JP2000238273A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To achieve a small size, simplification and power saving of a power source device for a charging device for charging a photosensitive drum and a driving circuit system. SOLUTION: An image forming apparatus for forming an image by jumping an ink 54 from a conductive ink thin layer 36 formed covering the surface of an ink carrying roller 30 according to an electrostatic latent image on a photosensitive drum 12 so as to adhere the jumped ink 54 onto a paper indirectly, wherein an insulating layer 42 is provided on the surface of the ink carrying layer 30 as well as a large number of minute conductive projection parts 40 are formed with each tip end projecting from the insulating layer 42, and a predetermined voltage having a polarity different from that of the electrostatic latent image is applied onto the projection parts 40 is provided.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming an electrostatic latent image on a latent image carrier or a recording ink applied to a recording electrode from a thin conductive ink layer formed over the surface of the ink carrier. And an image forming apparatus that forms an image by causing the flying ink to adhere to a recording medium indirectly or directly.

[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 problems, the present invention provides a method of forming an electrostatic latent image on a latent image carrier from a thin conductive ink layer formed over the surface of the ink carrier. In an image forming apparatus which forms an image by causing ink to fly in accordance with a recording voltage applied to an electrode and indirectly or directly attaching the flying ink to a recording medium, an insulating layer is provided on the surface of the ink carrier. A large number of minute conductive protrusions, each of which protrudes from the insulating layer, are formed, and a predetermined voltage having a polarity different from the electrostatic latent image or the recording voltage is applied to these protrusions.

In the image forming apparatus of the present invention, it is preferable that the insulating layer has an ink contact angle of about 50 ° or more, and the protrusion has an ink contact angle of about 30 ° or less.

[0007]

According to the image forming apparatus of the present invention, the conductive ink thin layer is formed on the surface of the ink carrier, and the electrostatic latent image or the recording is formed on each protrusion on the surface of the ink carrier. A predetermined voltage having a polarity different from the potential of the voltage is applied. When the ink carrier faces, for example, the latent image carrier in this state, charges having a polarity opposite to the latent image potential are intensively induced at the tip of each protrusion by electrostatic induction, and this charge is applied to each protrusion. Injected into a thin layer of conductive ink. An electric field is formed between the charge of the conductive ink thin layer thus injected and the charge of the latent image carrier due to the difference therebetween. This electric field is not generated between the insulating layer between the projections and the latent image carrier, but is generated intensively between each projection and the latent image carrier. Due to the action of the electric field, a Coulomb force in the direction toward the latent image carrier acts on the ink around each protrusion, whereby the ink rises on the protrusion to form a meniscus. At this time, since the tips of the projections protrude beyond the insulating layer on the surface of the ink carrier, a meniscus is easily formed on the ink layer covering the tips of the projections.

When the thin ink layer on which the meniscus is formed faces the electrostatic latent image on the latent image carrier, the Coulomb force acting on the meniscus is further increased, and the ink droplet separates from the tip of the meniscus. 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, it is easy to form a meniscus on the projection by projecting the projection from the insulating layer, and by providing the insulating layer between the projections. Since the electric field is generated intensively at the position corresponding to the above, the ink can easily fly even at a low electric field intensity. Thus, stable ink flying can be realized even when the potential of the electrostatic latent image or the recording voltage is lowered, and the power supply device and the drive circuit system for charging the latent image carrier or applying the recording voltage can be downsized and simplified. Power can be saved, and costs 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.

Further, in the image forming apparatus of the present invention,
When the insulating layer has an ink contact angle of about 50 ° or more, and the protrusion has an ink contact angle of about 30 ° or less,
The ink repelled by the insulating layer gathers on the protrusions having good wettability and the meniscus is more easily formed,
The electric field strength required for ink flying can be further reduced.

[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.
2, a corona charging device 14 for uniformly charging the surface of the photosensitive drum 12, and an exposure for writing an electrostatic latent image 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. 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 paper S as a recording medium, and a photosensitive drum after transfer A cleaning device 22 that collects ink remaining on the surface of the cleaning device 12 and a static elimination device 24 that erases an electrostatic latent image are arranged.

The method of writing an electrostatic latent image is not limited to the 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 includes a casing 26 having an opening facing the photosensitive drum 12. A conductive ink 28 is accommodated inside the casing 26. At the opening of the casing 26, an ink carrying roller 30 is disposed in parallel opposition to the photosensitive drum 12 with a slight gap therebetween, and is rotatable in the direction of arrow b. The ink carrying roller 30 is electrically connected to an offset power supply 38. A seal roller 32 is provided between the upper edge 26a of the casing 26 and the ink carrying roller 30,
This prevents leakage and drying of the ink. A regulating blade 34 is provided at an upper edge of the casing 26 opposite to the seal roller 32 with respect to the ink carrying roller 30 so as to adjust a gap between the ink carrying roller 30 and the ink carrying roller 30. Thus, when the ink carrying roller 30 rotates, the ink carrying roller 30 facing the photosensitive drum 12 is rotated.
A thin conductive ink layer 36 is formed covering the surface of the conductive ink. The thin ink layer 36 can be regulated to a predetermined thickness by adjusting the regulating blade 34.

As shown in FIG. 3A, a large number of minute projections 40 are formed on the surface of the ink carrying roller 30 in a matrix arrangement. However, the projections 40 are not limited to the matrix arrangement, but may be, for example, a staggered arrangement as shown in FIG. The columnar projection 40 is made of, for example, a conductive material such as a metal. This material has an ink contact angle of about 30 °
It has the following properties with good ink wettability. Further, a polarity different from the latent image potential, for example, a predetermined positive voltage, is applied to each of the protrusions 40 on the ink carrying roller 30 from the offset power supply 38. The predetermined voltage may be used as the ground voltage by directly grounding the ink carrying roller 30.

As shown in FIG. 4, the ink carrying roller 30
An insulating layer 42 is provided between the respective protrusions 40 on the surface of the substrate, and the tip of each protrusion 40 protrudes from the insulating layer 42. The insulating layer 42 is made of an ink repellent material having an ink contact angle of about 50 ° or more, and has a surface tension of 45 dyn.
e / cm or less. Suitable materials include polyvinyl chloride, polyethylene terephthalate, polyvinyl fluoride, polymethyl methacrylate, polystyrene, polyvinylidene fluoride, polyethylene, polytrifluoroethylene, polypropylene, and tetrafluoroethylene.
Examples include ethylene copolymer, paraffin, polytetrafluoroethylene, hexatriacontan, and propylene hexafluoride.

The pitch p of the projections 40 in the axial direction and the rotation direction of the ink carrying roller 30 is 20 to 100 μm.
m is preferable. The ratio a: b of the width a of the projection 40 to the width b between the projections 40 does not necessarily have to be 1: 1.
It is preferably in the range of 7: 3 to 3: 7. Insulating layer 4
The height c of the protrusion 40 from the second surface is preferably about 10 to 100 μm. The thickness d of the insulating layer 42 is preferably about 1 to 50 μm.

The shape of the projection 40 is not limited to a column, but may be a rectangular parallelepiped. Further, as shown in FIG. 5A, the tip of the projection 40 may be formed in a hemispherical shape. In this case, it is only necessary that the tip of the protrusion 40 slightly protrudes from the insulating layer 42, and the insulating layer 42 may be formed to a thickness such that it covers the rounded portion of the tip of the protrusion 40. Further, as shown in FIG. 5B, the protrusion 40 may be formed in a conical or pyramid shape, or as shown in FIG. 5C, the protrusion 40 may be formed in a truncated cone or truncated pyramid shape. May be.

Next, the image forming apparatus 10 having the above configuration
Will be described. When the ink carrying roller 30 is driven to rotate in the direction of arrow b, the thin ink layer 36 is uniformly formed by covering the surface of the ink carrying roller 30 facing the photosensitive drum 12 by being regulated by the regulating blade 34. Is done. In addition, each protrusion 4 on the ink carrying roller 30
A positive predetermined voltage is applied to 0 from the offset power supply 38.

In this state, when each projection 40 on the ink carrying roller 30 faces the grounded photosensitive drum 12,
As shown in FIG. 6, a charge having a polarity opposite to the latent image potential, that is, a positive charge is induced at the tip of each protrusion 40 by electrostatic induction, and the positive charge covers each protrusion 40. Injected into 36. An electric field is formed between the positive charge of the thin ink layer 36 thus injected and the charge of the photosensitive drum 12 between them. This electric field is
It does not occur between the insulating layer 42 between the projections 40 and the photosensitive drum 12, but occurs intensively between each projection 40 and the photosensitive drum 12. Due to the action of the electric field, a Coulomb force in the direction toward the photosensitive drum 12 acts on the ink around each of the protrusions 40, whereby the ink rises on the protrusions 40 to form a meniscus 52. At this time, each projection 4
Since the leading end of 0 protrudes beyond the insulating layer 42 on the surface of the ink carrying roller 30, the meniscus 52 is easily formed on the thin ink layer 36 covering the leading end of the projection 40.
Further, since the insulating layer 42 has a property of repelling ink,
The ink easily gathers around the protrusions 40 having good ink wettability, which also makes it easier for the meniscus 52 to be formed.

When the thin ink layer 36 on which the meniscus 52 is formed is opposed to the negatively charged electrostatic latent image on the photosensitive drum 12, the Coulomb force acting on the meniscus 52 is further increased. As a result, the meniscus 52 52
The ink droplet 54 separates and flies from the tip of the ink droplet. The flying ink droplet 54 once adheres to the electrostatic latent image to form an ink image, and is then 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
After an ink image is formed by being once attached to the upper electrostatic latent image, the ink image is transferred to paper S, and so on.
The image formation is performed by indirectly adhering ink droplets from the ink carrying roller 30 to the paper S.

As described above, according to the image forming apparatus 10 of the present embodiment, the protrusion 40 protrudes from the insulating layer 42 so that a meniscus is easily formed on the protrusion 40, By providing the insulating layer 42 on the surface, the electric field is generated intensively at the position corresponding to the protrusion 40, so that the ink can easily fly even at a low electric field intensity. As a result, even if the potential of the electrostatic latent image is lowered, stable ink flying can be realized, and a power supply device and a drive circuit system for charging the photosensitive drum can be reduced in size, simplified, and power-saving, and cost can be reduced. Can be inexpensive.

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 electric influence such as electric discharge, so that the ink image forming system as a whole becomes stable, and the durability and reliability against environmental changes are improved. Can be very high.

The insulating layer 42 has an ink contact angle of about 5
0 ° or more, and the protrusion 40 has an ink contact angle of about 3
Since the angle is equal to or less than 0 °, the ink repelled by the insulating layer 42 gathers on the protrusions 40 having good wettability and the meniscus 5
2 is more easily formed, which can also contribute to a reduction in the strength of the ink flying electric field.

Here, an ink flying experiment was performed using the image forming apparatus 10 of the present embodiment. 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
And

Further, regarding the ink carrying roller 30,
The diameter is 100 mm, the peripheral speed is 200 mm / sec, the pitch p of the projections 40 is 50 μm, the ratio a: b of the width a of the projections 40 to the width b between the projections 40 is 1: 1, and the height of the projections 40 c
Was set to 20 μm, and the thickness d of the insulating layer 42 was set to 5 μm.
Such an ink carrying roller 30 first applies a polypropylene resin to the surface of an aluminum tube by dipping to a thickness of 5 μm, and then removes the polypropylene resin at a position corresponding to the protrusion 40 by excimer laser processing in a circular shape, and The aluminum tube was used as an electrode, and nickel was electroformed on the resin-removed portion to form the projection 40, thereby manufacturing the device.

Each projection 40 has an offset power source 3
8, a voltage of +1.5 kV was applied. Further, 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 87 wt% of water as a solvent.
%, 1 wt% of polyethylene glycol as viscosity modifier
%, Styrene acrylate as a dispersant was 2 wt%, and the surface tension of the ink at that time was 45 dyne / cm.
Met. Experiments under these conditions showed that the ink flew well against the electrostatic latent image.

On the other hand, in the comparative experiment, when the height c of the projection 40 was set to 0 and the ink carrying roller 30 was made to have a smooth surface, and the other conditions were the same as in the above experiment, the ink did not fly. Accordingly, it was confirmed that the image forming apparatus 10 of the present embodiment can stably fly the ink even under a low electric field intensity.

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. 7, 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 principle of ink flying in the image forming apparatus 60 is the same as that described above with reference to FIG. As shown in FIG. 8, 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. Image forming apparatus 60 of the present embodiment
Accordingly, 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 this image forming apparatus 70, the recording electrode 72 is
Is opposed to the ink carrying roller 30 of the ink developing device 18 via the. 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. 10, the recording electrode 72 includes a number of individual electrodes 74 arranged at regular intervals in a direction orthogonal to the paper transport direction, and the individual electrodes 7.
4 and a protective insulating portion 76 that covers the periphery of the semiconductor device 4. 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 image information, so that a recording voltage having a negative polarity is applied to the individual electrode 74 at a position where a dot is to be formed by flying ink. In addition,
The configuration of the recording electrode 72 is illustrated in FIG.
2 is not limited to this form, and another form of multi-stylus electrode may be used.

The principle of flying ink 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 0, 60, and 70, the roller 30 was used as the ink carrier. However, as shown in FIG. 11, an ink carrying belt 48 having the same surface layer structure 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. On the contrary, the present invention can be applied 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 and 3B are partially enlarged plan views showing an arrangement pattern of protrusions on an ink carrying roller.

FIG. 4 is a sectional view taken along line IV-IV of FIG.

FIGS. 5A to 5C are partially enlarged cross-sectional views showing a modification of the shape of the protrusion.

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

FIG. 8 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. 9 is a schematic configuration diagram of an image forming apparatus according to still another embodiment of the present invention.

FIG. 10 is a partially enlarged view of a recording electrode.

FIG. 11 is a schematic configuration diagram of an image forming apparatus showing a modified example using a belt as an ink carrier.

[Explanation of symbols]

10 image forming apparatus, 12 photosensitive drum (latent image carrier), 30 ink carrier roller (ink carrier), 36
... a thin conductive ink layer, 40 ... a protrusion, 42 ... an insulating layer, 5
2: Meniscus, 54: Ink droplet.

Claims (2)

[Claims] An ink is ejected from a conductive ink thin layer formed over the surface of an ink carrier according to a recording voltage applied to an electrostatic latent image on a latent image carrier or a recording electrode,
In an image forming apparatus for forming an image by indirectly or directly attaching the flying ink to a recording medium, an insulating layer is provided on the surface of the ink carrier, and a large number of minute conductive members each of which protrudes from the insulating layer. An image forming apparatus comprising: forming protrusions; and applying a predetermined voltage having a polarity different from the electrostatic latent image or the recording voltage to the protrusions. 2. The image forming apparatus according to claim 1, wherein said insulating layer has an ink contact angle of about 50 ° or more, and said projection has an ink contact angle of about 30 ° or less.