JPH11149218A - Developing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the deterioration of a developer and to provide an excellent image stably by forming a developer thin layer on a developing roll in a developing device using a binary developer containing a toner and a carrier so as to visualize an electrostatic latent image, without mechanically regulating the thickness of the developer layer. SOLUTION: A developing roll 12 arranged so as to closely face to an image carrier is equipped with a magnetic recording layer 12b and a conduction layer 12a, and the magnetic recording layer is alternately polarized into N poles and S poles. The respective magnetic poles have such magnetic flux densities perpendicular to the peripheral face of the developing roll as having distributions with two peak values. A spacing P of adjoining opposite polarity magnetic poles is 25 μm to 250 μm, and the relationship of a toner particle size (d), to a carrier particle size D is (D+2d)/2<=P<=(D+2d)×5. The spacing L between two peaks in the distribution of the respective magnetic pole magnetic flux densities is 300 μm or less, and satisfies a relationship, (D+2d)/4<=L.

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. 33 is a schematic diagram showing an example of the above-mentioned contact type two-component developing device, in which a developing roll 401 (developer carrier) having 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, a developing device according to the first aspect of the present invention includes a developing device that comes into close proximity to or separates from an image carrier on which an electrostatic latent image is formed. And a developer carrying member having a peripheral surface rotatably supported. The developer carrying member carries a two-component developer containing a toner and a magnetic carrier on the peripheral surface thereof, and conveys the developer. A developing bias voltage is applied between the developer carrier and the image carrier to transfer toner to the image carrier at a position facing the developer carrier to form a toner image. A plurality of magnetic poles are provided on the peripheral surface so that a pair of N and S poles has a substantially constant pattern, and each magnetic pole has a magnetic flux density in a direction perpendicular to the peripheral surface of the developer carrier. Has a distribution having a plurality of peak values, and has adjacent peaks of different polarities. Magnetic pole interval P is approximately 25μ
m and not more than 250 μm, and the distance P, the particle size d of the toner, and the particle size D of the magnetic carrier have a relationship of (D + 2d) / 2 ≦ P ≦ (D + 2d) × 5. I do.

At this time, the plurality of magnetic poles may be arranged such that adjacent two magnetic poles may be magnetic poles having different polarities or magnetic poles having the same polarity. The poles need only be arranged in a substantially constant pattern.

In such a developing device, when the developer is supplied to the surface of the developer carrier, the carrier is attracted to the plurality of magnetic poles, and a thin layer of a two-component developer is formed on the surface of the developer carrier. Is done. At this time, since the paired N-pole and S-pole are magnetized in a substantially constant pattern as described above, generally used carriers having a particle size of about 25 μm to 200 μm can be substantially changed according to the magnetization pattern. Only one layer can be adsorbed.

The principle of forming a substantially thinner layer of carriers by such a plurality of magnetic poles can be considered as follows. As an example of the above magnetic pole, FIG.
For example, N poles and S poles are alternately magnetized on the peripheral surface of the developer carrier, and the magnetic flux density of each magnetic pole in the direction perpendicular to the peripheral surface of the developer carrier is two. The distribution has a peak value.

In such a magnetic pole, as shown in FIG. 34, a strong magnetic field is formed between the position of the N-pole peak (M ₂ ) and the position of the S-pole peak (M ₃ ) adjacent to each other at a narrow magnetic pole interval. Is done. Further, on both sides of these magnetic pole peaks, the other N-pole peak (M ₁ ) forming a two-peak distribution shape is provided.
And an S-pole peak (M ₄ ), but most of the magnetic flux wraps around between M _{2 and} M ₃ , so that the magnetic flux hardly distributes between M _{1 and} M _{2 and} between M _{3 and} M _4. State. For this reason, compared with the case where a plurality of magnetic poles are arranged at equal intervals as shown in FIG. 36, the magnetic flux concentrates near the surface of the developer carrier between the adjacent N-pole peak position and S-pole peak position. However, the magnetic field component in the direction perpendicular to the surface of the developer carrier is rapidly attenuated, and the magnetic field does not reach far.

In such a state where the magnetic flux is distributed, FIG.
As shown in FIG. 5, the carrier adsorbed between the N-pole peak position and the S-pole peak position (between M _{2 and} M ₃ ) becomes substantially a single layer, and when the carrier layer is further formed on the peripheral surface, the magnetic field lines are formed. Pass through the carrier layer and hardly distribute outside thereof. Therefore, it is possible to form a substantially single-layer uniform developer layer between the N-pole peak position and the S-pole peak position (between M _{2 and} M ₃ ). Further, since a strong magnetic binding force acts on the magnetic carrier due to the strong magnetic field, scattering of the developer and adhesion of the carrier to the image carrier do not occur.

On the other hand, between two peak positions of each magnetic pole (M
In between ₁ ~M ₂ and M ₃ ~M ₄ between), magnetic binding force acting on the carrier in the magnetic field is very weak is weakened, it is impossible to hold the developer layer. Therefore,
Only between the N pole peak position and the S pole peak positions strong magnetic field is formed (between M ₂ ~M _3), a substantially uniform developer layer of a single layer is formed.

These magnetic poles are determined by the strength of the magnetic field to be generated and the distance P between the adjacent N-pole peak position and S-pole peak position.
Is set so that a carrier layer as described above can be formed. That is, the distance P and the toner particle size d and the carrier particle size D of the developer carried on the peripheral surface of the developer carrying member are set such that (D + 2d) / 2 ≦ P ≦ (D + 2d) × 5. When magnetized, generally used carriers having a particle size of about 25 μm to 200 μm can be almost uniformly adsorbed.

In the magnetic pole shown in FIG. 34, N poles and S poles are alternately arranged, and the magnetic flux density of each magnetic pole in the direction perpendicular to the peripheral surface of the developer carrier has a distribution having two peak values. However, the present invention is not limited to this, and may have a configuration in which magnetic poles of the same polarity are adjacent to each other, or a distribution in which the magnetic flux density of each magnetic pole has a plurality of peak values. Good. In such a magnetic pole arrangement, magnetic flux concentrates between a pair of N poles and S poles arranged in a substantially constant pattern, and magnetic flux lines are hardly distributed between a plurality of peak positions on both sides of the magnetic poles. The magnetic carrier is adsorbed between the N pole and the S pole forming a pair. At this time, by appropriately setting the magnetic pole interval between the adjacent N pole and S pole as described above, it is possible to form a developer layer composed of a substantially single-layer carrier.

Also, as in the invention described in claim 2,
Among the plurality of peaks in the magnetic flux density distribution of each magnetic pole, the interval L between the peaks at both ends is about 300 μm or less, and the interval L, the particle size d of the toner, and the particle size D of the magnetic carrier Is preferably in a relationship of (D + 2d) / 4 ≦ L. For example, in the magnetic pole arrangement shown in FIG. 34, M ₁ to M _1, which are between two peak positions of each magnetic pole,
The interval L between M ₂ and M _{3 to} M ₄ is 300 μm or less, and the interval L, the toner particle size d, and the carrier particle size D are set in the above ranges.

When the distance L is large, the area where the developer does not adhere is widened, and stripe-shaped density unevenness is likely to occur. On the other hand, when the interval L is small, the attenuation of the magnetic field component in the direction perpendicular to the surface of the developer carrier is moderate, and the distribution of the magnetic field is such that a plurality of magnetic poles are arranged at equal intervals as shown in FIG. Get closer to the case. Accordingly, minute layer thickness unevenness is likely to occur. If there is such a minute unevenness in the layer thickness, a minute unevenness in the density in the low-density portion and a poor reproducibility of the fine line occur.

Further, it is desirable that the difference ΔT in the magnetic flux density between the peak portion and the valley portion between the peaks in the magnetic flux density distribution of each magnetic pole is about 5 mT or more. When the difference ΔT of the magnetic flux densities is smaller than 5 mT, the distribution state of the magnetic field becomes close to the case where the magnetic poles are arranged at equal intervals as shown in FIG. It will be easier.

As described above, the distance L between the peak positions at both ends in the magnetic flux density distribution of each magnetic pole and the difference ΔT in the magnetic flux density between the peaks and the valleys between the peaks are determined by the developer layer formed by the magnetic poles. And setting L and ΔT within the above ranges makes it easy to form almost one layer of developer on the developer carrier.

In the above-described developing device, a thin layer of the 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 carrier, 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. In addition, 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.

The difference ΔT in the magnetic flux density between the peak and the valley between the peaks in the magnetic flux density distribution of each magnetic pole is about 5 m.
If it is a value of T or more, it can be set as appropriate. For example, a configuration in which ΔT is substantially equal in all magnetic poles, or a configuration in which ΔT is not equal in each magnetic pole may be employed. Further, in the present invention, the magnetic flux density in the direction perpendicular to the peripheral surface of the developer carrying member has a distribution having a plurality of peak values. An appropriate value can be set according to the state and the like.

The interval between the magnetic poles having a plurality of peaks in the magnetic flux density distribution can be appropriately set as long as it satisfies the above range. For example, as described in claim 4, the magnetic poles can be arranged at substantially equal intervals. By the same effect as described above, a developer layer composed of a substantially single-layer magnetic carrier is formed on the developer carrier. It can be formed almost uniformly. However, the present invention is not limited to this, and it is desirable to appropriately arrange the magnetic poles according to the strength of the magnetic field between the paired north and south poles, the state of adhesion of the developer, and the like. The interval between the plurality of peak positions is
The intervals may not be equal or may be set as appropriate.

As described in claim 5, the distribution of the magnetic flux density is such that for each pair of magnetic poles having the plurality of peaks,
A non-magnetized area or a low-magnetized area may be provided. In such a magnetized pattern, since the magnetic field in the non-magnetized area or the low magnetized area is extremely weak, the magnetic binding force acting on the carrier is weak. For this reason, it is difficult to hold the developer in such a region, but the N
A strong magnetic field is formed between the pole and the S pole, and a developer layer substantially consisting of a single carrier is formed by the same effect as described above. At this time, by adjusting the strength of the adjacent N pole and S pole and the distance between the non-magnetized area and the low magnetized area,
An almost uniform thin layer of the developer can be formed, and the occurrence of striped development density unevenness can be prevented.

Further, as set forth in claim 6, the developer carrier is provided with the plurality of magnetic poles in a substantially constant pattern over the entire area in the circumferential direction, and the magnetic poles are configured to move circumferentially. 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 rotation of the sleeve is performed with the magnet roll fixed. The developer is conveyed according to the formula (1), 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 around the developer carrying member including the magnetic poles 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 carrying member. It can be almost fixed on the top,
Therefore, it is possible to prevent minute density unevenness and poor reproducibility of fine lines in the low density area.

As described above, in the developing apparatus of the present invention, it is possible to form a uniform thin layer of developer without mechanically regulating the thickness of the developer layer, and to reduce the deterioration of the developer. It is. 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 in the above configuration 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.

[0045]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A developing device according to the present invention will be described below with reference to the drawings. FIG. 1 is a schematic configuration diagram illustrating an example of an image forming apparatus using a developing device according to an embodiment of 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 is indicated by an arrow A shown in FIG.
Is rotated in the direction of. Around the photoreceptor drum 1, along a rotation direction thereof, a charger 2, an exposure device 3, and a developing roll 12 formed of a cylindrical member
Developing device 4 facing photoreceptor drum 1, corotron 5 before transfer, transfer corotron 6, and peeling corotron 7
, A cleaner 8 and a light 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. 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 recording paper peeling process is completed, the residual toner is cleaned by the cleaner 8, and the residual charge is removed by the exposure by the light eliminator 9. In the image recording step. The pre-transfer corotron 5 provided on the downstream side of the developing device 4 in the rotation direction of the photosensitive drum 1 is
This is used when investigating the amount of transfer of the carrier to the photosensitive drum at the time of development. The toner image formed on the photosensitive drum 1 is uniformly negatively charged. 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.

[First Embodiment] <a. Configuration and Operation of Developing Apparatus> Next, a developing apparatus according to an embodiment of the present invention will be described. FIG.
A developing device that can be used in the image forming apparatus and is a first embodiment of the invention according to claim 1, claim 2, claim 3, claim 4, or claim 6. It is a schematic block diagram. The developing device 4 is provided with an opening for development at a portion of the developing housing 11 in which the developer is accommodated, the portion being opposed to the photosensitive drum 1.
2 and two screw augers 13 and 14 are provided behind it. 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. As shown in FIG. 4A, a magnetic recording layer 12b and a conductive layer 12a formed on the peripheral surface thereof are formed. The main part is constituted by. This developing roll 1
2 has an outer diameter of 18 mm and a peripheral speed of 320 mm /
s, the gap between the photosensitive drum 1 and the developing roll 12 is 300
μm, and the developer layer is
Is held in a non-contact state.

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, density unevenness corresponding to the frequency of the developing bias occurs on an image. On the other hand, if the frequency is too high, the movement of the toner cannot follow the change in the electric field, and the development efficiency is reduced. On the other hand, when the peak-to-peak voltage of the AC component is too low, a sufficient electric field does not act on the toner, so that the developing efficiency is reduced. On the other hand, if the peak-to-peak voltage is too high, fogging on the background and adhesion of carriers to the photoreceptor are likely to occur. From the above points, it is preferable that the frequency is set in the range of 0.4 to 10 kHz and the peak-to-peak voltage is set in the range of about 0.8 to 3 kHz. In the present 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 1.
It was set to 5 kV.

On the other hand, the magnetic recording layer 12b has the structure shown in FIG.
As shown in (a), magnetization is performed so that S poles and N poles are alternately arranged at equal intervals over the entire circumference. As shown in FIG. 4B, each magnetic pole has a distribution in which the magnetic flux density in the direction perpendicular to the circumferential surface of the developing roll 12 has two peak values, and the adjacent N pole and S pole are Interval P
(P ₂₃ , P ₄₁ shown in the figure) is about 25 μm or more and 250
μm or less and set at substantially equal intervals. Further, when the particle size of the toner is d and the particle size of the magnetic carrier is D, the interval P is set so as to satisfy the following relationship: (D + 2d) / 2 ≦ P ≦ (D + 2d) × 5.

In the distribution of the magnetic flux density of each magnetic pole,
The distance L between the two peak positions is set to 300 μm or less, and the distance L, the particle diameter d of the toner, and the particle diameter D of the magnetic carrier satisfy the relationship of (D + 2d) / 4 ≦ P. Is set to Further, the difference ΔT in the magnetic flux density between the peak and the valley between the peaks in the magnetic flux density distribution of each magnetic pole is set to about 5 mT or more. The method of such magnetization will be described later.
The magnetic recording layer 12b is made of a ferrite magnet, and the conductive layer 12a is formed by laminating an aluminum layer on this ferrite to a thickness of about 1 μm.

The developer used in the developing device is a two-component developer in which a non-magnetic toner and a magnetic carrier are mixed. 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. On the surface of the developing roll 12, as shown in FIG. 5, a strong magnetic field is formed between the N-pole peak position (M ₂ ) and the S-pole peak position (M ₃ ) which are adjacent at a narrow magnetic pole interval. Between two peak positions (M ₁ to
A state in which the magnetic flux hardly distributed to M between ₂ and between M ₃ ~M _4). Therefore, the magnetic flux concentrates near the developing roll surface between the adjacent N-pole peak positions, and the magnetic field component in the direction perpendicular to the developing roll surface is rapidly attenuated, and the magnetic field becomes distant. No longer reach. By such a magnetic field, a certain amount of the developer is adsorbed on the peripheral surface of the developing roll 12 between the adjacent N-pole peak positions. In other words, the carrier electrically adsorbed with the toner is almost uniformly attached to only one layer, and the developer layer is formed without using the layer thickness regulating member. Then, the developer layer is conveyed to a developing area facing the photosensitive drum 1 with the rotation of the developing roll 12, and is used for developing an electrostatic latent image on the photosensitive drum 1.

<B. Next, a method of magnetizing the magnetic recording layer 12b will be described. 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 as shown in FIG. 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 from a power supply to the coil 202 via 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 from the tip of the core 201. It passes through the magnetic recording layer 12b. Thereby, the magnetic recording layer 12b is magnetized. The magnetizing current supplied to the coil 202 is supplied intermittently or with an appropriately changed current direction via a magnetizing signal generator, and the developing roll 1 is driven to rotate as shown in FIG.
2 is magnetized in a predetermined magnetized pattern. In the present embodiment, the peak value of the magnetic flux density in the radial direction on the surface of the developing roll, that is, in the direction perpendicular to the developing roll surface is set to 50 by using the alternating magnetization of the N pole and the S pole in the circumferential direction of the developing roll 12.
mT.

<C. Magnetic pole interval P between adjacent N and S poles
Experiment for investigating the relationship between image density, image uniformity, and carrier adhesion> Next, in a developing device shown in FIG. A description will now be given of the results obtained by changing the magnetic pole interval P between the adjacent N pole and S pole of the magnetic recording layer 12b and examining the image density, the adhesion of the carrier to the photoconductor, and the uniformity of the image.

In general, 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 diameter 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 preferably 100 μm or less. In this test, carriers having an average particle size of 35 μm, 50 μm, and 100 μm are used.

The magnetic carrier is 10 ⁶ / (4π) A
/ M in a magnetic field of about 45 kA / m or more and 36
It is desirable to use one having a value of 0 kA / m or less. When the magnetization of the magnetic carrier is small, the force attracted onto the developing roll by the magnetic field formed by the magnetic poles decreases. 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 developing roll is rapidly attenuated, a portion where the carrier is not attracted to the surface of the developing roll (peeling of the developer layer) occurs. It will be easier. 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, if the magnetization of the magnetic carrier is large, a strong attraction force acts according to the magnetization pattern of the developing roll,
It becomes difficult to form a substantially uniform developer layer between the magnetic poles and between the magnetic poles, that is, a developer layer without a peak-valley structure. 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, it is desirable to use a magnetic carrier having a residual magnetization, that is, a magnetization in a no-magnetic field 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, fine unevenness, that is, magnetic aggregation occurs in the developer layer on the developing roll, and more developer layers are formed. Are formed. 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 pole. By setting the magnetization and the residual magnetization within the above ranges, Thus, it becomes easy to form almost one layer of the developer on the developing roll. Therefore, it is preferable that the magnetization and the residual magnetization of the carrier are within the above-mentioned ranges. In this test, a carrier having the magnetization and the residual magnetization within the above-mentioned ranges is used.

When the volume resistivity of the carrier is low, charge injection into the carrier occurs in the developing region, so that the Coulomb force acting on the magnetic carrier becomes stronger than the magnetic restraining force, so that the carrier is exposed to light. Transfer on the body drum becomes easy, and carrier adhesion occurs. Therefore, the volume resistivity of the carrier is preferably 10 ¹⁰ Ω · cm or more in an electric field of 10 ⁶ V / m. The carrier used in this test has a volume resistivity of 10 ¹⁵ to 10 ¹⁶ Ω · cm in an electric field of 10 ⁶ V / m.
It is adjusted to be within the range. Table 1 shows the six types of carriers used in this test.

[0067]

[Table 1]

In Table 1, "-" represents a magnetic powder-dispersed resin carrier, and "-" represents a ferrite carrier. 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 was 5 kA / m for all carriers.
Is less than.

Further, it is desirable that the toner particle diameter of the developer used in the developing device of the present invention is not more than the particle diameter of the magnetic carrier of the developer and not more than 15 μm. The greater the particle size of the toner, the greater the distance between the carrier and the surface of the developing roll. For this reason, the magnetic restraining force acting on the carrier is weakened, and the developer is liable to be scattered or adhered to the carrier.

On the other hand, when the particle size of the toner is 15 μm
By setting the particle diameter to be equal to or less than the particle diameter of the carrier, the distance between the carrier and the developing roll can be reduced, and the magnetic binding force by the magnetic pole can be strengthened to prevent the developer from scattering and the carrier from adhering. Furthermore, even when the amount of charge of the toner increases due to a low-humidity environment or aging, and the amount of charge of the carrier increases accordingly, even when the Coulomb force acting on the carrier at the time of applying the developing bias increases, a sufficient magnetic binding force can be obtained. Thereby, the carrier can be held on the surface of the developing roll. Therefore, the toner particle size is
It is preferably not more than 15 μm and not more than the particle diameter of the magnetic carrier. In this test, the toner particle diameter was 7 μm as described above.

The mixing ratio of the toner and the carrier in the developer is
The weight ratio of the toner in the developer.
5% by weight, and 7.9% by weight for
The toner amount per unit volume is set to be substantially equal. The charge amount of the toner is -15 mC to -20 mC.
/ Kg range.

For the developing roll 12, the interval P between the magnetic flux density peak positions of the adjacent N pole and S pole is 13 μm,
5 μm, 50 μm, 100 μm, 250 μm, 500 μ
m were used. However, the interval P is a value obtained by rounding off the first decimal place. As described above, the peak value of the magnetic flux density having a two-peak distribution shape at each magnetic pole is:
It was set to 50 mT. The distance L between the two peak positions of each magnetic pole was set to 50 μm. Further, the difference ΔT in the magnetic flux density between the peak portion of the magnetic flux density and the valley portion between the peaks, each having a two-peak distribution shape, was set to 5 mT.

The image density was evaluated 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 ×.

Further, the carrier is adhered by developing a so-called alternating line in which the image area and the background area are arranged in parallel at regular intervals in the direction perpendicular to the process direction, as shown in FIG. The amount of adhesion was measured and evaluated. The cycle of the alternating line 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 at a very small interval exists on the surface of the photoconductor,
A so-called fringe electric field is generated near the surface of the photoconductor layer,
At 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. The uniformity of the image was evaluated with respect to a solid image. A state where density unevenness was not visually observed was rated as “〇”, a level where there was a small amount of density unevenness but no practical problem was indicated as “△”, and an unusable level was rated as “x”.

Tables 2 and 3 show the results obtained by the above method. In these tables, the comprehensive evaluation was evaluated as 〇 when all of the above three items did not have x, and x when there was at least one of them.

[0077]

[Table 2]

[0078]

[Table 3]

According to Tables 2 and 3, the magnetic pole interval P was 25 μm.
At least 250 μm and the magnetic pole interval P
And the toner particle size d of the developer and the carrier particle size D satisfy the following relationship: (D + 2d) / 2 ≦ P ≦ (D + 2d) × 5. It can be seen that an image density can be obtained.

When the magnetic pole interval P is smaller than 25 μm, or when P <(D + 2d) / 2, it is difficult to arrange magnetic carriers along the magnetic field, and the developer layer is generally sparse. . For this reason, a sufficient density cannot be obtained, and the uniformity of an image is 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 P is smaller, and thus acts on the magnetic carrier on the developing roll when the magnetic pole interval P is smaller than 25 μm. The magnetic restraining force is weakened, and carrier adhesion occurs due to the above-mentioned fringe electric field. 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 magnetic pole interval P is wider than 250 μm, or when P> (D + 2d) × 5, the magnetic binding force acting on the magnetic carrier in the magnetic pole portion 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 corresponding to the magnetized pattern, and the developed image has a magnetized pattern-like unevenness. 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 and the developer is scattered.

On the other hand, the magnetic pole interval P is not less than 25 μm and not more than 250 μm, and the magnetic pole interval P, the toner particle size d of the developer, and the carrier particle size D are (D + 2d) / 2 ≦ P ≦ (D + 2d ) × 5, the relationship on the developing roll
The magnetic carriers are arranged neatly along the magnetic field.
For this reason, a developer layer having a substantially constant thickness without a portion where the developer is not attached and having no peak-valley structure is formed on the developing roll, and the developer layer is conveyed while being held by magnetic force. .

Accordingly, an image with high uniformity can be obtained without using a layer thickness regulating member. Also,
Since the developer conveyance amount does not depend on the component accuracy, high-precision assembly accuracy is not required. Further, since a strong magnetic binding force acts on the developer layer on the developer carrier, the carrier does not adhere to the photoconductor and the developer is not scattered. Also, since the developer layer on the developing roll is almost fixed on the surface of the developing roll, there is no need to mechanically rub the surface of the photoreceptor, thus eliminating image defects such as brush marks and sweeping. An extremely uniform image can be obtained.

<D. Configuration Example in Which Developing Device Can Be Changed> 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,
Similar results can be obtained when the developer layer is set so as to be in contact with the photosensitive drum 1. In this case,
Although the photoreceptor surface is mechanically rubbed by the developer layer, the developer layer is almost fixed on the developing roll, and a magnetic brush such as a conventional contact type two-component developing device is used. Since there is no movement due to rolling or vibration on the developing roll, image defects such as brush marks and sweeping hardly occur.

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.

In place of the above configuration, a configuration in which a thin magnetic recording layer is formed on a conductive layer may be adopted. FIG. 8 shows an example of this configuration. The magnetic recording layer 112b is formed by coating a powder of a ferromagnetic material dispersed in a binder resin on the conductive substrate 112a with a thickness of 50 μm. Γ-Fe ₂ as ferromagnetic material
O ₃ and polyurethane are used as a binder resin.
As the magnetic material, any material known as a magnet material or a magnetic recording material can be used.
In addition to e ₂ O ₃ , CrO ₂ , Ba ferrite, Sr ferrite and 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. In addition to the above-mentioned polyurethane, for example, polycarbonate, polyester and the like can be used. Furthermore, conductive fine particles and the like can be added to the magnetic recording layer 112b as needed.

Further, a magnetic metal material can be used for the magnetic recording layer 112b. 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 or the like can be used. Further, in this developing device, N
Although the poles and S poles are alternately magnetized, similar results are obtained when the N poles and S poles are alternately magnetized in the longitudinal direction of the developing roll. Similar results can be obtained when the N and S poles are magnetized so as to be arranged in a mosaic pattern on the surface of the developing roll.

The magnetic recording layer 122b can be magnetized by using a magnetic recording head 210 as shown in FIG. When such a magnetic recording head 210 is used, it is assumed that the developing roll has the magnetic recording layer 122b provided on the soft magnetic layer 122a. Soft magnetic layer 12
Any known material can be used as 2a, 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.

<E. Experiment for investigating the relationship between the interval L between the two peak positions and the image density, adhesion of carriers, occurrence of density unevenness, and reproducibility of fine lines> Next, in the developing device shown in FIG. The result of examining the image density, the carrier adhesion, the density unevenness in the low density portion, and the reproducibility of the fine line by changing the position interval L will be described.

The developing roller 12 has a magnetic pole interval P between adjacent N and S poles of 100 μm, and two peak position intervals L of 10 μm, 20 μm, 30 μm, 100 μm, 20 μm.
Seven types of 0 μm, 300 μm, and 350 μm were used. The difference ΔT in the magnetic flux density between the peak of each magnetic pole and the valley between the peaks was set to 5 mT. The toner was the same as the toner used in the previous experiment, and the carriers shown in Table 1 were used. The uniformity of the image in the low-density portion was evaluated visually with respect to a halftone dot image having an area ratio of 20%, and a state where no minute density unevenness was observed was evaluated as ○. The level was marked as “△”, and the unpractical level was marked as “x”. For evaluation of reproducibility of fine lines, width 130 μm
The line image of m was visually inspected, and the state where no jagged edge and density unevenness were observed in the edge portion was evaluated as ○, the level where there was a small amount of jagged area and density unevenness but there was no practical problem, and the level where impractical was x And The image density and carrier adhesion were evaluated in the same manner as in the previous experiment.

The results of such an experiment are as shown in Table 4. The comprehensive evaluation was as follows: も の for all of the above four items without △ and ×, △ for one with △ but without X, and one for But ×
Are marked with x.

[0093]

[Table 4]

As shown in this table, the distance L between the two peak positions of each magnetic pole is 300 μm or less, and the distance L, the toner particle diameter d and the carrier particle diameter D are (D + 2d) / 4 ≦ It can be seen that if L 1 is satisfied, 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 are improved.

The reason why the interval L between the two peak positions of each magnetic pole affects the uniformity of the low density portion and the reproducibility of the fine line can be considered as follows. When the interval L between the two peak positions is smaller than (D + 2d) / 4, the attenuation of the magnetic field component in the direction perpendicular to the surface of the developing roll becomes gentle, and the distribution shape of the magnetic field becomes as shown in FIG. Are arranged at equal intervals. Therefore, FIG.
As shown in FIG. If there is such a minute unevenness in the layer thickness, minute unevenness in the density in the low-density portion and poor reproducibility of the fine line will occur.

On the other hand, the interval L between the two peak positions is 300
If it is larger than μm, the area where the developer does not adhere becomes large, and stripe-like density unevenness that can be visually observed is likely to occur. For the reasons described above, the interval L between the two peak positions is set to 300 μm or less, and the interval L, the toner particle size d, and the carrier particle size D are set so as to satisfy (D + 2d) / 4 ≦ L. If this is the case, 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 fine line reproducibility can be improved.

In this experiment, the magnetic pole interval P between the adjacent N pole and S pole was set to 100 μm, but the magnetic pole interval P was set to 25 μm.
μm or more and 250 μm or less, the magnetic pole interval P, the toner particle size d and the carrier particle size D are (D + 2d) / 2 ≦ P
A similar result can be obtained if the setting is made so as to satisfy ≦ (D + 2d) × 5.

<F. The difference ΔT in the magnetic flux density between the peak of each magnetic pole and the valley between the peaks and the image density, carrier adhesion,
Experiment for investigating the relationship between the occurrence of density unevenness and the reproducibility of fine lines> Next, in the developing device shown in FIG. 3, the difference ΔT in the magnetic flux density between the peak and the valley between the peaks in the magnetic flux density distribution of each magnetic pole. And the results of examining the image density, carrier adhesion, density unevenness in low-density portions, and reproducibility of fine lines will be described.

In the developing roll 12, the magnetic pole interval P between the adjacent N and S poles was set to 100 μm, and the interval L between the two peak positions was set to 50 μm. Further, a difference Δ in magnetic flux density between a peak portion and a valley portion between peaks in the magnetic flux density distribution of each magnetic pole.
T used four kinds of 1mT, 3mT, 5mT, and 7mT. The toner was the same as the toner used in the above experiment, and the carrier shown in Table 1 was used.

The results of such an experiment are as shown in Table 5. The comprehensive evaluation was as follows: を for all of the above four items without Δ and ×, Δ for those with Δ but no ×, But ×
Are marked with x. Below margin

[0101]

[Table 5]

As shown in this table, if the difference ΔT in the magnetic flux density between the peak and the valley between the peaks is set to be 5 mT or more, a sufficient image density can be obtained without causing carrier adhesion. 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.

The reason why the difference ΔT in the magnetic flux density between the peak portion and the valley portion between the peaks in the magnetic flux density distribution of each magnetic pole affects the uniformity of the low concentration portion and the reproducibility of the fine line is as follows. Can be thought of as When the difference ΔT in the magnetic flux density between the peak and the valley between the peaks is smaller than 5 mT, the distribution of the magnetic field is close to the case where the magnetic poles are arranged at equal intervals as shown in FIG. Accordingly, minute layer thickness unevenness as shown in FIG. 37 is likely to occur. If there is such a minute unevenness in the layer thickness, minute unevenness in the density in the low-density portion and poor reproducibility of the fine line will occur.

If the difference ΔT in the magnetic flux density between the peak portion and the valley portion between the peaks is set to 5 mT or more, the magnetic flux is hardly distributed between the two peak positions. Can be suppressed. Therefore,
The difference ΔT in magnetic flux density between the peak and the valley between the peaks is 5 m.
If it is set to T or more, 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.

In this experiment, the magnetic pole interval P between the adjacent N pole and S pole was set to 100 μm.
μm or more and 250 μm or less, the magnetic pole interval P, the toner particle size d and the carrier particle size D are (D + 2d) / 2 ≦ P
A similar result can be obtained if the setting is made so as to satisfy ≦ (D + 2d) × 5.

<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 shown in FIG. 10, and the result was shown in the developing device shown in FIG. Compare with the results obtained in

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 amount -15 to −20 mC / kg Further, the magnetic pole interval P between the adjacent N pole and S pole on the surface of the developing roll is 100 μm. The interval L between the two peak positions of each magnetic pole is set to 50 μm, and the difference ΔT in the magnetic flux density between the peak and the valley between the peaks is set to 5 mT.

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 3 rotatably driven around the magnet roll 312a.
12b, and the magnet roll 312a is provided with five magnetic poles in the circumferential direction. Due to the magnetic field generated by the magnetic poles, the developer is attracted to the surface of the sleeve 312b and moves with the rotation of the sleeve 312b. The amount of the developer is regulated at a position facing the layer thickness regulating member 315, and the developer is regulated. 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

The above two developing devices each accommodate 400 g of the developer in the 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. 11 and 12 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. 10). 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, in the conventional developing device 300 as a comparative example, a sharp decrease in the density and a decrease in the 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 investigating 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 at the time of forming the developer layer, 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, in the developing device according to the present invention, it can be seen that good image quality can be stably maintained over a long period of time. Further, in the developing device of the present invention, even when the charge amount and the resistance value of the carrier fluctuate due to the environment and aging, the carrier is almost fixed on the developing roll by the magnetic binding force in the developing region. So
The state of the developer layer is kept almost constant. Therefore, stable image reproduction that is not affected by changes in the environment or influence over time can be achieved.

[Second Embodiment] Next, a description will be given of a developing device according to a second embodiment of the present invention described in claim 1, claim 2, claim 3, claim 4, or claim 6. FIG.
FIG. 3 is a schematic configuration diagram showing the developing device and a partially enlarged cross-sectional view of a developer carrier. In this developing device, an opening for development is provided at a portion of the developing housing 21 in which the developer is accommodated, facing the photosensitive drum 1, 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 substantially equal intervals over the entire circumference of the belt 22, and form a magnetized pattern similar to the embodiment shown in FIG. ing. As the magnetic material of the magnetic recording layer 22b, γ-Fe ₂ O ₃ is used, and as the binder resin, polyurethane is used. The thickness of the magnetic recording layer 22b is 50 μm.

For the magnetization of the magnetic recording layer 22b, a magnetic recording head similar to that shown in FIG. 6 is used.
N-poles and S-poles are alternately magnetized in the circumferential direction of the belt, and the direction of magnetization is set such that N-poles and S-poles are generated in the horizontal direction. Further, the magnetic pole interval P between the N pole and the S pole adjacent to each other on the surface of the belt is set to 100 μm, the interval L between two peak positions of each magnetic pole is set to 50 μm, Magnetic flux density difference ΔT is 5m
T, the peak value of the magnetic flux density in the vertical direction is 50 mT. The other configuration of this developing device is the same as that of the developing device shown in FIG.

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 the 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.

A long-term development experiment of 100,000 sheets was performed using the above-described developing device in the same manner as the developing device 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.

[Third Embodiment] FIG. 14 shows the third embodiment.
FIG. 11 is a schematic sectional view showing a developing device according to a third embodiment of the invention described in claim 2, 3, 4, or 6. 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 is composed of a drive roll 33, two support rolls 34 and 35, and an endless belt 32 stretched over them.
Is driven to rotate by the rotation of. In this developer carrier, since two support rolls 34 and 35 are disposed at a position facing the photosensitive drum 1, the approaching position between the endless belt 32 and the photosensitive drum 1 is shown in FIG. As compared with the developing device, a developing region having a larger area is formed.
The other configuration of this developing device is the same as that of the developing device shown in FIG.

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.

[Other Embodiments] The developer carrying member used in the above-described developing device has a substantially constant pattern formed by alternately magnetizing N poles and S poles at substantially equal intervals. The present invention is not limited to this, and various magnetized patterns as shown below can be used.

FIG. 15 is an explanatory diagram showing a magnetic flux density distribution in a direction perpendicular to the surface of the developing roll of the developing device according to the fourth embodiment of the present invention. The developing roll used in this developing device has N poles and S poles alternately arranged similarly to the above-described embodiment, and each magnetic pole has a magnetic flux density in a direction perpendicular to the peripheral surface of the developing roll of approximately two. The distribution has a peak value. The distance between the N pole peak and S poles adjacent peaks P (P _23, P ₄₁ shown in FIG. 15) has become a 250μm or less at about 25μm or more, these pole interval P
It is set alternately to different intervals as P _23, P ₄₁ in FIG. Further, the interval P and the toner particle diameter d
And the particle diameter D of the magnetic carrier are set so as to satisfy the following relationship: (D + 2d) / 2 ≦ P ≦ (D + 2d) × 5.

The distribution of the magnetic flux density of each magnetic pole
The interval L between the two peaks (L ₁₂ and L ₃₄ shown in FIG. 15) is 3
The distance L, the particle diameter d of the toner, and the particle diameter D of the magnetic carrier are set so as to satisfy the relationship of (D + 2d) / 4 ≦ L. Further, the difference ΔT in the magnetic flux density between the peak and the valley between the peaks in the magnetic flux density distribution of each magnetic pole is set to about 5 mT or more. In the present embodiment, set to be substantially equal to the L ₁₂ and L ₃₄ in FIG. 15, or may be different intervals. The other configuration of this developing roll is the same as that of the developing roll shown in FIG.

In such a developing roll, FIG.
As shown in (1), the magnetic flux concentrates near the surface of the developing roll between the adjacent N-pole peak and S-pole peak, and the magnetic flux hardly distributes between the two peaks of each magnetic pole.

Further, since every other interval between adjacent N-pole peaks and S-pole peaks has a different interval, a strong magnetic field is generated between the magnetic poles having a narrow interval (between M _{4 and} M ₁ ). It is formed. In other words, compared to the case where the magnetic poles are arranged at equal intervals, since the magnetic pole interval is narrower and the magnetic flux density is biased, the magnetic field component in the direction perpendicular to the surface of the developing roll is attenuated sharply when it moves away from the developing roll surface, Will not reach far. Therefore, it is possible to form a substantially single-layer uniform developer layer between the magnetic poles M _{4 to} M ₁ .
Further, since a strong magnetic binding force acts on the magnetic carrier due to the strong magnetic field, scattering of the developer and adhesion of the carrier onto the photosensitive drum do not occur.

On the other hand, between the other magnetic poles (between M _{2 and} M ₃ ), that is, between the magnetic poles having a larger interval, the above magnetic poles (M
₄ ~M for pole gap is wider than in the ₁ between), attenuation of the magnetic field component in the direction perpendicular to the surface of the developing roller becomes gentle. However, the magnetic field formed between the magnetic poles is weaker than that between the magnetic poles (between M _{4 and} M ₁ ), so that the magnetic restraining force acting on the carrier at a position distant from the surface of the developing roll is weakened. Multi-layered developer layers cannot be retained. Therefore, the distance between the magnetic poles (M _{2 to} M ₃₎
Also during (interval), it is possible to form a substantially single-layer uniform developer layer. Further, since a sufficient magnetic binding force acts on the held magnetic carrier, the scattering of the developer and the adhesion of the carrier to the photosensitive drum do not occur.

In this way, the carrier does not concentrate on the portion above the magnetic pole but adheres almost only one layer along the magnetic field. At this time, a portion where the carrier hardly adheres is formed periodically, but since the interval L between the two peaks of each magnetic pole is appropriately set, the density unevenness and the fine line reproduction unevenness due to the layer thickness unevenness do not occur. . Therefore, a thin layer of the developer can be formed without imposing a load on the developer, and a good image can be obtained.

FIG. 17 is an explanatory diagram showing a magnetic flux density distribution in a direction perpendicular to the surface of the developing roll of the developing device according to the fifth embodiment of the present invention. In this developing roll, N poles and S poles are alternately arranged at substantially equal intervals as in the embodiment shown in FIG. 3, and each magnetic pole has a magnetic flux density in a direction perpendicular to the peripheral surface of the developing roll. The distribution has two peak values. The interval P between adjacent N-pole peaks and S-pole peaks (P ₂₃ shown in FIG. 17) is not less than 25 μm and not more than 250 μm, and the interval P, the toner particle diameter d, and the magnetic carrier Is set so as to satisfy the relationship of (D + 2d) / 2 ≦ P ≦ (D + 2d) × 5.

Further, non-magnetized regions are provided at substantially constant intervals between adjacent N-pole peaks and S-pole peaks. Magnetic poles M _{4 to} M including such non-magnetized regions
The sum of the interval between ₁ (X ₄₁ shown in FIG. 17) and the interval between two peaks provided on both sides thereof (L ₃₄ and L ₁₂ shown in FIG. 17) (X ₄₁ + L ₃₄ + L ₁₂ ) Is set to 300 μm or less, and furthermore, X ₄₁ + L ₃₄ + L
₁₂ , the particle size d of the toner, and the particle size D of the magnetic carrier are set so as to satisfy the relationship of (D + 2d) / 4 ≦ X ₄₁ + L ₃₄ + L ₁₂ . In the present embodiment, although the above-described L ₃₄ and L ₁₂ is set to be substantially equal or may be different intervals. The other configuration of this developing roll is the same as that of the developing roll shown in FIG.

In such a developing roll, FIG.
As shown in ( ₂ ), the magnetic flux wraps around between the adjacent N-pole peak and S-pole peak (between M _{2 and} M ₃ ) and hardly distributes on the opposite side. Therefore, the magnetic flux is from M ₂ to
The concentration of the magnetic field in the direction perpendicular to the surface of the developing roll concentrates near the surface of the developing roll between M ₃ , and the magnetic field does not reach far. Therefore, between the adjacent N-pole peak and S-pole peak (between M _{2 and} M ₃ ), a substantially single-layer developer layer can be formed.

Further, between the magnetic poles provided with the non-magnetized regions (M
₄ In ~M between _1), the magnetic field is weakened magnetic binding force acting on the carrier in order to be very weak, it is impossible to hold the developer layer. Therefore, between the N pole peak and the S pole peak where a strong magnetic field is formed (between M _{2 and} M ₃ )
Only in this case, a substantially single-layer uniform developer layer is formed. At this time, as described above, the gap (X ₄₁ + L ₃₄ + L ₁₂ ) between the magnetic poles adjacent to each other with the non-magnetized region interposed therebetween is set to 300 μm or less, and no stripe-like development density unevenness occurs. When such a developing roll is used, a thin layer of the developer can be formed without imposing a load on the developer, and a good image can be obtained.

FIG. 19 is an explanatory diagram showing a magnetic flux density distribution in a direction perpendicular to the surface of the developing roll of the developing device according to the sixth embodiment of the present invention. Similar to the magnetized pattern shown in FIG. 17, this developing roll has non-magnetized regions at almost regular intervals between adjacent N poles and S poles. The interval P between the pole peak and the S pole peak
There are set alternately to different intervals as P _23, P ₆₇ shown in FIG. 19. The other configuration of the developing roll is the same as the developing roll of the embodiment shown in FIG.

In such a developing roll, as shown in FIG. 20, the magnetic flux is generated between the adjacent N-pole peak and S-pole peak (between M _{2 and} M _{3 and} between M _{6 and} M ₇ ). The magnetic flux is concentrated near the surface, and the magnetic flux is hardly distributed between the magnetic poles adjacent to each other across the non-magnetized region and between two peaks (M _{3 to} M ₆ ) of the magnetic poles. Therefore, the developer is N
The developer substantially adheres to the monolayer between the pole peak and the S pole peak, and the developer hardly adheres between adjacent magnetic poles across the non-magnetized region and between two peaks of the magnetic poles. This allows
A thin layer of the developer can be formed without imposing a load on the developer, and a good image can be obtained.

FIG. 21 is an explanatory diagram showing a magnetic flux density distribution in a direction perpendicular to the surface of the developing roll of the developing device according to the seventh embodiment of the present invention. This developing roll, there is 250μm or less in pairs (P ₂₃ shown in FIG., P ₄₁₎ distance P between the N pole and S pole forming the approximately 25μm or more are set at substantially regular intervals, these Magnetic poles of the same polarity are arranged adjacent to both sides of the N pole and the S pole. At this time, the distance P, the particle size d of the toner, and the particle size D of the magnetic carrier are set so as to satisfy the relationship of (D + 2d) / 2 ≦ P ≦ (D + 2d) × 5. The distance L between adjacent magnetic poles of the same polarity (L ₁₂ , L ₃₄ shown in the figure) is 3
00 μm or less, and the distance L and the particle diameter d of the toner
And the particle diameter D of the magnetic carrier are set so as to satisfy the relationship of (D + 2d) / 4 ≦ L. In the present embodiment, although the above-described L ₁₂ and L ₃₄ is set to be substantially equal or may be different intervals. The other configuration of this developing roll is the same as that of the developing roll shown in FIG.

In such a developing roll, as shown in FIG. 22, the magnetic flux is applied between the adjacent N pole and S pole (M _{2 to} M _3).
Concentrated and between M ₄ ~M near the surface of the developing roll ₁ between), between the poles of the same polarity adjacent (M ₁ ~M ₂ between and M ₃
~M a state in which magnetic flux is hardly distribution to ₄ between).
For this reason, the developer adheres almost to a single layer between the adjacent N pole and S pole, and the developer hardly adheres between the adjacent magnetic poles of the same polarity due to a weak magnetic binding force. Thereby, a thin layer of the developer can be formed without imposing a load on the developer, and a good image can be obtained.

FIG. 23 is an explanatory diagram showing the magnetic flux density distribution in the direction perpendicular to the surface of the developing roll of the developing device according to the eighth embodiment of the present invention. As in the embodiment shown in FIG. 21, this developing roll is provided on both sides of a pair of a north pole and a south pole.
Magnetic poles of the same polarity are arranged adjacent to each other.
Distance P between the poles and the S poles are alternately set to different intervals as P _23, P ₄₁ shown in FIG. 23. The other structure of the developing roll is the same as the developing roll of the embodiment shown in FIG.

In such a developing roll, as shown in FIG. 24, the magnetic flux is applied between the adjacent N pole and S pole (M _{2 to} M _3).
To concentrate near the surface of the developing roller between and M ₄ ~M between _1), the developer is uniformly adhered to the substantially single layer between these magnetic poles, between the poles of the same polarity adjacent (M ₁ ~M Between ₂ and M
₃ ~M ₄ between) is not the developer is hardly attached. Thereby, a thin layer of the developer can be formed without imposing a load on the developer, and a good image can be obtained.

FIG. 25 is an explanatory diagram showing a magnetic flux density distribution in a direction perpendicular to the developing roll surface of the developing device according to the ninth embodiment of the present invention. In this developing roll, magnetic poles having the same polarity are arranged at substantially equal intervals on both sides of an N pole and an S pole arranged adjacent to each other. Each magnetic pole has a distribution in which the magnetic flux density in the direction perpendicular to the peripheral surface of the developing roll has approximately two peak values, and the interval P between the adjacent N pole peak and S pole peak (P ₂₃ shown in the figure) , P ₄₁ ) are substantially equal, and are set to be not less than 25 μm and not more than 250 μm. Further, the distance P and the toner particle diameter d
And the particle diameter D of the magnetic carrier are set so as to satisfy the following relationship: (D + 2d) / 2 ≦ P ≦ (D + 2d) × 5.

Further, among the plurality of peaks in the magnetic flux density distribution of adjacent magnetic poles of the same polarity, the interval L between the peaks at both ends (L ₁₂ , L ₃₄ shown in the figure) is 300 μm or less, and The distance L, the particle size d of the toner, and the particle size D of the magnetic carrier are set so as to satisfy the relationship of (D + 2d) / 4 ≦ L. In the present embodiment, although the above-described L ₁₂ and L ₃₄ is set to be substantially equal or may be different intervals. Further, a difference ΔT in magnetic flux density between a peak portion and a valley portion between the peaks in the magnetic flux density distribution of each magnetic pole is set to about 5 mT or more. In addition,
The other structure of this developing roll is the same as that of the developing roll shown in FIG.

In such a developing roll, as shown in FIG. 26, the magnetic flux is applied between the adjacent N-pole peak and S-pole peak (between M _{2 and} M _{3 and} between M _{4 and} M ₁ ). Concentrated near the surface and between adjacent peaks of the same polarity (M ₁
ＭM ₂ and M ₃ ＭM ₄ ). For this reason, the developer adheres almost uniformly to a single layer between the adjacent N-pole peak and the S-pole peak, and the developer does not adhere between the adjacent magnetic pole peaks of the same polarity because the magnetic binding force is weak. . At this time, since the distance between the peaks at the ends of the same polarity magnetic poles L (L ₁₂ and L ₃₄ in the figure) is set properly, reproduction unevenness of density unevenness and fine lines caused by the thickness irregularity occurs do not do. For this reason,
A thin layer of the developer can be formed without imposing a load on the developer, and a good image can be obtained.

FIG. 27 is an explanatory diagram showing the magnetic flux density distribution in the direction perpendicular to the surface of the developing roll of the developing device according to the tenth embodiment of the present invention. As in the embodiment shown in FIG. 25, this developing roll has magnetic poles of the same polarity adjacent to each other on both sides of a pair of N and S poles. distance P between the peaks is set alternately to different intervals as P _23, P ₄₁ shown in FIG. 27. The other configuration of the developing roll is the same as the developing roll of the embodiment shown in FIG.

In such a developing roll, as shown in FIG. 28, the magnetic flux is generated between the adjacent N-pole peak and S-pole peak (between M _{2 and} M _{3 and} between M _{4 and} M ₁ ). A magnetic pole of the same polarity concentrated near the surface and between adjacent peaks (M ₁
ＭM ₂ and M ₃ ＭM ₄ ) hardly distributes magnetic flux. For this reason, the developer adheres almost to a single layer between the adjacent N pole peak and S pole peak, and hardly adheres between the adjacent peaks of the same polarity magnetic pole. Thereby, a thin layer of the developer can be formed without imposing a load on the developer, and a good image can be obtained.

FIG. 29 is an explanatory diagram showing the magnetic flux density distribution in the direction perpendicular to the surface of the developing roll of the developing device according to the eleventh embodiment of the present invention. In this developing roll, magnetic poles of the same polarity are arranged at substantially equal intervals on both sides of a pair of N pole and S pole, and each magnetic pole has a magnetic flux in a direction perpendicular to the peripheral surface of the developing roll. The density has a distribution having almost two peak values. Further, as shown in FIG. 29, non-magnetized regions at substantially constant intervals are provided between adjacent magnetic poles of the same polarity (between M _{4 and} M ₅ in the figure).

The intervals P between adjacent N-pole peaks and S-pole peaks (P ₂₃ , P ₆₇ shown in the figure) are set at substantially equal intervals, and are set to 25 μm or more and 250 μm or less.
Further, the distance P, the particle diameter d of the toner, and the particle diameter D of the magnetic carrier are set so as to satisfy the following relationship: (D + 2d) / 2 ≦ P ≦ (D + 2d) × 5. In addition, the distance between the magnetic poles M _{4 to} M ₅ including the non-magnetized region (X ₄₅ shown in the figure) and the distance between two peaks on both sides thereof (L ₃₄ and L ₅₆ shown in the figure) are shown. total _{(L 34 + X 45 + L} 56) is 3
00μm is set to, further, the L ₃₄ + X
₄₅ + and L _56, and the particle diameter d of the toner, the particle diameter D of the magnetic carrier
Are set to satisfy the relationship of (D + 2d) / 4 ≦ L ₃₄ + X ₄₅ + L ₅₆ . In the present embodiment, although the above-described L ₃₄ and L ₅₆ is set to be substantially equal or may be different intervals. The other configuration of this developing roll is the same as that of the developing roll shown in FIG.

In such a developing roll, as shown in FIG. 30, the magnetic flux is generated between the adjacent N-pole peak and S-pole peak (between M _{2 and} M _{3 and} between M _{6 and} M ₇ ). The magnetic flux is concentrated near the surface, and the magnetic flux is hardly distributed between the magnetic poles adjacent to each other across the non-magnetized region and between two peaks (M _{3 to} M ₆ ) of the magnetic poles. Therefore, the developer adheres to a substantially single layer between the adjacent N-pole peak and S-pole peak, and hardly adheres between adjacent magnetic poles of the same polarity across the non-magnetized region. Thereby, a thin layer of the developer can be formed without imposing a load on the developer, and a good image can be obtained.

FIG. 31 is an explanatory diagram showing the magnetic flux density distribution in the direction perpendicular to the surface of the developing roll of the developing device according to the twelfth embodiment of the present invention. In the developing roll, similarly to the embodiment shown in FIG. 29, magnetic poles of the same polarity are arranged adjacent to both sides of a pair of N pole and S pole, and between these magnetic poles of the same polarity, Although non-magnetized regions are provided at regular intervals, the interval P between adjacent N-pole and S-pole peaks is
Are set to different intervals alternately as P _23, P ₆₇ shown in FIG. 31. The other structure of this developing roll is the same as that of the developing roll of the embodiment shown in FIG.

In such a developing roll, as shown in FIG. 32, the magnetic flux is applied between the adjacent N-pole peak and S-pole peak (between M _{2 and} M _{3 and} between M _{6 and} M ₇ ). Since the developer is concentrated near the surface, the developer adheres almost to a single layer between the N-pole peak and the S-pole peak, and almost no developer is present between adjacent magnetic poles of the same polarity across the non-magnetized region. Does not adhere. Thereby, a thin layer of the developer can be formed without imposing a load on the developer, and a good image can be obtained.

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

In the above embodiment, various magnetization patterns of the developer carrier are shown, but the present invention is not limited to this. For example, each magnetic pole may have a peak distribution having two or more peak values, and the interval between each peak and the magnetic flux density of each peak may be set to different values. Also, the difference ΔT in the magnetic flux density between the peak and the valley between the peaks may be set to different values. In the above embodiment, the developer carrier including the magnetic pole is configured to move around, but 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, 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. It is possible to use Ni as the metal sleeve and polyethylene terephthalate, polyurethane, polycarbonate, polyimide or the like as the resin sleeve.

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, but 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.

In the above embodiment, a two-component developer in which a non-magnetic toner and a magnetic carrier are mixed is used as the developer. Is also good. Further, a negatively chargeable polyester-based toner is used as the toner, but the present invention is not limited to this, and a toner having an arbitrary charge polarity can be used. The toner may have any shape such as an irregular shape or a spherical shape. Further, any method such as kneading and pulverization, a polymerization method, and a dissolution suspension method can be used as a method for producing the toner. Further, as the carrier, a so-called magnetic powder-dispersed resin carrier and a ferrite carrier were used, but the present invention is not limited to this, and a carrier having an arbitrary configuration can be used. In the above-described embodiment, the developing bias voltage is an AC voltage obtained by superimposing a DC voltage, and the waveform of the AC voltage is a rectangular wave. A development bias voltage can be used.
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, the screw auger is used as the developer stirring / transporting means. However, the present invention is not limited to this, and any stirring / transporting means depending on the purpose or application may be used. 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, a color image recording is performed 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.
Further, the present invention can be similarly applied to a color recording apparatus that sequentially transfers toner images of each color onto recording paper or an intermediate transfer body, a cleanerless image recording apparatus, and the like. 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.

[0158]

As described above, in the developing device according to the present invention, a thin layer of the developer is formed by the action of the plurality of magnetic poles provided on the developer carrier without using the layer thickness regulating member. Therefore, it is possible to prevent the developer from deteriorating without imposing a large load on the developer. Further, since the developer layer is formed only by the magnetic force of the developer carrier, the amount of the developer transported does not vary depending on the component accuracy, and the state of the formed developer layer varies over time. Not even. 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 a strong magnetic binding force acts on the carrier layer on the developer carrier, the developer does not scatter and the carrier does not adhere to the image carrier. Further, at a 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 rubbing occurs, so that a high-quality image can be reproduced without image quality defects such as brush marks and sweeping. Further, since the state of the developer layer in the developing area is kept substantially constant regardless of the environment and aging, stable image reproduction is possible. Further, since the thickness of the developer layer can be reduced, the gap between the developer carrier and the image carrier can be set to be small.
High-speed and high-quality development can be performed.

[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 first embodiment of a developing device according to the present invention.

4 is a partially enlarged sectional view of a developing roll used in the developing device shown in FIG. 3 and a diagram showing a magnetic flux density distribution in a direction perpendicular to the surface of the developing roll.

FIG. 5 is a schematic diagram showing a magnetic flux near a surface of a developing roll having a magnetic flux distribution shown in FIG.

6 is an explanatory view showing a method of magnetizing the developing roll shown in FIG.

FIG. 7 is a diagram showing an image pattern used to investigate an amount of transfer of a carrier of a developing device to a photosensitive drum in the image forming apparatus shown in FIG.

FIG. 8 is a partially enlarged sectional view of a developing roll of another embodiment used in the developing device shown in FIG.

9 is an explanatory view showing another method of magnetizing the developing roll shown in FIG.

FIG. 10 is a schematic configuration diagram showing a conventional developing device used for comparing performance with the developing device shown in FIG. 3;

11 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.

12 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.

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

FIG. 14 is a schematic configuration diagram showing a third embodiment of the developing device according to the present invention.

FIG. 15 is a diagram showing a magnetic flux density distribution in a direction perpendicular to the surface of a developing roll in a fourth embodiment of the developing device according to the present invention.

16 is a schematic diagram showing a magnetic flux near the surface of the developing roll having the magnetic flux distribution shown in FIG.

FIG. 17 is a diagram illustrating a magnetic flux density distribution in a direction perpendicular to the surface of a developing roll in a fifth embodiment of the developing device according to the present invention.

18 is a schematic diagram showing a magnetic flux near the surface of the developing roll having the magnetic flux distribution shown in FIG.

FIG. 19 is a view illustrating a magnetic flux density distribution in a direction perpendicular to the surface of a developing roll in a sixth embodiment of the developing device according to the present invention.

20 is a schematic diagram showing a magnetic flux near the surface of a developing roll having a magnetic flux distribution shown in FIG. 19 and a state of developer adhesion.

FIG. 21 is a diagram illustrating a magnetic flux density distribution in a direction perpendicular to the surface of the developing roll in a seventh embodiment of the developing device according to the present invention.

FIG. 22 is a schematic diagram showing a magnetic flux near the surface of the developing roll having the magnetic flux distribution shown in FIG.

FIG. 23 is a view illustrating a magnetic flux density distribution in a direction perpendicular to the surface of the developing roll according to the eighth embodiment of the developing device according to the present invention.

24 is a schematic diagram showing a magnetic flux near the surface of the developing roll having the magnetic flux distribution shown in FIG.

FIG. 25 is a view illustrating a magnetic flux density distribution in a direction perpendicular to a surface of a developing roll in a ninth embodiment of the developing device according to the present invention.

26 is a schematic diagram showing a magnetic flux near the surface of the developing roll having the magnetic flux distribution shown in FIG.

FIG. 27 is a diagram illustrating a magnetic flux density distribution in a direction perpendicular to the surface of a developing roll in a tenth embodiment of the developing device according to the present invention.

28 is a schematic diagram showing a magnetic flux near the surface of the developing roll having the magnetic flux distribution shown in FIG.

FIG. 29 is a view showing a magnetic flux density distribution in a direction perpendicular to the surface of the developing roll in the eleventh embodiment of the developing device according to the present invention.

30 is a schematic view showing a magnetic flux near the surface of the developing roll having the magnetic flux distribution shown in FIG. 29 and a state of developer adhesion.

FIG. 31 is a view illustrating a magnetic flux density distribution in a direction perpendicular to the surface of the developing roll in a twelfth embodiment of the developing device according to the present invention.

32 is a schematic view showing a magnetic flux near the surface of the developing roll having the magnetic flux distribution shown in FIG.

FIG. 33 is a schematic configuration diagram illustrating an example of a conventional developing device.

FIG. 34 is an explanatory diagram showing a magnetic flux distribution when each magnetic pole has a magnetic flux density distribution having a double peak distribution shape.

35 is a schematic view showing a magnetic flux near the surface of the developing roll having the magnetic flux distribution shown in FIG.

FIG. 36 is an explanatory diagram showing a magnetic flux distribution when each magnetic pole is a magnetic flux density distribution having a single peak distribution shape.

FIG. 37 is a schematic view showing a magnetic flux near the surface of the developing roll having the magnetic flux distribution shown in FIG.

[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 Power supply for developing bias 21, 31 Developing housing 22, 32 Belt (developer carrying member) 22a Conductive substrate 22b Magnetic recording layer 23, 33 Drive roll 24, 34 Support roll 25, 35 Support roll 26, 36 Screw Augers 27, 37 Screw augers 112a Conductive substrate 112b Magnetic recording layer 122a Soft magnetic layer 122b Magnetic recording layer 200 Magnetic recording head 201 Core 202 Coil 203 Magnetic flux 210 Magnetic recording head Reference Signs List 11 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 401a magnet roll 401b sleeve 402 supply member 403 layer thickness regulating member 410 image carrier 501 magnetic flux 502 Agent

Claims (6)

[Claims] 1. A developer carrying member provided in close proximity to or separated from or in contact with an image carrier on which an electrostatic latent image is formed on a surface, and a peripheral surface of which is supported so as to be rotatable. A two-component developer containing a toner and a magnetic carrier is carried and conveyed on the peripheral surface, and a developing bias voltage is applied between the developer carrying member and the image carrying member. Is transferred to the image carrier to form a toner image. On the peripheral surface of the developer carrier, a plurality of pairs of N poles and S poles are formed so as to form a substantially constant pattern. Magnetic poles are provided, and in each magnetic pole, a magnetic flux density in a direction perpendicular to the peripheral surface of the developer carrier has a distribution having a plurality of peak values, and an interval P between adjacent magnetic poles of different polarities is provided. About 25 μm or more and 250 μm or less; And d, wherein the particle size D of the magnetic carrier, a developing device, characterized in that a relation of (D + 2d) / 2 ≦ P ≦ (D + 2d) × 5. 2. The developing device according to claim 1, wherein an interval L between peaks at both ends of the plurality of peaks in the magnetic flux density distribution of each of the magnetic poles is about 300 μm or less. The developing device according to claim 1, wherein a particle diameter d of the toner and a particle diameter D of the magnetic carrier have a relationship of (D + 2d) / 4≤L. 3. The developing device according to claim 1, wherein a difference ΔT in magnetic flux density between a peak portion and a valley portion between the peaks in the magnetic flux density distribution of each magnetic pole is about 5 mT or more. A developing device, characterized in that: 4. The developing device according to claim 1, wherein each magnetic pole having a plurality of peaks in the distribution of magnetic flux density is:
A developing device, wherein the developing devices are arranged at substantially equal intervals. 5. The developing device according to claim 1, wherein the magnetic flux density distribution is in a non-magnetized region or a low magnetic region for each of the pair of magnetic poles having the plurality of peaks. A developing device comprising a magnetized region. 6. The developing device according to claim 1, wherein the plurality of developer carriers are provided in a substantially constant pattern over the entire circumferential direction. Wherein the magnetic pole moves around the magnetic pole.