JPH0364073B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention provides a method for converting a latent image formed on an image carrier by a photophotographic method, an electrostatic recording method, an electrostatic printing method, or a magnetic recording method into a toner. Regarding the image forming method of developing into an image,
In particular, the present invention relates to an image forming method in which a latent image on an image carrier is developed into a toner image by generating an oscillating electric field in a developing area where a rotating image carrier and a developer transport carrier face each other.

[Prior art]

The above-mentioned image forming method is disclosed in Japanese Patent Application Laid-open No. 1973-
No. 94335, No. 50-30537, No. 55-18656, No. 56
−144452, No. 57-139761, No. 57-147652,
It is known from publications such as No. 58-48065 and USP No. 4076857. Such an image forming method is
It is also used under the condition that the developer layer on the surface of the developer transporting carrier is in contact with the surface of the image carrier, but the action of the oscillating electric field causes the toner to fly from the developer layer and transfer to the image carrier. There are no sweeping marks on the image. In addition, it is possible to easily prevent the occurrence of fogging in which toner adheres to the background area.
It is preferable to use the developer layer under conditions such that it does not come into contact with the surface of the image carrier, thereby making it possible to form a clear toner image without any scratches or fogging.
However, on the other hand, the toner tends to fly due to the action of the oscillating electric field and scatter out of the developing device from the gap with the image carrier, and the toner images are overlapped on the image carrier by multiple developing devices. In the case of color image formation in which alignment is performed, there are problems in that toners of different colors are likely to be mixed into the developing device due to toner reverse transfer, and power consumption is also large due to the generation of an oscillating electric field.

Therefore, an oscillating voltage is applied to the developer transport carrier only when the latent image on the image carrier passes through the development area.
In other cases, an image forming method in which the developer transporting carrier is grounded or floating, or a DC voltage is applied to the developer transporting carrier, is known from US Pat. It is being According to this method, the above-mentioned problems can be solved to a considerable extent. but,
In this method, the timing at which a predetermined oscillating voltage is applied to the developer transport carrier is simply timed to coincide with the timing at which the latent image on the image carrier passes through the development area. Sometimes, if a sufficient oscillating electric field is not yet generated, or if the timing of applying the oscillating voltage is advanced to prevent this, toner scattering or development may occur at a lower potential than the background potential, as in the method described above. In reversal development, in which toner charged to the same polarity as the background potential is attached to an electrostatic latent image with an opposite polarity potential, toner may be wasted as the toner adheres to a non-image charged area with a background potential. I have a problem to say.

[Purpose of the invention]

The present invention has been made to solve the above-mentioned problem, and a sufficient oscillating electric field is generated when the latent image on the image carrier reaches the development area.
Able to form stable and clear toner images,
To provide an image forming method that prevents toner scattering and waste, and consumes less power.

[Structure of the invention]

The present invention relates to an image forming method in which a latent image on an image carrier is developed into a toner image by generating an oscillating electric field in a developing area where a rotating image carrier and a developer transport carrier face each other. Before the latent image reaches the development area, a unidirectional electric field is generated in the development area in advance, and the electric field is changed continuously or stepwise to the oscillating electric field, and then the latent image on the image carrier is transferred to the development area. The image forming method is characterized by allowing the light to pass through the image, and with this configuration, the above object is achieved.

〔Example〕

The present invention will be explained below using illustrated examples.

FIG. 1 is a schematic configuration diagram showing an example of a recording device that implements the method of the present invention, FIG. 2 is a partial diagram showing an example of a developing device, and FIGS. Time charts showing examples of bias voltages, and FIGS. 6 to 8 are circuit diagrams showing examples of configurations of bias power supplies that apply the bias voltages shown in FIGS. 3 to 5, respectively.

The recording device shown in FIG. 1 uses a signal processing device 1 to process image data I obtained from a signal input from a document image sensor, other equipment, data in a data storage unit, etc. )
An image signal composed of converted pixel data (hereinafter referred to as a binary image) is obtained, and the pixel data of this binary image is used to control a laser beam scanner consisting of a laser, an acousto-optic modulator, a lens device, a rotating polygon mirror, etc. The Yana 2 is controlled ON and OFF for each pixel, rotates in the direction of the arrow, and performs image exposure with a laser spot on the surface of the photoconductor layer of the image carrier 3, which is uniformly charged by the charger 4. A toner image is formed by depositing toner charged to the same polarity as that of the image carrier 3 under an oscillating electric field using a developing device 5 as shown in detail in FIG. 2 on the exposed portion.
Then, the formed toner image is transferred by a transfer device 6 to a recording paper P that is fed so as to be in contact with the surface of the image carrier 3 in synchronization with the rotation of the image carrier 3, and the toner image is transferred. The separated recording paper P is separated from the surface of the image carrier 3 by a separator 7, then fixed with the toner image by a roller fixing device 8, and discharged from the recording apparatus. On the other hand, the surface of the image carrier 3 to which the toner image has been transferred is neutralized by a static eliminator 9, and then residual toner is removed by a cleaning device 10 to complete one image forming process.

The developing device 5 shown in FIG. 2 is an image carrier in which a bias voltage is applied by a bias power supply 11 to a developer transport carrier 51 made of a non-magnetic material such as aluminum or stainless steel, and whose base portion is grounded. An electric field is created in the development zone between 3 and 3. A magnet body 52 having a plurality of N and S magnetic poles on its surface is provided inside the developer transport carrier 51 . When the developer transport carrier 51 stands still or rotates counterclockwise and the magnet body 52 rotates clockwise or stands still, the magnetic force of the magnet body 52 causes the developer reservoir 5
3, the developer adsorbed on the surface of the developer transport carrier 51 is moved counterclockwise by one or both of the rotations. The developer transported in this manner is regulated to a layer thickness within a range that does not contact the surface of the image carrier 3 by the layer thickness regulating blade 54, and the toner is removed from the developer layer by the action of the oscillating electric field in the development area A. The electrostatic latent image on the image carrier 3 is developed by flying. Note that, from the viewpoint that the influence of unevenness of the developer layer is less likely to appear in the development, it is preferable that the magnet body 52 rotates to convey the developer layer.

The remaining developer layer that has passed through the development area A is removed from the surface of the developer transport carrier 51 by the cleaning blade 55 and returned to the developer reservoir 53.
The developer in the developer reservoir 53 is a so-called two-component developer containing a mixture of toner and carrier, and is stirred by the stirring blade 56 so that the toner is charged to the same polarity as the image carrier 1 . Since the toner is consumed during development, it is replenished from the toner hopper 57 to the developer reservoir 53 by the toner replenishment roller 58.

In order to make the toner charged to the same polarity as that of the image carrier 3 fly from the developer layer on the developer transport carrier 51 in the development area A and adhere to the image exposure area of the electrostatic latent image, the developer transport carrier is used. A bias voltage that is a superimposition of a DC voltage and an AC voltage of the same polarity close to the background potential of the image carrier 3 is applied to 51 . The bias power supply 11 applies this bias voltage in accordance with FIGS. 3 to 5.
This is done as shown in the figure to prevent toner scattering and wasted costs. In addition, 1
2 is a protective resistance.

In FIGS. 3 to 5, T ₀ is the time period during which the uncharged area of the image carrier 3 that is not charged by the charger 4 passes through the development area A, and T _v is the time period when the charger 4 passes through the developing area A.
The non-image-charged area of the image carrier 3 which has been charged by , but is not subjected to image exposure, is the development area A.
, T _i is the time period during which the image forming area of the image bearing member 3 subjected to image exposure passes through the developing area A, and T _v ′ is the time period during which the non-image forming area following the image forming area passes through the developing area A. The passing time period T ₀ ' indicates the time during which the uncharged area, which has been charged by the charger 4, passes through the development area A. Figure 3 shows the time period T _v
First, a DC voltage is applied, and then an AC voltage of a constant period is superimposed with the amplitude gradually increasing. When the amplitude of the AC voltage reaches a predetermined value, the image forming area of the image carrier 3 reaches the development area A. During time period T _i , this bias voltage, which is a superimposition of DC voltage and AC voltage, is maintained, and when time period T _v ' begins, the amplitude of AC voltage is attenuated and DC voltage is applied. In this example, the application of the DC voltage is stopped before the uncharged area passes through the development area A. In this way, a unidirectional electric field is generated before the image forming area reaches the development area A, and then the oscillating electric field is gradually strengthened to bring about the predetermined development conditions, so that a strong oscillating electric field suddenly acts on the developer. Therefore, there is no toner scattering, and there is less toner waste due to toner adhering to non-image charged areas.
When the image forming area passes through the developing area, a predetermined oscillating electric field is maintained, and a clear toner image without fogging can be developed, and power consumption can be kept to a minimum. FIG. 4 shows an example in which, instead of gradually increasing and attenuating the amplitude of the AC voltage in the example of FIG. 3, a half-wave rectified AC voltage is superimposed on the DC voltage. In this example as well, the same effect as in the example of FIG. 3 can be obtained. Figure 5 shows that instead of first applying only a DC voltage to generate a unidirectional electric field in the examples of Figures 3 and 4, the superimposed voltage applied during development is half-wave rectified. A unidirectional electric field is generated by applying a pulsed voltage that exhibits only the same polarity, thereby increasing and attenuating the AC voltage amplitude as shown in Figure 3 or the half-wave rectified AC voltage as shown in Figure 4. An example is shown in which it also serves the same role as the superimposition of . In other words, in this example as well, Figures 3 and 4
The same effect as in the example shown in the figure can be obtained.

The example of FIG. 3 can be implemented by using a circuit as shown in FIG. 6 for the bias power supply 11.
In other words, the switch 13 is activated without operating the oscillation circuit.
When the A contact is turned on, a DC voltage is applied to the developer transport carrier 51, and the movable short-circuit contact 1 of the secondary coil is turned on.
4 is connected to the complete short-circuit position shown in the figure, if the oscillation circuit is activated and the movable short-circuit contact 14 is moved upward, the alternating current voltage will gradually increase in amplitude and be superimposed, causing the alternating voltage If the movable short-circuiting contact 14 is returned to the original position from the position where the amplitude of The application of the bias voltage is stopped. Note that instead of using the movable short-circuit contact 14 in the secondary coil, the amplitude of the alternating current voltage may be gradually increased or attenuated on the oscillation circuit side.

The example of FIG. 4 can be implemented by using a circuit as shown in FIG. 7 for the bias power supply 11.
In other words, the switch 13 is activated without operating the oscillation circuit.
When the A contact is turned on, a DC voltage is applied to the developer transport carrier 51, and when the oscillation circuit is operated with the switch 15 of the rectifier circuit turned on, a half-wave rectified AC voltage is superimposed on the DC voltage. , switch 1
When switch 5 is turned off, a superimposed voltage of DC voltage and AC voltage is applied, and when switch 15 is turned on again, the state returns to the state where a voltage where half-wave rectified AC voltage is superimposed on DC voltage is applied, and then oscillation starts. By stopping the operation of the circuit and further turning on the switch 13 to the b contact, the bias voltage application shown in FIG. 4 is performed.

The example of FIG. 5 can be implemented by using a circuit as shown in FIG. 8 for the bias power supply 11.
That is, when the switch 15 of the rectifier circuit is turned on, the oscillation circuit is operated with the switch 13 turned on to the B contact, and the switch 13 is turned on to the A contact, a superimposition of DC voltage and AC voltage is applied to the developer transport carrier 51. A pulsed unidirectional polarity bias voltage obtained by rectifying the voltage is applied. Next, when the switch 15 is turned off, the bias voltage becomes a superimposed voltage of DC voltage and AC voltage. When the switch 15 is turned on again, the pulsed unidirectional polarity bias voltage is applied. The application of the bias voltage is stopped by returning the bias voltage to the state shown in FIG.

In the examples shown in FIGS. 3 to 5, when the developer transport carrier 51 and the magnet 52 rotate to transport the developer layer, if the period includes the time period T _i , the uncharged area is the development area. may include passing through A,
This reduces toner scattering and waste costs, and ensures that a developer layer with sufficient toner is transported to the development area A when the image forming area passes through the development area A. It is preferable to start the conveyance at a time point before the application of the oscillating voltage component to the developer conveying carrier 51 in the developer transport carrier 51, and it is also preferable _to stop the conveyance in the time period Tv _' . In addition, in the examples shown in FIGS. 3 to 5, it is of course preferable to perform the process for each image formation when a plurality of images are formed continuously, but the intermediate image The period during the formation may be included in the time period T _i , and even then, a certain degree of effect can be obtained.

The present invention has been described above with reference to an example of reversal development, but the recording device is one in which toner charged to the opposite polarity (opposite to the charged polarity of the image carrier 3) is attached to the electrostatic latent image. The present invention can also be applied to those using electrostatic recording method or magnetic recording method. The unidirectional electric field previously generated in the development area may be one that promotes the transfer of toner from the developer layer, or may be one that suppresses the transfer to prevent fogging. Further, although the present invention is preferably based on non-contact development conditions or conditions using a two-component developer as the developer, it is not limited thereto.

In the present invention, the oscillating electric field generated in the development area A during development when the image forming area on the image carrier 3 passes through the development area A is set to a condition that allows a clear and fog-free toner image to be obtained. Of course. That is, the DC voltage and AC voltage applied to the developer transport carrier 51 are determined to provide such an oscillating electric field. Therefore, in order to easily determine the bias voltage, a two-component developer containing toner particles and insulating magnetic carrier particles with a resistivity of 10 ⁸ Ωcm or more, particularly 10 ¹³ Ωcm or more, must be used. It is preferable to use As such carrier particles, carrier particles made of resin particles containing a fraction of magnetic particles are preferably used. Note that the resistivity of insulating particles is
After placing the particles in a container with a cross-sectional area of 0.5 cm ² and tapping them, a load of 1 Kg/cm ² was applied on the packed particles, and a voltage was applied to generate an electric field of 1000 V/cm between the load and the bottom electrode. This is the value found by reading the current value at that time. At this time, the thickness of the carrier is
The carrier amount was set to be about 0.2 mm.

In order for development to be carried out clearly and with good resolution, the average particle diameter of the toner particles in the two-component developer must be 20 μm or less.
In particular, it is preferably 1 to 10 μm, and the average particle size of the carrier particles is also preferably 5 to 50 μm. The average particle size of these particles is a weight average particle size, and is measured with a Coulter Counter (manufactured by Coulter) or Omnicon Alpha (manufactured by Boshilom). If the average particle size of the toner particles becomes too small, the amount of charge due to friction of a single toner particle becomes small, and the van der Waals force becomes large.
It becomes easier to aggregate, it becomes difficult to separate and fly, and on the other hand, if the average particle size becomes too large,
The amount of charge for superimposition decreases, making it difficult to control flight and reducing resolution. Furthermore, if the average particle size of the carrier particles becomes too small, the force of attraction by the magnetic force of the magnet body 52 becomes weak, but the electrical Coulomb force and Van der Waals force become strong, which causes the carrier particles to become too small. The particles tend to migrate to the surface of the image carrier 3 together with the toner particles, and on the other hand, if the average particle size becomes too large, the developer layer formed on the developer transport carrier 51 becomes rough, and the developer layer becomes rough. It becomes difficult to form the toner particles thinly and uniformly, and the state of adhesion of the toner particles in the developer layer also becomes uneven, and breakdown and discharge of the voltage applied to the developer transport carrier 51 are more likely to occur. Transition flight control becomes difficult.

Furthermore, in order to effectively control toner flight by applying a bias voltage to the developer transport carrier 51, the gap between the image carrier 3 and the developer transport carrier 51 must be in the range of several tens to 200 μm. Therefore, it is preferable that the thickness of the developer layer regulated by the layer thickness regulating blade 54 be made thinner than that. If the gap in this development zone is made too narrow, the thickness of the developer layer must be made very thin, which makes it impossible to obtain a uniform layer thickness and therefore provides a stable supply of toner particles to the development zone. Not only is this impossible, but also discharge is likely to occur between the developer transport carrier 51 and the image carrier 3, damaging the developer and causing toner particles to scatter. On the other hand, if the interval between the development areas is made too wide, it becomes difficult to control the flying of toner using the oscillating electric field.

Developing is carried out under the preferable conditions described above,
If image formation is performed by changing the bias voltage applied to the developer transport carrier 51 during development as shown in FIGS. 3 to 5, a clear recorded image with excellent reproducibility and no fog can be obtained. This results in less toner waste and toner scattering, and reduced power consumption.

More specific examples of the present invention will be shown below.

Example 1 An electrophotographic copying machine having the same configuration as that shown in FIG. 1 was used except that image exposure was performed by a slit exposure device.

The image carrier 3 has an image forming layer made of an organic photoconductor OPC on its surface, rotates in the direction of the arrow at a surface speed of 120 mm/sec, is uniformly charged to -500V by a charger 4, and is exposed to an image. is incident on the surface and −50V is applied to the surface.
An electrostatic latent image of -500V is formed against the background potential of . The gap between the image carrier 3 and the developer transport carrier 51 in the development area A is 700 μm, and the outer diameter of the developer transport carrier 51 is 30
mm, counterclockwise rotation speed 65 rpm, magnet body 52 has magnetic flux density
It has 8 N and S magnetic poles of 900 Gauss at equal intervals in the circumferential direction, and rotates at 700 rpm in the direction of the arrow. The developer in the developer reservoir 53 is a resin with a specific resistance of 10 ¹⁶ containing magnetic powder dispersed in a resin with a superimposed average particle diameter of about 30 μm.
Insulating carrier of Ωcm and superimposed average particle size of 14μm
A two-component developer mixed with an insulating non-magnetic toner that is charged to about 20 μC/g is used, and the layer thickness of the developer layer formed on the developer transport carrier 51 is controlled by the layer thickness regulating blade 54 to approximately 500 μm. to be regulated. The bias power supply 11 is applied to the developer transporting carrier 51 at a voltage of -150V at the same time as the image carrier 3 is charged by the charger 4.
DC voltage is applied, and the AC component is continuously increased for 0.1 seconds at the same time as image exposure, so that the electrostatic latent image is developed in the development area A.
-150V DC voltage and 2kHz, 1kV before reaching
A bias voltage with a superimposed AC voltage of is applied,
Development is performed under these conditions, and the electrostatic latent image is formed in the development area A.
After passing through, the AC component was attenuated to 0 in 0.1 seconds, and the DC component was also reduced to 0 after 1 second. Note that the rotation of the developer transport carrier 51 and the magnet body 52 is as follows.
It started after applying the DC voltage and before applying the AC component, and stopped when the DC component was set to 0. The developed toner image is transferred onto plain paper by a transfer device 6 and fixed by a roller fixing device 8 whose surface temperature is 140°C.

The recorded images obtained in the above manner had excellent reproducibility, no fog, high density, and extremely clear images. Even when recording was performed on 50,000 sheets of plain paper, it was possible to obtain recorded images that remained stable from beginning to end, and there was no toner scattering from the gap between the developing device 5 and the image carrier 3. The amount of toner collected by the cleaning device 10 was also small, and power consumption was also low.

On the other hand, if a bias voltage in which the same DC voltage and AC voltage are superimposed is suddenly applied to the developer transport carrier 51 at the same time as the image carrier 3 is charged by the charger 4, the toner scatters significantly. The maximum number of recordings is 10,000 sheets, and the amount of toner collected by the cleaning device also increases.

Note that the AC voltage component of the bias voltage applied to the developer transport carrier 51 during development has a frequency of 100~
10000Hz, preferably 1000-50000Hz, RMS amplitude
At 200 to 5000V, the effective value between the image forming member 3 and the
A type that produces an electric field strength of 5000 V/mm is preferably used, and the waveform is not limited to a sine wave, but may be a rectangular wave or a triangular wave.

〔Effect of the invention〕

According to the image forming method of the present invention, a clear recorded image without fogging can be obtained without scattering toner or wasted toner, and power consumption is also saved.

In the present invention, the oscillating electric field is generated in the developing area not only by applying a bias voltage to the developer transport carrier, but also by using electrode wires, electrode nets, etc. between the developer transport carrier and the image carrier. Stretch the
It may also be done by applying a bias voltage thereto. Further, the present invention can be applied to the development of a magnetic latent image by using a magnetic toner as the developer. Of course, the present invention can also be applied to an image forming method in which an insulating layer is provided on the surface of a photoreceptor. Also, a color image recording device having a plurality of developing devices and an image recording device that superimposes toner images on an image carrier (Patent Application No. 58-184381, No. 58-183152, No. 58-187000)
It can also be applied to

[Brief explanation of drawings]

FIG. 1 is a schematic configuration diagram showing an example of a recording device that implements the method of the present invention, FIG. 2 is a partial diagram showing an example of a developing device, and FIGS. 3 to 5 are bias voltages applied to the developing sleeve, respectively. FIGS. 6 to 8 are circuit diagrams showing examples of configurations of bias power supplies that apply the bias voltages shown in FIGS. 3 to 5. 3... Image carrier, 4... Charger, 5... Developing device, 51... Developer transport carrier, 52... Magnet,
53... Developer reservoir, 54... Layer thickness regulation blade, A... Development area, 11... Bias power supply, T ₀ ,
T ₀ ′... Time period for passing through the non-charged area, T _v , T _v ′... Time period for passing through the non-image charged area, T _i ... Time period for passing through the image forming area.

Claims (1)

[Scope of Claims] 1. In an image forming method in which a latent image on an image carrier is developed into a toner image by generating an oscillating electric field in a developing area where a rotating image carrier and a developer transport carrier face each other, Before the latent image on the body reaches the development area, a unidirectional electric field is generated in the development area in advance, and the electric field is continuously or stepwise changed to the oscillating electric field,
An image forming method characterized in that the latent image on the image carrier is then passed through a development area. 2. The image forming method according to claim 1, wherein after the unidirectional electric field is generated and before the unidirectional electric field is changed to an oscillating electric field, driving of the developer conveying carrier to convey the developer is started.