JPH09319229A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an image forming device with high resolution by developing an electrostatic latent image with a fine fog-like developer to which an electrostatic charge is supplied. SOLUTION: An ultrasonic vibrator 4 arranged in the bottom part of a developer 3 housed in a developing container 2 is vibrated by using an oscillation circuit 5, to generate a fog 15 from the surface of the developer 3. An induction charge electrode 8 is installed at a fixed interval above the surface level of the developer 3 and connected to a high-voltage power source 12 and the developer 3 is grounded, so that the fog 15 is charged by the induction charge electrode 8, simultaneously with the generation of the fog 15. This fog 15 is circulated in a fixed direction by fans for blowing 6 and 9. Further, an opening part 19 is provided in the wall surface of the developing container 2 on this side of the point where the fog 15 charged by the induction charge electrode 8 reaches a developing position 18 and a corona electrode 7 is arranged in the opening part 19. Then, the fog 15 divided into fine liquid drops by the corona electrode 7 is further carried by an air flow, to reach the developing position 18.

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 used in printers, facsimiles, copiers and the like.

[0002]

2. Description of the Related Art Conventionally, as a developing method for an electrophotographic system, a powder developing method using a powder toner or a liquid developing method in which toner dispersed in a highly insulating liquid is attached to an electrostatic latent image by electrophoresis. Are well known. this house,
The liquid developing method can use a small particle diameter toner having a diameter of 3 μm or less, which cannot be used in the powder developing method, and is therefore an effective developing method for obtaining a high resolution image. However, the highly insulating liquid used in the liquid development method is mainly a petroleum solvent, and there is a problem in terms of danger of ignition and environmental safety.

On the other hand, a so-called mist developing method is widely known in which a developing solution is atomized and droplets of the mist are attached to an electrostatic latent image. For example, Japanese Patent Publication No. 57-3069 discloses the following mist developing method. FIG. 3 is a schematic view of the first conventional example of the mist developing method disclosed in Japanese Patent Publication No. 57-3069.

As shown in FIG. 3, the developing device includes a developing container 102 filled with a developing solution 103 and a developing container 1.
An ultrasonic transducer 104 arranged on the bottom surface of 02 and an oscillator 105 connected to the ultrasonic transducer 104 are arranged. By vibrating the ultrasonic vibrator 104 by the oscillator 105, the surface of the developer swells and the fog 1
07 occurs. A photosensitive paper 101 that moves in the direction of arrow A is placed on top of the developing container 102. Photosensitive paper 10
The upper one carries an electrostatic latent image having a negative charge. The blower 106 conveys the fog 107 toward the photosensitive paper 101 (in the direction of arrow B). Blower 1
When the fog 107 is conveyed to the vicinity of the photosensitive paper 101 by 06, a positive charge is induced in the fog 107 to the photosensitive paper 101 side by electrostatic induction. The fog 107 in which the positive charge is induced on the photosensitive paper 101 side is attracted to the electrostatic latent image having the negative charge and adheres to the electrostatic latent image. On the other hand, photosensitive paper 1
Since there is no electric charge in the background portion on 01, the fog 107 does not adhere to the background portion, and only the electrostatic latent image portion is visualized.

This mist developing method does not require a fixing step, can use a safe developing solution mainly composed of water, and can relatively easily use a micro liquid having a diameter of several microns by using an ultrasonic vibrator. Since droplets can be generated, there is an advantage that high-resolution image formation can be performed.

[0006]

However, in the above-mentioned mist developing method, while the droplets of the mist generated on the surface of the developer are suspended, some droplets are combined with each other and the particle diameter gradually becomes smaller. The phenomenon often becomes large and the resolution is lowered. FIG. 4 is a graph showing changes in the particle size distribution of the fog immediately after the fog is generated and subsequent changes in the particle size distribution of the fog.

Curve A of the three particle size distributions shown in FIG.
Indicates the number of droplets with respect to the droplet diameter of the fog immediately after the fog is generated. On the other hand, the blower 106 (see FIG.
When the fog 107 is conveyed in the developing container 102 by using the above method, the fog droplets combine with each other to increase the number of droplets having a large diameter, and the particle size distribution shifts to the large diameter side as shown by the curve B. . When development is performed using such coarsened droplets, the resolution of the image naturally lowers. The curve C
Will be described later.

Japanese Unexamined Patent Publication (Kokai) No. 51-3246 proposes a method for preventing such coarsening of mist droplets. FIG. 5 is a schematic view of a developing device of a second conventional example described in the above-mentioned JP-A-51-3246. As shown in FIG. 5, the developing device was connected to the developing container 102 filled with the developing solution 103, the ultrasonic vibrator 104 disposed on the bottom surface of the developing container 102, and the ultrasonic vibrator 104. And an oscillator 105. Oscillator 1
When 05 is operated, the ultrasonic vibrator 104 vibrates, and the surface of the developing solution becomes wavy, so that fog 107 is generated. Fog 10
7 is conveyed in the direction of arrow B by the circulation pump 111 and circulated through the flow path 112. An image carrier 108 carrying an electrostatic latent image moves in the direction of arrow A above the developing container 102, and the fog 107 is attracted to the electrostatic latent image to perform development. At the top of the developing container 102, the fog 107 forms the image carrier 10.
The corona electrode 1 for improving the developing speed by applying an electric charge to the fog 107 in a portion before coming into contact with
09 is arranged. Corona electrode 109 is high voltage power supply 1
Power is supplied by 10. In this developing device, coarse droplets in the fog 107 are settled and removed in the flow path 112, whereby the particle size distribution of the fog is shifted to the fine particle side.

However, in order to settle coarse droplets using such a flow path, a flow path of a considerable length is required, so that there is a drawback that the entire developing device becomes large and the structure becomes complicated. Further, in this developing device, the fog 107 just generated from the surface of the developing solution 103 has no electric charge,
Fog 107 until charged by corona electrode 109
The Coulomb repulsive force does not act between the droplets, and the droplets tend to become coarse. Level of developer 103 and corona electrode 109
In this developing device separated from each other, especially the coarsening of the droplets easily occurs. Therefore, the effect of removing coarse droplets by the channel 112 is diminished, and the effect of improving the resolution of the output image cannot be expected.

In view of the above circumstances, it is an object of the present invention to provide a high resolution image forming apparatus by developing an electrostatic latent image with a fine mist-like developer.

[0011]

An image forming apparatus of the present invention which achieves the above object comprises an image carrier on which an electrostatic latent image is formed, and a fog generating means for atomizing a developing solution, In the image forming apparatus, which visualizes the electrostatic latent image by adhering the fog generated by the fog generating means to the electrostatic latent image formed on the image carrier at a predetermined developing position, the fog generating means A first charging unit that supplies a charged electric charge to the fog generated or generated, a conveying unit that conveys the charged fog to the developing position, and a charged fog that is being conveyed by the conveying unit. It is characterized by further comprising a second charging means for further supplying a charging charge of the same polarity as the charging charge of the charged mist.

Here, it is preferable that the fog generating means atomize the developing solution by an ultrasonic vibrator.
Further, the first charging means has a charging electrode arranged along the surface of the developer at a position apart from the surface and upward, and a power source for applying a voltage between the charging electrode and the developer. And may be provided.

The second charging means may supply the charged mist with a charged charge having the same polarity as that of the charged mist by corona discharge.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below. FIG. 1 is a schematic diagram showing an embodiment of an image forming apparatus of the present invention. As shown in FIG. 1, in this image forming apparatus, an image carrier 1 carrying an electrostatic latent image 16, a developer container 2 containing a developer 3, and an ultrasonic vibration for atomizing the developer 3 are provided. The child 4 and its oscillation circuit 5, the induction charging electrode 8 and its high-voltage power supply 12 for supplying the charged electric charge to the fog 15 generated by the ultrasonic transducer 4, and the charged fog at the developing position 18.
Blower fans 6 and 9 for conveying to
The corona electrode 7 and its high-voltage power supply 11 that further supply the charged electric charge having the same polarity as the charged electric charge of the mist to the fog carried by 9 toward the developing position 18 and the developing electrode 17 and its high-voltage power supply 13 are provided. There is.

Next, the operation of this image forming apparatus will be described. The ultrasonic oscillator 4 arranged at the bottom of the developing solution 3 contained in the developing container 2 is vibrated by using the oscillation circuit 5, so that the fog 15 is generated from the surface of the developing solution 3.
An induction charging electrode 8 is installed above the liquid surface of the developer 3 with a predetermined distance from the liquid surface, the induction charging electrode 8 is connected to a high voltage power source 12, and the developer 3 is grounded. ,
The fog 15 is charged by the induction charging electrode 8 at the same time as it is generated. In order to provide the fog 15 with an appropriate charge and not to generate a charge of the opposite polarity, the dielectric charging electrode 8 has a voltage within the range of 100V to 2kV, preferably 500V.
A voltage within the range of ˜1 kV is applied. In this embodiment, since the induction charging electrode 8 is positively biased, a negative charge is induced on the liquid surface to generate the fog 1
5 has a negative polarity. This induction charging electrode 8
As a result, a negative electric charge is induced in each droplet of the fog 15, and a Coulomb repulsive force acts between the droplets of the fog 15 so that the droplets combine with each other while being transported in the developing container 2. However, coarsening is prevented. Therefore, each droplet of the fog 15 after the induction charging is conveyed to the next portion with the particle size distribution at the time of fog generation shown by the curve A in FIG.

The fog 15 is indicated by an arrow B by the blower fans 6 and 9.
Direction and arrow C direction. The blower fan 9 also plays a role of transporting the mist 15 generated from the surface of the developing solution 3 to the upper part of the developing container 2 without adhering to the induction charging electrode 8. The fog 15 charged by the induction charging electrode 8 is at the developing position 18
An opening 19 is provided on the wall surface of the developing container 2 on the front side of the corona electrode 7, and the corona electrode 7 is arranged in the opening 19. The corona electrode 7 is connected to the high voltage power supply 11. Further, a grounded counter electrode 10 is attached to a wall surface of the developing container 2 facing the corona electrode 7. The polarity of the corona electrode 7 is the same as the charged electric charge of the fog 15, that is, the negative polarity. Negative ion wind is sent from the corona electrode 7 to the counter electrode 10,
The electric charge of the fog 15 having a negative electric charge, which has been conveyed between the opening 19 and the counter electrode 10, is further increased to the negative side. However, in general, the number of charges that a droplet can have has an upper limit value called the Rayleigh limit. This Rayleigh limit is said to be proportional to the 1.5th power of the diameter of the droplet. When the number of charges of the droplet exceeds the Rayleigh limit, the repulsive force between the charges exceeds the limit of surface tension, and therefore, there are multiple droplets. (See reference: "Aerosol Technology", published by Inoue Shoin, p.290-p.291).

When an excessive electric charge exceeding the Rayleigh limit is supplied to the fog 15 by the corona electrode 7, the droplets of the fog 15 become fine, and the particle size distribution of the fog 15 changes from curve A to curve C in FIG. Shift to the smaller diameter side. Since the fine droplets after splitting also have the same electric charge as each other, and the corona electrode 7 is arranged at a position close to the developing position 18, the fine droplets can combine with each other. The sex is low. Here, the electric potential of the corona electrode 7 is set to a voltage equal to or higher than the corona discharge starting voltage determined by the distance between the corona electrode 7 and the counter electrode 10.

The mist 15 which has been divided into fine droplets by the corona electrode 7 is carried by the air flow and further conveyed to the developing position 1.
Reach 8. The developing position 18 and the corona electrode 7 should be as close as possible to each other in order to prevent the fog 15 that has become fine droplets from becoming coarse again. At the developing position 18, a developing electrode 17 is arranged facing the image carrier 1. The developing electrode 17 is connected to the high voltage power supply 13. The surface of the developing electrode 17 is improved in maintainability by a water repellent treatment. By coating the surface of the developing electrode 17 with a water repellent Teflon material or the like, the maintainability can be further improved.

Since the developing method in the embodiment of FIG. 1 is reversal developing and the electrostatic latent image 16 on the image carrier 1 is negatively charged, the potential of the developing electrode 17 is also set to negative and the image is The fog 15 adheres to the background portion of the carrier 1 on which the electrostatic latent image 16 is not present, and the developed image 14 is formed. The fog 15 that has not adhered to the image carrier 1 at the developing position is sucked in the direction of arrow C and recirculated.

The potential of the developing electrode 17 is set to the electrostatic latent image 16
By making the potential higher than the electric potential of, a good image without fog can be obtained. The situation will be described with reference to FIG. FIG. 2 is a graph showing the relationship between the potential of the image carrier and the potential of the developing electrode. As shown in FIG. 2, the developing electrode potential is set to a potential closer to the background portion potential on the image bearing member than the potential of the electrostatic latent image portion on the image bearing member to make a sufficient developing electric field and Since the cleaning bias is the difference from the background potential, a good image without fog can be obtained.

Further, by applying a voltage in which an AC voltage is superimposed on a DC voltage to the developing electrode 17, the developing efficiency can be increased. The frequency of the alternating current component to be superimposed at this time is in the range of 0.5 to 10 kHz, preferably 0.8.
The range of 0.5 to 2.5 kHz is preferable, and the peak voltage Vp-p is in the range of 0.5 to 5 kV, preferably 1 to 2 kV.

Next, an embodiment using the image forming apparatus shown in FIG. 1 will be described.

[0023]

EXAMPLE A phthalocyanine-based organic photoconductor was used as the image bearing member 1, which was charged to -650V, and then an electrostatic latent image was formed by a laser optical system (not shown). The potential of the image portion was -200V. Met. As the developer 3,
An ink for ink jet containing water as a main component (viscosity at 25 ° C .: 2 mPa · s) was used. The electric potential of the induction charging electrode 8 was set to + 500V, and the fog 15 was charged negatively. The fog 15 was circulated in the arrow B direction and the arrow C direction by the blower fan 9 and the blower fan 6. Corona electrode 7
And the potential of the developing electrode 17 is -500 kV.
When the electrostatic latent image 16 on the image carrier 1 is visualized as V and the developed image 14 is pressure-transferred onto the recording sheet by a transfer device (not shown), the resolution is higher than that when the corona electrode 7 is floated. A high and good image could be obtained.

As described above, in the image forming apparatus of this embodiment, the atomized droplets of the developing solution are used as the induction charging electrodes 8.
After being charged by induction, the corona electrode 7 supplies an excessive electric charge immediately before the developing position to make the liquid droplets fine, and the fine liquid droplets perform development, so that a high-resolution image can be obtained. You can In the above embodiment, the ultrasonic transducer 4 and the oscillation circuit 5 constitute the fog generating means according to the present invention, but the fog generating means is limited to the method using the ultrasonic transducer. Instead, a method using heat, pressure, or electric discharge can be adopted. However, it is preferable to use the fog generating means by the ultrasonic vibrator because it is small and can generate the fog stably.

The induction charging electrode 8 and the high voltage power source 12 constitute the first charging means in the present invention.
The first charging means is not limited to the flat plate-shaped induction charging electrode 8 as shown in FIG.
The electrodes may have any shape such as a grid electrode or a ring electrode. Alternatively, an electrode in which these shapes are combined may be used in order to further improve the charge application efficiency.
Further, the first charging unit may not be an induction charging type, but may be a type in which a corona discharge device is used to charge the fog from the outside, but as shown in the above embodiment, fog generation is performed. At the same time, the method of inductively charging the mist is preferable because the charging device can be simplified, and moreover, as will be described later, the droplets of the mist 15 are less likely to be combined and coarsened.

Although the blower fans 6 and 9 constitute the conveying means in the present invention, the conveying means is not limited to the blowing fan and any conveying means may be used. However, it is necessary to select a transportation means that does not coarsen the fog droplets. Further, the corona electrode 7 and the high-voltage power supply 11 compose the second charging means in the present invention, but the second charging means is not limited to only the corona electrode, and the charged electric charge of fog and Any charging means can be used as long as it is a charging means capable of further increasing the charges of the same polarity.

In the embodiment described above, the fog 15
However, if the polarities of the high voltage power source 12 and the high voltage power source 11 are reversed, the fog can be positively charged for development. Further, the developing method is not limited to the reversal developing, and the normal developing can be performed by changing the polarity of the electrostatic latent image 16 and the potential of the developing electrode 17 and the charging polarity of the fog 15.

As the solvent of the developing solution, an organic solvent such as glycol ether or isoparaffin may be used, but water is preferably used in consideration of safety.
As the colorant, a known pigment or dye, or a toner composed of a polymer resin and a pigment is used. Further, a moisturizing agent, an antifungal agent, a surfactant for improving dispersibility and fixing property to paper, a water-soluble polymer and the like are appropriately used as necessary. Among various physical properties of the developing solution, the viscosity is particularly important. If the viscosity of the developer is too high, atomization will be difficult. Specifically, it is desirable that the viscosity is in the range of 0.5 to 100 mPa · s, preferably 1 to 10 mPa · s.

[0029]

As described above, according to the image forming apparatus of the present invention, after the electric charge is applied to the mist-like developing solution by the first charging means, the second charging means causes an excess of the same polarity. By supplying electric charges, the fog droplets are further miniaturized, and the fine droplets are attached to the electrostatic latent image for development, so that a high-resolution image can be obtained.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing an embodiment of an image forming apparatus of the present invention.

FIG. 2 is a graph showing the relationship between the potential of the image carrier and the potential of the developing electrode.

FIG. 3 is a schematic diagram of a mist developing method of a first conventional example.

FIG. 4 is a graph showing a particle size distribution of the mist immediately after the mist is generated and a change in the particle size of the mist after that.

FIG. 5 is a schematic view of a developing device of a second conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Image carrier 2 Development container 3 Developer 4 Ultrasonic vibrator 5 Oscillation circuit 6 Blower fan 7 Corona electrode 8 Induction charging electrode 9 Blower fan 10 Counter electrode 11, 12, 13 High voltage power supply 14 Developed image 15 Fog 16 Electrostatic latent Image 17 Development electrode 18 Development position 19 Opening

Claims (4)

[Claims] 1. An image bearing member on which an electrostatic latent image is formed, and a fog generating means for atomizing a developing solution, wherein the fog generated by the fog generating means is carried at the predetermined developing position. An image forming apparatus which visualizes an electrostatic latent image by adhering it to an electrostatic latent image formed on a body, the first fog being generated by the fog generating means or supplying a charging charge to the generated fog. Charging means, a carrying means for carrying the charged fog to the developing position, and a charged fog having the same polarity as the charged electric charge of the charged fog, to the charged fog being conveyed by the carrying means. An image forming apparatus, comprising: 2. The image forming apparatus according to claim 1, wherein the fog generating means atomizes the developing solution with an ultrasonic vibrator. 3. The first charging means applies a voltage between a charging electrode disposed at a position along the surface of the developing solution and apart from the surface above the developing solution, and between the charging electrode and the developing solution. The image forming apparatus according to claim 1, further comprising a power supply for applying the voltage. 4. The second charging unit supplies the charged mist with a charged charge having the same polarity as the charged charge of the charged mist by corona discharge. Image forming device.