient developed density. In this way, when the gap between the developer transport carrier and the image carrier becomes extreme, it becomes impossible to make the thickness of the developer layer on the developer transport carrier appropriate. In the range of 1000 μm, the developer layer can be formed with an appropriate thickness. Therefore, it is particularly preferable to set the gap and the thickness of the developer layer so that the ears of the magnetic brush do not come into contact with the surface of the image carrier and are as close as possible to the surface of the image carrier when no oscillating electric field is applied. . This is because the toner development of the latent image is prevented from having scratches or fog caused by the rubbing of the magnetic brush.

Further, development under an oscillating electric field is preferably carried out by applying an oscillating bias voltage to the sleeve of the developer carrying member. Further, it is preferable to use a bias voltage that is a combination of a direct current voltage that prevents toner particles from adhering to non-image areas and an alternating current voltage that makes it easier for toner particles to separate from carrier particles. However, the present invention is not limited to the method of applying an oscillating voltage to the sleeve or the method of applying a superimposed DC and AC voltage.

The developing method of the present invention as described above is carried out using the apparatus illustrated in FIGS. 1 to 4.

FIG. 4 shows a cross section of the main parts of the developing device 1, in which 16 is a photoreceptor, 2 is a housing, 3 is a developing sleeve, 4 is a magnet roller, and 5 is a rigid body that regulates the amount of developer. A cylindrical rod 15 is a holder for holding the cylindrical rod 5, and 6 is a spring member for enabling the developer to be conveyed by the pressure between the cylindrical rod 5 and the developing sleeve 3. The cylindrical rod 5 is pressed against the developing sleeve 3 with a constant load without the presence of developer. 7 and 8 are first and second stirring members, 9 is a supply roller, 10 is a scraper, 11 is a stirring partition plate, and 12 is a bias power supply that applies a bias voltage to the developing sleeve 3 via a protective resistor 13.

The toner replenished into the developing device 1 is transferred to the carrier by the first stirring member 7 rotating in the direction of the arrow and the second stirring member 8 rotating in the opposite direction so as to overlap with each other. The upper developer D is sufficiently stirred and mixed with the upper developer D and is sent to the developing sleeve 3 via the supply roller 9.

[0034] The first stirring member 7 and the second stirring member 8
is a screw-like member with a left-handed helical angle that rotates in opposite arrow directions, and the toner and carrier transported to the back side by the thrust of the second stirring member 8 are transported in the back direction in the drawing. The stirring partition plate 11 has an upper edge that is sloped low.
The developer D is transferred to the first agitation member 7 side by its thrust and transported to the front side of the drawing by its thrust, and the homogeneous developer D is triboelectrically charged by the mixing action of the toner and carrier during this time, and is spongy. The supply roller 9 rotates in the direction of the arrow, and the developer is deposited in a layer on the circumferential surface of the developing sleeve 3.

Further, the N and S magnetic poles of the magnet roller 4 are normally magnetized to a magnetic flux density of 500 to 1500 Gauss, and the layer of the developer D as described above is formed on the surface of the developing sleeve 3 by the magnetic force. That is, a magnetic brush is formed.

In the above-described apparatus, the surface gap between the developing sleeve 3 and the photoreceptor 16 is several tens to one.
The photoreceptor 16 is set to be within the range of 000 μm.
When an electrostatic image is developed, the magnetic brush formed on the surface of the developing sleeve 3 vibrates because the magnetic flux density on the surface changes as the developing sleeve 3 or the magnetic roller 4 rotates. While moving over the developing sleeve 3, it stably and smoothly passes through the gap between the photoreceptor 16 and a uniform developing effect on the surface of the photoreceptor 16. This enables stable development with high toner density. In order to prevent the occurrence of fogging and to improve the developing effect, a bias voltage having an alternating current component vibrating by the bias power source 12 is applied to the developing sleeve 3 between the base body 16a of the photoreceptor 16 and the grounded substrate 16a. is applied to. As mentioned earlier, this bias voltage uses a preferable superimposed voltage of DC voltage and AC voltage, which prevents the DC component from causing fog, and the AC component gives vibration to the magnetic brush to improve the developing effect. do. Note that a voltage of 50 to 600 V that is approximately equal to or higher than the non-image area potential is normally used for the DC voltage component, and a voltage of 100 Hz to 10 KHz is used for the AC voltage component.
, preferably a frequency of 1 to 7 KHz is used. Further, the waveform of the AC voltage component is not limited to a sine wave, but may be a rectangular wave or a triangular wave. Note that when the toner particles contain a magnetic material, the DC voltage component may be lower than the non-image area potential. If the frequency of the AC voltage component is too low, the effect of imparting vibration will not be achieved, and if it is too high, the developer will not be able to follow the vibrations of the electric field, resulting in a decrease in developer density and the inability to obtain clear, high-quality images. There is a tendency to say. In addition, the voltage value of the AC voltage component is also related to the frequency, but the higher the voltage value, the more the magnetic brush will vibrate and the more effective it will be. It also makes it easier for dielectric breakdown to occur. However, the fact that the carrier particles of the developer D are insulated and made spherical by a resin or the like prevents dielectric breakdown, and the occurrence of fog can also be prevented by the DC voltage component. Incidentally, the surface of the developing sleeve 3 to which the alternating current voltage is applied may be coated with a resin or an oxide film for forming an image or semi-insulating.

As described above, although FIGS. 1 to 4 show an example in which an oscillating bias voltage is applied to the developing sleeve, the developing method of the present invention is not limited thereto.
The developing effect can also be improved by extending several electrode wires around the developing area of the photoreceptor 16 and applying a vibrating voltage to them. In that case as well, a DC bias voltage may be applied to the developing sleeve 3, or oscillating voltages of different frequencies may be applied. Furthermore, the method of the present invention can be similarly applied to reversal development and the like. In that case, the DC voltage component is set to a voltage approximately equal to the potential received by the non-image background portion of the photoreceptor 16. Furthermore, the method of the present invention can be similarly applied to the development of the photoreceptor 16 having a recording layer and the development of a magnetic latent image. In addition, the present applicant previously developed the photoreceptor 16 repeatedly to form a color image by overlapping a plurality of toners.
It is also possible to apply the method described in No. 8-187001.

In the present invention, in order to eliminate the above-mentioned problems and form a uniform thin layer of developer D on the surface of the developing sleeve 3, the cylindrical rod 5, which is a developer layer forming means, is arranged as follows. did.

That is, as shown in FIG. 4, the magnet roller 4 has 12 equal magnetic poles in which N and S are alternately arranged at equal intervals.
Although it is composed of a magnet with one pole, one pole is missing to make 11 poles, and a notch groove 4a is provided across the width direction of the magnet roller 4 in the missing part, and the notch groove 4a is sandwiched. N-pole magnetic poles are provided on both sides of the developing sleeve 3, and the developing sleeve 3 is fixedly contained therein so that repulsion magnetic poles are formed on the surface of the developing sleeve 3. The surface of the developing sleeve 3 has two peaks P1 and P2 in the moving direction of the developer D shown by the arrow in FIG. 3, corresponding to the repulsive magnetic field formed on both sides of the notched groove 4a. A magnetic field with a vertical magnetic field strength distribution is formed on the surface of the developing sleeve 3.

On the other hand, as shown in FIG. 4, the cylindrical rod 5 is a rigid rod-shaped member located below the developing sleeve 3 and pivotally supported by the holder 15 so as to be movable up and down. The cylindrical rod 5 is provided at a position facing the notched groove 4a of the fixed magnet roller 4, which is set at the position shown in the figure. An elastic member 6, such as a sponge or a spring member, is appropriately provided in the axial direction on the lower surface of the holder 15, which faces the circumferential surface of the cylindrical rod 5, which is pivotally supported by the holder 15. The elastic member 6
The developing sleeve 3 is pressed against the surface of the developing sleeve 3 with a predetermined pressing force so as to be in uniform contact with the surface of the developing sleeve 3. The material of the cylindrical rod 5 may be either magnetic or non-magnetic.

When the distance between the peaks P1 and P2 of the magnetic force formed on the surface of the developing sleeve 3 shown in FIG. 3 is d, the diameter φ (mm) of the cylindrical rod 5 is 0.5d≦φ≦
The numerical value is selectively set within the range of 3d.

If the diameter φ of the cylindrical rod 5 is smaller than 0.5d, a thin layer of the developer D cannot be formed uniformly, and if its straightness is imperfect, a uniform thin layer cannot be formed. On the other hand, when the diameter φ is larger than 3d, the regulating position where the developer D flows becomes larger than the peak interval of the magnetic field strength distributions P1 and P2, and the regulating effect of the repulsive magnetic field becomes insufficient.

[0043] The diameter of the developing sleeve 3 is 10~
The diameter φ of the cylindrical rod 5 is preferably 30 mm and 3 to 10 mm. The magnetic flux density of magnetic field peaks P1 and P2 is 300~
800 Gauss, magnetic flux density in the valley between P1 and P2 is 200 ~
500 Gauss is preferred.

Further, the cylindrical rod 5 is connected to the developing sleeve 3.
As shown in FIG. 2, there is a gap C between the circumferential surface of the cylindrical rod 5 and the circumferential surface of the developing sleeve 3, as shown in FIG.
may also be arranged.

Further, the cylindrical rod 5 is not limited to a non-magnetic material, but may also be made of a magnetic material. In this case, it is possible to widen the regulatory gap.

[0046] The distance of the gap C is 0.05 to 1.0 mm.
The value is selectively set within the range.

Since the cylindrical rod 5 is a round bar member, it has extremely straightness compared to a plate-like member and can be brought into even and close contact with the surface of the developing sleeve 3, and even if there is a gap, the cylindrical rod 5 can be brought into close contact with the surface of the developing sleeve 3 uniformly over the entire area. This allows for a gap to be obtained.

The developing sleeve 3 configured as described above
A thin layer of the developer D is formed on the surface of the developing sleeve 3 in the following manner by the repulsive magnetic field formed on the surface and the cylindrical rod 5.

That is, the toner replenished into the developing device 1 is transferred to the carrier by the first stirring member 7 rotating in the direction of the arrow and the second stirring member 8 rotating in the opposite direction so as to overlap with each other. After sufficient stirring and mixing, the developer D is sent to the developing sleeve 3 via the supply roller 9.

As described above, the spikes of the developer D are dense in the portion facing the position of the peak P1 of the magnetic force, and the spikes of the developer D are sparse in the portion facing the notch groove 4a. Since the cylindrical rod 5 is provided at a position facing the notch groove 4a, the amount of the developer is controlled in a state where the spikes of the developer D are sparse. Therefore, when the developing sleeve 3 rotates in the direction of the arrow, the developer D stays on the right side of the cylindrical rod 5 as shown in FIG.
The amount of developer is controlled by being conveyed to the left along the curved surface of the cylindrical rod 5 with a predetermined curvature and passing between the developing sleeve 3 and the cylindrical rod 5 against the elastic member 6. A thin layer of the developer D is formed on the surface of the developing sleeve 3.

Further, due to the curved surface of the cylindrical rod 5, the developer D is smoothly conveyed through the cylindrical rod 5 without damaging the coating film of the carrier.

The electrostatic latent image thus formed on the photoreceptor 16 is developed into a good toner image.

The developer layer forming means of the present invention is not limited to the aforementioned cylindrical rod 5, but may also be a rigid plate-like member whose surface facing the developing sleeve 3 has a curved surface having a predetermined curvature. If so, a uniform thin layer of the developer D is formed on the surface of the developing sleeve 3, similar to the cylindrical rod 5.

[0054] The developer D described above is a two-component developer. Although a one-component developer is also applicable, a two-component developer has a more effective regulatory effect. This is because the magnetic force of the magnetic carrier is higher in the two-component developer, and the effect of the repulsive magnetic field works more effectively. This effect is most preferably achieved under the carrier particle size and magnetization conditions described above.

Based on the configuration explained above, the diameter φ of the cylindrical rod 5 and the distances and specific values of the magnetic field strength distributions P1 and P2 are set for the arrangement conditions of the developing sleeve 3 and the cylindrical rod 5. Examples 1, 2, and 3 that were carried out will be described below.

Example 1 The magnet roller 4 used in Example 1 was fixed, and the cylindrical rod 5 and the developing sleeve 3 were of a contact type, and the cylindrical rod 5 had a diameter of 7 mm, was made of nonmagnetic stainless steel, and had magnetic field strength distribution The distance between P1 and P2 is set to 5 mm.

As a carrier, spherical ferrite particles were coated by a spray coating method to obtain coated carrier sample I having an average particle diameter of about 30 μm.

When this sample I was measured under 1000 Gauss, it was found to be 20 emu/g, and the resistivity of each sample was 1014 Ωcm or more.

The toner was pulverized and granulated with an average particle diameter of 10 μm, consisting of 100 parts by weight of a styrene-acrylic resin (HIMER UP 110, manufactured by Sanyo Chemical Co., Ltd.), 10 parts by weight of carbon black (MA-100, manufactured by Mitsubishi Chemical Industry Co., Ltd.), and 5 parts by weight of nigrosine. Using non-magnetic particles obtained by the method, the developer was mixed with the carrier sample and loaded into a copying machine equipped with the developing device shown in FIG. 4, and a large number of continuous copying experiments were conducted. .

In this case, the photoreceptor 16 is an amorphous silicone photoreceptor whose circumferential speed is 180 mm/sec.
The highest potential of the electrostatic image formed on the magnetic roller 6 is -500V, the lowest potential is -100V, the outer diameter of the developing sleeve 3 is 20 mm, its rotation speed is 200 rpm, the main magnetic pole is 900 Gauss, and the other N and S magnetic poles of the magnetic roller 4. The magnetic flux density is 500 Gauss, P1 and P2 is 700 Gauss, and between P1 and P2 is 50 Gauss.
The thickness of the developer layer in the 0 Gauss development area A is approximately 0.2 mm, and the gap between the developing sleeve 3 and the photoreceptor 16 is 0.3 mm.
That is, the bias voltage applied to the developing sleeve 3 has a DC voltage component of -250V and an AC voltage component of 5KH.
z and 500V. That is, in this case, the developer layer is not in contact with the surface of the photoreceptor 16.

Development was carried out under conditions such that the toner particle ratio of developer D in the developer reservoir was 10 wt % relative to the carrier. The average charge amount of the toner was 15 μC/g.

A test chart was copied as a subject, developed under the above conditions, transferred to plain paper using a corona discharge transfer device, and fixed by passing through a heat roller fixing device with a surface temperature of 140°C. Copies were obtained and their image quality was visually evaluated.

Subsequently, 50,000 sheets of recording paper were obtained, and a stable and unchanged image was obtained from beginning to end.

Example 2 The magnet roller 4 used in Example 2 was fixed and was of a non-contact type with a gap of 0.3 mm between the cylindrical rod 5 and the developing sleeve 3, and the diameter of the cylindrical rod 5 was φ. is a 10 mm non-magnetic stainless steel material, magnetic field strength distribution P1, P
The distance between the two is set to 10 mm.

100 parts by weight of fine powder ferrite and 50 parts by weight of styrene-acrylic resin were premixed in a ball mill and thoroughly melted and kneaded using an extruder. The kneaded material was cooled and pulverized with a jet pulverizer, further treated in hot air at about 300°C with a spray dryer to make it spherical, and classified with an air classifier to obtain a dispersed carrier sample II with an average particle size of 30 μm. . When the magnetization of the sample was measured under 1000 Gauss, Sample 2 was found to be 15 emu. Further, the resistivity of both samples was 1014 Ωcm or more. A toner having almost the same composition as that used in Example 1 and having an average particle diameter of about 5 μm was used, mixed with the carrier sample II to prepare a developer, and equipped with a developing device shown in FIG. 4.
In other respects, a copying machine having the same configuration as that used in Example 1 was loaded, and a continuous copying test was conducted on a large number of sheets.

In this case, the conditions of the photoreceptor 16 are the same as in Example 1, the outer diameter of the developing sleeve 3 is also 20 mm, however, its rotation speed is 150 rpm, and the magnetic flux density of the magnetic pole facing the developing area A of the magnetic roller 4 is is 1200 Gauss, the magnetic flux density of the N and S magnetic poles of the other magnets is 500 Gauss, P1,
P2 is 600 Gauss, the distance between P1 and P2 is 300 Gauss, the thickness of the developer layer is 0.4 mm, the gap between the developing sleeve 3 and the photoreceptor 16 is 0.6 mm, that is, 600 μm, and the bias voltage applied to the developing sleeve 3 is DC voltage component -200
V, AC voltage component 2KHz, and 1000V. In this embodiment, the developer layer on the developing sleeve 3 is not in contact with the surface of the photoreceptor 16. The toner particle ratio of the developer D in the developer reservoir is 20wt to carrier particles.
%. The average charge amount of toner is 2
It was 0 μC/g.

[0067] The image was very clear and had a high density, and although 50,000 sheets of recording paper were subsequently obtained, it was possible to obtain an image that remained stable and unchanged from beginning to end.

Example 3 The magnetic roller 4 used in Example 3 was a non-contact type in which the cylindrical rod 5 and the developing sleeve 3 were fixed and had a gap of 0.5 mm, and the diameter of the cylindrical rod 5 was φ. The settings were the same as in Example 2 except that the material was a 5 mm magnetic stainless steel material. That is, a developer prepared using the carrier sample II and toner used in Example 2, except that the layer forming conditions were changed, was loaded into the copying machine used in Example 2, and a copying test was conducted. The resulting image on the recording paper was extremely clear with no edge effect or fog, and had a high density, and was superior to the image in Example 2 in terms of higher resolution and higher density. Subsequently, 50,000 sheets of recording paper were obtained, and images remained stable and unchanged from beginning to end.

[0069]

Effects of the Invention: A uniform thin layer of developer is formed on the surface of the developing sleeve by the repelling magnetic pole formed on the surface of the developing sleeve and the developer layer forming means (cylindrical rod) having curvature. A good toner image is developed on the body surface. Further, the developer is transported smoothly without damaging the coating film of the carrier.

[Brief explanation of the drawing]

FIG. 1 is a side view showing a developer layer forming means (cylindrical rod) according to one embodiment of the present invention and a state in which it is placed in pressed contact with a developing sleeve. FIG. 2 is a side view showing a state in which a developer layer forming means (cylindrical rod) is arranged with a gap in a developing sleeve according to an embodiment of the present invention. FIG. 3 is a diagram showing the magnetic field strength distribution on the surface of the developing sleeve. FIG. 4 is a side sectional view showing the configuration of a developing device according to an embodiment of the present invention.

[Explanation of symbols]

1...Developing device
3...Developing sleeve 4...Magnetic roller
4a...Notch groove 5...Cylindrical rod (developer layer forming means)
6...Elastic member 15...Holder
16...Photoreceptor D...
developer

Claims (4)

[Claims] 1. A developing device for an image forming apparatus using a two-component developer consisting of a magnetic carrier and a toner, wherein like magnetic poles are juxtaposed in a developing sleeve that magnetically holds and conveys the developer. A developing device comprising a developer layer forming means that forms a repulsive magnetic field and has a curvature at its tip facing the surface of the developing sleeve on which the repulsive magnetic field is formed to regulate the developer. 2. The developing device according to claim 1, wherein the developing layer forming means is provided in pressure contact with the surface of the developing sleeve. 3. The developing device according to claim 1, wherein the developing layer forming means is provided with a distance of 0.05 to 1.0 mm from the surface of the developing sleeve. 4. In claims 1, 2, and 3, the diameter φ of the tip of the developer layer forming means satisfies 0.5d≦φ≦3d, where d is the peak interval of the magnetic force on the surface of the developing sleeve. A developing device characterized by being set within a range.