JPH1115276A - Developing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce a deterioration in a developer and to stably obtain an excellent image without a defect in image quality and the sticking of carriers, in a developing device using a two-component developer including toner and the carriers and making an electrostatic latent image visualizable. SOLUTION: A developer carrier arranged to be proximate to and face an image carrier 1 is provided with a magnetic recording layer 12b and a conductive layer 12a. The magnetic recording layer is magnetized to alternately obtain the S- and N-poles and the distance between adjacent magnetic poles is 25 μm-250 μm. Magnetic force by such a magnetic pole is rapidly attenuated in a vertical direction from the surface of the developer carrier and a nearly uniform thin developer layer is formed on the surface of the developer carrier. The developer layer becomes an almost fixed state on the periphery of the developer carrier by magnetic restraining force, so that the mechanical rubbing of the surface of the image carrier 1 with the carriers does not occur. Thus, a high-quality image without the defect in the image quality such as a printing nap mark and a brushing bias can be reproduced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a developing device which is used in an electrophotographic recording device or an electrostatic recording device or the like, and selectively transfers toner to a latent image due to a difference in electrostatic potential to visualize the developing device. The present invention relates to a developing device using a two-component developer in which a magnetic carrier and a toner are mixed.

[0002]

2. Description of the Related Art As image forming apparatuses such as copying machines and printers, electrophotographic or electrostatic recording apparatuses are widely used. Such an apparatus is configured to form an electrostatic latent image on an image carrier, transfer toner to the latent image to form a visible image, and then transfer the toner image to recording paper or the like.

A developing device for visualizing an electrostatic latent image on the image carrier has a so-called contact type in which a two-component developer comprising a toner and a magnetic carrier is brought into contact with the surface of the image carrier and development is performed by transferring the toner. There is a two-component developing device. Although this developing device has a problem that it is necessary to control the toner concentration in the developer, a mechanism for stirring the developer is required, and the device becomes large, however, in terms of image quality characteristics and developer transportability, etc. It is excellent and has become the mainstream of developing devices.

FIG. 14 is a schematic structural view showing an example of the above-mentioned contact type two-component developing apparatus, in which a developing roll 401 (developer carrying member) provided with a magnet roll 401a and a sleeve 401b driven to rotate around the magnet roll 401a is used. Have. Further, a supply member 402 for supplying a two-component developer to the peripheral surface of the sleeve 401b and a layer thickness regulating member 403 called a trimmer are provided, whereby a developer layer having an appropriate thickness is formed on the sleeve. Form. The developer layer thus formed forms a so-called magnetic brush in which carriers are connected in a spike shape in accordance with a magnetic field generated by the magnet roll 401a.
The toner is transferred in contact with the image carrier 410 at a position opposed to the image carrier 410.

In such a contact-type two-component developing device, since the magnetic brush of the developer mechanically rubs the surface of the image carrier, image defects such as so-called brush marks and sweeping by the magnetic brush are likely to occur. . Therefore, there have been proposed a number of methods for avoiding the above-described image quality defect in a contact type two-component developing device, and a so-called non-contact type two-component developing device for performing development without bringing a developer into contact with the surface of an image carrier.

[0006] For example, in the developing method disclosed in Japanese Patent Publication No. 8-33691, a developer layer is provided with a toner layer and a magnetic brush layer formed of toner and a magnetic carrier. The electrostatic latent image on the image carrier is developed while applying a bias electric field composed of an AC component and a DC component to the carrier, and a space formed by the image carrier and the developer carrier in the developing section is developed. 1.5% to 30% of the volume occupied by the magnetic carrier present in the developing unit with respect to the volume
In the developing section, charge is injected into the magnetic carrier by the action of the AC bias. Then, the magnetic carrier holding the electric charge is reciprocated and vibrated between the developer carrier and the image carrier, and the toner on the developer carrier and the toner carried on the surface of the magnetic carrier in the developing section are carried on the image carrier. It is designed to be transferred to the body.

In this method, the volume occupied by the magnetic carrier present in the developing section, that is, the filling rate is set relatively low, thereby reducing the mechanical rubbing of the magnetic brush and suppressing the image quality defect. is there. At this time, the magnetic brush is sparse and the interval between the magnetic brushes, ie, the gap between the magnetic brushes is widened, and the decrease in the developing performance is caused by the reciprocating and oscillating motion of the magnetic carrier and the toner layer being formed in the gap between the magnetic brushes. The leverage toner is supplemented by being subjected to development, thereby achieving high-density image reproduction.

Further, non-contact two-component developing device disclosed in Japanese Patent Kokoku 3-2304 uses insulating magnetic carrier, amplitude V _AC (V) of the AC component of the developing bias,
When the frequency is f (Hz) and the gap between the image carrier and the developer carrier is d (mm), 0.2 ≦ V _AC / (d · f) ｛(V _AC / d) −1500） / It is configured to satisfy f ≦ 1.0. This image forming apparatus includes:
By appropriately selecting the frequency, amplitude and the like of the AC component of the developing bias, it is intended to prevent image disturbance and color mixing.

[0009]

However, in the method disclosed in Japanese Patent Publication No. 8-33691, the surface charge amount of the carrier caused by frictional charging between the toner and the carrier, and the charge injected into the carrier in the developing unit The amount fluctuates with changes in the environment and the passage of time, and the state of the reciprocating and oscillating motion of the magnetic carrier in the developing section changes. For this reason, there is a disadvantage that the stability of the image density is lacking.

Further, although the mechanical rubbing of the magnetic brush is reduced, the magnetic carrier and the image carrier are in contact with each other. However, image quality defects such as brush traces and sweeps still exist, and there is a difficulty in improving image quality.

Further, in the apparatus disclosed in Japanese Patent Publication No. 3-2304, although the occurrence of image quality defects such as brush marks and sweeping is avoided by using a non-contact type, the magnetic carrier is transferred to the image carrier. There is a disadvantage that so-called carrier adhesion is apt to occur. This carrier adhesion is likely to occur at the peripheral portion or between the lines of a line image, particularly in an image having a high spatial frequency such as a kanji having many strokes. This is because a so-called fringe electric field is generated at the boundary (edge) between the image portion and the background portion of the electrostatic latent image, and the electrostatic attraction acts on the magnetic carrier charged to the opposite polarity to the toner at the peripheral portion of the image. To do that.

When the carrier adheres, the magnetic carrier transferred onto the image carrier comes into contact with the recording paper in the transfer area together with the toner image, so that the toner image may be chipped or missing, or the magnetic carrier may not be recorded. The image quality is deteriorated, such as being transferred to the paper and causing a black point. In addition, since the magnetic carrier flows out little by little from the inside of the developing device, the interval between replenishment and replacement of the developer becomes short.
Furthermore, it causes in-flight contamination.

In the two-component developing apparatus, the above-mentioned layer thickness regulating member is used regardless of whether it is a contact type or a non-contact type.
Since the developer is excessively filled, a strong compressive force acts on the developer. Further, when the developer passes through the gap between the layer thickness regulating member and the developer carrier, a strong frictional force acts on the developer. Such a force causes deterioration of the developer. The above-mentioned deterioration of the developer is roughly classified into the deterioration of the toner and the deterioration of the carrier, and both are caused by a compressive force, a frictional force, and the like. It is.

In general, an external additive added for improving the chargeability and fluidity is attached to the toner surface. When a compressive force or a frictional force acts on the developer, the external additive is removed from the toner surface. Peeling or burying in toner resin. Such a state in which the external additive has been peeled or buried is a typical form of toner deterioration. When such deterioration proceeds, the triboelectric charging characteristics change, and the charge amount distribution of the toner is extremely wide and unstable. Becomes For this reason, a toner having a low charge amount and a toner charged to a polarity opposite to a predetermined polarity (hereinafter, referred to as a toner of opposite polarity) are generated, and fogging to a background portion is generated.

Further, when the toner is deteriorated as described above, the contact area between the toner and the carrier increases.
The adhesion between the toner and the carrier increases. For this reason, it is difficult for the toner to peel off from the surface of the carrier, and the amount of toner to be developed is reduced, and the image density is reduced.
In particular, in non-contact two-component development, since there is no adhesive force between the toner and the image carrier, the coulomb force acting on the toner by the electric field causes the toner to separate from the carrier surface due to the electric field. Occurs when the adhesive force is overcome. Therefore, the decrease in image density is remarkably caused by the increase in the adhesive force between the toner and the carrier due to the toner deterioration. As described above, when an image defect occurs due to deterioration of the toner, it means that the life of the developer has expired, and the developer needs to be replaced.

On the other hand, the deterioration of the carrier is caused by the adhesion of the toner and the external additive of the toner to the surface of the carrier. When such deterioration occurs, the difference in the triboelectric charging order between the toner and the carrier is smaller than before the deterioration because the same material as the toner exists on the carrier surface. Accordingly, the charge amount of the toner decreases with the deterioration of the carrier, and a toner having a low charge amount and a toner of the opposite polarity are generated, so that fogging to the background portion occurs.

Another problem with the two-component developing apparatus using the layer thickness regulating member is as follows. When a layer thickness regulating member (trimmer) made of a non-magnetic or magnetic material is used, the amount of developer transported depends on the gap between the layer thickness regulating member and the surface of the developer carrier, and the position of the magnetic pole of the developer carrier. Since the relationship depends on the relationship, the dimensional accuracy and the setting accuracy of the layer thickness regulating member greatly affect the image quality. Therefore, in order to obtain a good image, it is necessary to set the gap with extremely high precision. For this reason, much labor is required for processing and installation of the layer thickness regulating member, and the manufacturing cost increases.

Particularly, in recent image forming apparatuses, it is necessary to perform development with excellent resolution and fine line reproducibility, to develop a latent image having a low potential, and to obtain high development efficiency in a high-speed process. In such a case, it is desirable to set the developing gap, that is, the gap between the developer carrier and the image carrier, to be small. At this time, the developer layer must be a thin layer with a smaller amount of conveyance, and the gap between the layer thickness regulating member and the surface of the developer carrier must be set smaller.

Also, in the method and apparatus disclosed in the above-mentioned Japanese Patent Publication No. 8-33691 and Japanese Patent Publication No. 3-2304, a thinner developer transport amount is required as compared with the conventional two-component development. Must be in layers. For this reason, it is necessary to set the gap between the layer thickness regulating member and the surface of the developer carrier to be narrower. The narrower the gap, the greater the effect on the image quality of the dimensional accuracy and setting accuracy of the layer thickness regulating member. . Further, as the gap becomes narrower, the compressive force and the frictional force acting on the developer increase, so that the deterioration of the developer is accelerated.

The present invention has been made in view of the above circumstances, and an object thereof is to form a uniform thin layer of developer without mechanically controlling the thickness of the developer layer. An object of the present invention is to provide a developing device which can form and reduce the deterioration of the developer, and can stably obtain a good image free from image quality defects and carrier adhesion using the thin developer layer.

[0021]

In order to solve the above-mentioned problems, in the developing device according to the first aspect of the present invention, a developer carrying member for carrying and transporting a two-component developer on a peripheral surface is provided. ,
It has a plurality of magnetic poles for adsorbing almost one layer of carriers almost uniformly, and at a position where the image carrier and the developer carrier are opposed to each other,
The magnetic carrier moves relatively fixedly on the peripheral surface of the developer carrying member and moves so that only the toner is transferred to the image carrying member to form a toner image.

These magnetic poles are set so that substantially the above-mentioned carrier layer can be formed by appropriately selecting the intensity of the magnetic field to be generated and the magnetic pole interval. For example, as in the developing device according to claim 2,
When the distance between adjacent magnetic poles magnetized in the vicinity of the peripheral surface of the developer carrier is about 25 μm to 250 μm, and the N pole and the S pole are alternately magnetized, the particle size generally used Can almost uniformly adsorb carriers having a size of about 25 μm to 200 μm.

The principle that a substantially uniform thin layer of carrier is formed by such a magnetic pole can be considered as follows. As described above, the magnetic field lines in the direction perpendicular to the surface of the developer carrying member, because the lines of magnetic force due to the magnetic poles arranged at narrow intervals are directed to adjacent magnetic poles having different polarities,
It rapidly attenuates near the surface of the developer carrier. Further, when the magnetic carrier layer is formed on the peripheral surface, the lines of magnetic force pass through the magnetic carrier layer that comes into contact with the peripheral surface of the developer carrying member, and are hardly distributed outside the magnetic carrier layer. Therefore, the carriers are not concentrated and attached to the portions above the magnetic poles, but are adsorbed in a state where almost only one layer is arranged in order along the magnetic field. For this reason, a thin developer layer having no non-adhered portion of the developer and no valley structure is formed on the developer carrier, and is transported to the development area while being held by the magnetic force.

In the above-described developing device, a thin layer of developer can be formed without using a layer thickness regulating member by the action of the magnetic pole provided on the developer carrier.
It is possible to prevent the deterioration of the developer without applying a large load to the developer. Further, since the developer layer is formed only by the magnetic force of the developer carrying member, the amount of the developer transported does not depend on the precision of the components and does not change with time.

Further, since the interval between the magnetic poles is set to be sufficiently small, the effect of the magnetic pole pattern does not occur, and an image with high uniformity can be obtained. Further, since the magnetic carrier forms a closed magnetic circuit-like bridge between the magnetic poles, a strong magnetic binding force acts on the carrier layer on the developer carrier. The state in which the magnetic carrier does not move relative to the peripheral surface of the developer carrying member, that is, the state in which the magnetic carrier is adsorbed on the peripheral surface without jumping, rolling, or stirring on the peripheral surface Transported as is. Therefore, the scattering of the developer and the adhesion of the carrier to the image carrier do not occur. Further, at a position where the image carrier and the developer carrier face each other,
The carrier is almost fixed on the peripheral surface of the developer carrier by the magnetic binding force and does not contact the image carrier, so that the carrier does not mechanically rub the surface of the image carrier, and hence the brush marks It is possible to reproduce a high-quality image free from image quality defects such as image sweeping and the like. Further, the state of the developer layer in the development area is hardly affected by the environment and the passage of time, and is kept almost constant, so that stable image reproduction is possible.

In addition, the magnetic carrier of the developer used in the developing device is charged with electric charge in a developing bias electric field formed at a position facing the image carrier and the developer carrier. It is preferable to use a material having a volume resistance value that is high enough not to cause such a problem.
0 volume resistivity in the electric field of ⁶ V / m is 10 ¹⁰ Omega
・ It is desirable to use one having a size of cm or more.

When the volume resistivity of the magnetic carrier is low, charge injection into the magnetic carrier is likely to occur in the developing region, and the Coulomb force acting on the magnetic carrier becomes stronger than the magnetic restraining force, so that the carrier is almost fixed. It is released from the state that was done. For this reason, the toner easily transfers onto the image carrier, and an image defect due to carrier adhesion occurs. As described above, the volume specific resistance of the magnetic carrier affects the fixed state of the magnetic carrier in the developing region,
By using a magnetic carrier having a high volume resistivity, it becomes easy to substantially fix one layer of the developer on the peripheral surface of the developer carrier.

Further, the magnetic carrier of the developer used in the developing device is 10 ⁶ / (4
(π) It is desirable to use a material having a magnetization of about 45 kA / m or more and 360 kA / m or less in a magnetic field of A / m.

When the magnetization of the magnetic carrier is small, the force attracted to the developer carrier by the magnetic field formed by the magnetic poles becomes small. For this reason, if the magnetic pole interval is set small and the magnetic field component in the direction perpendicular to the surface of the developer carrier is rapidly attenuated, the portion where the carrier is not adsorbed on the surface of the developer carrier (the portion of the developer layer) Dropout) easily occurs. If such a developer layer is omitted, minute density unevenness in a low density portion and poor reproducibility of a fine line occur.

On the other hand, when the magnetization of the magnetic carrier is large, a strong attraction force acts according to the magnetization pattern of the developer carrier, and the developer layer is substantially uniform on and between the magnetic poles, that is, the developing layer has no peak-valley structure. It becomes difficult to form an agent layer. When the developer layer has such a peak-valley structure, density unevenness corresponding to the magnetic pole pitch occurs in a low-density portion, or minute unevenness occurs in the width of a thin line.

Further, as the magnetic carrier of the developer used in the developing device, it is desirable to use a magnetic carrier having a residual magnetization of about 25 kA / m or less.
If the residual magnetization of the magnetic carrier is large, magnetic aggregation of the carrier is likely to occur, and due to this effect, the developer layer on the developer carrier has minute unevenness, that is, more developer layers due to magnetic aggregation. A part to be formed occurs. When such unevenness occurs, minute density unevenness in a low density portion and poor reproducibility of a fine line occur. As described above, the magnetization and the residual magnetization of the magnetic carrier affect the state of the developer layer formed by the magnetic poles. It is easy to form the developer layer on the developer carrier.

Further, the developer carrier is provided with the plurality of magnetic poles at substantially equal intervals over the entire region in the circumferential direction, and the magnetic poles are configured to move circumferentially. It is desirable. For example, when a developing roll having a plurality of magnetic poles for adsorbing substantially one layer of carriers substantially uniformly is constituted by a magnet roll and a sleeve that is driven to rotate around the magnet roll, the developer is fixed according to the rotation of the sleeve with the magnet roll fixed. Is transported, and almost one layer of the developer moves on the fixed magnetic pole. At this time, the rolling of the developer layer corresponding to the magnetic pole pattern as in the conventional two-component developing device does not occur, and although the above-mentioned substantially fixed state is almost maintained, the developer particles collide with each other, Due to this effect, fine irregularities are likely to be formed on the developer layer during transportation. When such unevenness occurs, density unevenness corresponding to the magnetic pole pitch occurs in the low density portion, or minute unevenness occurs in the width of the fine line.

Therefore, by moving the developer carrier including the magnetic poles around and transporting the developer on the peripheral surface to the developing area, almost one layer of the developer layer can be more reliably formed on the peripheral surface of the developer carrier. It is possible to make it almost fixed above.

As described above, in the developing apparatus of the present invention, it is possible to form a uniform thin layer of the developer without mechanically regulating the thickness of the developer layer, and to reduce the deterioration of the developer. is there. Further, it is possible to stably obtain a good image free from image quality defects and carrier adhesion by using the thin developer layer.

A technique of providing magnetic poles at a small pitch on a developer carrying member in the same manner as described above is disclosed in Japanese Unexamined Patent Publication No. Hei.
No. 259,276. According to the technology described in this publication, a developing roll (developer carrier) is constituted by a single rotating body, magnetic poles are provided around the periphery at a small pitch of about 100 μm or less, and a one-component magnetic developer is adsorbed around the periphery. Is what you do. As a result, it is possible to reduce the occurrence of unevenness of the developer layer adsorbed corresponding to the position of the magnetic pole, and to use the developer layer for forming a toner image in a development area. With such a configuration, development without density unevenness can be performed with a simple configuration without having a structure having a magnet roll in which a developing roll is fixedly supported and a sleeve that rotates around the magnet roll.

However, the developing device described in this publication is based on the premise that a one-component magnetic developer is used. The one-component developer has a particle diameter of 7 to 15 μm and a magnetization pitch of 100 μm.
Even if it is less than about m, the adsorbed developer forms spikes on the peripheral surface of the developing roll. Therefore, a uniform developer layer cannot be formed unless the height of the spikes is mechanically regulated by the layer thickness regulating member, and it is assumed that the layer thickness regulating member is used. As described above, the techniques described in the above publications are different from the invention according to the present invention in terms of the developer to be treated and have different purposes, and are based on completely different technical ideas.

[0037]

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, embodiments of the present invention will be described in the following order. [1. Image forming apparatus using developing device according to the present invention] [2. First Embodiment] <a. Configuration and operation of developing device><b. Method of magnetization><c. Experiment for investigating the relationship between the magnetic pole interval, etc. and the image density, image uniformity, and carrier adhesion><d. Generation of carrier magnetization / magnetic pole spacing and density unevenness
Experiment for investigating the relationship between reproducibility of fine lines and carrier adhesion><e. An experiment for investigating the relationship between the residual magnetization of the carrier and the occurrence of density unevenness, fine line reproducibility, and carrier adhesion><f. Experiment for Investigating Relationship between Carrier Specific Volume and Carrier Attachment><g. Experiment on maintainability> [3. Second Embodiment] [4. Third Embodiment] [5. Modifiable Configuration of the Above Embodiment]

[1. Image Forming Apparatus Using Developing Apparatus According to the Present Invention] FIG. 1 is a schematic configuration diagram showing an example of an image forming apparatus using a developing apparatus according to the present invention.
This image forming apparatus includes a photosensitive drum 1 in which a photosensitive layer is provided on a peripheral surface of a substantially cylindrical conductive substrate, and the photosensitive drum 1 rotates in the direction of arrow A shown in the figure. It is designed to be driven. Around the photoconductor drum 1, along a rotation direction thereof, a charger 2, an exposure device 3, and a developing device 4 in which a developer carrier 12 formed of a cylindrical member is opposed to the photoconductor drum 1. , Pre-transfer corotron 5
, A transfer corotron 6, a peeling corotron 7, a cleaner 8, and an optical neutralizer 9.

The conductive substrate of the photosensitive drum 1 is electrically grounded. In addition, a negatively charged organic photoreceptor (OPC) is used for the photoreceptor layer. When the photoreceptor layer is almost uniformly charged and then irradiated with image light, the charge in the exposed portion flows to the conductive substrate, and the potential is changed It is designed to attenuate. The photosensitive drum 1 can be set, for example, to have an outer diameter of 100 mm and a moving speed of the peripheral surface, that is, a process speed of about 160 mm / s.

The exposure device has a laser generator which blinks based on an image signal, and a polygon mirror which reflects a laser beam emitted from the laser generator while rotating the laser beam. Is exposed and scanned to form an electrostatic latent image. This exposure scanning may be performed by exposing the image area or exposing the non-image area. The image is formed by appropriately selecting the charging polarity of the photoconductor and the charging polarity of the toner. The toner can be transferred to the portion and visualized. In this image forming apparatus, the photosensitive member and the toner are negatively charged, and are set so as to expose the image portion.

Next, the operation of the image forming apparatus will be described. First, the surface of the photosensitive drum 1 is uniformly charged to -450 V by the charger 2 (FIG. 2A). Subsequently, the image portion is exposed by a laser beam to form a negative latent image having an exposed portion potential of approximately -200 V [FIG.
(B)]. Then, the toner is transferred to the exposed portion of the negative latent image by the developing device 4 to be visualized [FIG.
(C)].

The toner image formed on the photosensitive drum 1 as described above is transferred onto a recording sheet by charging the transfer corotron 6. Thereafter, the recording paper is peeled off from the surface of the photosensitive drum 1 by the charging of the peeling corotron 7, and is conveyed to a fixing device (not shown). In the fixing device, the toner image is fixed on the recording paper by heating and pressing.

On the other hand, the surface of the photoreceptor drum 1 after the transfer of the toner image and the peeling of the recording paper are completed, the residual toner is cleaned by the cleaner 8, and the residual charge is removed by the exposure by the light neutralizer 9. In the image recording step. The pre-transfer corotron 5 provided on the downstream side of the developing device in the rotation direction of the photosensitive drum 1 is used when investigating the amount of carrier transferred to the image carrier during development. Uniform negative charging is performed on the toner image formed thereon. As a result, the carrier transferred onto the photosensitive drum 1 unintentionally during the development is negatively charged and is transferred together with the toner onto the recording paper. An assessment can be made.

[2. First Embodiment] Next, a developing device according to an embodiment of the present invention will be described. <A. Configuration and Operation of Developing Apparatus> FIG. 3 is a schematic structural view showing a developing apparatus which can be used in the above-described image forming apparatus and is an embodiment of the present invention. The developing device 4 includes a developing housing 1 in which a developer is stored.
An opening for development is provided at a position opposed to the photosensitive drum 1 of the photoconductor 1, and a developing roll 12 is disposed in the opening.
Two screw augers 13 and 14 are provided on the rear side. Further, a scraper 15 for removing the developer adhered on the developing roll 12 is provided so as to be in contact with the developing roll 12.

The screw augers 13 and 14 are provided in two developer agitating / transporting chambers partitioned by a partition wall 16 in the developing housing, and are driven to rotate so as to transport the developer in opposite directions. is there. The two developer stirring / transfer chambers communicate with each other at both ends, and the developer conveyed by the screw augers 13 and 14 circulates and moves in the two developer stirring / transfer chambers while being stirred.

The developing roll 12 is supported so as to be rotatable about an axis, and as shown in FIG. 4, a magnetic recording layer 12b and a conductive layer 12a formed on the peripheral surface thereof.
And the main part is constituted. The outer diameter of the developing roll 12 is 18 mm, the peripheral speed during driving is 320 mm / s, and the gap between the photosensitive drum 1 and the developer carrier 12 is 30 mm.
The thickness is set to 0 μm, and the developer layer is held so as not to be in contact with the photosensitive drum 1.

A developing bias voltage is applied to the conductive layer 12a by a developing bias power supply 17. As the developing bias voltage, an AC voltage obtained by superimposing a DC voltage is employed. The DC component is -4 to prevent the occurrence of ground fog.
It is set to 00V. If the frequency of the AC component of the developing bias voltage is too low, uneven shading corresponding to the frequency of the developing bias occurs on the image, and if the frequency is too high, the movement of the toner cannot follow the change in the electric field and the developing efficiency decreases. Resulting in. On the other hand, if the voltage between the peaks of the AC bias is too low, the developing efficiency decreases because a sufficient electric field does not act on the toner, and if the voltage between the peaks is too high, fog on the background and carrier adhesion on the photoconductor are reduced. Is more likely to occur. From the above points, the frequency is 0.4 to 10 kHz.
z and the peak-to-peak voltage are preferably set in the range of about 0.8 to 3 kV. In this embodiment, the AC component of the developing bias voltage is a rectangular wave having a frequency of 6 kHz, and the peak-to-peak voltage is set to 1.5 kV.

On the other hand, on the magnetic recording layer 12b, S poles and N poles are alternately arranged at equal intervals (25 to 250 μm) over the entire circumference.
m) so as to be parallel. This magnetization will be described later. The magnetic recording layer 12b is made of a ferrite magnet, and the conductive layer 12a is formed by stacking an aluminum layer on this falite to a thickness of about 1 μm.

The developer used in the developing device is a two-component developer obtained by mixing a non-magnetic toner and a magnetic carrier. As the toner, a polyester toner having a weight average particle diameter of 7 μm and a negative charge property is used. Have been. As the carrier, a so-called magnetic powder-dispersed resin carrier in which magnetic powder is dispersed in a binder resin, or a so-called ferrite carrier in which spherical ferrite particles are coated with a resin are used.

In such a developing device 4, the developer sufficiently stirred by the screw augers 13 and 14 comes into contact with the developer carrier in a region X shown in FIG. You. Then, the magnetic recording layer 12
A certain amount of the developer is attracted to the peripheral surface of the developing roll 12 by the magnetic field formed by b. In other words, almost one layer of the magnetic carrier electrically adsorbing the toner is almost uniformly attached, and the developer layer is formed without using the layer thickness regulating member. Then, this developer layer is applied to the developing roll 12
Is transported to a development area facing the photoconductor drum 1 with the rotation of the photoconductor drum 1, and is used for developing an electrostatic latent image on the photoconductor drum 1.

In this developing device, the developing roll 12
To the magnetic recording layer 12b and the conductive layer 1 formed on the peripheral surface thereof.
2a, a ferrite magnet was used for the magnetic recording layer 12b and aluminum was used for the conductive layer 12a, but the present invention is not limited to these configurations and materials. Any material capable of forming a magnetization pattern can be used for the magnetic recording layer 12b. For example, a so-called plastic magnet in which a powder of a ferromagnetic material is dispersed in a thermoplastic or thermosetting resin, or a so-called rubber magnet in which a powder of a ferromagnetic material is dispersed in a flexible material is used. be able to. In this case, as the material having flexibility, any material that can be mixed with a large amount of a magnetic material and can maintain flexibility can be used. For example, Hypalon, polyisobutylene, neoprene rubber , Nitrile rubber, chlorinated polyethylene and the like can be used. Further, as the conductive layer 12a, any material to which a developing bias voltage can be applied can be used. For example,
Ni, Ti, Cu, Cu-Ni alloy, titanium nitride, or the like can be used.

Further, a thin film magnetic recording layer may be formed on the conductive layer. FIG. 5 shows an example of this configuration. The magnetic recording layer 122b is obtained by dispersing a powder of a ferromagnetic material in a binder resin and forming the conductive base 122a.
It is constituted by coating with a layer thickness of 50 μm on top. As the magnetic material, any material known as a magnet material or a magnetic recording material can be used.
In addition to γ-Fe ₂ O ₃ , CrO ₂ , Ba ferrite, S
r Ferrite or the like can be used. Further, as the binder resin, any one constituting a magnetic recording layer such as a tape, a disk, and a card can be used, and for example, polycarbonate, polyester, polyurethane and the like can be used. Further, conductive fine particles and the like can be added to the magnetic recording layer 122b as needed.

Further, a magnetic metal material can be used for the magnetic recording layer 122b. In this case, any known material such as a magnet material or a magnetic recording material can be used. For example, Co-Ni-P, Co-Ni, Co-C
r, Fe-Cr-Co, Mg-Al, Al-Ni-Co
Etc. can be used. Further, the magnetic recording layer 122b may have a configuration in which a magnetic material is dispersed in a flexible material. In this case, as the material having flexibility, any material that can be mixed with a large amount of magnetic material and can maintain flexibility can be used. For example, Hypalon, polyisobutylene, neoprene rubber, nitrile Rubber, polyethylene chloride and the like can be used.

<B. Next, a method of magnetizing the magnetic recording layer 12b will be described. As shown in FIG. 6, the magnetization of the magnetic recording layer is performed by a magnetic recording head 200 arranged close to the peripheral surface of the developing roll 12. The magnetic recording head 200 includes a core 201 made of a soft magnetic material and having both ends arranged in parallel at intervals.
A coil 202 wound around the core 201,
The core 201 is arranged so that both ends thereof are close to the peripheral surface of the developing roll. A magnetizing current is supplied to the coil 202 from a power supply controlled by a magnetizing signal generator. When a current flows through the coil 202, a magnetic flux is generated in the core 201, and the magnetic flux is generated in the core 201. It passes through the magnetic recording layer 12b from the tip. Thereby, the magnetic recording layer 12b is magnetized. The magnetizing current supplied to the coil 202 is supplied intermittently or with the direction of the current being changed intermittently based on a signal from the magnetizing signal generator, and as shown in FIG. It is magnetized into a predetermined magnetization pattern. In the present embodiment, the N and S poles are alternately magnetized in a sine wave pattern in the circumferential direction of the developing roll 12, and the peak value of the magnetic flux density in the radial direction on the surface of the developing roll is set to 50 mT.

The magnetic recording layer 122 shown in FIG.
The magnetic recording head 21 shown in FIG.
0 can also be used. When such a magnetic recording head 210 is used, it is assumed that a magnetic recording layer 122b is provided on a conductive base 122a made of a soft magnetic material as a developing roll. As the soft magnetic material forming the conductive substrate 122a, any known soft magnetic material can be used, and examples thereof include iron, an iron-silicon alloy, and an iron-nickel alloy.

The magnetic recording head 210 has a shape in which the cross section is reduced so that one end 211a of the core becomes a small end surface, while the other end 211b has a shape in which a large end surface faces the peripheral surface of the developing roll. Has become. When a current is supplied to the coil 212 wound around the core 211, the magnetic flux generated in the core 211 passes through the magnetic recording layer 122b from a small end face, and further passes therethrough a soft magnetic layer (conductive base). 122a) to the other end 211b of the core whose end face is larger. Therefore, at the position facing the small end face 211a of the magnetic recording layer 122b, an N pole and an S pole are formed in the thickness direction of the magnetic recording layer 122b, while the portion facing the large end face is hardly magnetized. By performing such magnetization over substantially the entire peripheral surface of the developing roll, the magnetic recording layer 122
The magnetic poles arranged in the thickness direction of b can be formed over almost the entire peripheral surface. By magnetizing in the thickness direction of the magnetic recording layer in this manner, a magnetic field having a large magnetic flux density can be formed, and such a magnetized pattern may be adopted according to the interval between the magnetic poles, the carrier used, and the like. it can.

<C. Experiments to investigate the relationship between magnetic pole spacing, etc. and image density, image uniformity, and carrier adhesion>
In the developing device shown in FIG. 3, a development test of an electrostatic latent image is performed, and the image density, carrier adhesion, and the like are changed by changing the type and particle size of the carrier and the magnetic pole interval of the magnetic recording layer 12b.
The result of examining the uniformity of the image will be described. Generally, in a developing method using a thin layer of a two-component developer, it is preferable to use a carrier having a small average particle size in order to obtain a fine-grained image. When a carrier having a large average particle size is used, the distance between the chains of the carriers arranged along the magnetic field is wide and coarse, so that it is difficult to obtain a highly uniform thin layer. Therefore, poor uniformity of the image and poor edge reproduction of the line image occur. Therefore, the average particle size of the carrier is 100 μm.
m or less, and in this test, the average particle size is 5
0 μm and 100 μm carriers are used. Table 1 shows the four types of carriers used. Below margin

[0058]

[Table 1]

The types of carriers in Table 1 are magnetic powder-dispersed resin carriers, and are ferrite carriers. The average particle size is a weight average particle size.
The magnetization per unit weight is a value in a magnetic field of 10 ⁶ / (4π) A / m. The residual magnetization is 5 for all carriers.
It is less than kA / m. The volume resistivity is 10 ¹⁵
It is adjusted so as to be in the range of 〜１０10 ¹⁶ Ω · cm.
The mixing ratio of the toner and the carrier in the developer is the weight ratio of the toner in the developer, and 15% by weight of the carrier and 7.9% by weight of the carrier, and the toner amount per unit volume is substantially equal. It is set to become. The charge amount of the toner is -15 to -20 mC /
Adjusted to the kg range. The developing roll 12 has a magnetic pole interval on its surface of 13 μm, 25 μm.
m, 50 μm, 100 μm, 250 μm and 500 μm. However, the magnetic pole interval is a value obtained by rounding off the first decimal place.

Evaluation of the image density is performed by developing a solid image and measuring the density with a reflection densitometer (trade name: X-RITE31).
The measurement is performed in step 0). If the measured value is 1.8 or more, both the solid image and the line image have a sufficient density.
8 or more is evaluated as ○, and less than 1.8 is evaluated as ×.

The so-called alternating line in which the image portion and the background portion are arranged in parallel at a fixed period in the direction perpendicular to the process direction as shown in FIG. The amount was measured and evaluated. The cycle of the alternating lines is 2 cycles / mm, and the ratio of the image portion to the background portion is 1: 1. In the development of such an alternating line, an electrostatic latent image in which the image portion and the background portion are adjacent to each other at a very small interval exists on the surface of the photoreceptor. Is generated, and in the peripheral portion of the image, electrostatic attraction acts on the carrier charged to the opposite polarity to the toner. Therefore, the alternating line is an image in which the carrier is likely to adhere, and is suitable for evaluating the carrier adhesion.

The evaluation index of the carrier adhesion amount was the area ratio of the carrier particles on the background of the alternating line. To measure the area ratio, an image analyzer (trade name: LUZEX-5)
000) was used. When the area ratio of the carrier particles is 1.0
% Or less, there is no practical problem.
○ indicates 1.0% or less, and X indicates 1.0% or more.

Further, the uniformity of the image was evaluated visually with respect to the solid image. A state where density unevenness was not visually observed was evaluated as ○. Level was marked as x. Table 2 shows the results of the evaluation performed by the method described above. In this table, the comprehensive evaluation was evaluated as follows:
At least one with x was marked as x. Below margin

[0064]

[Table 2]

From Table 2, it can be seen that the magnetic pole interval is 25 μm or more and 250 μm or more.
It can be seen that in the range of μm or less, a sufficient image density can be obtained without causing carrier adhesion or poor uniformity. If the magnetic pole interval is smaller than 25 μm, it becomes difficult to arrange the magnetic carriers along the magnetic field, and the developer layer is entirely sparse. For this reason, a sufficient concentration cannot be obtained,
Image uniformity is also impaired. In addition, the magnetic field at a portion distant from the surface of the developing roll 12 rapidly attenuates and becomes weaker as the magnetic pole interval is smaller. Therefore, when the magnetic pole interval is smaller than 25 μm, the magnetic constraint acting on the magnetic carrier on the developing roll is reduced. The force is weakened, and carrier adhesion occurs due to the action of the fringe electric field described above. Further, a phenomenon in which the developer was scattered by the centrifugal force acting when the developing roll was rotated was observed.

On the other hand, when the interval between the magnetic poles is wider than 250 μm, the magnetic binding force acting on the magnetic carrier in the portion between the magnetic poles becomes extremely weak. For this reason, the developer is intensively attached near the magnetic pole. Therefore, the state of the developer layer is such that peaks and valleys are formed in accordance with the magnetization pattern, and the developed image has unevenness in the shape of the magnetization pattern.
Further, as described above, since the magnetic binding force acting on the magnetic carrier attached to the gap between the magnetic poles is weak, the carrier is attached to the photoconductor and the developer is scattered.

On the other hand, the distance between the magnetic poles should be 25 μm or more and 2
When the thickness is 50 μm or less, the magnetic carriers are arranged neatly along the magnetic field on the developing roll. For this reason, a developer layer in which there is no portion where the developer does not adhere and there is almost no magnetic carrier having no peak and valley structure is formed on the developing roll, and this developer layer is held by magnetic force. Conveyed. Therefore, an image with high uniformity can be obtained without using a layer thickness regulating member. Further, since the developer conveyance amount does not depend on the component accuracy, high accuracy is not required for assembly. Furthermore, since a strong magnetic binding force acts on the developer layer on the developing roll,
Adhesion of the carrier to the photoconductor and scattering of the developer do not occur. Also, the developer layer on the developing roll is conveyed without being relatively moved while being substantially fixed on the surface of the developing roll. It is possible to obtain an image with extremely high uniformity without image quality defects such as shifting.

In the developing device shown in FIG. 3, the developer layer on the developing roll 12 is in a non-contact state with the photosensitive drum 1, but the developer layer is in contact with the photosensitive drum 1. A similar result can be obtained even when it is set. In this case, the surface of the photoreceptor is mechanically rubbed by the developer layer. However, the developer layer is almost fixed on the developing roll, and the conventional contact-type two-component developing device is used. Since there is no such movement due to rolling or vibration of the magnetic brush on the developing roll, image quality defects such as brush marks and sweeping hardly occur.

In this developing device, the developing roll 12
N and S poles were alternately magnetized in the circumferential direction, but when the N and S poles were alternately magnetized in the longitudinal direction of the developing roll or when the N and S poles were The same result can be obtained when the magnets are magnetized so as to be arranged in a mosaic pattern.

<D. Experiment for investigating the relationship between carrier magnetization and magnetic pole interval and occurrence of density unevenness, reproducibility of fine wires, and carrier adhesion> Next, in the developing device shown in FIG. 3, the carrier magnetization and magnetic pole interval were changed. The results of an investigation of carrier adhesion, density unevenness in a low density portion, and reproducibility of fine lines will be described. In this experiment, ten kinds of carriers shown in Table 3 are used, all of which are ferrite carriers, and the true density is 4.5 g / cm ³ . The average particle size is a weight average particle size, and the magnetization is 1
It is a value in a magnetic field of 0 ⁶ / (4π) A / m. Below margin

[0071]

[Table 3]

The residual magnetization was 5 kA / m for all carriers.
Is less than. The volume resistivity is 10 ¹⁵ to 10 ¹⁶ Ω
・ Adjusted to be within the range of cm. The mixing ratio of the toner and the carrier in the developer was 7.9% by weight in terms of the weight ratio of the toner in the developer. The charge amount of the toner is-
It is adjusted in the range of 15 to -20 mC / kg. As the developing roll, the magnetic pole interval on the surface is 25 μm.
m and 250 μm were used.

In the experiment, an image was formed under the above conditions, and the following evaluation was performed on the output image. The uniformity of the image in the low-density part is evaluated by visually checking a halftone image having an area ratio of 20%, and a state in which no minute density unevenness is observed. , And the unusable level was marked as x.
Regarding the reproducibility of fine lines, a line image having a width of 130 μm was visually evaluated, and a state in which no jagged edges and uneven density were observed in the edge portion was evaluated. , And the unusable level was marked as x. Regarding the carrier adhesion,
Evaluation was performed in the same manner as in the previous experiment.

The results of such experiments are as shown in Table 4. The comprehensive evaluation was as follows: 〇 for all of the above four items without △ and ×, △ for one with △ but without ×, and one for But those with x are marked as x. From the results shown in this table, the carrier magnetization is 45 kA / m or more and 360 kA / m.
If it is below, it can be seen that a sufficient image density can be obtained without causing carrier adhesion, and at the same time, the uniformity of the low density portion and the reproducibility of the fine line are improved. Below margin

[0075]

[Table 4]

The reason why the magnetization of the carrier affects the uniformity of the low-density portion and the reproducibility of the fine line can be considered as follows. As described above, the developing roll 12
The magnetic field at a position distant from the surface of the first magnetic field attenuates rapidly and becomes weaker as the magnetic pole interval is smaller. Therefore, as the magnetic pole interval is smaller, the developer layer is more likely to come off, that is, a portion where the developer is not attached. On the other hand, by setting the magnetization of the carrier to 45 kA / m or more and increasing the magnetic restraining force acting on the carrier, it is possible to suppress the occurrence of the removal of the developer layer. Therefore, the uniformity of the low density portion and the reproducibility of the fine line can be improved. On the other hand, when the magnetization of the carrier is smaller than 45 kA / m, it is difficult to uniformly attach the carrier on the surface of the developing roll without causing the so-called removal of the developer. Although this is not a level that makes it practically difficult to use, the uniformity and the fine line reproducibility of the low density portion are reduced.

Further, as the magnetic pole interval of the developing roll is wider,
The developer layer can easily form a peak-valley structure according to the magnetization pattern. However, the magnetization of the carrier is set to 360 kA / m or less to weaken the magnetic binding force acting on the carrier, whereby the peak-valley structure of the developer layer is generated. Can be suppressed. Therefore, the uniformity of the low density portion and the reproducibility of the fine line can be improved. On the other hand, when the magnetization of the carrier is larger than 360 kA / m, the above-mentioned peak-valley structure becomes remarkable, which is not a level that makes the use of the carrier practically difficult. I will.

For the above reasons, the magnetic pole interval is set to 25
In the case of not less than μm and not more than 250 μm, 10 ⁶ / (4
π) 45 kA of carrier magnetization in a magnetic field of A / m
By setting it to be not less than / m and not more than 360 kA / m, a sufficient image density can be obtained without causing carrier adhesion, and at the same time, uniformity of a low density portion and reproducibility of fine lines can be improved. In this experiment, a ferrite carrier was used. However, if the magnetization was within the above range, similar results were obtained when a so-called magnetic powder-dispersed resin carrier in which magnetic powder was dispersed in a resin was used. Can be

<E. Experiment for investigating the relationship between the residual magnetization of the carrier and the occurrence of density unevenness, fine line reproducibility, and carrier adhesion> Next, in the developing device shown in FIG. 3, the residual magnetization of the carrier, that is, the magnetization in the absence of a magnetic field was changed. A description will now be given of the results of an investigation on the adhesion of a carrier to a photoreceptor, the occurrence of density unevenness in a low density portion, and the reproducibility of fine lines. In this experiment, eight types of carriers shown in Table 5 were used, all of which were magnetic powder-dispersed resin carriers in which magnetic powder was dispersed in resin, and had a true density of 2.2 g / g.
cm ³ . The average particle size is a weight average particle size,
The magnetization per unit weight in a magnetic field of 10 ⁶ / (4π) A / m is 40 Am ² / kg, and the magnetization is 88 kA / m.

[0080]

[Table 5]

The volume resistivity is 10 ¹⁵ to 10 ¹⁶ Ω.
・ Adjusted to be cm. The mixing ratio between the toner in the developer and the carrier was 15% by weight based on the weight of the toner in the developer. The charge amount of the toner is -15
It is adjusted to the range of -20 mC / kg. The developing roll used had a magnetic pole interval of 100 μm on its surface. The adhesion of the carrier, the density unevenness in the low-density portion, and the reproducibility of the fine line were evaluated by the same method as in the previous experiment. The results of this experiment are as shown in Table 6. The comprehensive evaluation was as follows: ○ for all of the above four items without △ and ×, △ for those with △ but no X, and × for at least one Things are marked as x. From this result, if the residual magnetization of the carrier is 25 kA / m or less, a sufficient image density can be obtained without causing carrier adhesion, and at the same time,
It can be seen that the uniformity of the low density portion and the reproducibility of the fine line are improved.

[0082]

[Table 6]

The reason why the residual magnetization of the carrier affects the uniformity of the low-concentration portion and the reproducibility of the fine line can be considered as follows. If the residual magnetization of the magnetic carrier is large, magnetic aggregation of the carrier is likely to occur, and due to this effect, the developer layer on the developing roll has delicate irregularities,
That is, due to magnetic aggregation, a portion where more developer layers are formed is generated. When such unevenness occurs, the uniformity and the reproducibility of fine lines in the low density portion are reduced. Therefore, by setting the residual magnetization of the carrier to 25 kA / m or less, a sufficient image density can be obtained without causing carrier adhesion, and at the same time, the uniformity of the low density portion and the reproducibility of fine lines can be improved. Although a magnetic powder-dispersed resin carrier was used in this experiment, similar results can be obtained when a ferrite carrier is used as long as the residual magnetization is within the above range. In this experiment, a developing roll having a magnetic pole interval of 100 μm was used. However, a similar result can be obtained when the magnetic pole interval is 25 μm or more and 250 μm or less.

<F. Experiment for Investigating Relationship between Carrier Volume Specific Resistance and Carrier Attachment> Next, in the developing device shown in FIG.
The result of investigating the occurrence of carrier adhesion will be described. In this experiment, eight types of carriers shown in Table 7 were used, all of which were ferrite carriers, and had a true density of 4.5 g / cm ³ . The average particle size is a weight average particle size, and the volume resistivity value is 10 ⁶ V / m.
Are values in the electric field. The specific volume resistance value is a value measured by placing each carrier in a cylindrical cell container having a diameter of 50 mm and a thickness of 1 mm, applying a load of 3,000 g thereon, and applying an electric field of 10 ⁶ V / m. It is.
Incidentally, 10 ⁶ / (4π) magnetization per unit weight in the field of A / m is 50A · m ² · kg, the magnetization 225
kA / m. The residual magnetization is 5 kA for all carriers.
/ M. The mixing ratio of the toner and the carrier in the developer was 7.9% by weight in terms of the weight ratio of the toner in the developer. The charge amount of the toner is -15 to -20 mC / k.
g. The developing roll used had a magnetic pole interval of 100 μm on its surface. Below margin

[0085]

[Table 7]

The carrier adhesion in this experiment was evaluated in the same manner as in the previous experiment. Table 8 shows the results.
From the results shown in Table 8, it can be seen that if the volume resistivity of the carrier in an electric field of 10 ⁶ V / m is 10 ¹⁰ Ω · cm or more, the carrier adhesion is at a level that causes no practical problem. Below margin

[0087]

[Table 8]

When the volume resistivity of the carrier in an electric field of 10 ⁶ V / m is lower than 10 ¹⁰ Ω · cm,
Since charge injection into the carrier occurs in the developing region, the Coulomb force acting on the magnetic carrier becomes stronger than the magnetic restraining force, and it becomes difficult to maintain the carrier in a substantially fixed state on the developing roll. Therefore, the carrier is easily transferred onto the photoreceptor, and carrier adhesion occurs. For the above reasons, the volume resistivity of the carrier in the electric field of 10 ⁶ V / m is set to 10 ¹⁰ Ω ·
When the density is not less than cm, sufficient image density can be obtained without causing carrier adhesion, and at the same time, uniformity of a low density portion and reproducibility of fine lines can be improved.

In this experiment, a ferrite carrier was used. However, if the volume resistivity is within the above range,
Similar results are obtained when a magnetic powder-dispersed resin carrier is used. In this experiment, the magnetic pole spacing was 10
Although a 0 μm developing roll was used, similar results can be obtained if the magnetic pole interval is in the range of 25 μm or more and 250 μm or less.

<G. Experiment on maintainability> Next, FIG.
An experiment conducted on the maintainability of the developing device shown in FIG. In this experiment, the image forming apparatus shown in FIG.
Develop 100,000 sheets of solid images continuously using the developing device shown in FIG. Then, after the development of a predetermined number of sheets, the development density of the solid image and the charge amount of the toner are measured, and the transition when the number of developed sheets is overlapped is investigated. Further, in order to investigate the effect of the developing device according to the present invention, similar development was performed using a conventionally known developing device, and the result was compared with the result obtained by the developing device shown in FIG. I do.

In this experiment, the following developers were used. ◎ Carrier: Ferrite carrier Average particle size 50 μm True density 4.5 g / cm ³ Magnetization per unit weight 50 A · m ² / kg Magnetization 225 kA / m Residual magnetization Less than 5 kA / m Volume resistivity 10 ¹⁵ Ω · cm ◎ Toner: Negatively chargeable polyester-based toner Weight average particle diameter 7 μm Charge -15 to −20 mC / kg The magnetic pole interval on the surface of the developing roll is 100 μm.

On the other hand, the conventional developing device used for comparison has a layer thickness regulating member 315 provided in close proximity to the developing roll 312 as shown in FIG. The developing roll 312 includes a fixedly supported magnet roll 312a and a sleeve 31 driven to rotate around the magnet roll 312a.
2b, and the magnetic roll 312a is provided with five magnetic poles in the circumferential direction. The developer is attracted to the surface of the sleeve 312b by the magnetic field generated by the magnetic pole,
It moves with the rotation of the sleeve 312b, and the amount of developer is regulated at a position facing the layer thickness regulating member 315, so that a thin layer of developer is formed.

The dimensions and settings of the main parts of this developing device are as follows. Developing roll: outer diameter 18 mm Circumferential speed of developing roll: 320 mm / s Setting of developing area: distance between photosensitive drum and developing roll: 500 μm Position where photosensitive drum and developing roll are closest to each other: magnetic pole N ₁ central angle ... 70 of substantially position of the magnetic pole S ₁ midpoints pole N ₁ of the magnetic pole S ₁ and
° Magnetic flux density at the position of the magnetic pole N _{1 and} the position of the magnetic pole S ₁ ··· 7
0 mT Development bias: DC superimposed AC voltage DC component: -400 V AC component: 6 kHz rectangular wave, peak-to-peak voltage 1.6
kV

Each of the above two developing devices accommodates 400 g of developer in a housing.
The toner is appropriately replenished so that the weight ratio of the toner in the developer becomes 7.5 to 8.5% by weight.

FIGS. 10 and 11 show the solid image density and toner charge when 100,000 sheets are developed using the developing device according to the present invention (FIG. 3) and the conventional developing device (FIG. 9). It shows the transition of the quantity. From these figures, it can be seen that in the developing device 4 according to the present invention, the image density and the toner charge amount are favorably maintained through the development of 100,000 sheets. On the other hand, the conventional developing device 3 as a comparative example
At 00, a sharp decrease in density and a decrease in toner charge amount occur. Due to this decrease in toner charge, ground fogging due to toner scattering occurred on 20,000 sheets, and the developer reached its end of life.

Further, as a result of examining the state of the developer after the long-term development experiment, the developer used in the conventional developing apparatus 300 showed significant toner deterioration and carrier deterioration. In the conventional developing device 300, the layer thickness regulating member 3
This is because a strong stress acts on the developer when the layer thickness is regulated by No. 15 and toner deterioration and carrier deterioration occur early. Due to this effect, the density decrease and the toner charge amount decrease as described above.

On the other hand, in the developing device 4 according to the present invention, since the layer thickness regulating member is not used, no stress acts on the developer when the developer layer is formed, so that the deterioration of the developer can be prevented. In the developer used in the developing device 4, the toner and the carrier after the long-term development experiment were in the same state as the initial state, and no deterioration state was observed. Further, there is almost no change in the amount of transported developer over 100,000 sheets.

As described above, it can be seen that the developing device according to the present invention can stably maintain good image quality over a long period of time. Further, in the developing device of the present invention, even when the charge amount or the resistance value of the carrier fluctuates due to the influence of the environment or aging, the carrier is almost fixed on the developing roll by the magnetic restraining force in the developing region. Therefore, the state of the developer layer is kept almost constant. Therefore,
It is possible to reproduce images stably without being affected by changes in the environment or influence over time.

[3. Second Embodiment] Next, a developing device according to another embodiment of the present invention will be described.
FIG. 12 is a schematic configuration diagram showing the developing device and a partially enlarged cross-sectional view of the developer carrier. The developing device includes a photosensitive drum 1 of a developing housing 21 in which a developer is stored.
An opening for development is provided at a portion opposed to the above, and a developer carrier is disposed in this opening. In addition, two screw augers 26 and 27 are provided behind the developer carrier as developer stirring and conveying means.

The developer carrier 22 is composed of a drive roll 23, two support rolls 24 and 25, and an endless belt 22 stretched over these rolls. The belt 22 is driven to rotate in the direction of the arrow shown. The outer diameter of the drive roll 23 is 1
0 mm, and is rotationally driven so that the belt moves at a peripheral speed of 320 mm / s.

The belt 22 is formed by laminating a magnetic recording layer 22b on a conductive substrate 22a. A developing bias voltage is applied to the conductive base 22a by a developing bias power supply (not shown). The developing bias voltage is an AC voltage on which a DC voltage is superimposed. The DC component is set to −400 V in order to prevent occurrence of ground fogging. The AC component is a rectangular wave having a frequency of 6 kHz and a peak-to-peak voltage of 1. It is set to 5 kV. In the magnetic recording layer 22b, S poles and N poles are alternately magnetized at equal intervals over the entire circumference of the belt 22. This magnetic recording layer 22
γ-Fe ₂ O ₃ is used as the magnetic material of b and polyurethane is used as the binder resin, and the thickness of the magnetic recording layer 22b is 50 μm.

The magnetization of the magnetic recording layer 22b is performed by the method shown in FIG.
A magnetic recording head similar to that shown in FIG. 1 is used, and N and S poles are alternately magnetized in a sine wave pattern in the circumferential direction of the belt. The direction of magnetization is set so that an N pole and an S pole are generated in the horizontal direction, the magnetic pole interval on the belt surface is 100 μm, and the peak value of the magnetic flux density in the vertical direction is 5 μm.
0 mT.

In such a developing device, when the developer is supplied to the belt 22, a certain amount of the developer adheres to the peripheral surface of the belt 22 by the magnetic field of the magnetic recording layer 22b, and a layer thickness regulating member is used. Without forming a thin layer of developer. Further, the developer is conveyed to a developing area facing the photosensitive drum 1 with the rotation of the belt 22, and is used for developing the electrostatic latent image on the photosensitive drum 1. At this time,
In the developer layer, substantially one layer of the carrier to which the toner is adhered is almost uniformly adhered to the peripheral surface of the belt, and the gap between the belt and the photosensitive drum is set to 300 μm, so that the developer layer is kept in non-contact. In such a developing step, the carrier is held by the magnetic poles of the belt, so that the developer does not scatter. Further, since a uniform thin layer of the developer is supplied to the developing area, a uniform high-quality image can be obtained.

Using the above-described developing apparatus, a long-term developing experiment was performed on 100,000 sheets in the same manner as the developing apparatus shown in FIG.
The image density and the toner charge amount were maintained satisfactorily throughout the thousands of sheets, and no deterioration was observed in the developer after the experiment. By using an endless belt for the developer carrying member as in this developing device, it is possible to obtain a higher degree of freedom in design than in the case of a cylindrical shape. For example, like this developing device, the drive roll can be made smaller in diameter than a cylindrical developer carrier, and the developing opening of the housing can be designed to be narrow. Therefore, it is possible to reduce the size of the developing device and the entire image forming apparatus. In addition, it is possible to arbitrarily design the drawing shape of the developer carrying member (belt) in a portion other than the developing portion, and it is possible to easily cope with optimum conditions in each portion.

[4. Third Embodiment] FIG. 13 is a schematic sectional view of a developing device according to another embodiment of the present invention. In this developing device, an opening for development is provided in a portion of the developing housing 31 opposed to the photosensitive drum 1 similarly to the developing device shown in FIG. 12, and a developer carrier is provided in this opening. ing. In addition, two screw augers 36 and 37 are provided behind the developer carrier as a means for stirring and transporting the developer.

The developer carrier comprises a drive roll 33, two support rolls 34 and 35, and an endless belt 32 stretched over these.
Is driven to rotate by the rotation of. In this developer carrier, since two support rolls 34 and 35 are arranged at positions facing the photosensitive drum 1, the approaching position between the endless belt 32 and the photosensitive drum 1 is As compared with the developing device, a developing region having a larger area is formed.

In such a developing device, the belt 3
Due to the magnetic field of the second magnetic recording layer, a thin layer of developer is formed on the peripheral surface, and is used for developing an electrostatic latent image on the photosensitive drum 1 in a developing area having a larger area. Therefore, even if the developing device is downsized, a sufficient developing time can be secured, and high-density development can be performed without lowering the developing efficiency.

[5. Modifiable Configuration of the Above Embodiment] The embodiment of the present invention according to the present application is not limited to the above-described embodiment. For example, the following items can be implemented by changing settings or conditions. .

In the above embodiment, the developer carrier including the magnetic pole is configured to move around. However, the developer carrier is configured by a magnet roll and a sleeve that is driven to rotate around the magnet roll, and the magnet roll is fixed. Then, the developer may be transported in accordance with the rotation of the sleeve. Further, the magnet roll and the sleeve may be rotated together. At this time, since the member forming the sleeve needs to exert a sufficient magnetic binding force on the magnetic carrier by the internal magnet, it is preferable that the thickness is 5 to several hundred μm. A metal formed by the above-mentioned method, a resin film formed by extrusion molding or the like is preferable. Ni as the metal sleeve, polyethylene terephthalate, polyurethane as the resin sleeve,
It is possible to use polycarbonate, polyimide or the like.

In the above embodiment, the pattern is formed by alternately magnetizing the N pole and the S pole of the magnetic poles at substantially equal intervals.
The present invention is not limited to this. For example, when the N pole and the S pole are alternately magnetized, the magnets may be magnetized so that the intervals between adjacent magnetic poles of different polarities are alternately different. Further, for example, a non-magnetized region or a low-magnetization region may be provided outside the pair of N pole and S pole. Further, for example, the magnetic poles adjacent to each other across the non-magnetized region or the low magnetization region may have the same polarity or different polarities. In the above embodiment, the moving speed of the peripheral surface of the developer carrier is set to 320 mm / s. However, the state of formation of the developer layer does not depend on the moving speed of the peripheral surface, and is 10 mm / s.
In the region from about s to 900 mm / s, a uniform developer layer can be formed, and the developer does not scatter when the developer carrier rotates. The direction of movement of the peripheral surface of the developer carrier is opposite to the direction of movement of the peripheral surface of the image carrier (photoreceptor drum). However, the present invention is not limited to this. Is also good.

The developing bias voltage is an AC voltage on which a DC voltage is superimposed, and the waveform of the AC voltage is a rectangular wave. However, the present invention is not limited to this. Voltage is available. For example,
A so-called DC bias of only a DC voltage or a DC bias applied intermittently can be used. As the AC voltage, a sine wave, a triangular wave, a sawtooth wave, an asymmetric rectangular wave, or the like can be used. In the above embodiment, as a stirring / transporting means of the developer,
Although a screw auger was used, the present invention is not limited to this.
Transport means can be used. For example, any means for mechanically, magnetically or electrostatically stirring and transporting the developer can be used. In the above embodiment, supply of the developer to the developer carrier
As the collecting means, a portion for bringing the developer into close contact with the developing roll and a scraper are provided. However, the present invention is not limited to this, and any supplying / collecting means depending on the purpose and application can be used. . Further, a developer flowing-down means for flowing down the developer and a means for magnetically holding the developer and transporting the developer on the peripheral surface of the developer carrying body are provided in parallel with the developer carrier, These may be used to supply and recover the developer to and from the developer carrier.

In the above-described embodiment, a single-color image recording apparatus is used. However, color image recording in which a color image is formed by a plurality of color toners on an electrostatic latent image holding member, and the toner images are collectively transferred onto recording paper. The same can be applied to the apparatus. In the above-described embodiment, the photosensitive member is used as the electrostatic latent image holding member.However, a dielectric material is used as the electrostatic latent image holding member, for example, a discharge recording head used in an electrostatic printer, An electrostatic latent image may be formed by an ion flow control head or the like disclosed in JP-A-59-190854.

[0113]

As described above, the developing device according to the present invention has a plurality of magnetic poles for adsorbing substantially one layer of carriers substantially uniformly on the peripheral surface of the developer carrying member, and the layer thickness regulating member is provided. Since the developer layer is formed only by the magnetic force of the developer carrying member without using the developer, a large load is not applied to the developer, and the deterioration of the developer can be prevented. Also, the developer transport amount does not fluctuate depending on the component accuracy,
Since the state of the developer layer formed does not fluctuate with the passage of time, an image having a stable density can be obtained. Further, in the developing device according to the invention of the present application, the S pole and the N pole are magnetized at a small pitch on the peripheral surface of the developer carrier, and almost only one layer is attracted to the peripheral surface of the developer carrier. A strong magnetic binding force acts on the magnetic carrier, thereby preventing scattering of the developer and transfer of the carrier to the image carrier.

On the other hand, at the position where the image carrier and the developer carrier are opposed to each other, the carrier is substantially fixed on the peripheral surface of the developer carrier by the magnetic restraining force. No mechanical scanning occurs, so that high-quality image reproduction without image quality defects such as brush traces and sweeping is possible. Further, since the developer layer is thinned as described above, the gap between the developer carrier and the image carrier can be set small, and high-speed, high-quality development can be performed.

Further, the developing device is configured such that a plurality of magnetic poles provided on the peripheral surface of the developer carrier move along with the orbital movement of the peripheral surface of the developer carrier. It becomes easy to convey the thin layer of the developer fixed on the peripheral surface of the developer carrier. As a result, variations in the thickness of the developer layer due to the collision of the developer particles with each other on the developer carrying member are less likely to occur, and a good image is obtained without unevenness in density in the low-density portion and unevenness in the width of the fine line. It becomes possible.

Further, as the magnetic carrier, 10 ⁶ / (4
π) By selecting a material having a magnetization of about 45 kA / m or more and 360 kA / m or less in a magnetic field of A / m, a portion where the developer is not adsorbed on the surface of the developer carrier or a valley-and-valley structure corresponding to the magnetization pattern is obtained. A uniform developer layer can be formed. Further, by using a magnetic carrier having a residual magnetization of about 25 kA / m or less, the developer layer can be prevented from becoming uneven due to magnetic aggregation of the carrier. In addition, by setting the magnetic carrier to have a volume resistivity of 10 ¹⁰ Ω · cm or more in an electric field of 10 ⁶ V / m, almost one layer of the developer is fixed on the peripheral surface of the developer carrier. It becomes easy to make the state.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram illustrating an example of an image forming apparatus using a developing device according to the present invention.

FIG. 2 is a diagram showing a change in potential on the surface of an image carrier when forming a toner image in the image forming apparatus shown in FIG. 1;

FIG. 3 is a schematic configuration diagram illustrating a developing device according to an embodiment of the present invention.

4 is a partially enlarged cross-sectional view of a developing roll used in the developing device shown in FIG.

5 is a partially enlarged sectional view of another developing roll that can be used in the developing device shown in FIG.

6 is a diagram showing a method of magnetizing the developing roll shown in FIG.

7 is a diagram illustrating an example of a magnetizing method that can be used for magnetizing the developing roll illustrated in FIG.

8 is a diagram showing an image pattern used to investigate an amount of transfer of a carrier of a two-component developing device to a photosensitive drum in the image forming apparatus shown in FIG.

FIG. 9 is a schematic configuration diagram illustrating a conventional developing device used for comparing performance with the developing device illustrated in FIG. 3;

10 is a diagram showing the relationship between the number of prints and the solid image density in the developing device shown in FIG. 3 and the developing device shown in FIG. 9;

11 is a diagram showing the relationship between the number of prints and the toner charge amount in the developing device shown in FIG. 3 and the developing device shown in FIG. 9;

FIG. 12 is a schematic configuration diagram illustrating a developing device according to another embodiment of the present invention, and a partially enlarged cross-sectional view of a developer carrying member used in the developing device.

FIG. 13 is a schematic configuration diagram showing a developing device according to another embodiment of the present invention.

FIG. 14 is a schematic configuration diagram illustrating an example of a conventional developing device.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Photoreceptor drum 2 Charger 3 Exposure device 4 Developing device 5 Pre-transfer corotron 6 Transfer corotron 7 Peeling corotron 8 Cleaner 9 Light eliminator 11 Developing housing 12 Developing roll 12a Conductive layer 12b Magnetic recording layer 13 Screw auger 14 Screw auger 15 Scraper Reference Signs List 16 partition wall 17 developing bias power supply 21 developing housing 22 endless belt 22a conductive base 22b magnetic recording layer 23 drive roll 24 support roll 25 support roll 26 screw auger 27 screw auger 31 developing housing 32 endless belt 33 drive roll 34 Support Roll 35 Support Roll 36 Screw Auger 37 Screw Auger 122a Conductive Base 122b Magnetic Recording Layer 200 Magnetic Recording Head 201 Core 202 Coil 203 Magnetic flux 210 Magnetic recording head 211 Core 212 Coil 300 Developing device 311 Developing housing 312 Developing roll 312a Magnet roll 312b Sleeve 313 Screw auger 314 Screw auger 315 Layer thickness regulating member 401 Developing roll 401a Magnet roll 401b Sleeve 402 Feeding member 403 Thickness regulating member 410 Image carrier

Claims (7)

[Claims] 1. A developer carrier which is provided close to or in contact with an image carrier having a surface on which an electrostatic latent image is formed, and whose peripheral surface is supported so as to be able to rotate, the developer carrier and the image carrier A developing bias power supply for applying a developing bias voltage between the developing device and the carrier, carrying and transporting a two-component developer containing toner and a magnetic carrier on the peripheral surface of the developer carrying member, A developing device for transferring a toner to the image carrier at a position facing the developer carrier and the developer carrier to form a toner image, wherein the developer carrier is substantially all over the peripheral surface of the developer carrier. A plurality of magnetic poles for adsorbing the magnetic carrier substantially uniformly, and transporting the adsorbed magnetic carrier together with the circumferential movement of the peripheral surface without moving relative to the peripheral surface of the developer carrier. A developing device. 2. The developing device according to claim 1, wherein the plurality of magnetic poles are arranged such that N poles and S poles are alternately arranged, and a magnetic field formed near a peripheral surface of the developer carrying member, The distance between the centers of the positions corresponding to the magnetic poles is 25 μm or more and 250
μm or less. 3. The developing device according to claim 1, wherein the magnetic carrier does not cause charge injection in a developing bias electric field formed at a position facing the image carrier and the developer carrier. A developing device having a high volume resistance value. 4. The developing device according to claim 1, wherein the magnetic carrier has a volume resistivity value of about 10 ¹⁰ Ω · cm or more in an electric field of 10 ⁶ V / m. A developing device. 5. The developing device according to claim 1, wherein the magnetic carrier has a magnetization of about 45 kA in a magnetic field of 10 ⁶ / (4π) A / m. / M or more and 360 kA / m or less. 6. The developing device according to claim 1, wherein the magnetic carrier has a residual magnetization of about 25 kA / m or less. Developing device. 7. The developing device according to claim 1, wherein the developer carrier is substantially equidistant over the entire circumferential direction. Wherein the plurality of magnetic poles are provided, and the magnetic poles move around.