JPH11348338A - Image formation apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make compact, simple and power-saving a power source device for a charging apparatus which charges a latent image hold body. SOLUTION: In this image formation apparatus, an ink hold body 30 is disposed near a latent image hold body 12. Ink drops 54 are flown, adhered from a conductive ink thin layer 36 coating a front face of the ink hold body 30 to an electrostatic latent image written on the latent image hold body 12, thereby developing the latent image. The developed ink image is transferred to a recording medium. A plurality of dot-like conductive parts 46 are formed and arranged on the front face of the ink hold body 30, and moreover a part other than the conductive parts 46 is made an insulating part 48. A predetermined voltage, e.g. a ground voltage of a polarity different from that of the latent image is impressed to a common electrode 42 connected to each conductive part 46.

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 for forming an image by attaching ink droplets to an electrostatic latent image, developing the electrostatic latent image, and transferring the developed image onto paper.

[0002]

2. Description of the Related Art Conventionally, for example, in JP-A-6-295131, ink droplets fly from an ink carrier onto an electrostatic latent image written on a latent image carrier and adhere to the electrostatic latent image. An image forming apparatus has been proposed which transfers an ink image to a recording medium such as paper to form an image.

[0003] In this type of image forming apparatus, the flying force of an ink droplet has a Coulomb force due to an electric field formed by a difference between the charge of the electrostatic latent image and the charge induced and injected into the ink on the ink carrier. It is obtained by acting. Therefore, as one method for realizing stable ink flying by increasing the Coulomb force, a method of increasing the electric potential of the electrostatic latent image to increase the electric field strength between the latent image carrier and the ink carrier is known. is there.

[0004]

However, in order to increase the potential of the electrostatic latent image, it is necessary to increase the charging potential on the surface of the latent image carrier, and for this purpose, the voltage of the charging device must be increased. Therefore, the size of the power supply device is inevitably increased.

[0005]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention disposes an ink carrier close to a latent image carrier and writes an electrostatic latent image written on the latent image carrier. An image forming apparatus for flying an ink droplet from a thin conductive ink layer covering the surface of the ink carrier onto an image, attaching and developing the ink droplet, and transferring the developed ink image to a recording medium, comprising: A plurality of point-shaped conductive portions are arrayed and formed on the surface of the substrate, and portions other than the conductive portions are set as insulating portions, and a predetermined voltage having a polarity different from the latent image potential is applied to a common electrode that is connected to the conductive portions. It was done.

In the image forming apparatus of the present invention, the predetermined voltage may be a ground voltage. Further, the predetermined voltage may be an AC voltage whose peak voltage has a polarity opposite to that of the latent image potential. Further, the plurality of point-like conductive portions may be arranged in a matrix.

[0007]

In the image forming apparatus of the present invention, a predetermined voltage having a polarity different from the latent image potential, for example, a ground voltage is applied to each conductive portion on the surface of the ink carrier via a common electrode. In this state, when each of the conductive portions opposes the electrostatic latent image, a charge having a polarity opposite to the potential of the latent image is induced in each conductive portion by electrostatic induction, and this charge covers the conductive portions. Injected into a thin layer of water-based ink. An electric field is formed between the charge of the conductive ink thin layer thus injected and the charge of the electrostatic latent image on the latent image carrier, and the action of the electric field causes the ink on each conductive portion to be formed. The Coulomb force in the direction toward the electrostatic latent image acts on the ink, and the ink rises to form a meniscus. Then, the Coulomb force in which the injected charges concentrate on the tip of the meniscus is further increased, and as a result, the ink droplet separates from the thin ink layer and flies. The flying ink drops adhere to the electrostatic latent image and develop it, whereby an ink image is formed on the latent image carrier. Thereafter, the ink image is transferred to a recording medium such as paper to form an image.

As described above, according to the image forming apparatus of the present invention, the meniscus is formed in the thin ink layer on each conductive portion facing the electrostatic latent image, so that the ink can fly even if the electric field intensity is not so strong. Easier to do. Thereby, even if the potential of the electrostatic latent image is lowered, stable ink flying can be realized, so that the power supply device for charging the latent image carrier can be downsized,
Simplification and power saving can be achieved.

Further, since the potential of the electrostatic latent image can be reduced, the electrical influence on other elements such as electric discharge can be reduced, so that the ink imaging system as a whole becomes stable, and its durability and durability can be improved. Very high reliability against environmental changes.

Furthermore, if the voltage applied to the common electrode is an AC voltage whose peak voltage is opposite to the potential of the latent image, the induced charge induced by the change in the voltage also changes. Because the Coulomb force changes with this,
The meniscus formed in the thin ink layer vibrates in accordance with the fluctuation of the voltage, whereby the ink is more likely to fly, and as a result, the latent image potential can be further reduced.

Further, if a plurality of dot-shaped conductive portions on the ink carrier are arranged in a matrix, an image including a linear portion in particular can be clearly formed.

[0012]

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a schematic configuration diagram of an image forming apparatus 10 according to an embodiment of the present invention. The image forming apparatus 10 includes a photosensitive drum 12 as a latent image carrier. The photosensitive drum 12 is driven to rotate in the direction of arrow a. Around the photosensitive drum 12, the photosensitive drum 1 is sequentially arranged along the rotation direction.
And an electrostatic latent image is written by exposing the uniformly charged surface of the photosensitive drum 12 to erase the charge of the exposed portion, thereby leaving the charge of the non-exposed portion. An exposure device 16, an ink developing device 18 for developing the written electrostatic latent image with conductive ink,
A transfer roller 20 for transferring the developed ink image to a sheet S serving as a recording medium;
And a static eliminator 24 for erasing the electrostatic latent image.

The method of writing the electrostatic latent image is not limited to the exposure method, and the electrostatic latent image may be written by another method, for example, an ion flow method or a pyroelectric method. Although not shown, an ink fixing device for drying and fixing the ink image transferred to the sheet S may be provided as necessary.

As shown in FIG. 2, the ink developing device 18 includes a casing 26 having an opening facing the photosensitive drum 12. A conductive ink 28 is accommodated inside the casing 26. An ink carrier roller 30 is disposed at an opening of the casing 26 so as to be rotatable in the direction of arrow b. A seal roller 32 is provided between the upper edge of the casing 26 and the ink carrier roller 30, thereby preventing leakage and drying of the ink. Further, an ink carrier roller 3 is provided on the upper edge of the casing 27 on the side opposite to the seal roller 32.
Regulating blade 3 arranged with a small gap between the regulating blade 3
4 are provided. Thus, when the ink carrier roller 30 rotates, the conductive ink thin layer 36 covers the surface of the ink carrier roller 30 facing the photosensitive drum 12.
Is formed. This thin ink layer 36 is
4 regulates the thickness to a predetermined value.

As shown in FIG. 3, the ink carrier roller 30 has a metal roller 38 at the center and an insulating layer 40 on the outer periphery. A conductive layer is provided on the outer periphery of the insulating layer 40 and serves as a common electrode 42. On the outer periphery of the common electrode 42, a matrix layer 44 serving as a surface layer is provided. As shown in FIG. 4, a plurality of circular point-like conductive portions 46 are arranged in a matrix on the surface of the matrix layer 44, and portions other than the conductive portions 46 serve as insulating portions 48. As shown in FIG. 5, the conductive portion 48 has a columnar shape, is formed so as to be embedded in the insulating portion 48, and is electrically connected to the common electrode 42 at a lower portion thereof. The above-mentioned point-shaped conductive part 46
Has a diameter of about 30 to 60 μm and a pitch of about 40 to 100
It is preferably about μm. Further, the thickness of the matrix layer 44 is preferably about 50 to 200 μm. Note that the shape of the point-shaped conductive portion 46 is not limited to a circle, but may be another shape, for example, an ellipse, a square, or the like. Also,
In the ink carrier roller 30, the dot-shaped conductive portions 46 are arranged in a matrix, but two rows of dot-shaped conductive portions adjacent in the axial or circumferential direction are slightly shifted from each other, and the dot-shaped conductive portions are arranged in a staggered manner. May be performed.

In the ink carrier roller 30, the dot-shaped conductive portion 46 is formed so as to be embedded in the insulating portion 48. However, as in the ink carrier roller 30a shown in FIGS. It may be formed by printing a silver paste. In this case, the surface of the insulating layer 40 provided on the outer periphery of the metal roller 38 is printed as shown in FIG. In this printing, a ring-shaped common electrode 42a is formed on the outer periphery of the end of the ink carrier roller 30a,
A large number of circular point-shaped conductive portions 46a are formed in a matrix, and each point-shaped conductive portion 46a and the common electrode 42a adjacent to each other in the roller axis direction are connected to each other by a connection line 50, thereby sharing the point-shaped conductive portions 42a. Conduction is made to the electrode 42a.
Also in this case, it is preferable that the diameter of the point-like conductive portion 42a is about 30 to 60 μm and the pitch is about 40 to 100 μm. The width of the connection line 50 is preferably about 5 μm.

Next, the image forming apparatus 10 having the above configuration
Will be described. As shown in FIG. 8, the common electrode 42 of the ink carrier roller 30 is connected to the ground. As a result, a ground voltage, which is a predetermined voltage having a polarity different from the polarity (minus) of the electrostatic latent image, is applied to each point-like conductive portion 46 on the surface of the ink carrier roller 30 via the common electrode 42. In this state, when each of the point-like conductive portions 46 faces the electrostatic latent image portion of the photosensitive drum 12, a charge of a polarity opposite to the latent image potential, that is, a positive charge, is applied to each of the point-like conductive portions 46 by electrostatic induction. Is induced, and this positive charge is injected into the conductive ink thin layer 36 covering each of the dot-shaped conductive portions 46. An electric field is formed between the positive charge of the conductive ink thin layer 36 thus injected and the negative charge of the electrostatic latent image on the photosensitive drum 12 between them, and by the action of this electric field, each point-like conductive material is formed. A Coulomb force in the direction toward the electrostatic latent image portion acts on the ink on the portion 46, whereby the ink of the conductive ink thin layer 36 located on each point-like conductive portion 46 rises to form a meniscus 52. Then, the Coulomb force in which the injected charges concentrate on the tip of the meniscus 52 further increases, and as a result, the ink droplet 54 separates from the conductive ink thin layer 36 and flies. The flying ink droplets 54 adhere to the electrostatic latent image and develop it, whereby an ink image is formed on the photosensitive drum 12. Thereafter, the ink image is transferred to the sheet S to form an image.

As described above, the image forming apparatus 10 of the present embodiment
According to the method, since the meniscus 52 is formed on the thin ink layer 36 on each of the point-like conductive portions 46 facing the electrostatic latent image portion, the ink can easily fly even if the electric field intensity is not so strong. As a result, even if the potential of the electrostatic latent image portion is lowered, stable ink flying can be realized.
The power source of the charging device 14 for charging the battery can be reduced in size and simplified, and power can be saved.

Further, since the potential of the electrostatic latent image portion can be lowered, the photosensitive drum 12 and the ink carrier roller 30,
Electric discharge between the regulating blade 34 and the casing 26 of the ink developing device 18 can be reduced.
As a result, the electrical influence on these other elements can be reduced, so that the ink imaging system as a whole becomes stable, and the durability and reliability against environmental changes can be extremely high.

Further, since the plurality of dot-shaped conductive portions 46 on the ink carrier roller 30 are arranged in a matrix, an image including a linear portion can be formed particularly clearly.

In the image forming apparatus 10, the ground voltage is applied to the common electrode 42 of the ink carrier roller 30. However, the invention is not limited to this, and a DC voltage having a polarity opposite to the latent image potential may be applied. Is also good. However, in this case, since the ink may fly to the non-latent image part depending on the voltage value, it is necessary to set the voltage value to a value that does not cause the ink to fly to the non-latent image part.

On the other hand, in the image forming apparatus 10 shown in FIG.
The common electrode 42 of the ink carrier roller 30 is
, And an AC voltage whose peak voltage is opposite to the latent image potential, that is, positive, is applied to the common electrode 42. In this case, the induced charge induced by the change in the voltage also changes, and the coulomb force changes accordingly, so that the meniscus 52 formed on the thin conductive ink layer 36 vibrates according to the voltage swing. However, this makes it easier for the ink to fly, and as a result, the latent image potential can be further reduced. When the frequency of the AC voltage is set to a value that matches the “pitch and peripheral speed of ink dots (conductive portions)”, image unevenness is reduced and fine line reproducibility is improved. Further, when the AC voltage is synchronized with image printing, image unevenness is further reduced, and a fine line reproducibility image is further improved. In this case, an induced charge is induced in the non-latent image portion of the photosensitive drum 12 by the opposing dot-shaped conductive portion 46, whereby the thin ink layer 36 on the point-shaped conductive portion 46 opposing the non-latent image portion is generated. Although the meniscus 52a is also formed, the non-latent image portion is not charged due to the elimination of the electric charge by exposure by the exposure device 16, so that the ink meniscus 52a
Has a weak Coulomb force, and ink does not fly.

Here, an ink flying experiment was performed using the image forming apparatus shown in FIG. The conditions at that time were as follows. An OPC photosensitive drum is used as the photosensitive drum 12, the charging potential of the photosensitive drum 12 (that is, the potential of the electrostatic latent image) is -300 volts, and the developing speed (that is, the peripheral speed of the photosensitive drum) is 200 mm. / Sec.
The diameter of the ink carrier roller 30 is 10
0 mm, the peripheral speed was 200 mm / sec, the diameter of the point-like conductive portions 46 was 30 μm, and the pitch of the point-like conductive portions 46 was 50 μm. Further, the AC voltage applied to the common electrode 42 had a frequency of 2 kHz and an amplitude of +1.2 kV to +0.3 kV. Then, the developing gap g was set to 500 μm. The composition of the conductive ink used was 10 wt% of carbon black (black), chromophthal yellow (yellow), quinacridone magenta (magenta), or copper phthalocyanine blue (cyan), and water was 86. 99% by weight, 0.01% by weight of a fluorine-based surfactant as a surfactant, 1% by weight of polyethylene glycol as a viscosity modifier, and 2% by weight of styrene acrylate as a dispersant. Experiments under these conditions showed that the ink flew well against the electrostatic latent image.

On the other hand, the condition that the charging potential of the photosensitive drum 12 is -600 V, and that no AC voltage is applied without providing the conductive portion of the ink carrier roller 30, and other conditions are the same as in the above experiment The ink did not fly. Thereby, according to the image forming apparatus of the present embodiment,
It was confirmed that stable ink flying was possible even when the potential of the electrostatic latent image was lowered.

In the above description, the polarity of the electrostatic latent image has been described as minus. On the contrary, the present invention can be applied to the case where the polarity of the electrostatic latent image is plus.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of an image forming apparatus.

FIG. 2 is an enlarged view of an ink developing device.

FIG. 3 is a partially enlarged view of an ink carrier roller.

FIG. 4 is an enlarged view of a portion A in FIG. 3;

FIG. 5 is a sectional view taken along line VV in FIG. 4;

FIG. 6 is a partially enlarged view of a modification of the ink carrier roller.

FIG. 7 is an enlarged view of a portion B in FIG. 6;

FIG. 8 is a partially enlarged view showing a flying state of ink when a ground voltage is applied to a common electrode.

FIG. 9 is a partially enlarged view showing a flying state of ink when an AC voltage is applied to a common electrode.

[Explanation of symbols]

10 image forming apparatus, 12 photosensitive drum (latent image carrier), 30 ink carrier roller (ink carrier), 3
6: conductive ink thin layer, 42: common electrode, 46: point-like conductive part, 48: insulating part. 54 ... Ink drops.

Claims (4)

[Claims] An ink carrier is disposed in proximity to a latent image carrier, and an electrostatic latent image written on the latent image carrier is applied to a conductive ink thin layer covering the surface of the ink carrier. What is claimed is: 1. An image forming apparatus for developing an ink image by flying and attaching ink droplets thereon and transferring the developed ink image to a recording medium, wherein a plurality of dot-shaped conductive portions are arranged and formed on the surface of the ink carrier. An image forming apparatus in which a portion other than the insulating portion is an insulating portion, and a predetermined voltage having a polarity different from a latent image potential is applied to a common electrode that is electrically connected to the conductive portions. 2. The image forming apparatus according to claim 1, wherein said predetermined voltage is a ground voltage. 3. The image forming apparatus according to claim 1, wherein the predetermined voltage is an AC voltage having a peak voltage having a polarity opposite to that of the latent image potential. 4. The image forming apparatus according to claim 1, wherein said plurality of point-like conductive portions are arranged in a matrix.