JP2000117986A - Imaging device and method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an imaging device and a method utilizing electrostatic attraction in which defective imaging due to fixing error of a developer or fluctuation of the electrode position is suppressed without requiring a highly accurate expensive control mechanism. SOLUTION: Ink 1 is supplied onto a substrate 2 while having a free face 1a. Ultrasonic wave is then radiated into the ink 1 by means of an acoustic transducer 3 to form a stable liquid column 1b without producing any mist. When a potential difference is generated between the ink 1 and an electrode 6, ink is moved from the liquid column 1b toward the electrode 6 by electrostatic attraction. If the liquid column 1b is unstable, the ink moves along the direction of electrostatic attraction regardless of some positional shift between the electrode 6 and the liquid column 1b (B). Consequently, ink can be moved toward the electrode 6 regardless of manufacturing error or assembling error of the acoustic transducer 3 or the electrode 6.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a copying machine, a printer, a facsimile, and the like. More specifically, the present invention relates to an image forming apparatus in which a liquid is moved to a recording medium using electrostatic attraction to form an image. The present invention relates to a forming apparatus.

[0002]

2. Description of the Related Art Conventionally, as recording systems used in the fields of copying machines, printers, facsimile machines, etc., there are a dot printer system, a dry electrophotographic system, a wet electrophotographic system, an ink jet system and the like. Each of these methods has advantages and disadvantages, and is used properly or used in combination depending on the application. Conventional techniques of a wet electrophotographic method and an ink jet method will be described as methods related to the present invention described later.

In a conventional wet electrophotographic developing method,
A developer is supplied between the surface of the latent image carrier on which the electrostatic latent image is formed, and a counter electrode arranged at regular intervals on the surface,
The developer is brought into contact with the surface of the latent image carrier. As the developing solution used at this time, for example, a developing solution obtained by dispersing a toner made of, for example, carbon black coated with a resin in a carrier liquid made of an aliphatic hydrocarbon such as Isopar is used.
Then, the electrostatic latent image formed on the surface of the latent image carrier can be developed by the electrophoretic phenomenon of the charged toner in the carrier liquid. This method is called a two-component development method because a developer composed of a toner and a carrier liquid is used.

In the two-component developing method, since the electrostatic latent image always contacts the toner at the time of development, no displacement or the like during the development can occur. However, since the toner is brought into contact not only with the image portion but also with the non-image portion, the toner adheres to the region where no image is formed due to the residual charge and the like.
Therefore, a large amount of toner adheres to the formed image even in an image forming area that should be a non-image portion, which causes deterioration of image quality.

[0005] In contrast to the two-component developing method described above, there is a so-called one-component developing method that does not require a carrier liquid. In this method, a developer in which a coloring material such as carbon or dye is dispersed or dissolved in a liquid is used. This developer has conductivity, and induces a charge of a polarity opposite to that of the electrostatic latent image in the developer by electrostatic induction, and causes the developer to adhere to the electrostatic latent image by Coulomb force. The entire developer exhibits the same behavior as the toner in the two-component developing method, and only the image portion of the electrostatic latent image can be selectively developed.

In the one-component developing method, since the developing solution does not adhere to the non-image area, the non-image is not stained more than in the two-component developing method. For example, U.S. Pat. No. 3,080,043 discloses that a conductive ink (one-component developer) as a one-component developer is supplied to a developing roller having a fine uneven surface.
In order to prevent contamination of the non-image area, the ink on the convex top is scraped off with a blade, and the ink is retained only in the concave. Then, the ink in which the opposite polarity charge is induced by the charge of the electrostatic latent image on the surface of the latent image carrier is attracted to the charge of the electrostatic latent image from the meniscus state to perform development.

However, in this method, the position of the concave portion filled with ink and the position of the electrostatic latent image on the photosensitive member must be accurately adjusted. The higher the resolution is, the more severe the required accuracy is. If the concave portion and the electrostatic latent image on the photosensitive member are displaced from each other and the development is attempted, an accurate amount of ink cannot be supplied to the latent image, and the density of the recorded image becomes uneven. The electrostatic attraction does not work and development becomes impossible.

Several approaches have been attempted to solve this problem, such as changing the parameters of the physical properties of the ink and the manner in which the electrostatic field is applied. Remains unresolved.

As another approach, a method of synchronizing the driving of the uneven drum and the photosensitive drum, for example, a configuration in which one of the drums drives the other drum has been considered. However, displacement due to slippage, wear, etc. still occurs. In addition, it is not possible to remove the deviation in the main scanning direction (the direction orthogonal to the rotation direction of the drum). This is a problem that occurs even if it is done.

As another wet electrophotographic system, there is a mist developing system. This is a method in which the ink is converted into a mist (fog), the ink mist is charged by corona discharge, and the charged ink mist is developed. In this method, if the density of the mist is high, the occurrence of misalignment can be reduced, so that the misalignment between the electrostatic latent image and the developer during development can be reduced as in the above-described two-component developing system. . However, in this method, the ink is always mist-like,
Must be charged. Normally, the image signal is ON
/ OFF is an arbitrary repetition, and it is rare that a continuous image signal is input such that the entire recording paper is painted. Therefore, there is a problem that the ink mist that does not move to the electrostatic latent image stays in the developing device, the mist is combined with each other, and the diameter of the ink droplet that moves to the electrostatic latent image varies. Further, there is a problem that the ink mist scatters outside the developing device and the inside of the image forming apparatus becomes dirty.

In order to prevent this, there is a configuration in which a porous cover is provided while the ink mist moves from the developing device to the photosensitive member, and the developing device is partitioned by the porous cover. by this,
Ink mist can be prevented from leaking out of the developing device without permission. However, the porous cover may be clogged due to the adhesion of the ink mist. As a result, development failure occurs on the photoreceptor, and problems such as missing colors and missing pixels in a recorded image occur. It is also necessary to match the position of the perforations with the position of the electrostatic latent image in the main scanning direction. This alignment requires control to adjust the exposure timing at the perforated position, and requires a high accuracy of, for example, 10 μm or less. In order to realize this, a position detecting device for detecting a precise position of the perforated hole is required, and the device becomes complicated and expensive.

As a developing method of developing a recording liquid into droplets by a method different from the mist, for example, Japanese Patent Laid-Open Publication No.
As described in Japanese Patent Laid-Open No. 2 (Kokai) No. 2, there is a device in which recording on a recording medium is performed using a permeation control member provided with micropores. This is to prevent ink droplets from being combined between adjacent ink droplets. However, also in this method, similarly to the above-described porous cover in the mist development method, it is necessary to position the through hole and the electrostatic latent image,
Have similar problems.

There is an ink jet system as a recording system different from the wet electrophotographic system. The inkjet method is
In recent years, it has been used as a small and low-cost printer.
In this ink jet method, usually, ink is moved to a recording medium by using pressure or electrostatic suction force from a nozzle,
Form an image. Since the ink jet method uses a nozzle, it is necessary to refill the nozzle with the ink after the ink moves. The speed required for this refilling decreases as the nozzle diameter decreases. In recent years, there has been a trend toward smaller droplets, and the nozzle diameter has been reduced to about 50 to 100 μm. Further, in order to arrange a large number of such small-diameter nozzles, it is necessary to precisely process all the nozzles by a high-precision microfabrication technique, which is very difficult to realize. As a result, high-speed printing cannot be performed as a result, and the printing speed is inferior to the electrophotographic method.

As a method for increasing the speed of an ink jet recording apparatus, there is a method in which a pressure by a piezo drive and an electrostatic attraction force are synchronously applied as described in, for example, JP-A-5-104725. In this way,
The force to move the ink is increased and the speed can be increased. However, although speeding up is improved, it is expected that the pressure by the piezo and the vector (direction) of the electrostatic attraction force do not always match due to the positional accuracy of the electrodes and the mounting error of the piezo. In this method, the ink drawn out of the nozzles overcomes the surface tension of the ink by the pressure of the piezo or the electrostatic attraction force, and is formed into droplets to perform printing on recording paper. Therefore, the vector of the electrostatic field and the direction of pressure by the piezo are major factors that determine the developing position on the recording paper. As described above, if there is a deviation between the pressure of the piezo and the vector of the electrostatic attraction force, it becomes impossible to perform recording at a desired position.

As another example of an ink-jet apparatus utilizing electrostatic attraction, there is an apparatus described in, for example, JP-A-2-52747. In this apparatus, ink droplets are formed on the entire surface of the belt by any method, the ink droplets are selectively charged, and the ink droplets are attracted to the recording medium by using electrostatic attraction at a transfer position to the recording medium. Then, an image is formed. This method is an effective method for increasing the speed of the ink jet system. However, it is difficult to selectively charge the battery according to the belt width, and there is a concern about a difference between the timing at which the ink droplet passes through the charging device and the charging timing by the charging device. Considering the current image forming resolution (300 to 600 dpi),
Since it is required that the belt drive and the like have a highly accurate control function of about 10 μm, it is difficult to realize the control function.

As described above, the problems of the prior art in which an electrostatic latent image is visualized by electrostatic attraction using ink are summarized as follows. 1. When a developing roll having unevenness is used, high accuracy of uneven patterning and a high-precision alignment control device are required, and the cost of the device is increased. 2. In the mist development method, it is necessary to prevent individual ink mist from being combined in the developing device, and it is necessary to take measures such as providing an aperture so that the mist does not scatter outside the developing device. The aperture has the problem of clogging due to mist adhesion, and the position of the aperture and the position of the electrostatic latent image need to be adjusted with high precision. Will be higher. 3. In a droplet developing method that does not form mist (ink penetrating type), it is necessary to provide a permeation control member having a through hole to selectively move ink on the photoreceptor. High-precision alignment becomes a problem, which increases the cost of the apparatus. 4. The ink jet method requires a precision device that drops ink and selectively charges the ink, and a highly accurate charge control device. When a nozzle is used, high-speed supply of ink becomes a problem.

[0017]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and in an image forming apparatus utilizing an electrostatic attraction, a high-precision and high-cost control mechanism is not required. An object of the present invention is to provide an image forming apparatus and an image forming method capable of forming an image with high image quality and at a high speed by reducing an image forming defect due to a mounting error of a developing device or a variation in an electrode position.

[0018]

According to the present invention, a liquid column is formed on a free surface of a liquid by applying an ultrasonic radiation pressure to the free surface of the liquid. Then, the liquid is moved from the liquid column to the recording medium by electrostatic attraction,
Form an image. In this configuration, since no fine holes such as nozzles are provided, no clogging or the like occurs, and no defective development occurs. In addition, if a good liquid column is formed, no mist is scattered and the inside of the housing is not stained. Further, since no nozzle is used, refilling of the recording liquid is performed at high speed, and high-speed recording can be performed.

Further, in the present invention, when a liquid column is formed on the free surface of the liquid, by applying an ultrasonic radiation pressure larger than that which balances with the surface tension of the liquid, the liquid becomes unstable without forming mist. A liquid column in a state is formed. Thereby, the holding force due to the surface tension of the liquid is reduced, and the liquid crystal is configured to obey the vector of the electrostatic suction force. Therefore, even if the vector of the electrostatic attraction force is slightly displaced, the liquid can be reliably moved to the recording medium, and the occurrence of image quality defects such as missing pixels and unevenness can be reduced. At this time, it is not necessary to use a high-precision alignment device or the like, and it is possible to suppress variations in the development position due to an error in mounting the device.

A plurality of liquid columns can be formed by individual ultrasonic wave generating means. Since the plurality of liquid columns formed on the free surface of the recording liquid are formed by the radiation pressure given from the corresponding ultrasonic wave generating means, it is possible to suppress the mutual interference with the adjacent liquid columns (printing portions). .

The recording medium can be a photoreceptor, recording paper, intermediate or the like. When a photoreceptor is used as a recording medium, electrostatic attraction can be generated by an electrostatic latent image formed on the photoreceptor surface, and liquid can be moved to the photoreceptor for development. At this time, a developing roller or the like having a highly accurate concavo-convex pattern as in the related art is unnecessary, and highly accurate alignment of the developing unit can be eliminated. When a recording paper or an intermediate is used as a recording medium, an electrode can be arranged on the back side of the recording paper or the intermediate to generate electrostatic attraction. At this time, it is possible to guarantee the image forming position without making the electrode attachment error and the processing accuracy strict.

Further, when a latent image is formed on the photosensitive member, by controlling the electrostatic attraction force according to the image, the amount of liquid can be freely controlled to form an image rich in gradation expression. .

[0023]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is an explanatory diagram of the principle configuration of the present invention. In the figure, 1 is an ink, 1a is an ink free surface, 1b is a liquid column, 2 is a substrate, 3 is an acoustic transducer, 4 is a high frequency power supply, and 5 is an acoustic wave. FIG. 1A shows a state in which the high-frequency power supply 4 is off. Substrate 2
Ink 1 which is a liquid for recording on the free surface 1a
It is supported with. An acoustic transducer 3, which is an ultrasonic wave generating means for generating ultrasonic waves, is provided on the substrate 2,
It is configured so that ultrasonic vibration can be irradiated toward the ink free surface 1a. In this figure, the substrate 2 is connected to a ground potential using a conductor or a material having conductivity by providing a conductive layer on the surface on the acoustic transducer 3 side, and is connected to one electrode of a plurality of acoustic transducers 3. Connected in common. However, substrate 2 is not necessarily
It is not necessary to impart conductivity to the acoustic transducers 3, and a lead may be drawn from each acoustic transducer 3. In FIG. 1A, the high-frequency power supply 4 is OFF as described above, and therefore, as shown in FIG. 1C, the voltage applied to the acoustic transducer 3 is 0V.

FIG. 1B is a diagram in which the high frequency power supply 4 is turned on. As shown in FIG. 1D, the high-frequency power supply 4 is constantly applied to the acoustic transducer 3 to generate an acoustic wave 5 in the ON state. By acoustic waves,
The liquid column 1b is formed. The ink is moved from the liquid column to a recording medium (not shown) to form an image. In the present invention, the movement of the ink is performed by an electrostatic suction force.

As the acoustic transducer 3, an appropriate element such as a piezoelectric element or a magnetostrictive element that can emit an acoustic wave into the ink by an applied voltage can be used.

FIG. 2 is an explanatory diagram of the formation of the liquid column. In the figure, the same parts as those in FIG. The illustration of the high-frequency power supply is omitted. Further, a piezoelectric element was used as the acoustic transducer 3. Also, an example is shown in which the driving frequency of the acoustic transducer 3 is about 5 MHz or less. FIG. 2A shows a state in which the voltage of the high-frequency power supply is not applied to the acoustic transducer 3.

FIG. 2B shows a state in which a high-frequency voltage has been applied to the acoustic transducer 3. The high frequency voltage is
A pulse voltage having a constant period was used. Acoustic waves 5 are radiated from the acoustic transducer 3 into the ink 1, and the radiation pressure causes a bulge of the ink on the ink free surface 1 a at the center of the acoustic transducer 3. However, when the voltage is low, the raised surface of the ink is somewhat unstable.

FIG. 2C shows a state where the voltage is increased. The bulge of the ink caused by the radiation pressure of the acoustic wave 5 becomes high, and the liquid column 1b starts to stabilize. FIG. 2D shows a state in which the voltage applied to the acoustic transducer 3 is further increased. In this state, the liquid column 1b is completely stabilized. FIG. 2E shows a state where the voltage applied to the acoustic transducer 3 is further increased. The liquid column 1b is higher and stable.

FIG. 2F shows a state in which the voltage applied to the acoustic transducer 3 is increased beyond the stable region. The liquid column 1b starts to oscillate and becomes unstable. FIG. 2G further shows the acoustic transducer 3.
Is a state in which the voltage applied to is increased. The liquid column 1b starts to deform and the shape becomes more and more unstable. FIG. 2 (H)
Further converts the voltage applied to the acoustic transducer 3 into
It is in a state of being raised. In the figure, atomized ink comes out from the unstable liquid column 1b.

As described above, when the ultrasonic energy radiated into the liquid is gradually increased from zero, a liquid column is gradually formed on the free surface of the ink. When the energy is very small, the liquid column is slightly unstable, but is stabilized when the energy exceeds a certain value. When the energy is applied beyond this stable range, the liquid column becomes unstable again. When a certain energy or more is applied, fine droplets are scattered in all directions from each part of the liquid column.

FIG. 3 is an explanatory diagram of the movement of the ink droplet.
In the figure, reference numeral 6 denotes an electrode. In the present invention, FIG.
As shown in (G), the liquid column is given higher energy than the ultrasonic energy that is formed stably, and the liquid column in an unstable state without forming mist is formed in advance. With respect to the liquid column in this state, droplets are directed from the liquid column toward the electrode 6 by electrostatic attraction generated between the liquid and the electrode 6 provided on the liquid as shown in FIG. To move. In particular, the electrostatic attraction becomes strongest at the top of the liquid column. Further, when the electrode 6 is located immediately above the liquid column, the electrostatic attraction force is the strongest.

In the present invention, an unstable liquid column is formed to the extent that the ink does not mist. In this state,
The holding force of the liquid column due to the surface tension of the ink is weak, and the top of the liquid column is shaking due to the unstable shape. Therefore, it is possible to follow the direction of the external force without resistance. If the electrode 6 is displaced from immediately above the liquid column as shown in FIG. 3B, the direction of the radiation pressure forming the liquid column and the direction in which the electrostatic attraction force acts are slightly different. Even in such a case, since the top of the liquid column is out of the balance between the radiation pressure and the surface tension, the force at which the top of the liquid column is restrained by the radiation pressure is weak. Therefore, at the top of the liquid column,
The force in the direction in which the radiation pressure is actually applied is substantially equal to the force in the other direction, and the force is distributed almost randomly. For this reason, even if the position of the liquid column is displaced from that of the electrode 6, the electrostatic attraction force from the liquid column toward the electrode 6 acts on the top of the liquid column to move the droplet toward the electrode 6. be able to.

When the liquid moves from the liquid column to the electrode 6, the ink in the form of droplets may fly as shown in FIGS. 3 (A) and 3 (B). As shown in FIG. 3 (C), the liquid column may extend in a string form and adhere to the recording medium.

In this manner, even if the position of the liquid column and the direction of the electrostatic attraction force by the electrode 6 and the like are slightly shifted,
Liquid can be moved. As a result, a configuration that does not require an expensive control mechanism for alignment can be realized. In addition, after the movement of the ink, since the periphery of the liquid column is the ink, the ink is supplied again quickly. Therefore, high-speed recording is possible.

In such a configuration, a member having an aperture between the ink and the photosensitive member or a member such as an ink carrier is unnecessary, and can be realized with a simple configuration. Further, since the ink is not used in a state where the ink is mist and floats as shown in FIG. 2 (H), it is possible that the mist-formed ink is combined during the floating and the ink droplets become large or the inside of the housing is contaminated. Absent.

Although only one liquid column is shown in each of the drawings described above, the liquid columns can be arranged one-dimensionally or two-dimensionally, for example, in a staggered manner. is there. In this case, the acoustic transducer 3 is provided for each liquid column.
Is provided. Each acoustic transducer 3 can also be individually controlled.

FIG. 4 is a schematic configuration diagram showing a first embodiment of the image forming apparatus of the present invention. In the figure, 11 is a photoreceptor, 12 is a charger, 13 is an exposure unit, 14 is a mirror, 15
Is an ink developing unit, 16 is an ink liquid column, 17 is a paper tray, 18 is a recording paper, 19 is a recording paper transport belt, 20 is a charging device for absorbing recording paper, 21 is a transfer device, and 22 is a cleaner. In this example, an example in which the photoconductor 11 is used as a recording medium is shown.

The photosensitive member 11 rotates clockwise in the figure,
First, the entire surface of the photoconductor is charged by the charger 12. Next, an optical signal corresponding to the image signal is generated by the exposure device 13 and the optical path is changed by a mirror 14 or the like as necessary.
A light signal is applied to the surface of the photoreceptor 11 charged in step (1). As a result, a potential contrast is generated between a portion irradiated with the optical signal and a portion not irradiated with the light signal, and an electrostatic latent image including an image forming portion and a non-image forming portion is formed. It should be noted that a configuration may be adopted in which the charge is removed first and then charged by irradiation of an optical signal by the exposure device 13. After the electrostatic latent image is formed on the photoconductor 11, the electrostatic latent image is developed by the ink developing unit 15. The ink developing unit 15 will be described later.

On the other hand, a medium on which an image is finally formed, such as recording paper 18 placed on the paper tray 17, is transported one by one by a recording paper transport belt 19. At this time,
The recording paper 18 is charged by the recording paper attraction charger 20 and is attracted to the recording paper transport belt 19 to ensure reliable transport. Of course, the recording paper may be conveyed without using the conveyance belt 19, for example, by a conveyance roller.

The developed image on the photoconductor 11 is transferred by the transfer unit 21 onto the recording paper 18 conveyed by the recording paper conveying belt 19. Recording paper 18 on which the image has been transferred
Is discharged outside. Photoconductor 11 after image transfer
Removes ink remaining without being transferred by the cleaner 22. In addition, static elimination or the like may be performed.

FIG. 5 is a schematic configuration diagram showing an example of the ink developing section. In the figure, 31 is a base material, 32 is a piezoelectric material, 33
Is an electrode, 34 is ink, 35 is a free surface, 36 is a liquid column,
37 is a drive unit. In the ink developing section 15, an acoustic transducer as an ultrasonic wave generating means is arranged on the bottom of the grounded base material 31. The acoustic transducer includes a piezoelectric material 32 and an electrode 33.
In addition, the ink 34 is stored in the upper part of the base material 31. The contained ink 34 forms a free surface 35 and faces the surface of the photoconductor 11. FIG.
Although only one electrode 33 is shown for explanation, a large number of electrodes 33 are arranged in the axial direction of the photoconductor 11.

An electric signal from the driving section 37 is input to the electrode 33. When a voltage is applied from the drive unit 37, the piezoelectric material 32 is distorted according to the voltage. Thereby, the base material 31
Push up. Thereafter, when the voltage from the driving unit 37 decreases or becomes 0, the distortion of the piezoelectric material 32 is released, and the base material 31 returns to the original state accordingly. By repeating this at a predetermined frequency, the acoustic wave propagates in the ink 34 and propagates to the free surface 35 of the ink 34. As described with reference to FIG. 2, if the voltage applied from the driving unit 37 is a predetermined voltage, an unstable liquid column 36 can be formed on the free surface 35 of the ink 34 without causing mist.

On the surface of the photoreceptor 11, an exposure unit 13 shown in FIG.
As a result, an electrostatic latent image is formed, and the image forming portion and the non-image forming portion have a potential contrast. For example, a bias potential is applied to the photoconductor 11 in advance, and the photoconductor 11 is charged by exposure so as to cancel the bias. As a result, the area where the exposure has not been performed is the ink developing unit 15.
, And the electrostatic attraction does not work. Conversely, the surface of the photoreceptor in the exposed area has the bias potential of the photoreceptor. Therefore, an electrostatic field is generated between the grounded base 31 of the ink developing unit 15 and the image forming portion of the electrostatic latent image formed on the photoreceptor 11, and an electric charge is generated in the liquid column 36 and its vicinity. Here, electric charges are also generated in a region other than the liquid column 36 on the free surface 35 of the ink 34, but usually, a large amount of electric charge concentrates on the convex portion in the electric field. Will receive. Therefore, especially the liquid column 36
Is attracted to the image forming portion of the electrostatic latent image on the photoreceptor 11, and the ink 34 on the top of the liquid column 36 separates from the liquid column 36, drops and moves to the electrostatic latent image on the photoreceptor 11. I do.

Here, since the top of the liquid column has only an unstable binding force, even if the position of the liquid column and the electrostatic latent image are shifted, the ink droplet is sucked toward the electrostatic latent image. . The displacement of the photoconductor 11 in the rotation direction will eventually pass above the liquid column due to the rotation of the photoconductor 11, but the displacement of the photoconductor 11 in the axial direction cannot be corrected during image formation. Therefore, conventionally, the photosensitive member 11 (or the exposure position by the exposure device 13) and the ink developing unit 15 have to be accurately positioned. However, in the present invention, since the liquid column is formed in an unstable state without forming a mist, even if the charged portion is slightly displaced as shown in FIG. 5, ink is transferred from the liquid column to the charged portion of the photoconductor 11. Can be moved. Therefore, even if there is a slight misalignment between the photoconductor 11 (or the exposure position by the exposure device 13) and the ink developing unit 15, a defect such as missing pixels is not caused.
The electrostatic latent image can be developed.

When an ink droplet is moved by using an electrostatic attraction force, the electrostatic attraction force becomes smaller in proportion to the square of the distance between the ink and the destination, so that this distance is made as short as possible, It is advisable to increase the suction force. For example, even if this distance is set to 400 to 500 μm,
A voltage of just under 3 kV is required. According to the configuration of the present invention,
Even if the distance between the surface of the photoconductor 11 and the free surface 35 of the ink in the ink developing unit 15 is set to, for example, 500 μm, the distance between the top of the liquid column 36 and the photoconductor 11 can be reduced by forming the ink column 36. It is reduced to 200 to 300 μm. Further, since a convex portion such as the liquid column 36 is provided,
Concentration of charges is likely to occur, and ink can be easily ejected at a voltage of, for example, about 1.5 kV. Further, for example, a displacement amount of about ± 40 μm can be allowed as an axial displacement amount of the photoconductor 11 between the liquid column and the charged region.

As described above, since the ink droplet is moved to the photosensitive member 11 by the electrostatic attraction force to perform the development, if the electrostatic attraction force by the electrostatic latent image can be changed, the ink droplet is moved to the photosensitive member 11. The amount of ink drops can be changed. That is, by modulating the intensity of the optical signal generated by the exposure device 13 in FIG. 4 according to the magnitude (density) of the image signal, the potential difference contrast of the electrostatic latent image on the photoconductor 11 can be adjusted. it can. FIG. 6 is a graph showing a specific example of the optical signal generated by the exposure device and the potential on the photoconductor. As shown in FIG. 6A, the drive current of the exposure device 13 is changed according to the density of the input image signal, and the intensity of the generated optical signal is changed. Then, the exposure unit 13
Then, an optical signal having an emission intensity as shown in FIG. 6B is emitted. When this light signal is irradiated onto the photoconductor 11, the surface potential becomes as shown in FIG.

As shown in FIG. 6, by increasing the optical signal when the image signal is large (the density is high), the potential difference of the electrostatic latent image becomes large. As a result, the electrostatic attraction force generated between the ink developing unit 15 and the ink developing unit 15 also increases, and the size of the ink droplet that moves to the photoconductor 11 increases. vice versa,
By weakening the optical signal when the image signal is small (the density is low), the potential difference of the electrostatic latent image is reduced, and the electrostatic attraction force generated between the electrostatic latent image and the ink developing unit 15 is also reduced.
The size of the ink droplet moving to the photoconductor 11 becomes smaller.

As described above, by modulating the light signal generated by the exposure device 13 in accordance with the magnitude (density) of the image signal, the surface potential on the photoconductor 11 becomes equal to the potential corresponding to the magnitude of the image signal. Become. Therefore, the photoconductor 1 generated in the liquid column 16
1, the size of the ink droplet moving to the photoreceptor 11 also changes.

By modulating the exposure intensity according to the density of the image signal in this manner, the amount of ink droplets during development can be changed. This change in the amount of ink droplets appears directly as the density of the image. Therefore, multiple gradations can be reproduced by one pixel, and a grayscale image can be reproduced favorably.

FIG. 7 is a schematic configuration diagram showing a second embodiment of the image forming apparatus of the present invention. In the figure, the same parts as those in FIG. 4 are denoted by the same reference numerals, and description thereof will be omitted. 41 is a belt photoreceptor. In this embodiment, a belt photoconductor 41 is used instead of the drum-shaped photoconductor 11. Further, as a conveyance means of the recording paper 18, the recording paper conveyance belt 1 is used.
The transfer roller and the like are used instead of the transfer roller 9. The configuration of the transport system for the recording paper 18 is generally omitted.

When the belt photoreceptor 41 is used, similarly to the first embodiment, the charging is performed by the charger 12 and the exposure is performed by the light signal generated by the exposure device 13 in accordance with the image signal. Thus, an electrostatic latent image is formed, and is developed by the ink developing unit 15. Then, the image is transferred to the conveyed recording paper 18 by the transfer device 21 to form an image on the recording paper 18. Thereafter, the belt photoconductor 41 is moved to the cleaner 22.
The remaining ink is removed.

When a drum-shaped photosensitive member is used as in the first embodiment, the distance between the photosensitive member and the ink developing section 15 can be maintained almost constant only in a narrow line-shaped area. However, in the configuration using the belt photoconductor 41 as in the second embodiment, the belt photoconductor 41 can be moved substantially in parallel with the ink developing unit 15. Therefore, the distance between the belt photoconductor 41 and the ink developing unit 15 can be kept substantially constant over a wide range. By utilizing this, the acoustic transducer can be arranged in the ink developing unit 15 over a wide area in a two-dimensional manner.

FIG. 8 is a plan view showing an example of the arrangement of the electrodes of the ink developing section in the second embodiment of the image forming apparatus of the present invention. In the figure, the up-down direction is the moving direction of the belt photoconductor 41, and the left-right direction is the width direction of the belt photoconductor 41. In this example, the electrodes 33 arranged in the moving direction of the belt photoconductor 41 are slightly shifted in the width direction of the belt photoconductor 41.

With such an arrangement, it is possible to perform recording with higher resolution than the arrangement interval of the electrodes 33 in the width direction of the belt photoconductor 41. That is, the interval recorded by the ink droplets flying by the electrodes 33 arranged in the width direction of the belt photoconductor 41 is the interval between the electrodes 33. However, during this interval, ink droplets can be recorded by the electrodes 33 in other rows, so that substantially high-resolution recording can be performed. Therefore, it is possible to obtain an image having a higher resolution than the arrangement interval of the electrodes 33 without arranging the electrodes 33 at high density.

FIG. 9 is a schematic diagram showing a third embodiment of the image forming apparatus of the present invention. In the figure, the same parts as those in FIG. 4 are denoted by the same reference numerals, and description thereof will be omitted. 15a-1
5d is an ink developing section for each color, 51 is a slider, and 52 is a transfer drum. In the third embodiment, an example of an image forming apparatus that forms a color image is shown. Here, inks of different colors are stored in the respective ink developing units 15a to 15d. These ink developing units 15 a to 15 d are mounted on the slider 51, and each of them is configured to be movable to the lower part of the photoconductor 11.

A medium for finally forming an image, such as the recording paper 18, is wound around the transfer drum 52. The recording paper 18 is supported on the transfer drum 52, for example, electrostatically or by a gripper. This transfer drum 5
An image of one color is formed on the recording paper 18 during one revolution of the recording paper 2. The process until this one-color image is formed on the recording paper 18 is the same as in the above-described first embodiment. For example, FIG.
In the state shown in (1), after the photoconductor 11 is charged by the charger 12 with the rotation of the photoconductor 11, an electrostatic latent image is formed by the exposure device 13, developed by the ink developing unit 15a, and developed by the transfer device 21. The image is transferred to the recording paper 18. by this,
On the recording paper 18, an image of the ink color contained in the ink developing unit 15a is formed.

After the transfer drum 52 makes one rotation and an image of one color is formed on the recording paper 18, the recording paper 18 is transferred to the transfer drum 5.
The slider 51 is slid while holding it at 2 to position, for example, the ink developing unit 15 b below the photoconductor 11. Then, as described above, the image of the ink color accommodated in the ink developing unit 15b is formed on the recording paper 18. As a result, two color images are formed in an overlapping manner. Similarly, the slider 51 is slid to position the ink developing units 15c and 15d below the photoreceptor 11, and images of the respective ink colors are superimposed and recorded on the recording paper 18. In this manner, while the transfer drum 52 rotates four times, the four-color images are formed on the recording paper 18 in a superimposed manner, and a full-color image can be obtained. Thereafter, the recording paper 18 on which the color image has been formed may be removed from the transfer drum 52 and discharged.

In the example shown in FIG. 9, a drum-shaped photoconductor 11 is used as the photoconductor 11, but as in the second embodiment shown in FIG. 7, a belt-shaped photoconductor 11 is used. May be appropriately selected in consideration of characteristics such as the cost, size, and recording speed of the apparatus.

FIG. 10 is a schematic configuration diagram showing a fourth embodiment of the image forming apparatus of the present invention. In the figure, the same parts as those in FIGS. 4, 7, and 9 are denoted by the same reference numerals, and description thereof is omitted. The fourth embodiment shows another example of an image forming apparatus for forming a color image. Here, four belt photoconductors 41 are arranged in parallel, each belt photoconductor 41 has a charger 12, an exposing device 13, a mirror 14, and a fixing device 21, and also has an ink developing section 15a to 15d for each color. are doing. In this configuration, for example, the recording paper 18 and the like conveyed by the recording paper conveyance belt 19 are sequentially imaged with the inks of the respective colors contained in the respective ink developing units 15a to 15d.
To 15d using the belt photoreceptor 41.

With this configuration, the image of each ink color is formed in a superimposed manner by passing the recording paper 18 only once through each transfer unit 21, and a full-color image can be formed.
Therefore, a color image can be formed at a higher speed as compared with the configuration in which the transfer drum 52 is rotated four times as shown in FIG. By using this configuration, the present invention can be applied to a light printing apparatus or the like that requires high-speed image formation.

In the example shown in FIG. 10, a belt-shaped photosensitive member is used. However, a drum-shaped photosensitive member can be used for the same configuration.

Further, in the examples shown in FIGS. 9 and 10, an example using four color inks is shown, but the present invention is not limited to this.
It is also possible to configure with three colors, five colors or more. Also,
In these examples, as described with reference to FIG. 6, by controlling the amount of exposure to change the amount of ink when each color ink is moved to the photoconductor, full-color expression can be performed for each pixel. Yes, a high-resolution color image can be obtained.

FIG. 11 is a schematic configuration diagram showing a fifth embodiment of the image forming apparatus of the present invention. In the figure, 61 is a recording head, 62 is a liquid column, 63 is an electrode, and 64 is a recording paper. In this example, a case where the recording paper 64 is used as a recording medium is shown. The recording head 61 has the same configuration as the ink developing unit 15 in FIG. The recording paper 64 is opposed to the free surface of the ink of the recording head 61.
Is fed. Further, an electrode 63 is arranged on the surface of the recording paper 64 opposite to the surface facing the free ink surface. The electrodes 63 are individually provided for each liquid column so as to basically pair with the liquid column and the ultrasonic element for forming the liquid column.

The image forming operation according to the fifth embodiment is as described with reference to FIG. That is, by applying a potential difference between the electrode 63 and the ink according to the image signal, an electrostatic attraction force is generated, and the ink is moved from the liquid column toward the electrode 63. Thereby, the ink can be attached to the surface of the recording paper 64 fed between the ink and the electrodes 63, and an image can be formed on the recording paper 64.

FIG. 12 is an enlarged view of the vicinity of a recording section in a fifth embodiment of the image forming apparatus of the present invention. As described with reference to FIG. 3 described above, in the present invention, an unstable liquid column is formed on the free surface of the ink without forming a mist, whereby, for example, as shown in FIG. Even if the positions of the columns are slightly shifted, the ink can be moved.

In particular, as shown in FIG. 12, when a large number of liquid columns are formed and electrodes 63 corresponding to the respective liquid columns are provided, an arrangement error between the electrodes 63 and an error in assembling the recording head 61 and the electrodes 63 are required. Alignment error occurs. for that reason,
Actually, it is difficult to arrange the electrodes 63 so as to completely coincide with a position that is paired with the liquid column and the ultrasonic wave generating means. Therefore, the positional relationship between the electrode 63, the liquid column, and the ultrasonic wave generating means after the actual assembly is slightly shifted in each group as shown in FIG.

In this case, the electric field generated between the electrode 63 and the liquid column is different from the direction of the radiation pressure for forming the liquid column (vertical direction in the figure). However, since the top of the liquid column is maintained in an unstable state, the force in the direction in which the radiation pressure is applied is almost negligible, and the ink moves substantially along the electric field. Therefore, even if the positions of the electrode 63 and the liquid column and the ultrasonic wave generating means are slightly shifted as shown in FIG. 12, the ink is transferred to the recording paper 64 according to the electrostatic attraction generated between the electrode 63 and the liquid column. Moving. This makes it possible to form a good image on the recording paper 64 without missing pixels.

A voltage is applied to the electrode 63 according to an image signal. Thus, the ink can be selectively moved to the recording paper 64 from the liquid columns formed in large numbers. FIG. 12 shows that a voltage is applied to the electrode 63 painted black, and the ink has moved to the recording paper 64 from the corresponding liquid column.

The electrostatic attractive force can be controlled by changing the voltage applied to the electrode 63 according to the density of the image, and the amount of ink moved to the recording paper 64 can be controlled. Thereby, gradation recording becomes possible.

In the recording head 61, for example, as shown in FIG. 8, ultrasonic generating means are arranged two-dimensionally to form liquid columns, and the electrodes 63 are two-dimensionally corresponding to each liquid column. It may be arranged to improve the resolution. Further, the recording head 6
A plurality of printheads 1 are arranged in accordance with the ink colors.
A color image can be formed by arranging the electrodes 63 corresponding to the liquid columns formed in the first column.

FIG. 13 is a schematic configuration diagram showing a sixth embodiment of the image forming apparatus of the present invention. In the figure, the same parts as those in FIG. 7 are denoted by the same reference numerals, and description thereof will be omitted. 71 is a recording head, 72 is a liquid column, 73 is an electrode, and 74 is an intermediate belt. This example shows an example in which an intermediate is used as a recording medium.

In the recording head 71, in this example, as shown in FIG. 8, the ultrasonic wave generating means is arranged two-dimensionally, and the liquid column 72 is formed and arranged two-dimensionally. Also,
The electrodes 73 are provided corresponding to these liquid columns so as to face the free surface of the ink.

An intermediate belt 74 is arranged so as to pass between the liquid column 72 and the electrode 73. The intermediate belt 74 is formed of, for example, a plastic belt made of a polyimide material or the like, and holds the ink moved from the liquid column 72. The movement of the ink from the liquid column 72 to the intermediate belt 74 is performed in the same manner as in the fifth embodiment. Even if the position of the liquid column 72 and the electrode 73 is slightly shifted, the ink is transferred to the intermediate belt 74. Can be moved to Of course, electrode 7
By controlling the voltage applied to 3 according to the density of the image, it is possible to control the amount of movement of the ink and to form a multi-tone image.

Normally, the recording paper has larger surface irregularities than the intermediate belt 74, and the recording paper contains water to some extent, so that the electric field is more likely to be disturbed. Therefore, when the intermediate belt 74 is used as the recording medium as in this embodiment, the positional accuracy of moving the ink can be improved.

The ink moved to the intermediate belt 74 is transferred to the recording paper 18 by the transfer device 21. Thus, an image is formed on the recording paper 18. The surface of the intermediate belt 74 transferred to the recording paper 18 is cleaned by the cleaner 22, and is repeatedly used for forming an image by the recording head 71.

In this example, an example in which a belt-shaped intermediate belt 74 is used as an intermediate is shown. However, the present invention is not limited to this, and a drum-shaped intermediate may be used. Although only one recording head 71 is shown in this example, a plurality of recording heads having different ink colors are arranged side by side to form a color image on the intermediate belt 74 and transfer the color image to the recording paper 18. It may be formed. In order to form a color image, a configuration in which a recording paper is wound around a transfer drum as shown in FIG. 9 may be used. In this case, an intermediate drum is used instead of the photoreceptor 11, and one color is applied to the intermediate drum. After recording, it can be transferred to recording paper. Further, an intermediate belt may be used instead of the photosensitive belt 41 in the configuration shown in FIG.

[0077]

As is apparent from the above description, according to the present invention, when an image is formed by moving a liquid by electrostatic attraction, a developing unit and a photoreceptor, a recording head and an electrode and the like are used. It is possible to reduce pixel omission and printing defects due to manufacturing errors and mounting errors, and obtain good image quality. As described above, there is an effect that it is possible to provide an image forming apparatus which is high in speed and has a simple configuration while ensuring high reliability.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of a basic configuration of the present invention.

FIG. 2 is an explanatory view of formation of a liquid column.

FIG. 3 is a diagram illustrating the movement of an ink droplet.

FIG. 4 is a schematic configuration diagram illustrating a first embodiment of the image forming apparatus of the present invention.

FIG. 5 is a schematic configuration diagram illustrating an example of an ink developing unit.

FIG. 6 is a graph showing a specific example of an optical signal generated by an exposure device and a potential on a photoconductor.

FIG. 7 is a schematic configuration diagram illustrating a second embodiment of the image forming apparatus of the present invention.

FIG. 8 is a plan view illustrating an example of an arrangement of electrodes of an ink developing unit according to a second embodiment of the image forming apparatus of the present invention.

FIG. 9 is a schematic configuration diagram illustrating a third embodiment of the image forming apparatus of the present invention.

FIG. 10 is a schematic configuration diagram showing a fourth embodiment of the image forming apparatus of the present invention.

FIG. 11 is a schematic configuration diagram showing a fifth embodiment of the image forming apparatus of the present invention.

FIG. 12 is an enlarged view of the vicinity of a recording unit according to a fifth embodiment of the image forming apparatus of the present invention.

FIG. 13 is a schematic configuration diagram showing a sixth embodiment of the image forming apparatus of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Ink, 1a ... Ink free surface, 1b ... Liquid column, 2 ...
Substrate, 3 acoustic transducer, 4 high frequency power supply, 5
... acoustic wave, 6 ... electrode, 11 ... photoconductor, 12 ... charger, 1
3 ... Exposure unit, 14 ... Mirror, 15, 15a-15d ... Ink developing unit, 16 ... Ink column, 17 ... Paper tray, 1
Reference numeral 8: recording paper, 19: recording paper transport belt, 20: recording paper suction charger, 21: transfer unit, 22: cleaner, 31: base material, 32: piezoelectric material, 33: electrode, 34: ink, 35
... Free surface, 36 ... liquid column, 37 ... drive unit, 41 ... belt photoconductor, 51 ... slider, 52 ... transfer drum, 61 ... recording head, 62 ... liquid column, 63 ... electrode, 64 ... recording paper, 7
1. Recording head, 72 liquid column, 73 electrode, 74 intermediate belt.

Claims (12)

[Claims] 1. An image forming apparatus for forming an image by moving a liquid to a recording medium by using an electrostatic attraction force, an ultrasonic generator for generating an ultrasonic wave in the liquid, and the ultrasonic generator. A driving unit for driving the liquid to form a liquid column on a free surface of the liquid; and a moving unit for applying an electrostatic attraction force to the liquid to move the liquid from the liquid column to the recording medium. Applies an energy larger than the energy balanced by the surface tension of the liquid and the radiation pressure given by the ultrasonic wave generating means to the ultrasonic wave generating means to form a liquid column in an unstable state without mist formation of the liquid. An image forming apparatus comprising: 2. The apparatus according to claim 1, wherein a plurality of said ultrasonic wave generating means are provided, and said driving means controls each of said ultrasonic wave generating means to individually form a plurality of liquid columns on a free surface of a liquid. The image forming apparatus according to claim 1, wherein: 3. The recording medium is a photoreceptor, a charging exposure unit for forming an electrostatic latent image on the photoreceptor in accordance with image information, and transferring the image formed on the photoreceptor to recording paper. The image forming apparatus further includes a transfer unit, wherein the moving unit moves the liquid from the liquid column onto the photoconductor by electrostatic attraction due to an electrostatic latent image formed on the photoconductor to form an image on the photoconductor. The image forming apparatus according to claim 1, wherein the image forming apparatus is formed. 4. The recording medium according to claim 1, wherein the recording medium is a recording paper, and an individual electrode is provided as the moving means on a back side of a free surface of the liquid of the recording paper. 3. The image forming apparatus according to 2. 5. The recording medium is an intermediate, an individual electrode is provided as the moving means on the back side of the free surface of the liquid of the intermediate, and an image formed on the intermediate is recorded. The image forming apparatus according to claim 1, further comprising a transfer unit configured to transfer the image onto paper. 6. The apparatus according to claim 1, wherein said moving means controls said electrostatic attraction force in accordance with an image signal to vary a liquid amount to be moved onto said recording medium. The image forming apparatus according to claim 1. 7. An image forming method for forming an image by moving a liquid to a recording medium using an electrostatic attraction force, wherein an ultrasonic wave is generated from inside the liquid toward a free surface of the liquid, and the liquid is mist Forming an unstable liquid column on the free surface of the liquid without causing the liquid column to move the liquid onto the recording medium by electrostatic attraction from the liquid column. 8. Generated individually controlled ultrasonic waves from a plurality of locations in the liquid toward a free surface of the liquid,
The image forming method according to claim 7, wherein a plurality of the liquid columns are formed on a free surface of the liquid. 9. The recording medium is a photoreceptor, forms an electrostatic latent image on the photoreceptor, and generates an electrostatic latent image on the photoreceptor by the electrostatic attraction force of the electrostatic latent image formed on the photoreceptor. 9. The image forming apparatus according to claim 7, wherein an image is formed on the photoconductor by moving a liquid onto the photoconductor, and the image formed on the photoconductor is transferred to recording paper. Image forming method. 10. The recording medium is a recording paper, and an electrostatic attraction force is generated by an individual electrode provided on the back side with respect to a free surface of the liquid of the recording paper. An image forming method according to claim 8. 11. The recording medium is an intermediate body, and an image is formed on the intermediate body by generating electrostatic attraction by an individual electrode provided on the back side of the free surface of the recording paper liquid. 9. The image forming method according to claim 7, wherein the image formed on the intermediate body is transferred to a recording sheet. 12. The apparatus according to claim 7, wherein said electrostatic attraction force is controlled in accordance with an image signal to change a liquid amount to be moved onto said recording medium. The image forming method as described in the above.