JPH0683117A - Electrostatic image forming method - Google Patents

Abstract

PURPOSE:To eliminate the need of high voltage, to prevent ozone from being produced, to enhance the degree of freedom in the selection of an image carrier, further to easily form an image having half tone, a large-sized image and a high-definition image, to easily make image forming speed higher, to simplify constitution and to reduce production cost. CONSTITUTION:The image carrier drum 11 is constituted by forming a dielectric layer 13 consisting of polyester on the outer periphery of a grounded aluminum cylinder 12, and provided so as to freely rotate in a direction shown by an arrow S. An electrostatic image forming head 14 is constituted by arranging plural sets of droplet jetting nozzle 21 and needle electrode 11 in a vertical direction to a paper surface. The image signal voltage of maximum 200-800V is impressed on the respective nozzles 21 through a signal line 23.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrostatic image forming method which is applied to an image forming apparatus such as a copying machine, a printer and a display and forms a developable electrostatic image with toner.

[0002]

2. Description of the Related Art An image forming apparatus such as a copying machine or a display for forming a toner image forms an electrostatic image on an image carrier and transfers the toner image obtained by developing the electrostatic image onto recording paper. Or to display it as it is. Various methods have been conventionally known as the method for forming the electrostatic image, and typical methods include the following. (1) An electrophotographic method of forming an electrostatic image by projecting a light image on a photoconductive layer charged by corona discharge or the like. (2) An electrostatic recording method in which electric charges are applied to a non-photosensitive electrostatic recording layer by an air discharge from an adjacent electrode. (3) Ion flow control for forming an electrostatic image by ionizing molecules in the air by the action of a high electric field to generate gas ions and controlling the amount of the gas ions reaching the electrostatic recording layer by a control electrode. Law.

[0003]

However, in any of the above methods, a high voltage is required to perform air discharge, and energy consumption is large. In addition, ozone is generated with the discharge in the air, which is not preferable in terms of environment. Moreover, in electrophotography, image quality depends on the photosensitivity of the photoconductive layer, making it difficult to obtain a long-life photoconductive layer with good photosensitivity. Moreover, since an optical system for projecting a light image or the like is required, the structure is complicated, the manufacturing cost is high, and large-sized image formation is difficult.

Further, in the electrostatic recording method, since the presence or absence of charge application to the electrostatic recording layer is determined depending on whether or not the voltage applied to the electrodes exceeds the threshold value of the air discharge, it is possible to form an image having a halftone. Have difficulty. On the other hand, in the ion flow control method,
Although it is possible to form an image having a halftone, it has hardly been put into practical use because the image forming speed is limited by the moving time of the gas ions to reach the electrostatic recording layer and the manufacturing cost is high. Is the reality.

In view of the above points, the present invention does not require high voltage and therefore does not generate ozone, and
Since the photoconductive layer is not used, the degree of freedom in selecting the image bearing member is high, and further, an image having a halftone or a large image,
High-definition images using small-diameter toner can be easily formed, and the image formation speed can be increased easily.
It is an object of the present invention to provide an electrostatic image forming method having a simple structure and capable of reducing manufacturing cost.

[0006]

In order to achieve the above object, the present invention relates to a method of depositing a droplet of an ionic liquid on one surface of an image carrier made of a dielectric and contacting the droplet. At least a first electrode and an image carrier
Between the second electrode arranged at the position opposite to the electrode of
It is characterized in that the contact between the droplet and the first electrode is released while applying a voltage according to the image signal.

[0007]

With the above structure, when the contact between the droplet and the first electrode is released in the state where the voltage is applied between the first electrode and the second electrode, the time when the contact is released. The ions in the droplets are fixed to the dielectric according to the applied voltage of.

[0008]

【Example】

(Basic Principle) First, the basic principle of electrostatic image formation according to the present invention will be described with reference to FIG. As shown in FIG.
Water 2 is brought into contact with the surface of the electrostatic recording layer 1 made of a dielectric,
When a voltage is applied between the electrode 3 in contact with the water 2 and the electrode 4 provided on the back surface of the electrostatic recording layer 1, the ions contained in the water 2 move to the surface of the electrostatic recording layer 1. The amount of ions that move at this time is determined according to the applied voltage.

In this state, as shown in FIG. 1B, the water 2 moves in the direction of the arrow (hereinafter referred to as the "scanning direction") together with the electrostatic recording layer 1 and the water 2 separates from the electrode 3. When,
Ions corresponding to the applied voltage at the moment of leaving remain on the surface of the electrostatic recording layer 1 and are fixed, and the electrostatic recording layer 1 is charged. This amount of charge does not change after the water 2 is separated from the electrode 3 except for spontaneous discharge. Further, even after the water 2 is removed by drying or the like, the electrostatic recording layer 1 has the same potential as when the electrode 3 separates, and the contact portion between the water 2 and the surface of the electrostatic recording layer 1 at that time. It has been confirmed by the study of the present inventor that the same charged state is maintained.

As described above, when water is brought into contact with the surface of the dielectric layer and the electrode and the water is separated from the electrode while applying a voltage, the surface of the dielectric layer changes depending on the applied voltage at the moment when the electrode is separated. Since the charged pattern remains, an electrostatic image is formed by applying a voltage corresponding to the image signal in synchronization with the movement of the dielectric layer. Here, the water 2 needs to contain aqueous ions for moving to the electrostatic recording layer 1, but hydrogen ions H ₃ due to the dissociation of water to the extent that they are also contained in what is generally called pure water. O ⁺ and, hydroxide ion OH ^-,
The carbonate ion CO ₃ ⁻ alone has sufficient conductivity in terms of static electricity, and is sufficient to obtain a normal image forming speed. Also, other inorganic or organic electrolytes can be added. In this case, the ion density is increased to facilitate faster electrostatic image formation. Not limited to water, alcohols such as ethanol and methanol, polar liquids such as ketones and esters, and mixtures thereof are applicable as long as they are ionic liquids. Further, an electrolyte may be added to these liquids. The ions contained in these liquids are consumed as they move to the electrostatic recording layer 1, but the amount thereof is not a problem at all.

Further, in order to increase the image forming speed, it is preferable that the electrostatic recording layer 1 has a large water repellency. For example, a water repellent polymer layer such as a polyester layer can be applied. Various resins and various inorganic ceramics are also applicable. The surface of the electrostatic recording layer 1 may be processed with a water repellent treatment agent such as silicon or fluorine.

The electrostatic image forming method using the above ionic liquid has the following features. (1) The relationship between the applied voltage and the surface potential of the electrostatic recording layer has a very good linear relationship as shown in FIG. Therefore, uneven charging does not occur and gradation reproducibility is good. Further, the electrostatic recording layer basically needs only to be a dielectric, and high image quality can be obtained regardless of the type. (2) The electrostatic potential of the electrostatic recording layer is almost equal to the applied voltage, and since ions that are naturally ionized in water are used, a high voltage is not required as in the case of performing air discharge. However, it does not generate ozone. (3) Since the resolution of the electrostatic image is determined according to the size of the droplet of the ionic liquid, the resolution can be easily increased. (4) The charge amount of the electrostatic recording layer is not affected by the charge amount before the contact with the ionic liquid. Therefore, it is not necessary to remove the charge before forming the electrostatic image. It is also easy to divide an image into a plurality of parts to form an electrostatic image. This is because even if a part of the electrostatic image to be formed later overlaps the electrostatic image formed first, mutual interference with the preceding electrostatic image does not occur. Furthermore, when the electrostatic recording layer itself is used as a recording medium and the developed visible image is dried and fixed as it is, a color image can be easily formed by superposing images of a plurality of colors. (5) Since a dielectric such as a water-repellent polymer layer is used as the electrostatic recording layer, the decay rate of the surface potential due to the diffusion of electric charges is, for example, as shown in FIG. Extremely small. Therefore, since the applied charge is retained for a long time, good development can be performed by a usual electrophotographic developing method or the like. Further, even when the toner image is exposed to light as in the case where it is displayed without being fixed, a high image remaining property can be obtained. (6) Since the movement of the ions to the electrostatic recording layer is substantially instantaneously performed, the image forming speed can be easily increased. (First Embodiment) Next, an example of an image forming apparatus to which the above electrostatic image forming method is applied will be described with reference to FIGS.

The image carrier drum 11 is constructed by forming a dielectric layer 13 made of polyester or the like on the outer periphery of a grounded aluminum cylinder 12, and is rotatably provided in the direction of arrow S in FIG. Around the image carrier drum 11, an electrostatic image forming head 14, an air nozzle 19 for drying droplets on the surface of the image carrier drum 11, a developing device 15 for developing toner with a magnetic brush, and a toner image. A transfer charger 17 for transferring to the recording sheet 16 and a cleaner blade 18 for removing residual toner are provided. It should be noted that no static eliminator for removing the electric charge of the dielectric layer 13 is provided. This is because, as described above, the charging state before forming a new electrostatic image does not affect the formation of the electrostatic image.

The electrostatic image forming head 14 is constructed by arranging a plurality of sets of liquid droplet jetting nozzles 21 and needle electrodes 22 in a direction perpendicular to the plane of the drawing. Each needle electrode 22 is provided in contact with or close to the surface of the dielectric layer 13 of the image carrier drum 11, and an image signal of 200 to 800 V at maximum depending on the density of each pixel via the signal line 23. A voltage is applied. For the needle electrode 22, for example, a conductive wire made of tungsten, phosphor bronze, stainless steel, carbon fiber or the like having a diameter of several tens of μm is used.

The droplet ejecting nozzle 21 has the same structure as a recording head provided in, for example, an ink jet recording type printer. Specifically, for example, as shown in FIG. 5, a piezoelectric element 21 a is provided and configured, and a minute liquid droplet 31 such as water or alcohol is directed toward the vicinity of the tip of the needle electrode 22 at a constant rate per unit time. It is designed to intermittently inject with an injection amount. The ejection amount of the droplet 31 per unit time may be changed in association with the image signal voltage applied to the needle electrode 22 so that the gradation reproducibility can be further improved.

Here, in order to increase the resolution of the electrostatic image, a small droplet 31 is formed and the needle electrode 22 is formed.
A thin one may be used. In the above configuration,
When the droplet 31 is ejected from the droplet ejecting nozzle 21, the droplet 31 adheres to the surface of the dielectric layer 13 of the image carrier drum 11 and contacts the tip of the needle electrode 22. Therefore, when the image carrier drum 11 is rotated while applying the image signal voltage to the needle-shaped electrode 22, the liquid droplet 31 is discharged.
Droplet 3 according to the voltage applied at the moment of leaving 2
Due to the movement of the ions in 1, the surface of the dielectric layer 13 at the portion where the droplet 31 is attached is charged and an electrostatic image is formed.

The droplet 31 is evaporated by the hot air blown from the air nozzle 19, but the electrostatic image is retained as it is. The electrostatic image is developed by the developing device 15, and the formed toner image is transferred to the recording sheet 16 by the transfer charger 17. Note that liquid development can be easily used instead of dry development using a magnetic brush as described above. This is because the dielectric layer 13 basically needs to be a dielectric as described above, and thus the solvent of the developer and the dielectric layer 13 that is not easily attacked by the solvent have a high degree of freedom.

Further, since it is easy to select a material having high heat resistance as the dielectric layer 13, the transfer charger 1
Instead of the electrostatic transfer of the toner image by 7, a heat transfer system in which the toner image is once adsorbed on a silicon-coated heat roller and then transferred and heat-fixed to the recording sheet 16 can be easily used. Polyimide, liquid crystal polymer, or the like is suitable as the material described above.

Further, the form of the image bearing member is not limited to the drum type as described above, and may be, for example, a belt type made of a dielectric film on which conductive layers are laminated.
The toner image or the like formed on such a film may be directly heat-fixed or dry-fixed on the film. Furthermore, a fixed electrode having the same function as the aluminum cylinder 12 may be provided separately from the dielectric film. In this case, in order to charge the dielectric film, the fixed electrode may be provided at least at a position facing the portion where the droplet 31 separates from the needle electrode 22, but the charge disappears due to discharge or the like. In order to prevent this, it is preferable to extend the fixed electrode to a position where the toner image is transferred, or to apply a counter charge to the back surface of the dielectric film by a conductive brush or the like.

Further, a display capable of repeatedly forming an image without fixing the toner image may be constructed. Also,
Since it can be charged to an accurate potential as described above, it is applicable not only to a practical image forming apparatus but also to an apparatus for studying developing characteristics.

[0021]

As described above, according to the present invention,
With relatively simple components, it does not generate harmful substances such as ozone, it uses a low voltage and is extremely efficient, and continuous tone reproduction is possible with good color reproducibility. An effect that an electrostatic image of a density can be formed is obtained.

Since the degree of freedom in selecting the dielectric is high,
For example, it is possible to directly form a color image using a durable thin dielectric film.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing the basic principle of electrostatic image formation according to the present invention.

FIG. 2 is a graph showing the relationship between the applied voltage and the surface potential of the electrostatic recording layer in the present invention.

FIG. 3 is a graph showing the decay rate of the surface potential of the polyester film applicable to the present invention.

FIG. 4 is a sectional side view showing the configuration of the image forming apparatus in the first embodiment.

FIG. 5 is a cross-sectional side view of essential parts showing the detailed configuration of the electrostatic image forming head.

[Explanation of symbols]

 1 Electrostatic Recording Layer 2 Water 3 Electrode 4 Electrode 11 Image Carrier Drum 12 Aluminum Cylinder 13 Dielectric Layer 14 Electrostatic Image Forming Head 19 Air Nozzle 21 Droplet Ejection Nozzle 21a Piezoelectric Element 22 Needle-like Electrode 23 Signal Line 31 Droplet

Claims (1)

[Claims] 1. An ionic liquid droplet is attached to one surface of an image bearing member made of a dielectric material, and a first electrode contacting the droplet and at least a first electrode via the image bearing member.
Between the second electrode arranged at the position opposite to the electrode of
A method for forming an electrostatic image, characterized in that the contact between the droplet and the first electrode is released while applying a voltage according to an image signal.