JP2008197609A - Developing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a developing device which is high in design latitude on electric field, material, control or the like, can make the charged amount of toner aptitude without increasing the splashing of toner and with a means less in mechanical stress applied to a developer, can form an image free from fogging, and has a long service life. <P>SOLUTION: A toner charging means 1 having electrode structures 20 and 21 for charging toner by repeatedly changing the direction of an electric field applied to the developer 8 by the movement of the developer 8, caused by the rotation of the developer carrier 2 are disposed facing the surface of the developer carrier 2 above an area between a regulating part 2a for a quantity of developer conveyance and a developing part 2b. The surface facing the developer carrier of the toner charging means 1 is covered with a leak-preventive dielectric film 23. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus using an electrophotographic system, for example, a developing apparatus using a two-component developer composed of a toner and a magnetic carrier used for a fuck simiri, a printer, a copying machine, an MFP (multifunction machine), etc. It is.

An image forming apparatus using a two-component developing apparatus is excellent in high-speed compatibility and long life, and has been put into practical use as many products such as monochrome and color copying machines, facsimiles, and printers.
In the two-component developing device, a two-component developer composed of toner and a magnetic carrier is carried on the surface of a developer carrying member made of a nonmagnetic rotating sleeve having a magnet fixed inside. The supported two-component developer is transported to a developing unit facing the latent image carrier on which the electrostatic latent image is formed after the transport amount is regulated by the developer amount regulating means.
The developing unit receives an electrostatic force that is attracted to the surface of the latent image carrier by the electric field formed by the difference between the bias applied to the developer carrier and the surface potential of the latent image carrier. Then, a force is applied in a direction repelling the surface of the latent image carrier. As a result, the toner on the surface of the developer carrying member adheres only to the latent image portion and can be developed.

In recent years, in order to perform printing with higher definition and higher image quality, an increasing number of devices use toner having a smaller particle size. In such a device, among the forces acting on the toner adhered to the magnetic carrier, the contribution ratio of the van der Waals force increases due to the particle size becoming smaller.
On the other hand, the bias applied to the developer carrying member is a bias in which direct current and alternating current are superimposed, and the electrostatic force is alternately switched in a short cycle that does not affect the development toward the latent image carrying member and the developer carrying member. Accordingly, many developing devices that have improved the developing ability and the image quality have been proposed and put into practical use.
The toner in the two-component developer has a large compressive force acting to partially block the flow of developer conveyance at the part that regulates the amount conveyed by rotation of the developer carrier, and the developers are strongly rubbed against each other. This increases the probability of frictional charging with the magnetic carrier, and most of the charge amount is obtained in this restricted portion.

FIG. 14 is a schematic view showing a conventional developing device. In FIG. 14, the developing device B is provided with agitation / conveying means 4 and 5 for replenishing the non-magnetic toner from the toner replenishing device into the developing container 6 and agitating and conveying the replenished toner and developer.
The toner is attracted in a developer state by a magnetic field formed by a magnetic pole on the stirring / conveying means 4 side of a non-rotating magnetizing roller provided inside the developer carrier 2 and is rotated by a rotating sleeve on the surface of the developer carrier 2. Be transported.
The conveyed toner is supplied to the developing unit in a state where the gap between the developer amount regulating unit 3 and the developer carrier 2 is adjusted by the developer amount regulating unit 3 made of non-magnetic SUS before the developing unit. .
A DC component is applied to the developer carrying member 2 from the developing bias applying means 12, and between the electrostatic latent image of the background portion and the image portion formed on the surface of the latent image carrying member 7 and the developer carrying member 2. Due to the generated electric field, the charged toner attached to the carrier surface moves from the developer carrying member 2 to the latent image carrying member 7 so that the electrostatic latent image pattern can be visualized.

However, the toner charged in this way is partly sandwiched between magnetic carriers as described above and frictionally charged while receiving a strong compressive force, and the external additive adhered to the surface by the strong compressive force at that time. Are embedded in the toner resin.
Or, if the toner is peeled off or severe, the toner will be cracked, so that the amount of weakly charged toner increases, resulting in a light stain on the printed background. The developing device and image forming unit may cause problems such as filming of toner fine powder that has been broken and aggregates of external additives that have been peeled off and remaining on the surface of the magnetic carrier or latent image carrier. There was a case where the lifetime of the was shortened.
The stress on the toner is caused by, for example, wax in order to prevent the toner from adhering to the fixing roller at the heat fixing unit because the toner for four colors adheres to the transfer paper in a color device such as a color copying machine. Is often mixed with toner. The toner itself is much softer than the toner of a monochrome machine, and the above problems are likely to occur.
In addition, since the toner and the magnetic carrier have a particle size that is about 10 times different, there is a toner that is not frictionally charged only by being attached to the carrier in the gap portion between the magnetic carriers. Since the amount of charge is low, the electrostatic repulsive force at the background portion is reduced, and adhesion to the background portion of the latent image carrier causes problems such as light stains on the printed background portion and increased toner consumption.

This problem inevitably reduces the chance of friction between the toner in the developer and the magnetic carrier when trying to reduce the stress in the developer regulating section in order to solve the developer stress problem as described above. , Toner with low charge amount increases.
For this reason, the life of the developing device is long, which is becoming an increasingly important issue in high-speed color devices. On the contrary, if the friction of the developer at the damming part is mechanically further increased, the toner is deteriorated due to the stress as described above, resulting in a rotational load. A color copying machine or the like having a single developing device has problems that lead to noise, power consumption, and an increase in the size of the apparatus.
For this reason, an electrode facing the surface of the developer carrying member between the developer conveying amount regulating portion and the developing portion and spaced from the developer is provided, and the toner is vibrated by an alternating electric field to cause the toner to vibrate. Has been proposed (see, for example, Patent Documents 1 and 2).
Further, in Patent Document 2, an electrode facing the surface of the developer carrying member between the developer conveying amount regulating portion and the developing portion and spaced from the developer is provided, and between the electrode and the developer carrying member. The space in which the toner in the developer moves is widened by lowering the ear density of the carrier by the magnetic field generated in the space.
JP-A-5-119607 Japanese Patent Laid-Open No. 11-288167

However, in the toner charging method as described in Patent Document 1, since the toner is caused to fly between the developer carrying member and the toner charging electrode to create a cloud state, a part of the toner is scattered in the image forming apparatus. There arises a problem that the inside of the image forming apparatus is easily soiled.
In order to apply an alternating electric field to the developer, an AC voltage is applied to the developer carrying member, or an AC voltage is applied to the electrode for charging the toner. There is a restriction on the degree of freedom in design that the condition of the alternating electric field for charging the toner is limited to the alternating voltage for developing the toner in the developing unit.
At the same time, when the resistance of the magnetic carrier of the developing device that develops the latent image with a DC electric field is low, an alternating electric field for charging the toner appears in the developing unit. For this reason, it is impossible to control the electric field for charging the toner according to the charging state of the toner when an alternating voltage is applied to the developer carrying member because an alternating electric field is used for development.
When an AC voltage is applied to the electrode for charging the toner, the developing ability varies greatly depending on whether the electric field for charging the toner is on or off, so that the control conditions and the electrical characteristics of the usable magnetic carrier are also limited.

In the case of Patent Document 2, similarly, a developing method is proposed in which the developer is vibrated by an alternating electric field to charge the toner. Therefore, the above-described toner scattering, electric field generation voltage design freedom, developer restriction, and the like are the same as in Patent Document 1.
In view of the above circumstances, the object of the present invention is to provide a wide range of design freedom in terms of electric field, material, control, etc., without increasing toner scattering inside, and without causing mechanical stress on the developer. An object of the present invention is to provide a developing device that can optimize the toner charge amount with a small number of means, can form an image without fogging, and has a long life.

In order to solve the above problems, the invention described in claim 1 has a stirring means for stirring a two-component developer containing at least a toner and a carrier, and supplies the developer to the developer carrier. In the developing device that controls the amount of the developer carrying member conveyed by the developer amount regulating means to a predetermined value and performs development with the toner in the developer conveyed to the developing unit, the developer conveying amount is The direction of the electric field applied to the developer is opposed to the upper surface of the developer carrying member between the regulating unit to be regulated and the developing unit, and the developer moves with the rotation of the developer carrying member. A toner charging means having an electrode structure for charging the toner repeatedly is provided, and a surface of the toner charging means facing the developer carrying member is covered with a dielectric film for preventing leakage. And
According to a second aspect of the present invention, in the state where the toner charging unit is not present with respect to the developer having a width wider than at least the printing region in the longitudinal direction of the developer carrying member, 2. The developing device according to claim 1, further comprising an electrode structure for generating an electric field substantially perpendicular to a length direction of the agent carrier.

According to a third aspect of the present invention, there is provided the developing device according to the first or second aspect, wherein the toner charging unit has a structure in which a distance between adjacent electrodes is not less than a width close to a particle diameter of the carrier. .
According to a fourth aspect of the invention, the toner charging unit alternately applies two DC voltage values to every other electrode of the toner charging unit every other electrode, and each electrode and the developer carrying member. 4. The developing device according to claim 1, wherein an electric field formed between the bodies is smaller than an electric field at which toner can fly from the carrier surface to the toner charging unit.
The invention according to claim 5 uses the toner charging means according to claim 4, and periodically switches between two DC voltage values of electrodes adjacent to the toner charging means. A developing device according to item 1 is characterized.
The invention according to claim 6 is characterized in that the electric field applied between the developer carrying member and the latent image carrying member for development is a DC electric field. And
According to a seventh aspect of the present invention, the electric field applied between the developer carrying member and the latent image carrying member of the developing device for development is an alternating electric field. The developing device is characterized.

According to the present invention, it is not necessary to increase the space area in which the toner is clouded by an alternating electric field for charging the toner, and therefore it is possible to provide a developing device that does not increase toner scattering into the image forming apparatus. It is.
In addition, the direction of the electric field applied to the developer is repeatedly changed by the rotation of the developer carrying member, and the effect of improving the toner charging property due to the collision between the toner and the magnetic carrier is obtained as in the case where an alternating electric field is applied. It is possible to provide a developing device having a high degree of freedom in designing power supply conditions for charging toner.
Further, even in the development using an alternating electric field used for improving the development efficiency and the like in the related art, it is possible to provide a developing device that can further shorten the time until the toner charging is stabilized.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a schematic view showing a developing device according to an embodiment of the present invention. FIG. 2 is a graph showing the relationship between the toner charge amount and the drive time in order to explain the effect of the present invention.
In FIG. 1, the developing device A includes a stirring / conveying means 4 and 5 that are partitioned by a separation plate that is a part of the developing container 6 in the developing container 6, and the developing container 6 is above the stirring / conveying means 4. And a developer amount regulating means 3 that is supported by the developer carrier 2 and faces the developer carrying member 2.
Further, the developing device A includes a toner charging unit 1, and the toner charging unit 1 is disposed at a position facing the developer amount regulating unit 3 with the developer amount regulating unit 3 and the developer carrier 2 interposed therebetween. It is arranged to face the surface above the developer carrier 2 between the latent image carrier 7 and the latent image carrier 7.
DC charging means 10 and 11 are connected to the toner charging means 1, and a developing bias applying means 12 is connected to the developer carrier 2. The developer carrying body 2 side facing the developer amount regulating means 3 is defined as a regulating section 2a, and the developer carrying body 2 side facing the latent image carrying body 7 is defined as a developing section 2b.

In the developing device A of FIG. 1, based on the detection result of a toner concentration sensor (not shown), the toner concentration in the developing container 6 from a toner replenishing device (not shown) is non-magnetic so as to become a predetermined concentration (7% in this embodiment). The toner is replenished, and the replenished toner and developer are refluxed by the agitating / conveying means 4 and 5.
More specifically, the agitating / conveying means 4 and 5 are screws having a rotation outer diameter of Φ14 and a screw pitch of 20 mm provided with a helical projection on the axis of Φ5. The two screws are rotated in the opposite direction at 300 rpm. The agitating / conveying means 4 conveys the developer in the rear direction in FIG. 1, and the agitating / conveying means 5 conveys the developer in the front direction in FIG.
An opening (not shown) having a width of 25 mm through which the developer can pass is provided at the back and front of the separation plate which is a part of the developing container 6 that partitions the stirring / conveying means 4 and 5. The developer is sent from the agitating / conveying means 4 side to the agitating / conveying means 5 side at the back side of the developing apparatus A, and the developer is sent from the agitating / conveying means 5 side to the agitating / conveying means 4 side before the developing apparatus A and refluxed. It has a structure.

The toner is uniformly mixed with a magnetic carrier having a silicon coating on the surface by stirring and diffusion during the reflux of the developer. The toner is also attracted in a developer state by a magnetic field formed by a magnetic pole on the stirring / conveying means 4 side of a non-rotating magnetizing roller provided inside the developer carrier 2.
The attracted toner is conveyed by a rotating sleeve on the surface of the developer carrier 2 that rotates at a linear speed of 250 mm / sec. The toner is transferred between the developer amount regulating means 3 and the developer carrier 2 so that the developer amount on the rotating sleeve is 450 g / m ² by the developer amount regulating means 3 made of non-magnetic SUS before the developing portion. The image is supplied to the developing unit 2b with the gap adjusted.
A DC component of −350 V is applied from the developing bias applying means 12 to the developer carrier 2. The charged toner adhering to the carrier surface is developed by the electric field generated between the electrostatic latent image formed on the surface of the latent image carrier 7 and having the background portion of about −550 V and the image portion of about −100 V and the developer carrier 2. The electrostatic latent image pattern can be visualized by moving from the agent carrier 2 only to the image portion of the latent image carrier 7.

Hereinafter, for comparison, the description will be made with reference to the conventional developing device B shown in FIG. The arrangement of the developer amount regulating means 3 in the conventional developing device B shown in FIG. 14 is configured to increase the developer density at the portion where the flow of the developer is blocked and to increase the developer friction.
On the other hand, in the present invention, the developer density at the developer retaining portion is small, the stress on the toner can be reduced, the life is long because the toner is less deteriorated, and the driving torque of the developing device A can be reduced. The arrangement of the developer amount regulating means 3 shown in FIG.
In the present invention, first, by setting the developer amount regulating means 3 as shown in FIG. 1, the rotational torque of the developer carrier 2 can be reduced by about 30% compared to the conventional developing device B of FIG. did it.
Therefore, as shown in FIG. 2, the developer on the developer carrier 2 (FIG. 1) is sampled at 1 second, 10 seconds, 30 seconds, 60 seconds, 120 seconds, and 300 seconds from the start of driving, and two-component development is performed. The relationship between the toner charge amount measured by using a blow-off device and an electronic balance, which are generally used to measure the toner charge amount in the agent, and the driving time was examined.
According to this investigation result, in the developing device without the toner charging means 1 in FIG. 1, it takes a long time to saturate the toner charge amount compared to the conventional developing device B (FIG. 14), and after a long period of non-operation. The weakly charged toner increased when the developing device was started up or immediately after toner replenishment, resulting in light stains on the printed background.

FIG. 3 is a graph showing the relationship between the developer speed and the distance from the developer carrier surface in order to explain the effects of the present invention. As shown in FIG. 3, the cause of the difference in toner charging performance due to the arrangement of the developer amount regulating means 3 (FIG. 1) was confirmed.
As a result, the developer speed change due to the distance from the surface of the developer carrier 2 (FIG. 1) is larger in the conventional developing device B shown in FIG. 14 than in the developing device A shown in FIG. It was found that the relative speed of the carrier in the developer was increased.
From this, the difference in time until the toner charge amount is saturated due to the arrangement of the developer amount restricting means 3 is that the developer amount restricting means 3 in the conventional developing device B is accompanied by the rotation of the developer carrier 2. When the developer density in front of is increased, the contact probability between the surface of the developer carrying member 2, the carrier in the developer, and the carriers in the developer increases.
At the same time, the velocity gradient of the carrier increases with the distance from the surface of the developer carrying member 2, that is, the relative velocity between the carriers increases or rotates to cause frictional charging between the toner adhering to the carrier surface and the carrier. This is thought to be easier.
In such a state, the toner is easily triboelectrically charged, but on the other hand, the probability that the toner is sandwiched between carriers increases and the toner is pressed with a stronger force, so that the hydrophobic silica externally added to the toner surface is contained in the toner resin. It can be said that the toner tends to deteriorate in the conventional developing device B shown in FIG.

FIG. 4 is a graph showing the relationship between the external additive burial degree rank and the developing device drive time in order to explain the effect of the present invention. In FIG. 4, a photograph of the toner surface enlarged with an SEM (scanning electron microscope) is taken. The degree to which the external additive of the toner is embedded is the burying degree rank 5 of the new toner and the burying degree rank 1 of the completely embedded toner.
A new toner is buried in a rank of 0.5 between the embedding degree rank 5 and the embedding degree rank 1 of the toner, and the relationship between the degree of embedding the external additive in the toner and the driving time when the developing device is not printing is shown. 15 is a result of comparison between the developing device A in FIG. 1 and the developing device B in FIG. 14.
As is apparent from FIG. 4, the developing device A in FIG. 1 is slower in embedding external additives on the toner surface than the conventional developing device B in FIG.

Next, in the first embodiment of the present invention, as shown in FIG. 1, the toner charging means 1 is placed at a position on the surface of the developer carrying member 2 between the developer amount regulating portion 2a and the developing portion 2b. Provided.
By applying a DC voltage to the toner charging unit 1 from the DC voltage supply units 10 and 11 and applying the present invention to a developing device that suppresses toner deterioration, the time until the toner charge amount is saturated can be improved. The results of confirming the effect will be described below.
FIG. 5 is a cross-sectional view showing an embodiment of toner charging means in the developing device of FIG. FIG. 6 is a sectional view showing in detail a part of the embodiment of the toner charging means of FIG.
1, 5, and 6, FIG. 5 is a more detailed explanation of the electrode shape of the toner charging unit 1 as viewed from the side facing the developer carrier 2, and FIG. 6 is a toner charging unit. 1 is a partially enlarged view of the opposing portion of 1 and the developer carrier 2.
As shown in FIGS. 1 and 6, the toner charging means 1 of this embodiment has an arc shape so that the gap distance between the surface facing the developer carrier 2 and the developer carrier 2 is substantially constant. The electrodes 20 and 21 made of aluminum are vapor-deposited on the polycarbonate substrate 22, and a silicon resin is coated thereon.

As shown in FIG. 5, the electrodes 20 and 21 of the toner charging unit 1 have a distance between the electrodes 20 and 21 parallel to the length direction of the developer carrying member 2 at least in the image area, and the distance between the electrodes is 100 μm. The electrode width is 300 μm, and the electrodes 20 and 21 are arranged in a comb shape.
As shown in FIG. 6, when voltages having different values are applied to the electrodes 20 and 21 having such shapes from the DC voltage applying means 10 and 11, the electrodes 20 and 21 are perpendicular to the length direction of the developer carrier 2, And the electric field of a reverse direction is formed in the adjacent gap part.
When the developer carrier 2 is rotated in this state, an electric field whose direction is repeatedly changed is applied to the developer 8 on the developer carrier 2 due to the movement accompanying the rotation. The toner in the developer 8 alternately receives a force including a component parallel to the surface of the developer carrier 2 in the traveling direction and the reverse direction of the surface of the developer carrier 2. As a result, the toner repeatedly moves and collides between adjacent carriers or between the carrier and the toner charging unit 1 surface.
In this embodiment, the gap between the toner charging unit 1 and the developer carrier 2 is 300 μm, and the voltages of the DC voltage applying units 10 and 11 are −300 V and −450 V, respectively.
Incidentally, as the material of the substrate 22 of the toner charging means 1, polycarbonate is used in the embodiment for explaining the present invention. However, any material may be used as long as it is an insulating material that can obtain shape stability in order to improve the gap with the developer carrier 2 and that does not leak the voltage applied to the electrodes 20 and 21.

As is apparent from the relationship between the toner charge amount after standing for a long time in the developing device and the driving time of the developing device shown in FIG. 2, the use of the toner charging means 1 of the present invention reduces the stress on the toner, With the developing device having a small driving torque, the time until the toner charge amount is saturated can be set to the same time as the conventional developing device of FIG.
As a result of checking the printing immediately after startup after being left for a long time or immediately after toner replenishment in the developing device A of this embodiment, the smudges on the printed background as occurred in the developing device without the toner charging means 1 do not occur. Thus, the effect of the present invention was confirmed.
Further, in the developing device A of the present invention, the toner is not brought into a cloud state by the alternating electric field, so that the toner scattering into the developing device A does not increase.

FIG. 7 is a graph showing the relationship between the voltage at which the developer on the developer carrying member passes through the voltage application portion and time. FIG. 8 is a graph showing the relationship between the voltage and time in FIG. 7 as an electric field. The developer on the developer carrier 2 of the present embodiment passes through a voltage application portion as shown in FIG. 7 at a position close to the toner charging unit 1 by the movement of the developer carrier 2 due to the rotation.
When this is rewritten into an electric field, the values differ strictly depending on the influence of the developer 8 (FIG. 6) and the dielectric film 23 (FIG. 6) on the surface, but as shown in FIG. An electric field is applied.
The strength of the electric field can be changed by the interelectrode distance between the DC voltage applying means 10 and 11 and the electrodes 20 and 21, and the electric field strength is applied to the developer carrier 2 regardless of the resistance of the carrier used. The development bias to be determined can be determined independently.

5 and 6, when a voltage is applied to the electrodes 20 and 21 in the absence of a dielectric film applied to the surface of the toner charging unit 1 facing the developer carrier 2, the gap between the electrodes When the voltage difference increases, leakage occurs between the electrodes.
For this reason, there is not only a problem that the electric field that can be generated becomes weak, but also when a carrier having a low electric resistance is used, a current flows from the electrodes 20 and 21 of the toner charging unit 1 to the developer carrying member 2 through the carrier, and development is performed. There arises a problem that the developing bias of the agent carrier 2 becomes unstable. Therefore, the toner charging unit 1 of the present invention needs to be provided with a dielectric film 23 for preventing leakage on the surface.
Even when the developer amount regulating means 3 with reduced stress on the developer is used, the time until the toner charging is stabilized by the toner charging means 1 of the present invention is short, and the waiting time until the start of printing can be shortened. It is possible to provide a developing device having a long life in which the background portion is not easily smudged.

FIG. 9 is a schematic sectional view showing the electrode structure of the toner charging means according to the present invention. In FIG. 9, this electrode structure according to the second embodiment of the present invention is based on the toner charging in which the direction of the electric field generated when there is no carrier between the electrode 24 and the electrode 25 is the length direction of the developer carrier 2. The means 26 is viewed from the side facing the developer carrier 2.
When the toner charging unit 26 is attached to the developing device A in FIG. 1 instead of the toner charging unit 1 and a halftone pattern of a dot grid of 600 dpi 1 dot on / 1 dot off is printed, it is thin and thin in some places. There are parts where the vertical and dark vertical stripes appear.
The thin, light and dark vertical stripes are generated at a portion where the gap between the electrodes of the toner charging unit 26 is present, and the toner is sent in the longitudinal direction of the developer carrier 2 at the electrode gap portion, so that the developer carrier 2 This is considered to be due to uneven density in the toner density above.
According to the second embodiment of the present invention, the toner charge amount of the developing device A (FIG. 1) of the present invention can be made uniform over the entire printing region, and uniform printing and the occurrence of light stains on the printed background are unlikely to occur. A developing device can be provided.
Further, at the tip of the comb teeth of the toner charging unit 1 shown in FIG. 5, in the portion where the electric field substantially perpendicular to the length direction of the developer carrier 2 cannot be formed in the absence of the developer, the above-mentioned thin and light. Light and dark vertical stripes may occur. Further, in a portion where the toner charging effect cannot be obtained, a light stain on the printed background after leaving for a long time occurs.
From this result, particularly in high-resolution printing, the electric field generation direction of the toner charging unit 1 is an electric field substantially perpendicular to the length direction of the developer carrier 2 as used in the embodiment of FIG. It has been clarified by the inventor's investigation that the electrode structure must be generated beyond the width of the print area.

FIG. 10 is a graph showing the relationship between the toner charge amount and the drive time in the third embodiment. In FIG. 10, in the third embodiment of the present invention, the distance between the electrodes 20 and 21 of the toner charging unit 1 used in FIG. 5 is 50 μm, 100 μm, and 150 μm.
FIG. 10 shows the same confirmation of the time until the toner charge amount confirmed in the above-described embodiment is saturated by changing the voltage so that the electric fields between the electrodes 20 and 21 are the same. This is a result obtained by using a carrier having a particle diameter of 100 μm. The reason for making the electric field the same is that the electrostatic force acting on the charged particles is generally proportional to the electric field, so that the same electric field is applied to the toner.
From the results shown in FIG. 10, when the distance between the electrodes is 50 μm, there is some effect compared to the case where there is no toner charging means, but the saturation time of the toner charge amount is longer than when the other two 100 μm and 150 μm are used. became.
When the distance between the electrodes is shorter than the particle diameter of the carrier, the effect of the toner charging unit 1 (FIG. 1) of the present invention is reduced because the distance between the electrodes is shorter than the distance between adjacent carriers. This is probably because the electric field is not applied and the effect of moving and colliding the toner between the carriers is reduced.
From the above, it can be said that the effect becomes large when the distance between the electrodes 20 and 21 of the toner charging means 1 of the present invention is longer than the particle diameter of the carrier. Thus, it is possible to provide a developing device capable of effectively generating the toner charging effect of the present invention.

FIG. 11 is a sectional view showing another electrode arrangement of the toner charging means according to the present invention. In FIG. 11, in the fourth embodiment of the present invention, an electrode having an electrode arrangement viewed from the developer carrier 2 (FIG. 1) side in the length direction of the developer carrier 2 is longer than the printing area. The toner charging means 1 having a plurality of electrode groups arranged in the rotation direction of the body 2 was used.
Each electrode was connected to DC power supply applying means 10 and 11 (FIG. 1) so that the same voltage could be applied every other electrode. Since the cross-sectional shape is the same as in FIG. 6, in the following description, electrode groups to which the same voltage is applied are described as electrodes 20 and 21, respectively.
In this developing apparatus, the difference between the DC voltages applied to the electrodes 20 and 21 in the embodiment of FIG. 1 is kept constant at 140 V, and the voltages applied to the electrodes 20 and 21 are (−200 V, −350 V), (−300 V). , −450V) and (−400V, −550V).

FIG. 12 is a graph showing the relationship between the toner charge amount and the drive time in the fourth embodiment. As shown in FIG. 12, the effect of charging the toner was obtained regardless of the voltage value during the time until the toner charge amount was saturated.
However, in the case of (−200V, −350V), when continuous printing is continued, a part where the halftone is partially darkened is formed, or a spot-like light stain is generated in the printed background.
As a result of confirming the cause, a large amount of toner adheres to the surface of the toner charging means 1 (FIG. 11), particularly the downstream side in the rotation direction of the position corresponding to the electrode 20 to which −200 V is applied. It was found that the toner carrier was scraped off by the developer moving with the rotation of the agent carrier 2 (FIG. 1), and the toner concentration was partially excessive, which occurred.

The adhesion of the toner to the toner charging unit 1 receives a force that attracts the toner in the developer to the toner charging unit 1 side by an electric field formed between the developer carrier 2 and the electrode of the toner charging unit 1. The toner was gradually accumulated in the toner charging means 1.
When a voltage of −300 V was applied to the electrode 20 of the toner charging unit 1, a slightly larger amount of streaky toner adhered to the position corresponding to the electrode 20 of the toner charging unit 1 than the electrode position applied with −400 V or more.
However, the toner attracting force due to the electric field formed between the developer carrying member 2 and the electrode 20 is weak and the amount of the adhering toner is small, and it is considered that the toner is always scraped off by the developer. Did not accumulate. From the above, the voltage applied to the electrodes 20 and 21 of the toner charging unit 1 needs to be a voltage at which the toner does not move from the carrier surface to the electrode.
According to the above-described fourth embodiment, it is possible to provide a developing device that can shorten the time until the toner charging is stabilized, can shorten the waiting time until the start of printing, and does not easily cause a light stain on the printed background. Can do.

In the fifth embodiment of the present invention, the same developing device as that used in the fourth embodiment is used, and the voltage applied to 21 (FIG. 11) with the electrode 20 of the toner charging unit 1 is 6. .Switch every 4 milliseconds. Further, the DC voltage values of two adjacent electrodes of the toner charging unit 1 are periodically switched.
For the electrode 20 and the electrode 21, three cases of the same voltages (-200V, -350V), (-300V, -450V), (-400V, -550V) as in the fourth embodiment were confirmed.
As a result, the accumulated amount of toner adhering to the surface of the developer carrying member 2 at the position corresponding to the electrode applied with −200 V or −300 V of the toner charging unit 1 can be reduced as compared with the case of the fourth embodiment.
This is because toner is charged to the toner charging means 1 when -400 V to -550 V, which is lower than the developing bias -350 V applied to the developer carrier 2 (FIG. 1), is applied to the electrode 20 (or 21) of the toner charging means 1. This is considered to be because the toner is less likely to accumulate due to the force from the toner toward the developer carrier 2.
Therefore, by periodically switching the applied voltage as in the fifth embodiment, there is an effect of reducing the amount of toner adhering to the toner charging means 1, and the present invention can be applied under a wider voltage condition.

In the sixth embodiment of the present invention, in the developing device A shown in FIG. 1, the electric field for development applied between the developer carrier 2 and the latent image carrier 7 is a DC electric field. Accordingly, it is possible to shorten the time until the toner charging is stabilized, to shorten the waiting time until the start of printing, and to provide a developing device in which the thin background of the printed background is less likely to occur.
In the seventh embodiment of the present invention, a DC voltage is applied to the developer carrier 2 by using the developing device of FIG. 1 describing the first embodiment and the toner charging means 1 having the electrode arrangement of FIG. The effect of the present invention in the case where a voltage in which AC voltage and AC voltage are superimposed is applied will be described.
In the developing device of the present invention, unlike the method of charging the toner by the alternating electric field between the toner charging means and the developer carrier 2 described in the prior art, for example, the toner charge amount becomes sufficiently high immediately after driving. If the alternating electric field for development is applied, the toner is likely to be scattered.
Therefore, even when the alternating electric field is turned off in order to prevent toner scattering into the image forming apparatus, the surface of the developer carrying member 2 generated by the toner charging unit 1 as described in the first embodiment is used. It goes without saying that the charging of the toner can be started even immediately after the start of driving after being left for a long time with an electric field that changes in parallel with the movement of the developer in parallel.

FIG. 13 is a graph showing the relationship between the toner charge amount and the drive time in the seventh embodiment. FIG. 13 shows a result of confirming that the effect of the present invention can be obtained after the developing device A shown in FIG. 1 is left for a long time.
In this case, a DC voltage of −350 V and an AC voltage of 1.2 kV are applied from the developing bias applying unit 12 to the developer carrying member 2 from the start of driving, −300 V to the electrode 20 of the toner charging unit 1, and −550 V to the electrode 21, respectively. . An AC voltage was applied to the developer carrier 2 by checking the time until the toner charge amount was saturated.
From FIG. 13, the time until the toner charge amount is saturated becomes shorter than in the first embodiment in which a DC voltage is applied to the developer carrier 2, and the AC voltage is applied to the developer carrier 2. It was also confirmed that the present invention is effective.
The reason why the time until the toner charge amount is saturated when an AC voltage is applied to the developer carrier 2 is that between the toner charging means 1 and the developer carrier 2 is perpendicular to the surface of the developer carrier 2. Both an alternating electric field in the direction and an electric field that is parallel to the surface of the developer carrying member 2 generated by the toner charging unit 1 and alternately changes in direction due to the movement of the developer are generated, and the toner can be charged efficiently. It is thought that it was made.

1 is a schematic view showing a developing device according to an embodiment of the present invention. FIG. 4 is a graph showing the relationship between toner charge amount and drive time in order to explain the effect of the present invention. FIG. 5 is a graph showing the relationship between the developer speed and the distance from the surface of the developer carrying member in order to explain the effect of the present invention. In order to explain the effect of the present invention, it is a graph showing the relationship between the rank of buried external additives rank and the developing device drive time. FIG. 2 is a cross-sectional view showing an embodiment of toner charging means in the developing device of FIG. 1. FIG. 6 is a cross-sectional view showing in detail a part of the embodiment of the toner charging unit of FIG. 5. It is a figure which shows the relationship between the voltage and the time which the developer on a developing agent carrier passes a voltage application part with a graph. FIG. 8 is a graph showing the relationship between voltage and time in FIG. FIG. 3 is a schematic sectional view showing an electrode structure of a toner charging unit according to the present invention. FIG. 10 is a graph showing a relationship between toner charge amount and drive time in a third embodiment. It is sectional drawing which shows the other electrode arrangement | positioning of the toner charging means by this invention. It is a figure which shows the relationship between the toner charge amount and drive time in 4th Embodiment with a graph. FIG. 17 is a graph showing the relationship between toner charge amount and drive time in a seventh embodiment. It is the schematic which shows the conventional image development apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS A Developing device 1 Toner charging means 2 Developer carrying body 2a Restricting part 2b Developing part 3 Developer amount regulating means 4 Stirring / conveying means 5 Stirring / conveying means 6 Developer container 7 Latent image carrier 8 Developer 10 DC voltage supply means DESCRIPTION OF SYMBOLS 11 DC voltage supply means 12 Developing bias application means 20 Electrode 21 Electrode 22 Substrate 23 Dielectric film 24 Electrode 25 Electrode 26 Toner charging means

Claims (7)

  An agitation unit for agitating a two-component developer including at least a toner and a carrier, supplying the developer to the developer carrier, and determining an amount of the developer carrier conveyed by the developer amount regulating unit; In a developing device that regulates to a predetermined value and performs development with the toner in the developer conveyed to the developing unit, the developer carrier between the regulating unit and the developing unit that regulates the developer conveyance amount A toner charging unit having an electrode structure for charging the toner is disposed opposite to the upper surface, and the direction of the electric field applied to the developer is repeatedly changed by the movement of the developer as the developer carrying member rotates. The developing device is characterized in that the surface of the toner charging unit facing the developer carrying member is covered with a dielectric film for preventing leakage.   The toner charging means is substantially the same as the length direction of the developer carrier in the absence of the developer with respect to the developer having a width wider than at least the printing region in the length direction of the developer carrier. 2. The developing device according to claim 1, further comprising an electrode structure for generating a vertical electric field.   The developing device according to claim 1, wherein the toner charging unit has a structure in which a distance between adjacent electrodes is equal to or larger than a width close to a particle diameter of a carrier.   The toner charging unit alternately applies two DC voltage values to every other electrode of the toner charging unit every other electrode, and generates an electric field formed between each electrode and the developer carrier from the carrier surface. The developing device according to claim 1, wherein the developing device is smaller than an electric field at which toner can fly to the toner charging unit.   5. The developing device according to claim 1, wherein the toner charging unit according to claim 4 is used, and two DC voltage values of electrodes adjacent to the toner charging unit are periodically switched. .   6. The developing device according to claim 1, wherein an electric field applied between the developer carrying member and the latent image carrying member for development is a direct current electric field.   6. The developing device according to claim 1, wherein the electric field applied between the developer carrying member and the latent image carrying member of the developing device for development is an alternating electric field.

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