JP2000221792A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To achieve miniaturization, simplification, and energy saving in a power source device and a drive circuit system which are used for electrifier for electrifying a latent-image carrier. SOLUTION: This image forming device forms an image by causing ink droplets 54 to fly according to an electrostatic latent image on a photoreceptor drum 12 from conductive ink held by an ink carrying roller 30, and by attaching the ink droplets 54 to paper indirectly. In the case, a large number of projections 40 are formed on the conductive surface of the ink carrying roller 30. A specific voltage that is different in polarity from the potential of the electrostatic latent image is applied to the projections 40, and also an ink thin layer 36 is spread over the ink carrying roller 30 so that its thickness is greater than the height of the projections 40.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of flying ink from a thin conductive ink layer held on an ink carrier in accordance with a recording voltage applied to an electrostatic latent image on a latent image carrier or a recording electrode. The present invention relates to an image forming apparatus that forms an image by indirectly or directly attaching the ink to a recording medium.

[0002]

2. Description of the Related Art Conventionally, for example, in JP-A-6-295131, a conductive ink droplet flying from an ink carrier is attached to an electrostatic latent image written on a latent image carrier,
There has been proposed an image forming apparatus that transfers an ink image developed as described above to a recording medium such as paper to form an image.

In this type of image forming apparatus, the flying force of a conductive ink droplet is controlled by an electric field formed by a difference between the charge of the electrostatic latent image and the charge induced and injected into the conductive ink on the ink carrier. It is obtained by the Coulomb force acting on the hydrophilic ink. 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 relates to a method for forming an electrostatic latent image or a recording electrode on a latent image carrier from a thin layer of conductive ink held on an ink carrier. In an image forming apparatus that forms an image by causing ink to fly in accordance with an applied recording voltage and indirectly or directly attaching the ink to a recording medium, a large number of protrusions are formed on the conductive surface of the ink carrier. And applying a predetermined voltage of a polarity different from the potential of the electrostatic latent image or the recording voltage to these protrusions, and applying a thin ink layer on the ink carrier to a thickness greater than the height of the protrusions. It is characterized by the following.

In the image forming apparatus of the present invention, it is preferable that h2 + 5 μm ≦ h1 ≦ h2 + 100 μm, where h1 is the thickness of the thin ink layer on the ink carrier and h2 is the height of the protrusion.

[0007]

According to the image forming apparatus of the present invention, a predetermined voltage having a polarity different from the potential of the electrostatic latent image or the recording voltage is applied to the projection on the surface of the ink carrier. In this state, when the ink carrier faces, for example, an electrostatic latent image on the latent image carrier, electrostatic induction induces intensively a charge having a polarity opposite to the latent image potential at the tip of each projection, and this charge Is injected into a thin layer of conductive ink on each protrusion. An electric field is formed between the electric charge of the conductive ink thin layer thus injected and the electric charge of the electrostatic latent image, and an electric field is formed between the ink around each protrusion by the action of the electric field. A Coulomb force acts in the direction to move, whereby the ink rises on the protrusions to form a meniscus.

When the meniscus is formed, the thin ink layer is formed to be thicker than the height of the protrusion, so that the thin ink layer is formed thinner than the height of the protrusion. The ink in the vicinity is easily moved so as to swell on the protrusion, thereby forming a relatively large meniscus on the protrusion. The injected charges concentrate on the tip of the meniscus, which further increases the Coulomb force acting on the tip. As a result, the tip of the large meniscus is closer to the latent image carrier, and a stronger Coulomb force acts on the tip to separate relatively large ink droplets.
To fly. The flying ink droplets once adhere to the electrostatic latent image to form an ink image and are then transferred to a recording medium to form an image, or the ink droplets directly adhere to the recording medium to form an image. .

As described above, according to the image forming apparatus of the present invention, a relatively large meniscus is formed in the ink thin layer on each of the projections facing the electrostatic latent image or the recording electrode.
Even if the electric field strength is not so strong, the ink can easily fly. As a result, even if the potential of the electrostatic latent image or the recording voltage is lowered, stable ink flying can be realized. Therefore, the power supply device for charging the latent image carrier or applying the recording voltage and the drive circuit system are reduced in size and simplified. Power can be saved, and the cost can be reduced.

Further, since the potential of the electrostatic latent image or the recording voltage can be reduced, the electrical influence on other elements such as discharge can be reduced, so that the entire ink image forming system becomes stable. Extremely high durability and reliability against environmental changes can be achieved.

[0011]

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 a corona charger 14 for uniformly charging the surface of the photosensitive drum 12 and exposing the uniformly charged surface of the photosensitive drum 12 to erase the charge on the exposed portion, thereby leaving the charge on the non-exposed portion to form an electrostatic latent image. Exposure device 16 for writing and ink developing device 18 for developing the written electrostatic latent image with conductive ink
A transfer roller 20 for transferring the developed ink image onto a sheet S as a recording medium; a cleaning device 22 for collecting ink remaining on the surface of the photosensitive drum 12 after the transfer; A static eliminator 24 for erasing is provided.

The method of writing an electrostatic latent image is not limited to an exposure method, but may be any other method, such as an ion flow method, a pyroelectric method, or a method in which a ferroelectric is polarized by heat or electricity. An electrostatic latent image may be written. Also, a large number of fine electrodes may be formed on the entire surface of the drum. These techniques are known. Further, 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 has a casing 26 having an opening facing the photosensitive drum 12. A conductive ink 28 is accommodated inside the casing 26. An ink carrying roller 30 is arranged at an opening of the casing 26 so as to be rotatable in the direction of arrow b. A seal roller 3 is provided between the upper edge of the casing 26 and the ink carrying roller 30.
2 is provided to prevent leakage and drying of the ink. Further, a regulating blade 34 is provided at the upper edge of the casing 26 opposite to the seal roller 32 with respect to the ink carrying roller 30 so as to adjust the gap between the ink carrying roller 30 and the ink carrying roller 30. Thus, when the ink carrying roller 30 rotates, the conductive ink thin layer 36 is formed to cover the surface of the ink carrying roller 30 facing the photosensitive drum 12. The thin ink layer 36 can be regulated to a predetermined thickness by adjusting the regulating blade 34.

The ink carrying roller 30 has at least a surface layer made of a conductive material, and has a large number of fine projections 40 formed on the surface thereof. These projections 40 may be formed by cutting, etching, electroforming, or the like on the surface of the metal roller, or by forming the projections on a resin roller and then sputtering the entire surface with metal. It may be covered with a thin film. Further, the ink carrying roller 30 is electrically connected to an offset power supply 38 so that the ink carrying roller 3
A polarity different from the latent image potential, for example, a positive predetermined voltage, is applied to each of the projections 40 on the surface of the zero.
The predetermined voltage may be used as the ground voltage by directly grounding the ink carrying roller 30.

FIG. 3A is a partially enlarged sectional view of the surface when the ink carrying roller 30 is cut in the axial direction. The columnar or rectangular parallelepiped projections 40 have a rectangular cross section and are arranged at an equal pitch p, and are arranged in a matrix when viewed as a whole surface of the ink carrying roller 30. The pitch p of the protrusions 40 is 20 to 1
It is preferably about 00 μm. Further, the ratio a: b of the width a of the protrusion 40 to the width b of the recess 42 does not necessarily need to be 1: 1, but may be in the range of a: b = 7: 3 to 3: 7.
In this case, if the ratio of the width a of the projection 40 is smaller than the above range, it is difficult to manufacture, and if it is larger, the resolution is reduced. Further, the height h2 of the protrusion 40 is 1
It is preferably about 0 to 100 μm. Its height h2 is 10μ
If it is smaller than m, the injection of charges into the ink thin layer 36 due to electrostatic induction is unlikely to be induced intensively, so that the latent image potential required for flying the ink becomes too high. Is difficult.

The cross-sectional shape of the projection 40 is not limited to a rectangle, but may be other shapes, for example, as shown in FIGS.
As shown in (d), the shape may be substantially semicircular, triangular, trapezoidal, or the like. When the cross-sectional shape of the protrusion 40 is rectangular, triangular, trapezoidal, or the like, the end face or side surface of the protrusion 40 may be rounded. Further, the ink carrying roller 3
4A, the projections 40 are arranged in a matrix as shown in FIG. 4A, but the projections 40 may be arranged in a staggered manner as shown in FIG. It may be arranged in a fixed pattern other than the above.

Next, the image forming apparatus 10 having the above configuration
Will be described. As shown in FIG. 5A, the ink 28 is applied on the ink carrying roller 30 while being regulated to a predetermined thickness h1 by the regulating blade 34, and an ink thin layer 36 having a flat surface is formed. The thickness h1 of the thin ink layer 36 is formed to be greater than the height h2 of the projection 40, and h2 + 5 μm ≦ h1 ≦ h2 + 10
It is particularly preferable to meet the condition of 0 μm. The reason will be described later. When the viscosity of the ink is low, it is preferable that the ink be regulated by the regulation blade 34 having high rigidity. However, as shown in FIG. 5B, the elastic blade 34 made of rubber or the like is used.
a may be deflected and regulated.

As shown in FIG. 6, a predetermined positive voltage is applied from an offset power supply 38 to each projection 40 on the ink carrying roller 30. In this state, when each of the protrusions 40 opposes the electrostatic latent image portion on the photosensitive drum 12, the tip of each of the protrusions 40 located at the latent image opposing portion has a polarity opposite to the latent image potential due to electrostatic induction. Is induced, and this positive charge is injected into the conductive ink thin layer 36 covering each projection 40. 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 the projections 40 by the action of the electric field. A Coulomb force in the direction toward the electrostatic latent image portion acts on the upper ink, whereby the ink on each projection 40 rises and a meniscus 52 is formed.

When the meniscus 52 is formed in this way, as shown in FIG.
When 1 is formed thinner than the height h2 of the protrusion 40, the ink in the vicinity of the protrusion 40 can move only along the protrusion 40 as shown by an arrow in the drawing, and the formed meniscus 52 It will be relatively small. Therefore, since the tip of the small meniscus 52 is located far from the photosensitive drum 12, that is, at a position where the Coulomb force is weak, a relatively large electric field strength is required to separate and fly the ink droplet 54 from the meniscus 52. The flying ink droplet 54 is also small. On the other hand, in the present embodiment, the thickness h1 of the ink thin layer 36 is
2, the ink near the protrusion 40 moves not only along the protrusion 40 as shown in FIG. 7B but also in the direction indicated by arrows 44 and 46.
The surface layer 6 also moves so as to swell over the protrusion 40, whereby a relatively large meniscus 52 is formed on the protrusion 40. As a result, a large meniscus 5
Since the leading end of 2 is closer to the photosensitive drum 12, a stronger Coulomb force acts on the leading end, and a relatively large ink droplet 54 separates and flies. From this, it can be said that when the thickness h1 of the thin ink layer is larger than the height h2 of the projections 40, the ink can be efficiently ejected even at a low electric field strength.

Here, the thickness h1 of the thin ink layer 36 is preferably formed to be about 5 to 100 μm thicker than the height h2 of the projection 40. If the thickness is smaller than 5 μm, the ink movement in the surface layer portion of the ink thin layer 36 in the vicinity of the protrusion 40 is not performed smoothly, and a large meniscus 52 cannot be formed. On the other hand, if it is larger than 100 μm, the meniscus 52 becomes too large, the flying ink droplets become large, and the resolution is reduced. This is because an image is degraded due to the occurrence of crosstalk caused by ink droplets flying or flying from the adjacent projections 40 affecting each other.

Ink droplets 54 flying from meniscus 52
Adheres to the electrostatic latent image and develops 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, in the image forming apparatus 10 of the present embodiment, the ink droplets flying from the ink carrying roller 30 are
Ink droplets from the ink carrying roller 30 are indirectly adhered to the paper S such that the ink image is transferred to the paper S after the ink image is formed by being once adhered to the electrostatic latent image on the paper 2. The formation is performed.

As described above, according to the image forming apparatus 10 of the present embodiment, each of the projections 40 facing the electrostatic latent image
Since the relatively large meniscus 52 is formed on the upper ink thin layer 36, the ink can easily fly even if the electric field intensity is not so strong. As a result, stable ink flying can be realized even when the potential of the electrostatic latent image is lowered, and the photosensitive drum 1
The size and simplification of the power supply and the drive circuit system for the charging device 14 for charging the battery 2 and the power saving can be achieved, and the cost can be reduced.

Further, since the potential of the electrostatic latent image can be reduced, other elements (for example,
0, the casing 26 of the ink developing device 18, the regulating blade 34, etc.), it is possible to reduce the electrical influence such as electric discharge, so that the whole ink imaging system becomes stable, and the durability and reliability against environmental changes are improved. Sex can be very high.

Further, since the projections 40 on the ink carrying roller 30 are arranged in a matrix, an image including a linear portion can be formed clearly.

Here, an ink flying experiment was performed using the image forming apparatus 10 shown in FIG. The conditions at that time were as follows. An organic 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 carrying roller 30 is 1
00 mm, the peripheral speed is 200 mm / sec, the pitch p of the projections 40 is 50 μm, and the width ratio a between the projections 40 and the recesses 42 is a:
b was set to 1: 1, the height h2 of the projection 40 was set to 20 μm, and the thickness h1 of the thin ink layer 36 was set to 30 μm. Further, a voltage of 1.5 kV was applied to each projection 40 by the offset power supply 38. Then, the developing gap g was set to 500 μm. Further, the composition of the conductive ink used was 10 wt% of one of carbon black (black), chromophthal yellow (yellow), quinacridone magenta (magenta) and copper phthalocyanine blue (cyan).
%, Water was 66.99 wt% as a solvent, 0.01 wt% of a fluorinated surfactant was used as a surfactant, polyethylene glycol was 21 wt% as a viscosity modifier, and styrene acrylate was 2 wt% as a dispersant. Experiments under these conditions showed that the ink flew well against the electrostatic latent image.

On the other hand, the thickness h1 of the thin ink layer 36 on the ink carrying roller 30 is changed to the height h2 (20
When the other conditions were the same as in the above experiment, the ink did not fly. As a result, the thickness h1 of the thin ink layer 36 is reduced to the height h2 of the protrusion 40.
It was confirmed that stable ink flying was possible by forming the layer thicker.

Next, an image forming apparatus 60 according to another embodiment of the present invention will be described with reference to FIGS. In the image forming apparatus 10 described above, an image is formed by indirectly adhering the ink droplets flying from the ink carrying roller 30 to the paper S. However, the image forming apparatus 60 according to the present embodiment uses the ink droplets flying from the ink carrying roller 30. Is attached directly to the sheet S to form an image. For this purpose, in the image forming apparatus 60, as shown in FIG. 8, the sheet S is transported between the opposing photosensitive drum 12 and the ink developing device 18 while contacting the photosensitive drum 12. . The other configuration is almost the same as that of the image forming apparatus 10, but the ink does not adhere to the photosensitive drum 12, so that the cleaning device 22 can be omitted. Further, in order to improve the adhesion of the sheet S to the photosensitive drum 12, a pair of adhesion rollers 62 and 64 may be provided as needed.

The ink flying principle in the image forming apparatus 60 is the same as that described above with reference to FIGS. As shown in FIG. 9, the ink droplet 54 flies from a position corresponding to the protrusion 40 on the ink carrying roller 30 toward the latent image portion of the photosensitive drum 12 and directly adheres to the sheet S to form an image. Is done. According to the image forming apparatus 60 of the present embodiment, the same effects as those of the image forming apparatus 10 can be obtained.

Next, an image forming apparatus 70 according to still another embodiment of the present invention will be described with reference to FIGS. In the image forming apparatus 70, the recording electrode 72 is connected to the ink carrying roller 30 of the ink developing device 18 via the paper S.
Facing. The sheet S is transported in the direction of the arrow while contacting the lower part of the recording electrode 72. As shown in FIG. 11, the recording electrodes 72 are composed of a large number of individual electrodes 74 arranged at equal intervals along a direction perpendicular to the paper transport direction, and a protective insulating portion 76 covering the periphery of the individual electrodes 74. Is done. The individual electrodes 74 are arranged at a density corresponding to the pixel density of an image, and each end is exposed below the recording electrode 72.
Each of the individual electrodes 74 is connected to a power supply 80 via a switch 78. The switch 78 is selectively turned on in accordance with the image information, so that a negative polarity recording voltage is applied to the individual electrode 74 at the position where the ink is to fly and adhere. Although the configuration of the recording electrode 72 is illustrated in FIG. 11, the recording electrode 72 is not limited to this mode, and a multi-stylus electrode of another mode may be used.

The ink flying principle in the image forming apparatus 70 is the same as that in the image forming apparatus 60. However, the photosensitive drum 12 is replaced by the recording electrode 72,
The latent image portion having a negative charge is merely replaced with the individual electrode 74 to which a negative polarity recording voltage is applied. When a recording voltage is applied to the individual electrode 74, an ink droplet flies from a position corresponding to the protrusion 40 of the ink carrying roller 30 opposed thereto, and the ink droplet directly adheres to the sheet S to form an image. You. As described above, also in the image forming apparatus 70 of the present embodiment, since the ink developing device 18 is used, the same effect as that of the image forming apparatus 10 can be obtained.

Each of the image forming apparatuses 1 described above
In FIGS. 0, 60 and 70, the roller 30 is used as an ink carrier, but as shown in FIG. 12, an ink carrying belt 48 having the same surface shape as the ink carrying roller 30 may be used in the ink developing device 18a. Good.

In the above description, the polarity of the electrostatic latent image or the recording voltage is described as minus, but the present invention is also applicable to the case where the polarity of the electrostatic latent image or the recording voltage is plus. Can be.

[Brief description of the drawings]

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

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

FIGS. 3A to 3D are partially enlarged cross-sectional views of a protrusion on the surface of an ink carrying roller.

FIGS. 4A and 4B are partially enlarged plan views showing an arrangement pattern of protrusions on an ink carrying roller.

FIG. 5 (a) shows a regulation blade having a large rigidity,
FIG. 3B is a partially enlarged cross-sectional view showing a state in which a thin ink layer is formed so as to cover each protrusion on the ink carrying roller while being regulated by elastic blades.

FIG. 6 is a partially enlarged view for explaining the principle of ink flying from a position corresponding to a protrusion on the ink carrying roller.

FIG. 7 is a partially enlarged view showing a state in which a meniscus is formed on a protrusion and ink flies, and (a) shows a case where the thickness of the ink thin layer is formed smaller than the height of the protrusion; b) shows a case where the thin ink layer is formed to be thicker than the height of the protrusion.

FIG. 8 is a schematic configuration diagram of an image forming apparatus according to another embodiment of the present invention.

FIG. 9 is a partially enlarged view showing a state in which ink flying from a position corresponding to a protrusion on the ink carrying roller is directly attached to a sheet.

FIG. 10 is a schematic configuration diagram of an image forming apparatus according to still another embodiment of the present invention.

FIG. 11 is a partially enlarged view of a recording electrode.

FIG. 12 is a schematic configuration diagram of an image forming apparatus showing a modified example using a belt as an ink carrier.

DESCRIPTION OF REFERENCE NUMERALS 10: image forming apparatus, 12: photosensitive drum (latent image carrier), 30: ink carrying roller (ink carrier), 36
... a thin conductive ink layer, 40 ... a protrusion, 42 ... a recess 52 ...
Meniscus, 54... Ink drops.

Claims (2)

[Claims] An ink is ejected from a thin layer of conductive ink held on an ink carrier in accordance with an electrostatic latent image on a latent image carrier or a recording voltage applied to a recording electrode, and the ink is recorded. In an image forming apparatus for forming an image by indirectly or directly adhering to a medium, a large number of projections are formed on a conductive surface of the ink carrier, and the electrostatic latent image or the recording voltage of the recording voltage is formed on these projections. An image forming apparatus, wherein a predetermined voltage having a polarity different from a potential is applied, and a thin ink layer on the ink carrier is applied thicker than the height of the protrusion. 2. The apparatus according to claim 1, wherein h2 + 5 μm ≦ h1 ≦ h2 + 100 μm, where h1 is the thickness of the thin ink layer on the ink carrier and h2 is the height of the protrusion. Image forming device.