JPS6325350B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electrophotographic developing method and apparatus,
More specifically, a composite developer such as a two-component developer is used, and a low frequency alternating electric field is applied between the electrostatic image holder and the development electrode supporting the developer during development. The present invention relates to an electrophotographic developing method and apparatus for obtaining a visible image with excellent image clarity and rich gradation without background fog.

Conventionally, there is no known method in which a one-component developer is used, the developer carrying member is placed opposite to the electrostatic image holder with a required gap, and the developer is flown through this gap (jumping) for development. (for example, Japanese Patent Publication No. 41-9475), or a high-frequency pulse bias (frequency 10 kilocycles/second ~ 3000 kilocycles/second, etc.) is applied,
Techniques are also known in which toner is attached to the image area of an electrostatic image holder, but not to the non-image area (for example, U.S. Pat. No. 3,890,929, U.S. Pat. No. 3,866,574, Specification No. 3893418, etc.)

However, all of these known examples use a one-component dry developer consisting only of toner, and from the viewpoint of preventing the toner from adhering to non-image areas, the electrostatic image carrier and the toner carrier are Between,
A configuration is adopted in which the two face each other with a gap large enough to allow the toner to fly.

In the present invention, a two-component composite developer having toner particles and carrier particles is used, and the composite developer is applied to an image area of an electrostatic image carrier (the area where the developer originally adheres and is visualized). and non-image areas (parts of the background to which developer should not originally adhere) are contacted indiscriminately, and at the same time, a low frequency alternating electric field is applied between the developer carrier and the electrostatic image holder. death,
It is an object of the present invention to provide a developing method and apparatus that can visualize only the image area and substantially eliminate the adhesion of developer to the non-image area.

The present invention solves the above problems, and includes:
A first aspect of the present invention is an electrophotographic developing method for visualizing an electrostatic image on an electrostatic image carrier using a composite developer containing carrier particles and toner particles charged to the opposite polarity to the carrier particles. An electrophotographic developing method is characterized in that a composite developer containing toner particles is developed by applying a low frequency alternating electric field, and the second invention comprises magnetic carrier particles and toner particles charged to the opposite polarity to the carrier particles. An electrophotographic developing device for visualizing an electrostatic image on an electrostatic image carrier using a composite developer comprising: a developer carrier carrying a composite developer comprising the magnetic carrier particles and the toner particles; An electrophotographic developing device characterized by comprising means for applying a low frequency alternating electric field to a development interval formed between an electrostatic image holder and the developer carrier.

Here, the low frequency referred to in the present invention refers to the above-mentioned high frequency and means less than 10 KHz, and the alternating electric field means that the direction of the electric field is alternating.

To summarize a preferred embodiment of the present invention, a low frequency alternating voltage is applied to the development electrode to generate an alternating electric field between the electrostatic image carrier and the development electrode. The higher the voltage applied to the developing electrode, the more effective it is in contributing to the above-mentioned improvement in image density and reduction in background fog density. It is necessary to take into account.
Further, the frequency of the alternating voltage applied to the developing electrode needs to be set to a frequency that does not cause density unevenness (so-called cycle unevenness) in the developed image. For this purpose, the higher the frequency, the greater this effect, but on the other hand, the leakage current increases, so this factor must also be taken into account and all the above factors must be set together.

In order to prevent density unevenness from appearing in the microscopic image, the development gap or the distance between the electrostatic image carrier and the developing electrode should be set to dmm, the moving linear velocity of the electrostatic image carrier should be set to vmm/sec,
Assuming that the frequency of the applied alternating voltage is Hz, it is necessary that ≧v/d (Hz) (1). Of course, there is an upper limit to this from the viewpoint of improving gradation reproduction, and values suitable for the present invention will be explained in detail in the description of the following examples. In addition, in order to prevent spark discharge from occurring due to dielectric breakdown at the shortest distance between the developing electrode and the electrostatic image holder, a protective resistor is installed between the developing electrode and the applied voltage source to limit the total current. It is preferable to insert it between. In this way, even if dielectric breakdown occurs for some reason, the total current is limited, and there is less risk of damage to the electrostatic image holding member due to spark discharge, etc., and the bias power source It will not cause any damage. Although it is possible to limit the total current depending on the alternating voltage generator used, the former method is preferable because the device becomes complicated and takes time to recover.

By applying a low frequency alternating electric field between the electrostatic image holder and the developing electrode, background fog can be reduced to a greater extent than when no alternating electric field is applied. When the electrostatic image carrier is composed of a photoconductor such as Se, ZnO, or an organic semiconductor, depending on its properties, the potential of the non-image area of the electrostatic image carrier may be set to a potential that prevents toner from adhering to the electrostatic image carrier. In such a case, it is necessary to generate a slight DC electric field in addition to an alternating electric field to suppress the adhesion of toner to the non-image area. In this case, in addition to the alternating voltage, a direct current voltage may be superimposed on the developing electrode, or an alternating voltage biased either positively or negatively may be applied. This further reduces fog due to the synergistic effect of the DC bias voltage and the alternating bias voltage application.
Moreover, it is possible to substantially eliminate it.

In this way, by applying an alternating bias voltage, the image density increases and the fog density decreases. It is particularly effective for developing electrostatic images that require a relatively low potential difference between bright and dark areas, such as the electrostatic image forming method (typically described in It is.

Embodiments to which the developing method and apparatus according to the present invention are applied will be described in detail below with reference to the drawings.

FIG. 1 is a sectional view of an embodiment of an electrophotographic apparatus having a developing device to which the developing method and device according to the present invention are applied, and FIG. 2 is an enlarged sectional view of the developing device.

In the figure, reference numeral 2 of the apparatus 1 indicates an outer casing, and an original or the like is placed on an original mounting table 3 made of a transparent member such as glass on the upper part of the outer casing 2. That is, the mounting table 3 does not move, and the image is irradiated onto the photosensitive screen 4 by optical means such as a moving/fixed mirror and a lens system. This optical means belongs to a conventionally well-known technique, and the first mirror 5 moves along the entire distance of the mounting table 3 at a speed v to the right-most dotted line position together with the original illumination lamp 6.
On the other hand, simultaneously with the movement of the mirror 5, the second mirror 7 moves at a speed of v/2 to the rightmost dotted line position. The original image guided by the first and second mirrors 5 and 7 is guided to the screen 4 via a lens system 8 having an aperture mechanism and a fixed mirror 9. Incidentally, the photosensitive screen 4 formed in an endless shape has the structure described in the above-mentioned Japanese Patent Laid-Open No. 51-341, and is made so that the side surface where the conductive member is exposed is on the inside. On the other hand, the formation of the primary electrostatic latent image by the photosensitive screen 4 is also carried out by the process clearly described in the above-mentioned Japanese Patent Laid-Open No. 51-341. (Of course, the present invention is not limited to this.) Among the structural members arranged around the screen 4 in the figure, one
0 is a pre-exposure lamp, which is provided in order to always use the photoconductive member constituting the screen 4 in a stable light history state. A corona discharger 11 is a primary voltage applying means, and has a sufficient length in the circumferential direction of the screen 4 in order to charge the screen 4 to a sufficient voltage. Next, 12 is a corona discharger which is a means for applying a secondary voltage, and in order to irradiate an image onto the screen 4 through the discharger 12, a part of the shield plate of the discharger 12 is configured to be optically open. have. A lamp 18 is for illuminating the entire surface.

The corona discharger 19 generates a modulating corona ion stream for forming a secondary electrostatic image. A secondary electrostatic latent image is formed on the surface insulating layer 21 of the drum 20 facing the discharger 19 with the screen 4 interposed therebetween. The insulating layer 21 of the drum 20 is arranged or attached to a conductive support 22, and the support 22 functions as a counter electrode in ion modulation. The drum 20 has the rotation direction (arrow) and speed (vmm/sec) of the photosensitive screen 4.
It rotates in the direction of the arrow corresponding to. By the way, the secondary electrostatic latent image formed on the insulating layer 21 is developed by the developing device 23 using the developing method according to the present invention, and becomes a toner image. The toner image is transferred to the transfer position 24.
The image is transferred onto copy paper using plain paper, which is a recording member that has been conveyed by the machine. Insulating layer 2 after transfer position 24
The residual toner on the insulating layer 21 is removed by a cleaning means 25 using a blade or the like, and then the insulating layer 21 is brought to a uniform surface potential by a corona discharger 26 to form a secondary electrostatic latent image again if necessary. On the other hand, the copy paper 27 to which the toner image is transferred is loaded in the storage cassette 28, and
The sheets are separated one by one by the separation claws 9 and 30 and conveyed to the transfer position. In the figure, 31 is a feed roller, 32
is the copy paper 2 when transferring the toner image with the corona discharger.
7, a bias voltage is applied.
After passing through the transfer position 24, the toner image is fixed on the copy paper 27 by the heater of the heat fixing means 33, and the finished copy paper storage tray 35 is transferred to the outside by the conveyor belt 34.
transported to.

The developing device shown in FIG. 2 has two non-magnetic hollow cylinders (hereinafter referred to as sleeves) facing a drum-shaped electrostatic latent image holder 21 and disposed within the downward rotation range of the holder. This figure shows an apparatus for developing an electrostatic image on the holder.

In the figure, the electrostatic image holder 21 is rotating in the direction of the arrow, and two non-magnetic rotating sleeves 36 are installed in the developing section so as to rotate in the same direction as the direction of the arrow.
A and 36B are arranged a short distance apart from each other. The rotational speed of this sleeve is
It is driven by a known driving means at a circumferential speed different from the circumferential speed of 1.

As an example, the peripheral speed of the electrostatic image holder is 50mm/
secThe peripheral speed of the sleeve in the front stage is 550mm/sec, the peripheral speed of the sleeve in the rear stage is 450mm/sec, and the diameter of the sleeve is
It was set to 63mm. Both sleeves have fixed magnetic means 37A, 37B inside them, and the magnetization poles of the respective magnetic means are different.

First, the magnetic pole arrangement of the first magnetic means 37A will be explained. The illustrated magnetic means 37A is formed as a magnetic roller, and has magnetized poles N ₂ , S ₂ , N ₃ equiangularly spaced apart from each other near its surface, and the N ₃ pole is closest to the surface of the electrostatic image carrier 21 . are placed next to each other.

Next, a second magnetic means 37B is disposed downstream along the electrostatic latent image carrier of the first magnetic means,
As shown in the figure, it is formed of a four-pole magnetized roller, and the _N1 pole and _S1 pole are magnetic poles that have the function of drawing up and transporting the developer. Both magnetic poles of S ₃ and S ₄ are
These magnetic rollers are developing magnetic poles that are spaced apart from each other by a predetermined angle θ in opposite directions from the point closest to the surface of the electrostatic image carrier. These developing magnetic poles S ₃ and S ₄ having the same polarity are selected to be different in polarity from the developing magnetic pole N ₃ of the first magnetic means.
Reference numeral 38 denotes a developer in the developing device housing 23a, which contains a mixture of magnetic carrier particles and developer toner particles. Also, within this housing, there are two screws 39A and 39B for stirring the developer 38 in the direction of rotation of the sleeve, a blade 43 for regulating the thickness of the developer pumped onto the surface of the sleeve 37B to a predetermined value, It has a cleaning blade 44 for removing residual developer from the sleeve surface after development, a replenishment developer storage chamber 40, and a replenishment roller 41 provided at the lower opening thereof. Due to the rotation of the roller 41, the developer that has entered the recess provided on the surface of the roller 41 is transferred to the housing 2 of the container.
The developer is dropped into the developing chamber 42 in which the sleeve 3a is provided, and the developer is replenished.

The sleeve 36A and the magnetic means 37A
constitutes a first developing section, and sleeve 36B and magnetic means 37B constitute a second developing section.

45 is a power source that applies a low frequency AC bias voltage to both sleeves 36A, 36B;
6 is the protection resistor mentioned above. The applied AC bias voltage was set to have an effective value of 200V. A rectangular wave was used as the voltage waveform. The frequency of the AC voltage is such that the minimum distance d between the developing sleeve and the electrostatic image holder in the developing section is approximately 5 mm, and the peripheral speed of movement of the electrostatic image holder, that is, the process speed V.
Since it is set to 500mm/sec, the frequency of the AC voltage should be ≧v/d=500/5=100 (Hz), but from the viewpoint of effectiveness, it should be a value of 500Hz or more, and its upper limit is As will be described later, good results were obtained when the frequency was set to 1 KHz in order to ensure sufficient fluidity of developer particles, maintain reproducibility of halftone images, and prevent deterioration of gradation.

When the protective resistor 46 is set to 100KΩ,
Even with an applied voltage of 200 V, no excess current of 2 mA or more flows through the sleeve, so there was no damage to the electrostatic image holder 21.

FIG. 3 shows a simplified configuration of the developing device shown in FIG. 2 by using only one sleeve. In the figure, 50 is
The electrostatic image carrier may be a photoreceptor on which an electrostatic image can be formed by directly performing processes necessary for electrostatic image formation such as photosensitive charging and image exposure.

For example, Japanese Patent Publication No. 42-23910, No. 42
-19748 Publication, 43-24748 Publication, 44-
Photoreceptors and electrostatic image forming processes described in other publications such as No. 13437 can be applied.

51 is a housing of a developing device; 52 is a developer containing the above-mentioned carrier particles and toner particles;
53 is a non-magnetic sleeve that is supported to rotate; 54 is a magnet roll enclosed in the sleeve; 55 is a plate member that regulates the thickness of the developer replenished onto the sleeve; a scraping plate for removing residual developer from the sleeve surface;
8 is a power source that applies an AC low frequency bias voltage to the sleeve via a protective resistor 57. The applied voltage, its frequency and protective resistance value are set in the same way as in the case of FIG.

Now, regarding the developing apparatus illustrated in FIGS. 2 and 3, the development and effects produced by generating an alternating electric field between the electrostatic image holder and the sleeve acting as a developing electrode will be described.

The developer applied to the present invention has a complex component, a second component, and a second component.
The developer illustrated in FIGS. 3 and 3 is a mixture of toner and carrier particles. It is thought that in a developer made of such a mixture, the fluidity of the developer particles is substantially improved by applying an AC bias voltage between the electrostatic image carrier and the development electrode in the development section. This is because by creating an alternating electric field between the electrostatic image carrier and the developing electrode or between the electrostatic image carrier and the developer, the developer particles are subjected to a force along the alternating electric field. Therefore, not only the developer particles already in contact with the electrostatic image carrier, but also the developer particles present in close proximity to the electrostatic image carrier are urged to move alternately through the development gap, and the electrostatic It will repeatedly come into contact with and separate from the image carrier. Therefore, the amount of developer particles contributing to development becomes larger than when no AC bias voltage is applied.

The two-component developer is supplied by a sleeve so as to be in contact with the image area and the non-image area of the electrostatic image holder. When the electric field is to be attracted in the direction of the image area, it is strongly attracted over a wide range and adheres to the image area. In this way, once the toner adheres to the electrostatic holder, physical adsorption force with the surface of the electrostatic holder acts, so that it becomes substantially difficult to separate even in the case of a reverse electric field.

On the other hand, in the non-image area, even if toner adheres once during the electric field that should be attracted toward the image area, due to the alternation of the electric field, when the electric field of the other polarity is applied, the adhered toner or the vicinity The toner particles present in the toner are stripped off again by vibration,
The developer is returned to the developer carrying sleeve side. What should be noted here is that not all of the developer particles present between the electrostatic image carrier and the developer carrying member contribute to development; in addition to the developer particles that come into contact with the electrostatic image carrier, The developer particles attracted to the electrostatic image holder by the alternating electric field contribute to development. At this time, other particles, for example, in the case of a two-component developer consisting of a toner and a carrier, the carrier behaves as a conductive particle, and the sleeve, which acts as a developing electrode, is farther away than the electrostatic image carrier. Even in this case, the carrier particles function as a developing electrode, and the distance between the electrostatic image holding surface and the carrier is reduced to about 10 to 40μ, which is approximately the distance of several toner particles. The developing electric field between the holder and the developing electrode is considerably larger than the electric field applied to the developer carrying member, so the effect is very large. The developer carrier particles that function as a developing electrode preferably have a volume resistivity of 10 ¹² Ω・cm.
Must be less than ¹⁰ Ω・cm.

Furthermore, the following effects can be considered as effects of the alternating electric field. First, the developer particles attached to the electrostatic image carrier are also affected by the alternating electric field, and the developer particles repeatedly separate from and adhere to the electrostatic image carrier, but even in this case, the Because the developer particle carrier or conductive toner, which serves as a typical development electrode, is in contact with the surface of the electrostatic image holder or exists with a gap of 10 to 40 μm between only the toner particles, the strength of the alternating electric field becomes extremely large, and the development This serves to remove excess toner that has adhered to unwanted non-image areas, so-called background fog.

Here, it is also possible to mix a third component in addition to the toner and carrier. For example, silica,
Examples include lubricants such as Teflon, and abrasives such as potassium oxide talc.Since these are electrically charged,
It will still be affected by the alternating current electric field.

The above examples are for explaining the present invention, and the present invention is not limited thereto. The waveform of the applied bias voltage may be any waveform as long as it is a low frequency alternating waveform, such as a sine wave, a rectangular wave, a triangular wave, or a sawtooth wave. Further, the wave does not necessarily have to be symmetrical, and in relation to the electrostatic image potential, it may be preferable to have a waveform in which a direct current component is superimposed, or a waveform biased toward positive or negative polarity.

As described above, the present invention provides an electrophotographic development method in which an electrostatic image is visualized by bringing a developer into contact with an electrostatic image holder, in which a composite developer containing composite components capable of being charged to different polarities is used. The present invention provides an electrophotographic developing method in which a low-frequency alternating electric field is applied between the electrostatic image carrier and the developing electrode when the electrostatic image carrier is brought into contact with the electrostatic image carrier, and an apparatus for carrying out the same.
Of the composite developer in contact with or close to the electrostatic image holder, toner particles and carrier particles charged with opposite polarity to the toner particles are charged according to the alternating frequency,
Since the electrostatic image holding surface is repeatedly attracted and separated, the toner can be sufficiently attached to the image area of the electrostatic image holding surface, and the toner can be produced with good tonality and excellent reproduction of halftone images. Not only can an image be obtained, but in the non-image area, the amount of toner that finally adheres to the non-image area is reduced due to the vibration caused by the application of an alternating electric field to the toner that has once adhered to the non-image area or the toner existing in the vicinity. , which is extremely small and can be suppressed to a level that does not actually cause any problems, which has the effect of providing beautiful images with almost no background fog.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of an electrophotographic apparatus to which the developing method and apparatus according to the present invention are applied, FIG. 2 is an enlarged cross-sectional view of the developing device shown in FIG. 1, and FIG.
FIG. 7 is a sectional view showing a modification of the developing device shown in the figure. 42, 52, 62, 66...Developer, 36A,
36B, 53, 60, 63...Developer carrier, 2
1, 50... Electrostatic image holder, 45, 58... Power source for applying low frequency alternating voltage.

Claims (1)

[Scope of Claims] 1. An electrophotographic development method for visualizing an electrostatic image on an electrostatic image carrier using a composite developer containing carrier particles and toner particles charged to the opposite polarity to the carrier particles, comprising: 1. An electrophotographic developing method characterized in that development is performed by applying a low frequency alternating electric field to a composite developer containing carrier particles and the toner particles. 2. The electrophotographic developing method according to claim 1, wherein the voltage waveform that provides the low-frequency alternating electric field is a waveform in which a DC voltage is superimposed on an AC voltage. 3. The electrophotographic developing method according to claim 1, wherein the voltage waveform providing the low-frequency alternating electric field is a waveform biased toward positive or negative polarity. 4. An electrophotographic developing device that visualizes an electrostatic image on an electrostatic image carrier using a composite developer containing magnetic carrier particles and toner particles charged with a polarity opposite to that of the carrier particles, A developer carrier carrying a composite developer containing toner particles, and means for applying a low frequency alternating electric field to a development interval formed between the electrostatic image carrier and the developer carrier. An electrophotographic developing device. 5. The electrophotographic developing device according to claim 4, wherein the voltage waveform that provides the low-frequency alternating electric field is a waveform in which a DC voltage is superimposed on an AC voltage. 6. The electrophotographic developing device according to claim 4, wherein the voltage waveform providing the low-frequency alternating electric field is a waveform biased toward positive or negative polarity. 7. The developer carrier has a magnetic field generating means for magnetically supporting the composite developer on its surface inside thereof, and the magnetic field of the magnetic field generating means acts on the development interval. The electrophotographic developing device according to item 4. 8. The electrophotographic developing device according to claim 4, wherein the developer carrier has a magnetic field generating means inside which arranges a pair of magnetic poles of the same polarity to face each other at the development interval.