JPH1063100A - Developing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce deterioration in developer and to stably obtain an excellent image, by forming a uniform developer layer on a developer carrier, without mechanically regulating the layer thickness of the developer layer, in a developing device using a two-component developer including toner and carriers, so as to make an electrostatic latent image on an image carrier visualizable. SOLUTION: The developer carrier 12 arranged near and opposedly to the image carrier 1 is provided with a cylindrical conductive substrate 12a and a magnetic recording layer 12b formed on the periphery of the substrate 12a. The magnetic recording layer is magnetized to alternately obtain the S- and N-poles and the interval between the magnetic poles having the same polarity is about 50μm-500μm. Then, the intervals of the adjacent magnetic poles whole polarities are different are different on both sides of the magnetic pole and the relation between the smaller magnetic pole interval XS and the interval between the magnetic poles having the same polarity [XS+XL] is 0.1<=XS/(XS+ XL)<=0.4.

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, and selectively transfers toner to a latent image due to a difference in electrostatic potential to visualize the toner. The present invention relates to a developing device using a two-component developer in which a 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 developing an electrostatic latent image on the image carrier has a so-called contact type in which a two-component developer composed of 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 transportability of the developer, etc. It has excellent characteristics and is the mainstream of developing devices.

FIG. 14 is a schematic structural view showing an example of the above-mentioned contact type two-component developing device, which has a developing roll 401 provided with a magnet roll 401a and a sleeve 401b which is driven to rotate around the magnet roll 401a. 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 is a magnet roll 401
A magnetic brush is formed in which carriers are spike-shaped according to the magnetic field generated by a, and only the toner is transferred by contacting the image carrier 410 at a position facing the image carrier 410.

Further, in the contact type two-component developing device, since the magnetic brush of the developer mechanically rubs the surface of the image carrier 410, image defects such as so-called brush marks and sweeping by the magnetic brush are likely to occur. . In order to avoid this drawback, there have been proposed many non-contact type two-component developing devices for developing without bringing the developer into contact with the surface of the image carrier.

[0006]

However, in the case where the layer thickness regulating member is used as described above, the developer is excessively filled on the back surface of the layer thickness regulating member, that is, on the upstream side in the developer conveying direction. As a result, 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 deterioration of the developer is roughly classified into the deterioration of the toner and the deterioration of the carrier. Both of them are generated by a compressive force, a frictional force, or the like. It is as follows. Generally, the deterioration of the toner is caused by the external additive added for improving the chargeability and the fluidity being peeled off from the surface of the toner or buried in the resin of the toner. As such deterioration proceeds, the triboelectric charging characteristics change, and the charge amount distribution of the toner becomes extremely wide and unstable. 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 above-mentioned deterioration of the toner occurs, the contact area between the toner and the carrier increases, so that
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. Transfer of toner occurs if the adhesive force is overcome. Therefore, a decrease in image density is conspicuously caused by an 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.

Further, there are the following problems as other problems of the two-component developing device using the layer thickness regulating member. When a trimmer made of a non-magnetic or magnetic material is used, the amount of developer transport depends on the gap between the layer thickness regulating member and the surface of the developer carrier, as well as the positional relationship between the magnetic poles of the developer carrier. 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. Is required, and in such a case, the above problem becomes more pronounced. In other words, in the above case, it is desirable to set the developing gap, that is, the gap between the developer carrier and the image carrier, to be small. In this case, the developer layer must be a thin layer with a smaller transport amount. . 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 promoted.

In a developing device using a one-component magnetic toner, for example, as described in Japanese Patent Application Laid-Open No. Sho 54-43038, a layer thickness regulating member made of an elastic material is pressed against a developer carrier to develop a toner. A technique for forming an agent layer has been used. Although it is conceivable to divert this technique to a developing device using a two-component developer, such a technique has a problem in that the transport amount of the developer changes due to the abrasion of the layer thickness regulating member over time, and the image quality varies. Have a point.

The present invention has been made in view of the above circumstances, and an object of the present invention is to form a uniform thin layer of developer without mechanically controlling the thickness of the developer layer. It is an object of the present invention to provide a developing device capable of forming a toner image and stably obtaining a good image by reducing deterioration of the developer.

[0014]

In order to solve the above-mentioned problems, in a developing device according to the present invention, a plurality of S poles and N poles are alternately magnetized on a peripheral surface of a developer carrier, and The magnetic poles are arranged so that the intervals between magnetic poles of the same polarity are substantially equal, and the interval is approximately 50 μm to 500 μm. Then, not equal spacing of the magnetic poles M ₂ of one polarity and the other polarity poles M _1, M ₃ of adjacent on both sides, Figure 10
As shown in the interval of M ₁ and M ₂ or M ₂ and M ₃ are magnetized to be larger than the other. The developer carrier that has been magnetized as described above may be a cylindrical member that is driven to rotate around an axis, and may be magnetized by providing a magnetic recording layer on its peripheral surface, or may be rotatable. It may be a supported endless belt. In such a developing device, when the developer is supplied to the surface of the developer carrier, the carrier is attracted to the magnetic pole, and a thin layer of the two-component developer on the surface of the developer carrier is formed. At this time, by setting the magnetic pole interval in the above range, generally used carriers having a particle size of about 25 μm to 200 μm can be adsorbed almost uniformly and almost one layer.

The principle that a substantially uniform thin layer of carrier is formed by such a magnetic pole can be considered as follows. As shown in FIG. 11, the magnetic field lines formed by the magnetic poles arranged at a narrow interval are directed to magnetic poles having different polarities as shown in FIG. Attenuates rapidly near the body surface. Further, when the layer of the magnetic carrier is formed on the peripheral surface, the lines of magnetic force pass through the layer of the magnetic carrier 22 that comes into contact with the peripheral surface of the developer carrier, and are hardly distributed outside the layer. Further, since adjacent magnetic poles of different polarities have different intervals every other, a strong magnetic field is formed between the magnetic poles X ₂₃ (X _s ) whose intervals are narrow. That is, FIG.
As compared with the case where the magnetic poles are arranged at equal intervals as shown in FIGS. 2 and 13, the magnetic pole component is narrower and the magnetic flux density is biased, so that the magnetic field component in the direction perpendicular to the surface of the developer carrier is When it leaves the body surface, it attenuates rapidly, and the magnetic field does not reach far. Therefore, it is possible to form a uniform developer layer substantially a monolayer in the inter-pole X _23. 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, the distance between the magnetic poles X ₁₂ (X _L ), that is, between the magnetic poles having a larger distance, is wider than the case where the magnetic poles are arranged at equal intervals. The attenuation of the magnetic field component in the direction perpendicular to the surface of the substrate becomes gentle. However, the magnetic field formed by the magnetic poles between X _L, since the magnetic poles is weakened as compared with the case arranged at equal intervals, the magnetic restraining force acting on the carrier at a site distant from the surface of the developer carrying member is weak In other words, it is not possible to hold a multi-layered developer layer. Therefore, this magnetic pole distance X _L
It is also 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 image carrier do not occur. In this way, the carrier is not concentrated and adhered to the portion above the magnetic pole, but is adsorbed in a state where almost only one layer is arranged in an orderly manner along the magnetic field. For this reason, a thin developer layer having no non-adhered portion of the developer and no valley structure is formed on the developer carrier, and is transported to the development area while being held by the magnetic force.

In the above-described developing device, a thin layer of 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 carrying member, the amount of the developer transported does not depend on the precision of the components and does not change with time. Furthermore, 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. Therefore, scattering of the developer and adhesion of the carrier onto the electrostatic latent image carrier do not occur.

Further, in the developing device according to the present invention,
Smaller X _S and, the same polarity magnetic pole spacing X ₁₃ i.e. of the distance X _12, X ₂₃ to different polarities poles of adjacent (X _S + X _L)
Is within the range of the following expression, so that the above-mentioned effect becomes more remarkable. 0.1 ≦ X _S / (X _S + _XL ) ≦ 0.4

The main part of the developer carrier used in the developing device is composed of a conductive layer and a magnetic recording layer formed thereon. can do. The toner is transferred to the latent image by applying a developing bias voltage to the conductive layer and forming an electric field between the conductive layer and the latent image on the image carrier.

The magnetic recording layer is magnetized by a magnetizing head. By arranging a soft magnetic layer below the magnetic recording layer, the thickness of the magnetic recording layer in the thickness direction is increased. N
It can be magnetized so that a pole and an S pole are generated, and a strong magnetic pole can be obtained. In other words, since the soft magnetic material layer serves as a magnetic flux path, when the magnetic recording layer is magnetized in a direction perpendicular to the surface of the developer carrier, the magnetizing head that magnetizes the magnetic recording layer is magnetically recorded. The magnetic flux is provided only on the layer side, and it is possible to form a magnetic flux that passes from the magnetized head vertically through the magnetic recording layer to the soft magnetic material layer behind. Here, the soft magnetic material is made of a material that is magnetized when placed in a magnetic field, but does not show magnetism when no external magnetic field acts.

A technique of providing magnetic poles at a small pitch on a developer carrying member as in the above configuration is disclosed in Japanese Patent Laid-Open No. 3-2.
No. 59276. According to the technique described in this publication, a developing roll (developer carrier) is constituted by a single rotating body, magnetic poles are provided around the periphery thereof at a small pitch of about 100 μm or less, and a one-component magnetic developer is provided on the peripheral surface thereof. Adsorbs. This reduces the occurrence of unevenness in the amount of developer adsorbed corresponding to the position of the magnetic pole, and uses this developer layer to form a toner image in the 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.

[0023]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of 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 the developing device according to the present application. This image forming apparatus includes a photosensitive drum 1 in which a photosensitive layer is provided on a peripheral surface of a substantially cylindrical conductive substrate, and the photosensitive drum 1 rotates in the direction of arrow A shown in the figure. It is designed to be driven. Around the photoconductor drum 1, along a rotation direction thereof, a charger 2, an exposure device 3, and a developing device 4 in which a developer carrier 12 formed of a cylindrical member is opposed to the photoconductor drum 1. , A pre-transfer corotron 5, a transfer corotron 6, a 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 reduced. 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 apparatus has a laser generator which blinks based on an image signal, and a polygon mirror which reflects a laser beam emitted from the laser generator while rotating the laser generator. 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 photosensitive drum 1 on which the transfer of the toner image and the peeling of the recording paper have been completed is cleaned of residual toner by a cleaner 8, and the residual charge is removed by exposure by a light neutralizer 9. In the image recording step. The pre-transfer corotron 5 provided on the downstream side of the developing device in the rotation direction of the photosensitive drum 1 is used when investigating the amount of carrier transferred to the image carrier during development. Uniform negative charging is performed on the toner image formed thereon. As a result, the carrier transferred onto the photosensitive drum 1 unintentionally during the development is negatively charged and is transferred together with the toner onto the recording paper. An assessment can be made.

Next, a developing device according to an embodiment of the present invention will be described. FIG. 3 is a schematic configuration diagram showing one embodiment of the developing device according to the first or second aspect of the present invention, which is a developing device that can be used in the image forming apparatus. 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 and facing the photosensitive drum 1, and a developing roll 12 is disposed in the opening and a developing roller 12 is provided behind the developing roll 12. Two screw augers 13 and 14 are provided. Also, the developing roll 1
A scraper 15 for peeling off the developer adhered on the surface 2 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.

As shown in FIG. 4, the developing roll 12 includes a cylindrical conductive base 12a supported so as to be rotatable around an axis and a magnetic recording layer 12b formed on the peripheral surface thereof. The main part is configured. 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 developer carrier 12 is 30
The thickness is set to 0 μm, and the developer layer is held so as not to be in contact with the photosensitive drum 1.

A developing bias voltage is applied to the conductive substrate 12a by a developing bias power supply 17. An AC voltage obtained by superimposing a DC voltage is employed as the developing bias voltage, and the DC component is set to -400 V in order to prevent occurrence of background fog. The AC component of the developing bias voltage is a rectangular wave having a frequency of 6 kHz, and the peak-to-peak voltage is set to 1.5 kV.

The magnetic recording layer 12b is obtained by dispersing a powder of a ferromagnetic material in a binder resin,
a is coated with a layer thickness of 50 μm, and γ-Fe ₂ O ₃ is used as a ferromagnetic material and polyurethane is used as a binder resin. As the magnetic material, any material known as a magnet material or a magnetic recording material can be used, and in addition to the above-mentioned γ-Fe ₂ O ₃ , CrO _{2 and the} like can be used. As the binder resin, any resin known as a resin constituting a magnetic recording layer such as a tape, disk, or card can be used.
For example, polycarbonate, polyester, polyurethane and the like can be used. Further, conductive fine particles and the like can be added to the magnetic recording layer 12b as needed.

As shown in FIG. 4, the magnetic recording layer 12b is magnetized so that S poles and N poles are alternately arranged in the circumferential direction over the entire circumference. The distance between these magnetic poles is set equal to 100 μm for magnetic poles of the same polarity, and the distance between adjacent magnetic poles of different polarity is different on both sides of one magnetic pole, and is equal to the smaller magnetic pole distance X _S. polarity magnetic pole spacing (X _S + X _L): relationship between the [X _L larger the opposite polarity magnetic pole spacing] is, are magnetized so that _{X S / (X S + X} L) = 0.25 I have. The method of such magnetization will be described later.

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

In such a developing device 4, when the developer is supplied to the developing roll 12, a certain amount of the developer is attracted to the peripheral surface of the developing roll 12 based on the magnetic field of the magnetic recording layer 12b. 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.

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 has a core 201 made of a soft magnetic material and having both ends arranged side by side at intervals and a coil 202 wound around the core 201. It is arranged so as to be 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. Coil 202
The magnetizing current supplied to the developing roller 12 is supplied intermittently or by changing the direction of the current intermittently through a magnetizing signal generator, and as shown in FIG. Magnetized. In the present embodiment, the N and S poles are alternately magnetized in the circumferential direction of the developing roll 12 in a wavy pattern as shown in FIG. 10, and the peak value of the magnetic flux density in the radial direction on the developing roll surface is reduced to 50 mT. Is set to

It is to be noted that a magnetic recording head 210 as shown in FIG. 6 can be used for magnetizing the magnetic recording layer. When such a magnetic recording head 210 is used, the developing roll is placed on the soft magnetic material layer 122a.
b is provided. Any known soft magnetic material can be used as the soft magnetic material 122a.
There are a 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 is 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 from the small end face, and further below the soft magnetic layer 122a.
Through to the other end 211b of the core having a larger end face. Therefore, at the position facing the small end face 211a of the magnetic recording layer, 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, magnetic poles arranged in the thickness direction of the magnetic recording layer 122b can be formed over substantially 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.

Next, in the developing device shown in FIG. 3, the ratio [X _S / (X _S) of the smaller one of the same magnetic pole spacing [X _S + _XL ] and the different polarity magnetic pole spacing and the same polarity magnetic pole spacing. + X
_L )], the results of experiments conducted to investigate image density, carrier adhesion, uniformity of low density areas, and reproducibility of fine lines will be described. Magnetization of the developing roll is performed when the magnetic pole interval of the same polarity is 25 μm, 50 μm, 100 μm, 250 μm.
m, 500 μm, and 1000 μm. Then, for each, X _S / (X _S + X _L ) is equal to 0.
Experiments were performed on those magnetized to be 05, 0.1, 0.25, 0.4, 0.45, and 0.5.

The toner used in this experiment is a polyester-based magenta toner having a weight average particle diameter of 7 μm and a negative charge property. The carrier used was a so-called ferrite carrier in which spherical ferrite particles were coated with a resin. The particle size and density are as follows. Average particle diameter: 50 μm True density: magnetization per unit weight in a magnetic field of 4.5 g / cm ³ 10 ⁶ / (4π) A / m: 50 A · m ² / Kg

In general, in a developing method using a thin layer of a two-component developer, in order to obtain a fine-grained image,
It is preferable to use a carrier having a small average particle size. 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, the carrier having the above particle size of 50 μm is used.

The mixing ratio of the toner and the carrier in the developer is
The weight ratio of the toner in the developer was 7.9% by weight. At this time, the charge amount of the toner is -15 to -20 mC / kg.
The range has been adjusted.

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 ×.

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

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

The uniformity of the low-density image was visually evaluated for a solid image having an area ratio of 20%, and a state where no minute density unevenness was observed was evaluated as 、. , And the unusable level was marked as x. Regarding the reproducibility of fine lines, a line image having a width of 130 μm was visually evaluated, and a state where no jagged edge was observed was evaluated as ○. Is indicated by x.

Tables 1 and 2 show the results of the evaluation performed by the method described above. In this table, the comprehensive evaluation was evaluated as ○ when there was no x in all of the above four items, and x when there was at least one x.

[0049]

[Table 1]

[0050]

[Table 2]

According to Tables 1 and 2, one cycle (X ₁₃ shown in FIG. 10 or 11) of the magnetic pole pattern on the peripheral surface of the developing roll 12 is in the range of 50 μm to 500 μm, and adjacent polarities different from each other. the magnetic pole interval when the X _12, X _23, and by disposing the X ₂₃ / X ₁₃ <0.5, i.e. X _12> X ₂₃ become as pole M _2, a sufficient image density can not be obtained Further, the uniformity of the low density portion and the reproducibility of fine lines can be improved without causing carrier adhesion. Also,
More preferably, X ₂₃ / X ₁₃ is set to 0.1 in the above setting.
By setting it to 1 or more and 0.4 or less, the uniformity of the low density portion and the reproducibility of fine lines can be further improved.

When X ₁₃ is smaller than 50 μm, it is difficult to arrange the magnetic carriers along the magnetic field, and the developer layer is generally sparse. In addition, the magnetic field at a portion distant from the surface of the developing roll rapidly attenuates and becomes weaker as the magnetic pole interval is smaller. Therefore, when X ₁₃ is smaller than 50 μm, the magnetic binding force acting on the magnetic carrier on the developing roll is reduced. Is weakened, and carrier adhesion occurs due to the action of the fringe electric field described above. Further, a phenomenon in which the developer was scattered by the centrifugal force acting on the developer when the developing roll 11 was rotated was observed.

On the other hand, when X ₁₃ is wider than 500 μm, the magnetically constraining force acting on the magnetic carrier in the region between the magnetic poles is extremely weak, so that the developer adheres intensively to the upper portion. Accordingly, the state of the developer layer has a peak-valley structure corresponding to the magnetization pattern, and unevenness in the shape of the magnetization pattern also occurs in the developed image. Further, as described above, since the magnetic binding force acting on the magnetic carrier attached to the portion between the magnetic poles is weak, the carrier is attached and the developer is scattered.

When X ₂₃ / X ₁₃ <0.1, the magnetic pole M ₂
Some striped developing density unevenness for the developer is less likely to adhere between the pole M ₃ is generated and, consequently uniformity and fine line reproducibility of the low density portion is at a level causing a practical problem No, but slightly lower. Further, X ₂₃ / X ₁₃ >
At 0.4, the uniformity of the low-density portion and the reproducibility of fine lines are slightly reduced, although they are not practically problematic, due to the influence of the slight developer layer thickness unevenness as described above.

Based on the above experimental results, the following is considered.
be able to. The magnetic pole pad on the peripheral surface of the developing roll
One cycle of turn X₁₃Is in the range of 50 μm or more and 500 μm or less.
And X₁₂> X_{twenty three}Develop by setting to
On the roll, almost single layer
It is possible to form a uniform developer layer. Therefore,
Because the occurrence of minute thickness unevenness of the developer is suppressed,
Excellent density uniformity and fine line image reproducibility in the image density area
Good image reproduction is possible. Also, the developer transport amount is
High accuracy of assembly is required because it does not depend on component accuracy
Not done. In this experimental example, the magnetic pole interval is set to X₁₂> X_{twenty three}When
Was set to be₁₂<X _{twenty three}And set it to
In the case where
It is.

Next, an experiment conducted on the maintainability of the developing device shown in FIG. 3 will be described. In this experiment, 100,000 sheets of A4 size solid images were continuously developed using the image forming apparatus shown in FIG. 1 and the developing apparatus 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.

In this experiment, the magnetic pole interval X _S of the same polarity on the peripheral surface of the developer carrying member was 100 μm, the ratio X ₂₃ / X ₁₃ between the smaller magnetic pole interval of the different polarity and the magnetic pole interval of the same polarity,
That is, X _S / (X _S + _XL ) is set to 0.25.

The above-mentioned developing device is housed in the housing at 40.
The toner contains 0 g of the developer, and the toner is appropriately replenished so that the toner weight ratio in the developer is 7.5 to 8.5% by weight.

FIGS. 8 and 9 show changes in solid image density and toner charge amount when 100,000 sheets are developed using the developing device (FIG. 3) according to the present invention. From these figures, in the developing device 4 according to the present invention,
It can be seen that the image density and the toner charge amount are favorably maintained through the development of 100,000 sheets. Further, as a result of examining the state of the developer after the long-term development experiment, the toner and the carrier 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. This can be considered to be a result of preventing the toner and the carrier from being deteriorated because no excessive force acts on the developer when the developer layer is formed because the layer thickness regulating member is not used. As mentioned above,
It can be seen that the developing device of the present invention can maintain good image quality stably for a long period of time.

In the developing device shown in FIG. 3, the magnetic recording layer 12b has a structure in which a magnetic material is dispersed in a binder resin. However, similar results can be obtained when a magnetic metal material is used. In this case, as the magnetic metal material, any known material such as a magnet material or a magnetic recording material can be used. For example, Co-Ni-P, Co-Ni, or Co-
Cr can be used.

Similar results can be obtained when the magnetic recording layer 12b has a structure in which a magnetic material is dispersed in a flexible material. In this case, as the material having flexibility, any material that can be mixed with a large amount of magnetic material and can maintain flexibility can be used. For example, Hypalon, polyisobutylene, neoprene rubber, nitrile Rubber, polyethylene chloride and the like can be used. Further, a conductive layer, a resistive layer, a protective layer, a wear-resistant layer, and the like may be provided on the magnetic recording layer. Further, an adhesive layer, an underlayer, a nonmagnetic layer, and an elastic layer may be provided between the conductive layer and the magnetic recording layer or between the soft magnetic layer and the magnetic recording layer.

Similar results can be obtained even if the following changes are made. a) In the above-described developing device, the magnetization pattern of the developer carrier is sinusoidal, but any magnetization pattern such as a triangular waveform can be used. b) In the developing device, the N pole and the S pole are alternately magnetized in the circumferential direction of the developing roll 12, but the same applies to the case where the N pole and the S pole are alternately magnetized in the longitudinal direction of the developing roll. Results are obtained. c) In the developing device, the surface moving linear velocity of the developer carrier is set to 320 mm / s. However, the state of formation of the developer layer does not depend on the surface moving linear velocity.
In the region of 10 mm / s to 900 mm / s, a substantially uniform developer layer can be formed, and the developer does not scatter when the developer carrier rotates. d) In the developing device described above, the surface moving direction of the developer carrier is opposite to the surface moving direction of the image carrier. However, the present invention is not limited to this, and may be in the same direction. e) In the above-described developing device, the developer carrier is cylindrical, but an endless belt-shaped carrier may be used. f) In the developing device, the developer layer on the developer carrier is
Although a non-contact state is set for the photoconductor drum, a similar result can be obtained when the developer layer is set so as to be in contact with the photoconductor drum. g) In the above-described developing device, the developing bias voltage is an AC voltage on which a DC voltage is superimposed, and the waveform of the AC voltage is a rectangular wave. However, the present invention is not limited to this. Can be used. h) The developing device is used for a single-color image recording device. However, a color image recording device that forms a color image with a plurality of color toners on an image carrier and collectively transfers the toner images onto recording paper is also used. It is equally applicable. i) The developing device uses a photoconductor as an image carrier,
It is used to visualize the latent image formed by irradiation of image light, but using a dielectric as an image carrier,
The present invention can also be applied to an apparatus for forming an electrostatic latent image by a discharge recording head used in an electrostatic printer, an ion flow control head disclosed in JP-A-59-190854, and the like.

[0063]

As described above, in the developing device according to the present invention, it is possible to form a substantially single-layer uniform developer layer without using a layer thickness regulating member. Since the occurrence of the layer thickness unevenness is suppressed, it is possible to perform good image reproduction excellent in density uniformity and fine line image reproducibility in a low image density portion. Further, since a sufficient magnetic binding force acts on the carrier, scattering of the developer and adhesion of the carrier to the image carrier do not occur. Further, since a thin layer of the developer can be formed without using the layer thickness regulating member, an excessive force does not act on the developer, and the deterioration of the developer at the time of forming the developer layer can be prevented. Further, since the developer layer is formed only by the magnetic force of the developer carrying member, the amount of the developer transported does not depend on the precision of the components, and does not change with time. Therefore, there is also an effect that the stability and maintainability of the image quality are excellent.

[Brief description of the drawings]

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

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

FIG. 3 is a schematic configuration diagram illustrating a developing device according to an embodiment of the invention described in claim 1 or 2;

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

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

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

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

8 is a diagram illustrating a relationship between the number of prints and the solid image density in the developing device illustrated in FIG. 3;

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

10 is a diagram illustrating a magnetic flux density distribution in a direction perpendicular to a surface of a developer carrier in the developing device illustrated in FIG. 3;

11 is a schematic diagram showing a magnetic flux near a surface of a developer carrier and a state of developer adhesion in the developing device shown in FIG. 3;

FIG. 12 is a diagram illustrating a magnetic flux density distribution in a direction perpendicular to the surface of the developer carrying member when the magnetization intervals are equal.

FIG. 13 is a schematic diagram showing magnetic flux near the surface of the developer carrying member and the state of developer adhesion when the magnetization intervals are equal.

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

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Photoreceptor drum 2 Charger 3 Exposure device 4 Developing device 5 Pre-transfer corotron 6 Transfer corotron 7 Peeling corotron 8 Cleaner 9 Optical neutralizer 11 Developing housing 12 Developing roll 12a Conductive substrate 12b Magnetic recording layer 13 Screw auger 14 Screw auger 15 Scraper 16 Partition wall 17 Power supply for developing bias 21 Magnetic flux 22 Magnetic carrier 200, 210 Magnetic recording head 201, 211 Core 202, 212 Coil 203 Magnetic flux

Claims (2)

[Claims] An image carrier on which an electrostatic latent image is formed on the surface thereof, wherein the developer carrier is provided so as to be close to or separated from the image carrier, and a peripheral surface of which is supported so as to be able to rotate; On the peripheral surface, a two-component developer containing a toner and a magnetic carrier is carried and conveyed, and the toner is transferred to the image carrier at a position facing the image carrier and the developer carrier to form a toner image. In the developing device to be formed, the developer carrier has a plurality of magnetic poles in which S poles and N poles are alternately arranged on a peripheral surface, and the magnetic poles are arranged such that magnetic pole intervals of the same polarity are substantially equal. The distances X ₁₂ and X ₂₃ between the magnetic pole M ₂ of one polarity and the magnetic poles M ₁ and M ₃ of the other polarity adjacent on both sides thereof are X _12> X ₂₃ or X ₁₂ <developing instrumentation, characterized in that it is arranged so that X ₂₃ . The developing apparatus according to claim 1, the person X _s smaller of the distance X ₁₂ of different polarities poles of adjacent, X _23, and the magnetic pole interval X ₁₃ of the same polarity, 0. A developing device characterized by being set in a range satisfying 1 ≦ X _s / X ₁₃ ≦ 0.4.