JPS60249171A - Image forming method - Google Patents

Abstract

PURPOSE:To constitute a device in such a manner that a toner can be stuck to an electrostatic latent image without scattering or wasteful consumption by changing a bias voltage so as to decrease the max. voltage having the same polarity as the polarity of the potential in a background part during the time when the potential surface of the background part passes the developing region after the electrostatic latent image passes the developing region. CONSTITUTION:When a switch 12 of a rectifier circuit is turned on to a bias power source 11, the bias consisting of the superposed DC voltage and AC voltage impressed to a developing sleeve 51 thus far is converted to an impulsive bias voltage and said voltage is so changed that the max. voltage having the same polarity as the polarity of the potential in the background part decreases. The force of the electric field in the developing region A trying to scatter the toner from the developer layer and to stick the toner to an image forming body 3 is thus surely weakened during the time when the non-image electrified region of the body 3 passes the region A. The toner is consequently returned to the developer layer by the repulsive force in the non-image electrified region of the body 3 and therefore the wastefull consumption of the toner as a result of the sticking to the region except the image forming region and the scattering of the toner are prevented.

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to an image forming method in an electrostatic recording device such as an electrophotographic copying machine, and in particular, the present invention relates to an image forming method in an electrostatic recording device such as an electrophotographic copying machine, and in particular, charging the surface of an image forming body with a background potential. The charged surface is neutralized or charged with the opposite polarity by means such as light irradiation or an electrostatic recording head, and the electrostatic latent image thus formed is then applied to the developing sleeve with an alternating current voltage and the same polarity as the background potential. Applying a bias voltage with a DC voltage superimposed thereon, the toner charged to the same polarity as the background potential is ejected from the developer layer on the developing sleeve in a developing area where the developing sleeve and the surface of the image forming body are close to each other. hand,
The present invention relates to an image forming method that performs development.

[Prior art]

As a typical image forming method as described above, an image forming body having a photoconductor layer on the surface is used, and -9 of the image forming body is
, there is a method in which spot exposure is performed on a charged surface using a laser beam scanner to form an electrostatic latent image composed of low potential dots, and toner charged to the same polarity as the charge on the image forming body is attached to the low potential dots. It will be done. Such a method is
Compared to an image forming method in which toner charged with the opposite polarity is caused to fly from the developer layer of a developing sleeve and adhere to an electrostatic latent image where the image area potential is higher than the background area potential, the toner is transferred to the image forming body. In order to make it adhere to the image forming body against the electrical repulsion from charging and not to cause fogging,
The DC component of the bias voltage applied to the developing sleeve is required to be close to the background potential, and the AC component is also required to have a large amplitude. Therefore, if the bias voltage is applied to the developing sleeve while the uncharged area of the image forming body is passing through the developing area, toner will be unnecessarily attached to the image forming body and excess This consumes toner, increases the burden on the cleaning device, etc., and causes the toner to scatter, increasing the occurrence of stains.

In an image forming method in which toner charged with the opposite polarity sticks to an electrostatic latent image whose image partial potential is higher, the uncharged area of the image forming body is used for development in order to save power and prevent toner from scattering. USP 3, 893, the application of bias voltage to the developing sleeve is stopped while the developing sleeve passes through the area.
, No. 418 and Japanese Unexamined Patent Publication No. 14266/1983.

However, in an image forming method in which toner charged to the same polarity as the image forming member is attached to an electrostatic latent image, the bias voltage to the developing sleeve is applied only while the uncharged area of the image forming member passes through the development area. Even if the application is stopped, it is insufficient to prevent toner scattering and wasted costs.

[Purpose of the invention]

The present invention prevents toner scattering and waste even if the application of the bias voltage is stopped only while the uncharged area of the image forming body passes through the development area. The influence of bias voltage application may also be affected when passing through an uncharged area, such as by floating due to stopping the application of the bias voltage, or by a large change in potential at the boundary between the charged and uncharged areas of the image forming body. This was done as a result of finding a method for applying a bias voltage that effectively prevents toner scattering and wasted costs, and reduces the risk of toner scattering and wasted costs. The present invention provides an image forming method in which toner charged to the same polarity as that of an image forming member is caused to fly from a developer layer on an equalizing sleeve and adhere to an electrostatic latent image.

[Structure of the invention]

The present invention applies a bias voltage in which an alternating current voltage and a direct current voltage having the same polarity as the background potential of an electrostatic latent image are superimposed on the developing sleeve, so that the developer layer on the developing sleeve has the same polarity as the background potential. In an image forming method in which an electrostatic latent image is developed by flying toner charged to The image forming method is characterized in that the voltage is changed so that the maximum voltage having the same polarity as the background potential stagnates, and this configuration achieves the above object.

〔Example〕

The present invention will be explained below using illustrated examples.

FIG. 1 is a schematic configuration diagram showing an example of a recording apparatus 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 6 are bias voltages applied to the developing sleeve, respectively. Graphs showing examples of the above, and FIGS. 7 to 9 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 processes image data obtained from a signal input from an original image sensor, other equipment, or data stored in a data storage unit using a signal processing device 1, thereby converting it into binary (i.e., black and white) data. An image signal composed of converted pixel data (hereinafter referred to as a binary image) is obtained, and this binary image is
Laser, acousto-optic modulator,
A lens device 2 A laser beam scanning device 2 consisting of a rotating polygon mirror, etc. is turned on and off for each pixel, and rotates in the direction of the arrow to photoconduct an image forming body 3 which is uniformly charged by a charger 4. Image exposure is performed on the surface of the body layer by a laser spot, and toner charged to the same polarity as that of the image forming body 3 is applied to the spot exposed area under an electric field by a developing device 5 as shown in FIG. 2 in detail. It is attached to form a toner image. Then, the formed toner image is transferred by the transfer device 6 to the recording paper P that is fed so as to be in contact with the surface of the image forming body 30 in synchronization with the rotation of the image forming body 3.
The recording paper P onto which the toner image has been transferred is separated from the surface of the image forming body 3 by a separator 7, and then transferred to a roller fixing device 8.
The toner image is fixed and discharged from the recording apparatus. On the other hand, the surface of the image forming body 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.

In the developing device 5 shown in FIG. 2, a bias voltage is applied by a bias power supply 11 to a developing sleeve 51 made of a non-magnetic material such as aluminum or stainless steel, and a developing sleeve 51 is connected to an image forming member 3 whose base portion is grounded. An electric field is generated in the development area A of . Inside the developing sleeve 51, a magnet body 52 having a plurality of N and S magnetic poles on its surface is provided. Then, as the developing sleeve 51 stands still or rotates counterclockwise, and the magnet body 52 rotates clockwise or stands still, the magnet body 5
The developing sleeve 51 is removed from the developer reservoir 53 by the magnetic force of 2.
The developer adsorbed on the surface of is moved counterclockwise by one or both of the rotations. The developer conveyed in this manner is regulated to a layer thickness within a range that does not come into contact with the surface of the image forming body 3 by the layer thickness regulating blade 54, and the toner is flown from the developer layer by the action of an electric field in the development area A. The electrostatic latent image on the image forming body 3 is developed.

Note that it is preferable that the magnet body 52 rotates in that the influence of unevenness of the developer layer is less likely to appear in the development.

The remaining developer layer that has passed through the developing area A is removed from the surface of the developing sleeve 510 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 in which toner and carrier are mixed.
It is charged with the same polarity as the charge. Since the toner is consumed during development, it is replenished from the toner hopper 57 to the developer reservoir 53 by a toner supply roller 58.

The toner charged to the same polarity as that of the image forming member 3 is transferred to the developing area A.
In order to develop the electrostatic latent image by flying the developer from the developer layer on the developing sleeve 51, a bias voltage in which a DC voltage and an AC voltage having the same polarity as the background potential of the image forming member 3 are superimposed is applied to the developing sleeve 51. Apply. The bias power supply 11 is
This bias voltage is applied as shown in FIGS. 3 to 6, thereby preventing toner scattering and unnecessary costs.

In FIGS. 3 to 6, T□ is a time period during which the image forming area of the image forming body 3 is subjected to image exposure and an electrostatic latent image is formed, passes through the development area A, and TV is the time period when the image forming body 3 To is the time period in which the uncharged area of the image forming body 3, which has been completely charged by the charger 4, passes through the developing area A after the image exposure is completed and the uncharged area of the image forming body 3, which is only charged, passes through the developing area A. Indicates the time period to be passed. FIG. 3 shows that in the time period T1, a bias voltage obtained by superimposing a DC voltage of 1°, which is slightly lower than the charged potential V of the image forming member 3, on the AC voltage is applied to the developing sleeve 31, and the bias voltage is applied to the developing sleeve 31 in the time period TV. FIG. 4 shows an example in which the bias voltage is rectified and converted into a pulsed voltage showing only a potential of opposite polarity to the charging of the image forming member 3, and then the application is stopped within the time period TV. , when entering the 1'14'i band Tv, the amplitude of the AC component of the bias voltage is attenuated and converted to 0, and then the DC component vDo is changed from 0 to a level showing the opposite polarity to the charging of the image forming body 3. Fig. 5 shows an example that differs from Fig. 3 in that when the time slot TV is entered, the blood flow component VDO of the bias voltage is first set to 0 or a level indicating the opposite polarity on the charge of the image forming body 3. This shows an example that differs from Fig. 3 or 4 in that the amplitude of the AC component is converted to 0 and then the amplitude of the AC component is attenuated to 0. Time zone T. An example is shown in which the points made after entering are different from those in Fig. 5.

The example of FIG. 3 can be implemented by using a circuit as shown in FIG. 7 for the bias voltage source 11, and the example of FIG. 4 can be implemented by using a circuit as shown in FIG. It can be implemented by a circuit that combines the GA circuits as shown in FIG. 9, and the examples in FIGS.
This can be implemented by using a circuit that is a combination of the circuit shown in FIG. 9 and the circuit shown in FIG. 8 for l. That is, in the circuit shown in FIG. 7, by turning on the switch 12 of the rectifier circuit, the bias consisting of the superposition of the DC voltage and AC voltage that had been applied to the developing sleeve 31 until then is changed as shown in FIG. It can be converted into a pulsed bias voltage, and by sliding the short-circuit contact 13 of the secondary coil toward the DC power source in the circuit shown in Fig. 8, the AC component of the bias voltage can be converted into a pulsed bias voltage. As shown in the figure, the amplitude can be attenuated to 0. In the circuit of Figure 9, by sliding the moving contact 14 of the variable resistor from top to bottom or from bottom to top, the DC component of the bias voltage can be attenuated to It can be changed as shown in FIG. 5, FIG. 6, or FIG. 4. Note that attenuation of the alternating current component is not limited to the above-mentioned example, and it goes without saying that the attenuation of the alternating current component may be performed on the oscillation circuit side. In addition, when changing the DC component to O, the 9th
Of course, the reverse potential circuit part on one side of the DC power supply circuit shown in the figure can be omitted, or even if the connection side of the secondary coil to the DC power supply is switched from the connection to the DC power supply to the ground using a switch. good.

By applying a bias voltage to the developing sleeve 31 as shown in FIGS. 3 to 6, the non-image charged area of the image forming member 3, which is charged so as to repel toner, forms the developing area A. During the passage, the force of the electric field in the developing area A to cause the toner to fly from the developer layer and adhere to the image forming member 3 is weakened, and as a result, the repulsive force of the non-image charged area of the image forming member 3 is reduced. Since the toner is returned to the developer layer, the toner is prevented from being wasted by adhering to areas other than the image forming area, or from being scattered.

Furthermore, since the alternating current component of the electric field plays a large role in making the toner fly from the developer layer, the example shown in Fig. 3 or 4 shows that the alternating current component of the bias voltage is first changed when the time slot TV starts. In the examples shown in Figs. 5 and 6, it is more preferable to use the example shown in Fig. 5, which attenuates the alternating current component quickly.Also, it is preferable to change the bias voltage as shown in Figs. This may be done each time image formation is performed, or in the case of continuous image formation, the bias voltage at the time of development is maintained during image formation in the middle, and the bias voltage is maintained during the time period Tv during final image formation. The bias voltage may also be changed.

The alternating current voltage component and direct current voltage component of the bias voltage during development are determined so that a clear and fog-free toner image can be obtained. In order to easily determine such a bias voltage, the two-component developer in the developer reservoir 53 uses insulating magnetic carrier particles having a resistivity of 108 Ωcm or more, particularly 1013 Ωcm or more. It is preferable. As such carrier particles, carrier particles having a resin coating formed on the end surfaces of magnetic particles, or carrier particles made of resin particles containing magnetic particles dispersed therein are used. Note that the resistivity of the insulating particles is 0.5 Cm2.
IK2/c is placed on the packed particles after tapping to a thickness of about IIIl++.
Apply a load of m2, and apply 1000V between the load and the bottom electrode.
This value is obtained by reading the current value when a voltage that generates an electric field of /crn is applied. In addition, in order for development to be carried out clearly with good resolution, the average particle diameter of the toner particles of the two-component developer is preferably 20 μm or less, particularly 1 to 10 μm, and the average particle diameter of the carrier particles is also 5 to 50 μm. It is preferable that there be. The average particle size of these particles is the weight average particle size, and is measured with a Coulter Counter (Coulter W) or Omnicon Alpha (Bausch & Lomb).If the average particle size of the toner particles becomes too small, the toner particles 1
As the amount of charge due to friction between the particles becomes smaller, the van der Waals force becomes larger, making it easier to aggregate.
On the other hand, if the average particle size is 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 adsorption force due to the magnetic force of the magnet body 52 becomes weak, but the electric R-Ron force and van der Waals force become strong, and therefore the carrier particles On the other hand, if the average particle diameter is too large, the developer layer formed on the developing sleeve 51 will become coarse, making it difficult to make the developer layer thinner. It becomes difficult to form the toner particles uniformly, and the state of adhesion of the toner particles in the developer layer also becomes uneven, making breakdown and discharge of the voltage applied to the developing sleeve 51 more likely to occur.As a result, the migration and flight control of toner particles becomes difficult. It becomes difficult to let go.

Furthermore, in order to apply a bias voltage to the developing sleeve 51 and effectively control the flight of toner, the gap between the image forming body 3 and the developing sleeve 51 must be in the range of several tens to 2000 μm, and therefore the thickness regulating blade It is preferable that the layer thickness of the developer layer regulated by 54 be made thinner. If the gap in the development zone is made too narrow, the thickness of the developer layer must be made extremely thin, which will not result in a uniform layer thickness, and will therefore result in a stable distribution of toner particles in the development zone. Not only will it not be possible to supply toner, but it will also become easy to discharge between the developing sleeve 51 and the image forming body 3, damaging the developer and causing toner particles to scatter. On the other hand, if the gap between the developing areas is made too wide, it becomes difficult to control the flying of toner using the oscillating electric field.

If development is performed under the preferable conditions as described above, and the bias voltage applied to the developing sleeve 51 during development is changed as shown in FIGS. 3 to 6, image formation is completed. Clear recorded images with no fogging can be obtained, and furthermore, toner costs and scattering can be reduced. Note that the rotation of the developing sleeve 51 and the magnet body 52 may be stopped at any time after the image forming area of the image forming body 3 passes through the developing area A; It is preferable to carry out this process in a subsequent step because it prevents the amount of toner collected into the developer layer from increasing locally.

Next, more specific embodiments of the present invention will be described.

Example 1゜ The apparatus shown in FIGS. 1 and 2 was used.

The image forming body 3 has a selenium photoreceptor layer on its surface, rotates in the direction of the arrow at a surface speed of 120 m/SeC, and is charged to 500 V by a charger 4. The laser beam scanner 2 forms an electrostatic latent image in the form of 50V dots. Gap between image forming body 3 and developing sleeve 510 in developing area A: 700μ
m1 developing sleeve 51 outer diameter 30cm, left rotation speed 65
The rpm s magnet body 52 has a magnetic flux density of 900 Gauss,
It has 8 S magnetic poles at equal intervals in the circumferential direction, and 70O in the direction of the arrow.
Rotates at rpm. The developer in the developer reservoir 53 is an insulating carrier with a specific resistance of 1016 Ωci++, which contains magnetic powder dispersed in a resin with a weight average particle diameter of about 30 μm;
A two-component plasticizer mixed with an insulating non-magnetic toner having a weight average particle diameter of 14 μm and positively charged to about 20 μC/f,
The thickness of the developer layer formed on the developing sleeve 51 was regulated to about 500 μm by a layer thickness regulating blade 54.

Simultaneously with the rotation of the image forming body 30, a DC voltage of -150 V is applied from the bias power supply 11 to the developing sleeve 51. The bias voltage 11 is configured to apply a bias voltage of 21 (V , the voltage is switched to a superimposed voltage of 2kHz AC voltage and 400V downward current voltage.At the same time, the developing sleeve 51 and the magnet body 52 are rotated.The image forming area is the developing area A.
While the non-image charged area passes through the developing area A, the bias power supply 11 reduces the AC component of the bias voltage and then changes the DC component to -150V. The rotation of the developing sleeve 51 and the magnet body 52 is stopped when the DC voltage component of the bias voltage is changed to 1150V. Then, the bias power supply 11 sets the bias voltage to 0 when the uncharged area passes through the development area A and the rotation of the image forming body stops. That is, the bias power supply 11 controls the bias voltage as shown in FIG.

Development was carried out under the above conditions, and the resulting toner image was transferred to recording paper P made of plain paper and fixed by roller fixing device 8 with a surface temperature of 140°C.

The recorded image thus obtained was extremely clear with high density and no fog. Even though we recorded images on 50,000 sheets of recording paper, we were able to obtain recorded images that remained stable from the beginning to the end, and the toner did not scatter from the gap between the developing device 5 and the image forming body 3. In addition, the amount of toner collected by the cleaning device 10 was also small.

On the other hand, if the bias power supply 11 inverts the DC component of the bias voltage and attenuates the AC component to O after the uncharged area of the image forming body 3 passes through the development area A, Not only did the amount of toner collected by the cleaning device 10 increase significantly, but also the amount of toner scattered from the developing device 5 increased, and the maximum number of recording sheets that could be obtained was 10,000 sheets.

Note that the frequency of the AC component of the bias voltage applied to the developing sleeve 51 during development is 100 to 100.

Hz, preferably 1,000 to 5,000 Hz, and an effective value amplitude of 200 to 5,000 V, and which generates an electric field strength of 300 to 5,000 V/vm in effective value between it and the image forming body 3 is preferably used. The waveform is not limited to a sine wave, but may be a rectangular wave or a triangular wave. Further, it is preferable to use a two-component developer as the developer, but USP 389
3418, a one-component developer known from Japanese Unexamined Patent Publication No. 55-18656 may be used.

〔Effect of the invention〕

According to the image forming method of the present invention, a clear toner image without fogging can be formed with toner charged to the same polarity as that of the image forming body, without wasting the cost of scattering the toner. .

The present invention is applicable not only to recording devices that use laser beam scanners but also to recording devices that use multi-needle electrodes and the like.

Further, the present invention can also be applied to an image forming method using an image forming body having an insulating layer on a photosensitive layer. Furthermore, the present invention provides a color image recording apparatus having a plurality of developing devices and a color image recording apparatus in which toner images are superimposed on an image forming member (Japanese Patent Application No. 58-184381, No. 5-8-183).
152, No. 58-187000).

Although the attenuation of the alternating current bias at the end of development has been described in the examples, by applying the alternating current bias at the start of development by a process reverse to that shown in FIGS. 3 to 6,
Needless to say, the desirable result is that toner scattering and consumption are reduced.

[Brief explanation of the drawing]

FIG. 1 is a schematic configuration diagram showing an example of a recording apparatus 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 6 are bias voltages applied to the developing sleeve, respectively. Graphs showing examples of the above, and FIGS. 7 to 9 are circuit diagrams showing examples of configurations of bias power supplies that apply the bias voltages shown in FIGS. 3 to 6vl. 2... Laser beam scanner, 3... Image forming body, 4... Charger, 5... Peek 2 image device, 51... Developing sleeve, 52... Magnet body,
53... Developer reservoir, 54... Layer thickness regulation blade,
A...Development area. 11...Bias power supply, T1...Image forming area passing time Charging TV...Uncharged area passing time period, To...Uncharged area passing time period. Patent applicant Konishiroku Photo Industry Co., Ltd. Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8

Claims (1)

[Claims] 1. A bias voltage in which an AC voltage and a DC voltage of the same polarity as the background potential of the electrostatic latent image are superimposed is applied to the developing sleeve to remove the background potential from the developer layer on the developing sleeve. In an image forming method in which an electrostatic latent image is developed by flying toner charged to the same polarity as the electrostatic latent image, after the electrostatic latent image passes through the development area, the subsequent background potential surface passes through the development area. An image forming method characterized in that the bias voltage is changed such that a maximum voltage having the same polarity as the background potential decreases. 2. The image forming method according to claim 1, wherein the change in the bias voltage is performed by blocking a voltage portion having the same polarity as the background potential through rectification. 6. The image forming method according to claim 1, wherein the change in the bias voltage is performed by attenuating the amplitude of the AC voltage. 2. The image forming method according to claim 1, wherein the image forming method is carried out by changing the polarity potential to opposite polarity.