JPH0643743A - Developing device - Google Patents

Abstract

PURPOSE:To obtain an image having stable high image quality without fogging development caused by the adhesion of carrier to an image forming body or a void phenomenon arround a place where the carrier adheres by specifying the voltage of DC bias electric field and the ratio of surface linear velocity between a sleeve and the image forming body. CONSTITUTION:Two-component developer is used, and a developing sleeve 2 in which magnetic poles are disposed and fixed avoiding a position closest to the image forming body 1 is provided opposite the image forming body 1, then AC bias electric field and the DC bias electric field are impressed between the image forming body 1 and the sleeve 2, so that a latent image on the image forming body 1 is developed by interpole development in a non- contact system. In such a case, when the surface linear velocity (vr) of the sleeve 2 is set to be >=100mm/s, the ratio (vr/vp) of the surface linear velocity between the sleeve 2 and the image forming body 1>=2, and the DC bias voltage VDC >=-800V, the carrier is made difficult to adhere to the image forming body 1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in a developing device used in a recording device such as an electrophotographic copying machine or a facsimile, and more particularly to an improvement in a developing device using a two-component developer in which a toner and a magnetic carrier are mixed. .

[0002]

2. Description of the Related Art A two-component developer in which a toner and a magnetic carrier are mixed is easier to control triboelectrification of the toner and less likely to cause aggregation of the toner, as compared with a one-component developer composed of a magnetic toner that does not use a magnetic carrier. Therefore, the toner transfer can be effectively controlled by the bias electric field, the magnetic substance does not need to be contained in the toner, and even if the magnetic substance is contained in the toner for preventing fogging, the amount thereof is small. In the case of, color sharpness can be obtained,
When the surface of the image forming body is rubbed with the developer layer, that is, in the case of the so-called magnetic brush developing method, the magnetic brush has good ears and excellent rubbing property. Further, the magnetic brush also cleans the surface of the image forming body. However, it is often used in spite of the fact that it is necessary to control the amount of toner with respect to the carrier because it has a feature that it can easily exhibit a sufficient cleaning effect.

A developing method using this two-component developer, a so-called two-component developing method, has been repeatedly improved to improve the developing performance. For example, USP 3,890,929, JP-A-55-18656 and the like are disclosed. It has been disclosed, as an example of applying the development under an oscillating electric field, which is an alternating electric field of a one-component developer, to a two-component developer, for example, JP-A-57-139761, 57-147652, 57-1.
Japanese Laid-Open Patent Publication No. 47653 discloses a developing method in which a two-component developer composed of a toner and a carrier is introduced between an image forming body (electrostatic image support) and a developing sleeve to develop in a contact or non-contact manner under an oscillating electric field. The law is disclosed. Compared with development under an oscillating electric field using a one-component developer, it is not necessary to mix a magnetic material for obtaining the toner itself carrying force, and it is suitable for colorization, and development characteristics due to changes in the oscillating electric field. Is superior to single-component development, and a large difference is recognized.

[0004]

As a developing device, a developing sleeve is fixed and a magnet body having a plurality of N and S poles in the circumferential direction is rotated, and both the developing sleeve and the magnet body are rotated. In many cases, those that rotate and the developing sleeve rotates and the magnetic poles inside are fixed. Among them, in the former two cases where the inner magnet body rotates, the developer layer formed on the surface of the developing sleeve becomes wavy and moves, so the layer thickness of the developer layer There is a feature that even if there is some inconsistency, the effect will be canceled by the movement of the wavy undulations so that it will not be a problem, but a large rotational force is required to rotate the magnet body at high speed and vibration will occur. However, there is a problem in that the rotation mechanism is complicated and strong, and the size is large. In that respect, the latter type having a fixed inner magnetic pole does not have the above-mentioned problem in the case where the magnet body rotates, but the position of the wavy undulation caused by the inner magnetic pole even if the developer layer moves. Has a problem that if the developer layers have different layer thicknesses, the effect is likely to appear. Further, the magnetic pole is provided at a position closest to the image forming body of the developing sleeve. Then, the above effect is more easily emphasized.

This is not a serious problem in the porcelain brush contact development, but it greatly affects the image quality such as the image density in the non-contact development.

In view of these points, in JP-A-60-14263, a fixed magnetic pole is provided in the developing sleeve, and since the fixed magnetic pole does not form a brush in the developing area, a developer layer is formed. However, in this case, since the magnetic force that binds the carrier is weak and the conductive carrier and toner are used as the developer, a breakdown occurs, the carrier adheres to the image forming body, or the fog phenomenon or the carrier occurs. The white spots (fireflies) were generated mainly in the areas where the ash had adhered.

In other words, the image quality has not reached the practical level yet, and even if the structure is relatively close, the fog phenomenon or the white spot phenomenon is likely to occur mainly at the place where the carrier is attached. there were.

The present invention has been made to solve the above problems. That is, it is an object of the present invention to provide a developing device capable of stably obtaining a high-quality image in which a carrier adheres to an image-forming body to cause fogging development, or a white spot phenomenon does not occur mainly at a place where the carrier adheres. It was done.

[0009]

The above object is to use a two-component developer in which a toner and a magnetic carrier are mixed, and fix the magnetic pole to the image forming body while avoiding the position closest to the image forming body. And a developing sleeve having the above-mentioned arrangement is provided so as to face each other, an AC bias electric field and a DC bias electric field are applied between the image forming body and the sleeve, and the latent image of the image forming body is developed by the non-contact method. In the developing device for developing by the method, the voltage of the DC bias electric field is -800 V or less, and the surface linear velocity ratio vr / vp of the sleeve and the image forming body is 2 or more. To be done.

However, let vr be the surface linear velocity of the sleeve and vp be the surface linear velocity of the image forming body.

The above-mentioned object is to use a two-component developer in which toner and magnetic carrier are mixed, and fix the magnetic pole to the image forming body while avoiding the position closest to the image forming body. Development in which developing sleeves are provided so as to face each other, an AC bias electric field and a DC bias electric field are applied between the image forming body and the sleeve, and the latent image of the image forming body is developed by a non-contact method by interelectrode development. In the device, the surface linear velocity of the sleeve is 100 mm / s or more, which is achieved by a developing device.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the drawings. FIG. 1 is a sectional view of an embodiment of the developing device of the present invention.

In FIG. 1, reference numeral 1 is a drum-shaped image forming body which has an image forming layer such as an electrophotographic photosensitive layer on its surface and rotates in the direction of the arrow to form an electrostatic latent image or the like. , A developing sleeve 3 made of a non-magnetic conductive material such as aluminum or stainless steel, which rotates in the direction of the arrow, is a magnet fixed inside the developing sleeve 2 and having a plurality of N and S magnetic poles arranged in the circumferential direction. The N and S magnetic poles are magnetized on the sleeve directly above the magnetic poles to a magnetic flux density of usually 500 to 1500 gauss.
Reference numeral 4 denotes a developer pool, and 5 denotes a stirring rotary blade that stirs the developer in the developer pool 4 in which the toner and the magnetic carrier are mixed to evenly mix the toner and the magnetic carrier, and frictionally charges the toner. When the developer in the developer reservoir 4 is attracted to the surface of the developing sleeve 2 by the magnetic forces of the N and S magnetic poles of the magnet body 3 and moves with the rotation of the developer sleeve 2 to form a developer layer 6, A layer thickness regulating blade composed of a magnetic substance or a non-magnetic substance for regulating the layer thickness of the developer layer, 7
Is a cleaning blade for removing the developer layer that has passed through the developing area where the developing sleeve 2 is close to the image forming body 1 from the surface of the developing sleeve 2 and returning it to the developer pool 4.
Applies an AC bias voltage to the developing sleeve 2 via the safety resistor 9 to generate an oscillating electric field between the developing sleeve 2 and the image forming body 1 whose ground portion is grounded. An AC bias power source for controlling the transfer of toner to the image forming body, and 8b applies a DC bias voltage to the developing sleeve 2 so as to superimpose the AC bias voltage on the developing sleeve 2 and the base portion is grounded as described above. A DC bias power source for transferring and adhering the toner of the developing sleeve 2 to the electrostatic latent image of the formed body 1, and a toner replenishing roller 10 for replenishing the developer reservoir 4 with the toner from the toner hopper 11.

The carrier used has an average particle size.
It is spheroidized to 40 μm and has a resin coating on the surface. Carrier resistance is 1 cm ² cell
Tapping at a pressure of 0.5 kg / cm and 3 in an electric field of 3 KV / cm
It was × 10 ¹² to ¹³ Ωcm (20 ° C 50%). The toner had an average particle size of 11 μm and a specific resistance of 10 ¹³ to ¹⁴ Ωcm.

Next, the known inter-electrode development according to this embodiment will be described.

The developing device described with reference to FIG. 1 is almost the same except for the conventional developing device in which the magnet body 3 is fixed and the positions where the N and S magnetic poles are arranged in the magnet body 3.
Even if the layer thickness of the developer layer is regulated by the layer thickness regulation blade 6, the layer thickness is likely to be inconsistent. Therefore, when the magnetic pole is provided at the position closest to the image forming body 1 of the developing sleeve 2 as in the conventional developing device, the rising of the developer layer occurs there, and the unevenness of the layer thickness is emphasized. However, it becomes difficult to stably carry out development in which a sufficient image density is obtained without fogging. Further, if it is attempted to make the layer thickness thin so as to keep the developer layer in non-contact with the image forming body 1, it is necessary to narrow the gap between the layer thickness regulating blade 6 and the developing sleeve 2, and dust, toner, etc. It is easy for clogging to occur in the regulation part due to the aggregation of the.

For this reason, in the developing device for the inter-electrode development of the present embodiment, the N and S magnetic poles are arranged so as to avoid the position where the developing sleeve 2 is closest to the image forming body 1, as shown in FIG. As described above, a horizontal magnetic field is formed in the developing area, and the developer layer is laid down without raising the ears. At this time, the angle between poles is 50 ° or more
Although 90 ° or less can be used, good results have been obtained when the range between the poles and about 15 ° is opposed to the image forming body. The horizontal magnetic force in this range is 200 G or more.
As a result, a developer layer having a uniform layer thickness is realized in the developing region, and even if the gap between the layer thickness regulating blade 6 and the developing sleeve 2 is widened, a thin layer of the developer layer is realized in the developing region, and the layer thickness is not different. It is possible to perform stable development that is not affected by.

As described above, in the inter-electrode development, the diameter of the developing sleeve 2 is made small so that the spikes of the developer at the positions of the N and S magnetic poles provided so as to avoid the center line position do not come into contact with the surface of the image forming body 1. The preferred range is 40 to 10 mm
It is in the range of φ. Similarly, the diameter of the drum-shaped image forming body 1 is preferably smaller, and the preferable range is 300 to 10 mmφ.
Is. When a belt-shaped image forming body 1 is used, a belt driving roller may be provided in the developing area so as to satisfy the above conditions.

As described above, in the developing device for the inter-electrode development of this embodiment, the magnetic pole fixedly disposed inside the developing sleeve 2 is located at the position where the developing sleeve 2 is closest to the image forming body 1. The developer layer, which is moved according to the rotation of the developing sleeve 2, is held in the developing region under the action of the horizontal magnetic field component so as to be disposed at the avoiding position. The gap between the image forming body 1 and the image forming body 1 can be narrowed so that the toner flying control can be sufficiently performed by the oscillating electric field, and therefore, an effect that development with high image density can be easily performed without fogging is obtained. . Therefore, the developing device for the inter-electrode development of this embodiment is suitably used for the non-contact developing method.

As described above, when the carrier adheres to the image forming body, the fogging phenomenon or white spot development (firefly) occurs mainly at the place where the carrier adheres. According to the graph shown in FIG. 3, the adhesion of the carrier to the image forming body is largely related to the surface linear velocity ratio between the developing sleeve and the image forming body and the DC bias voltage between the developing sleeve and the image forming body. I found that.

FIG. 3 is a graph showing the rotational speed of the developing sleeve and how the DC bias voltage between the developing sleeve and the image forming body relates to the amount of carrier and toner attached to the image forming body.

Therefore, first, the adhesion state of the carrier and the toner to the image forming body will be described with reference to the graph of FIG.

In the graph of FIG. 3, when the rotation speed Nr of the developing sleeve indicated by the square points is 160 rpm, it is -5 when the DC bias voltage VDC of the developing sleeve is -600V.
At 00V, the amount of carrier adhered to the image forming body was reduced from about 25 to about 11. The toner adhesion amount is reduced from about 1.25 mg / cm ² and about 1.15 mg / cm ² but shows no great difference.

When the rotation speed Nr of the developing sleeve indicated by the triangular points is 244 rpm, the DC bias voltage VDC is -6.
At -500V and -450V as compared with 00V, it is shown that the amount of the adhered carrier is reduced from about 17 to about 10 and to about 2.5. Incidentally, the adhesion amount of the toner decreases from about 1.57 mg / cm ² to about 1.5 mg / cm ² and about 1.33 mg / cm ² but shows no great difference.

When the rotational speed Nr of the developing sleeve indicated by the circle is 320 rpm, the DC bias voltage VDC is -600.
At -500V and -450V compared to V, it is shown that the amount of the adhered carrier is reduced from about 13 to about 3.5 and then to about 3. Incidentally, the adhesion amount of the toner decreases from about 1.7 mg / cm ² and about 1.55 mg / cm ² and about 1.43 mg / cm ² but shows no great difference.

That is, the graph of FIG. 3 shows that the higher the rotation speed Nr of the developing sleeve and the higher the DC bias voltage VDC of the developing sleeve, the more the amount of carrier adhered to the image forming body decreases sharply. . The amount of toner attached to the image forming body increases as the rotation speed of the developing sleeve increases.
It shows that it does not change significantly even when the DC bias voltage increases.

Next, the above phenomenon will be described with reference to FIG.

FIG. 4A is an explanatory view showing that the amount of carrier adhered to the image forming body decreases as the rotation speed of the developing sleeve becomes faster, and FIG. 4B shows the amount of carrier adhered as the DC bias voltage increases. It is an explanatory view showing that it decreases.

In FIG. 4A, the carrier of the developer layer of the developing sleeve is negatively charged by the charge injection into the carrier by the DC bias voltage in the developing area. Further, the negative charge due to the charge injection of the carrier becomes smaller as the developer, that is, the time for which the carrier passes through the developing area, becomes shorter. Therefore, as the rotation speed of the developing sleeve is faster and the charge injection time to the carrier is shorter, the negative charge amount of the carrier is smaller and the carrier adhesion amount to the image forming body to which the positive voltage is applied by the DC bias voltage becomes smaller. become.

In the case of toner, the toner is negatively charged by frictional charging with the carrier before entering the developing area, has a high specific resistance, is hardly affected by charge injection, and the developing sleeve rotates at a high rotation speed one after another. Since new negatively charged toner enters the developing area, the higher the rotation speed of the developing sleeve, the greater the amount of toner adhered to the image forming body to which the positive voltage is applied by the DC bias voltage. This is a preferable tendency because it improves the developability of the toner.

Next, in FIG. 4B, as described above, the carrier of the developer layer of the developing sleeve is negatively charged by the charge injection into the carrier by the DC bias voltage in the developing area. The negative charge of becomes larger exponentially as the negative voltage of the DC bias voltage becomes higher. Therefore, the lower the DC bias voltage of the developing sleeve, the smaller the negative charge amount of the carrier, and the smaller the amount of carrier adhesion to the image forming body to which the positive voltage is applied by the DC bias voltage.

In the case of toner, new negatively charged toner is successively carried to the developing area by the developing sleeve, so if a certain amount of DC bias voltage is applied, the DC bias voltage will be slightly lower after that. Even so, the amount of toner adhering to the image forming body decreases as the electric field in the developing region decreases, but the ratio is a linear function, which is far smaller than the influence of charge injection into the carrier.

FIG. 5 is a graph showing the relationship between the amount of carrier adhered to the image forming body in the inter-electrode developing and the super developing in the state where the magnetic pole in the developing sleeve is closest to the image forming body.

In the graph of FIG. 5, there is a clear difference between the extreme development indicated by the circle points and the interdevelopment development indicated by the triangle points, indicating that the interdevelopment has less carrier adhesion. The effect is that the carrier resistivity is 10 ¹⁴
When the toner has a specific resistance of 10 ¹³ Ωcm or more and the toner has a specific resistance of 10 ¹³ Ωcm or less.

Next, specific developing conditions of the developing device of this embodiment will be described.

First, the sleeve diameter of the developing sleeve is 18 mmφ
Is. The surface linear velocity vr is preferably 100 mm / s or more, and the best result is obtained when it is 230 mm / s.

Next, the surface linear velocity vp of the image forming body is 30 to 300 m.
m / s is preferable, and the best result is obtained at 74 mm / s.

The ratio of the surface linear velocity vr of the developing sleeve to the surface linear velocity vp of the image forming member is preferably 2 or more,
The best result was obtained in the case of 3 because of the constitution of the developing device.

The gap between the developing sleeve and the image forming body is 300
.About.1000 .mu.m is preferable, and 570 .mu.m gives the best result.

The AC bias voltage Vp-p between the developing sleeve and the image forming member is preferably 1 to 3.5 KV, and the frequency f is preferably 1 to 12 KHz. The best results are obtained when Vp-p is 2.6 KV and f is 8 KHz. Was given.

The DC bias voltage VDC of the developing sleeve is
-300 to -800V is preferable, and -600V gives the best result.

The present invention will now be further described by the above, and.

The sleeve diameter of the developing sleeve is 18
mmφ, and the surface linear velocity vr of the developing sleeve is preferably 100 mm / s or more, but if it is too high, the mechanical load will increase.
It was shown that 230 mm / s was the optimum. Therefore, it is advantageous that the surface linear velocity vp of the image forming body is higher because carrier adhesion is reduced even with the same linear velocity ratio. 30mm in the experiment
It was shown that 74 mm / s is optimal although it is preferable if it is / s or more. And the surface linear velocity of the developing sleeve
It is shown that the ratio vr / vp of vr to vp of the surface linear velocity of the image forming body is preferably 2 to 5, and 230/74 = 3.11≅3 in the present embodiment is optimum. Further, it has been shown that the DC bias voltage VDC of the developing sleeve is preferably -300 to -800V, and optimally -600V.

This means that the surface linear velocity ratio vr / vp = 3, as well as the surface linear velocity of the developing sleeve vr230 mm /
s, the absolute value of the surface linear velocity vp74 mm / s of the image forming body itself has an important meaning as a condition for making it difficult for the carrier to adhere to the image forming body. Therefore, if the surface linear velocity vr of the developing sleeve is 100 mm / s or more, the surface linear velocity ratio vr / vp of the developing sleeve and the image forming body is 2 or more, and the above-mentioned DC bias voltage VDC is -800 V or more, the carrier Can be made difficult to adhere to the image forming body. Further, in addition, by performing the inter-electrode development of the present embodiment as described above, the effect of making it difficult for the carrier to adhere to the image forming body is increased. In addition,
The same result was obtained in any rotation direction of the developing sleeve.

FIG. 6 is a diagram showing another embodiment of the developing device configuration.

The layer thickness of the developer layer of the developing sleeve 2 is regulated by a magnetic rod 61 made of a magnetic material. As a result, the developer has a thickness of only one layer of the carrier, and the present invention can be more effectively carried out. In addition, 51 and 52 are agitation rollers, 7 is a cleaning blade, 10 is a toner replenishing roller, 11 is a toner hopper, 8a is an AC bias power source, and 8b is a DC bias power source, which have the same functions as those described in FIG.

[0047]

According to the present invention, there is provided a developing device capable of stably obtaining a high-quality image in which a carrier adheres to an image forming body and a fog phenomenon or a white spot phenomenon does not occur mainly at a place where the carrier adheres. It will be provided.

[Brief description of drawings]

FIG. 1 is a sectional view of an embodiment of a developing device according to the present invention.

FIG. 2 is a diagram showing a state of inter-electrode development.

FIG. 3 is a graph showing the effect of adhesion of carrier and toner to the image forming body by the DC bias voltage and the developing sleeve rotation speed.

FIG. 4 is a diagram illustrating the rotation speed of the developing sleeve and the carrier and toner adhesion to the image forming body due to the DC bias voltage.
(B) is an explanatory view of adhesion by a DC bias voltage.

FIG. 5 is a graph showing the effect of adhesion of the carrier to the image forming body in the inter-electrode development and the super development.

FIG. 6 is a diagram showing another embodiment of the developing device configuration.

[Explanation of symbols]

 1 image forming body 2 developing sleeve 3 magnet body 8a AC bias power source 8b DC bias power source Nr developing sleeve rotation speed vr developing sleeve surface linear velocity vp image forming surface linear velocity VDC DC bias voltage

Claims (2)

[Claims] 1. A two-component developer containing a mixture of toner and a magnetic carrier is used, and a developing sleeve provided with magnetic poles is opposed to an image forming body while avoiding a position closest to the image forming body. In the developing device, an AC bias electric field and a DC bias electric field are applied between the image forming body and the sleeve, and the latent image of the image forming body is developed by a non-contact method by the gap development. DC bias field voltage is -8
And a surface linear velocity ratio vr / vp of the sleeve and the image forming body is 2 or more. However, let vr be the surface linear velocity of the sleeve and vp be the surface linear velocity of the image forming body. 2. A two-component developer containing a mixture of toner and a magnetic carrier is used, and a developing sleeve provided with magnetic poles is opposed to an image forming body while avoiding a position closest to the image forming body. And a bias electric field of alternating current and a bias electric field of direct current are applied between the image forming body and the sleeve to develop the latent image of the image forming body by a non-contact method in the inter-electrode development. The surface linear velocity of the sleeve is 100 mm /
A developing device characterized by being s or more.