JPH10202883A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus having high ejection frequency and capable of forming a high density image of high quality free from blur. SOLUTION: An ink jet printer has the recording head arranged in opposed relation to a platen roller and the recording head has a plurality of ejection electrodes to which ink is supplied. A platen roller is set to predetermined potential VO and, in such a state that all of ejection electrodes are set to bias potential Vb, recording voltage Vp is applied to the electrodes selected corresponding to an image signal and ink is allowed to fly to form an image. When the above mentioned recording operation is completed, all of the ejection electrodes are returned to bias potential and the potential of the platen roller is controlled to cleaning potential V1. At this time, the cleaning potential V1 is determined so as to form Vp-VO<Vb-V1. By this constitution, the ink stagnated at an ejection point without being allowed to fly is allowed to fly by a stronger electric field and new ink is supplied.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ink in which charged colorant particles are dispersed in an insulating liquid, whereby an electrostatic force is applied to the ink to cause ink droplets containing the colorant particles to fly on a recording medium. The present invention relates to an image forming apparatus that forms an image.

[0002]

2. Description of the Related Art In recent years, in the field of personal printers, ink jet recording type printers which form an image on a recording medium by flying ink droplets toward the recording medium have become widespread.

A recording head of such an ink-jet printer includes a plurality of discharge electrodes provided in parallel with each other and arranged at equal intervals, and coloring material particles charged at a discharge point at the tip of each discharge electrode in an insulating liquid. And an ink supply device for supplying the dispersed ink.

Further, a recording head has a bias power supply for applying a bias voltage to each ejection electrode, and a recording voltage (a voltage having the same polarity as that of the colorant particles) is selectively applied to each ejection electrode according to an image signal. And a recording voltage generator for applying the voltage.

Further, a grounded counter electrode is provided at a position facing the discharge point at the tip of each discharge electrode at a predetermined distance, and a recording medium is disposed between the counter electrode and the discharge electrode. .

When an image is formed on a recording medium by the ink jet printer configured as described above, first, ink is supplied to each discharge point of a recording head by an ink supply device. Then, a predetermined bias voltage having the same polarity as that of the colorant particles is applied to each ejection electrode. By applying the bias voltage, the colorant particles are repelled from the ejection electrodes and moved between the electrodes, and are moved toward the ejection point.

Subsequently, a recording voltage is applied to a discharge electrode selected in accordance with an image signal, and an electric field large enough to fly an ink droplet is formed between the discharge electrode and the counter electrode.
As a result, the colorant particles are further moved to the discharge point of the selected discharge electrode, and an electrostatic force, which is the product of the electric charge of the moved colorant particles and the electric field generated by the recording voltage, acts on the colorant particles. When the electrostatic force becomes larger than the surface tension of the ink droplet formed at the ejection point, the ink droplet is separated from the ejection point and flies toward the counter electrode. Therefore, the flying ink droplets adhere to the recording medium disposed between the ejection point and the counter electrode, and an image corresponding to the image signal is formed on the recording medium.

[0008]

However, in the above-described conventional recording head, the concentration of colorant particles contained in ink droplets flying from a discharge point selected according to an image signal is applied to a discharge electrode. It is known that it depends on the applied time of the applied bias voltage. For this reason,
When ink droplets are continuously ejected from one ejection point, a sufficient amount of colorant particles cannot be collected at this ejection point in a short time in each flight stage, and the concentration of the colorant particles in the ejected ink droplets Is unstable.

In addition, since a large amount of time is required to move the colorant particles having a sufficient charge amount required for flight to the discharge point of the selected discharge electrode, a high discharge frequency of ink droplets can be obtained. There is a problem that becomes difficult.

An object of the present invention is to provide an image forming apparatus having a high ejection frequency and capable of forming a high-density and high-quality image without bleeding.

[0011]

According to a first aspect of the present invention, there is provided an image forming apparatus, comprising: a recording liquid formed by dispersing charged colorant particles in an insulating liquid; Supply means for supplying to a discharge position separated by a predetermined distance from the forming medium, and forming a first electric field at the discharge position;
The supply means aggregates the colorant particles contained in the recording liquid supplied to the discharge position, forms a second electric field stronger than the first electric field at the discharge position, and covers the aggregated colorant particles. Recording means for flying toward the image forming medium, and forming a third electric field stronger than the second electric field at the ejection position;
And removing means for removing a residue containing the insulating liquid that has not been flown from the discharge position by flying from the discharge position.

According to a second aspect of the present invention, there is provided an image forming apparatus comprising: a conveying means for conveying an image forming medium to a predetermined transfer position; and charged colorant particles dispersed in an insulating liquid. A supply unit for supplying a recording liquid to a discharge position separated by a predetermined distance from the transfer position, and a first electric field from the discharge position to the transfer position in a state in which the image forming medium is transported by the transport unit. Then, the colorant particles contained in the recording liquid supplied to the discharge position by the supply unit are aggregated, and the first color particles from the discharge position to the transfer position are aggregated.
A recording means for forming a second electric field stronger than the electric field of (1) and causing the aggregated colorant particles to fly toward the image forming medium; and discharging the ink in a state where the image forming medium is not conveyed by the conveying means. Forming a third electric field that is stronger than the second electric field from the position to the transfer position, and removing the residue containing the insulating liquid that has not been flown from the discharge position by flying from the discharge position. And a collecting means for collecting the residue removed by the removing means.

According to a third aspect of the present invention, there is provided an image forming apparatus comprising: a supply unit for supplying a recording liquid formed by dispersing charged colorant particles in an insulating liquid to a predetermined discharge position; A plurality of ejection electrodes each having a leading end extending to a position, a counter electrode disposed at a predetermined distance from the discharge position, and a predetermined transfer position between the plurality of discharge electrodes and the counter electrode, the image forming medium. A first electric field directed from the plurality of ejection electrodes to the counter electrode while the image forming medium is being conveyed by the conveyance unit, and the supply unit moves to the ejection position by the supply unit. The colorant particles contained in the supplied recording liquid are aggregated near the respective tips of the plurality of ejection electrodes, and are stronger than the first electric field from the ejection electrode selected according to an image signal to the counter electrode. Form 2 electric fields Recording means for causing the colorant particles aggregated near the tip of the discharge electrode to fly toward the image forming medium, and the plurality of discharge electrodes in a state where the image forming medium is not being conveyed by the conveying means. A third electric field, which is stronger than the second electric field toward the counter electrode, is formed, and the residue containing the insulating liquid that has not been flown near the tip of each of the discharge electrodes and flies is directed toward the counter electrode. The apparatus includes a removing unit and a collecting unit that collects the residue flying by the removing unit from the counter electrode.

According to another aspect of the present invention, there is provided an image forming apparatus, comprising: a supply unit for supplying a recording liquid, which is obtained by dispersing charged colorant particles in an insulating liquid, to a predetermined discharge position; A recording head having a plurality of ejection electrodes having a tip extending to a position, a conductive platen roller arranged at a predetermined distance from the ejection position, and a recording medium between the recording head and the platen roller. A conveying unit that conveys the image forming medium along the outer peripheral surface of the platen roller through a predetermined transfer position between the plurality of ejection electrodes and the platen roller in a state where the image forming medium is conveyed by the conveying unit. A first electric field is applied from the plurality of ejection electrodes to the platen roller by applying a potential difference of 1 to the colorant particles contained in the recording liquid supplied to the ejection position by the supply unit. And a second potential difference greater than the first potential difference is applied between the ejection electrode selected in accordance with an image signal and the platen roller, and the selected ejection is performed. A second electric field, which is stronger than the first electric field from the electrode toward the platen roller, is formed to direct the agglomerated colorant particles near the tip of the discharge electrode toward the image forming medium conveyed along the platen roller. A third potential difference larger than the second potential difference is applied between the plurality of ejection electrodes and the platen roller in a state where the image forming medium is not transported by the recording means and the transporting means. A third electric field stronger than the second electric field from the plurality of ejection electrodes to the platen roller.
Removing means for forming an electric field of the above, and flying the residue containing the insulating liquid remaining without flying near the tip of each of the discharge electrodes toward the platen roller; and A collecting means having a cleaning roller for collecting the residue flying on the outer peripheral surface of the platen roller by the means.

According to another aspect of the present invention, an image forming apparatus supplies a recording liquid formed by dispersing charged colorant particles in an insulating liquid to a discharge position separated by a predetermined distance from an image forming medium. A first electric field is formed at the discharge position, and a colorant particle contained in the recording liquid supplied to the discharge position is aggregated by the supply means, and the first electric field is formed at the discharge position. Recording means for forming a stronger second electric field and causing the aggregated colorant particles to fly toward the image forming medium; and a third electric field opposite to the first and second electric fields at the discharge position; And a fourth electric field stronger than the second electric field.
The electric field is formed alternately, a removing means for applying vibration to the residue containing the insulating liquid remaining without flying from the discharge position and removing the residue by flying from the discharge position is provided. I have.

According to a sixth aspect of the present invention, in the image forming apparatus, a conveying means for conveying the image forming medium to a predetermined transfer position, and the charged colorant particles are dispersed in an insulating liquid. A supply unit for supplying a recording liquid to a discharge position separated by a predetermined distance from the transfer position, and a first electric field from the discharge position to the transfer position in a state in which the image forming medium is transported by the transport unit. Then, the colorant particles contained in the recording liquid supplied to the discharge position by the supply unit are aggregated, and the first color particles from the discharge position to the transfer position are aggregated.
A recording means for forming a second electric field stronger than the electric field of (1) and causing the aggregated colorant particles to fly toward the image forming medium; and discharging the ink in a state where the image forming medium is not conveyed by the conveying means. A third electric field opposite to the first and second electric fields and a fourth electric field which is stronger than the second electric field from the ejection position to the transfer position are alternately formed at positions, and a third electric field is formed from the ejection position. Removing means for applying vibration to the residue including the insulating liquid remaining without flying and removing the residue by flying from the discharge position, and collecting means for collecting the residue removed by the removing means And

According to another aspect of the present invention, there is provided an image forming apparatus comprising: a supply unit for supplying a recording liquid, which is obtained by dispersing charged colorant particles in an insulating liquid, to a predetermined discharge position; A plurality of ejection electrodes each having a leading end extending to a position, a counter electrode disposed at a predetermined distance from the discharge position, and a predetermined transfer position between the plurality of discharge electrodes and the counter electrode, the image forming medium. A first electric field directed from the plurality of ejection electrodes to the counter electrode while the image forming medium is being conveyed by the conveyance unit, and the supply unit moves to the ejection position by the supply unit. The colorant particles contained in the supplied recording liquid are aggregated near the respective tips of the plurality of ejection electrodes, and are stronger than the first electric field from the ejection electrode selected according to an image signal to the counter electrode. Form 2 electric fields Recording means for causing the colorant particles aggregated near the tip of the discharge electrode to fly toward the image forming medium; and a plurality of the plurality of the colorant particles from the counter electrode in a state where the image forming medium is not being conveyed by the conveying means. A third electric field directed toward the discharge electrode and a fourth electric field which is stronger than the second electric field directed from the plurality of discharge electrodes toward the counter electrode are alternately formed, and do not fly near the tip of each discharge electrode. Removing means for vibrating the residue containing the insulating liquid remaining on the surface and causing the residue to fly toward the counter electrode; and collecting means for collecting the residue flying by the removing means from the counter electrode. And

Further, in the image forming apparatus according to the present invention, there is provided an image forming apparatus comprising: a supply means for supplying a recording liquid, which is obtained by dispersing charged coloring material particles in an insulating liquid, to a predetermined discharge position; A recording head having a plurality of ejection electrodes having a tip extending to an ejection position, a conductive platen roller arranged at a predetermined distance from the ejection position, and And a transport unit that transports the image forming medium along the outer peripheral surface of the platen roller through a predetermined transfer position, and sets the potential of the platen roller to a reference potential V0 while transporting the image forming medium by the transport unit. The potential of the plurality of ejection electrodes is set to a bias potential Vb to provide a first potential difference between the plurality of ejection electrodes and the platen roller. A first electric field is directed toward the discharger, and the colorant particles contained in the recording liquid supplied to the discharge position by the supply unit are aggregated near the tips of the plurality of discharge electrodes. The potential of the ejection electrode selected according to the image signal is changed to the recording potential Vp higher than the bias potential Vb
To apply a second potential difference VA larger than the first potential difference to the platen roller, thereby forming a second electric field stronger than the first electric field from the selected discharge electrode toward the platen roller. Recording means for causing the colorant particles aggregated near the tip of the discharge electrode to fly toward the image forming medium conveyed along the platen roller, and the image forming medium is not conveyed by the conveying means In this state, the potentials of the plurality of ejection electrodes are changed to the bias potential Vb.
In addition, the potential of the platen roller is set so that the potential difference VD between the first cleaning potential higher than the recording potential and the bias potential Vb lower than the bias potential Vb is larger than the second potential difference VA. A third electric field from the platen roller toward the plurality of discharge electrodes and a fourth electric field stronger than the second electric field from the plurality of discharge electrodes to the platen roller alternately with a second cleaning potential. A removing means for vibrating the residue including the insulating liquid remaining without flying near the tip of each of the discharge electrodes and causing the residue to fly toward the platen roller; and A cleaning roller that is rolled on the roller and collects the residue flying on the outer peripheral surface of the platen roller by the removing unit; It includes a collecting unit that, the.

[0019]

Embodiments of the present invention will be described below in detail with reference to the drawings. As shown in FIG. 1, an ink jet printer 1 as an image forming apparatus according to the present invention includes a housing 2. A recording head 10 for forming an image by causing ink droplets to fly on recording paper in accordance with an image signal is provided at a predetermined position in the housing 2.
(Described later) are provided. The print head 1 is located at a position facing the front end of the print head 10 at a predetermined distance from the leading end of the ink droplet, that is, substantially at the center of the housing 2.
A platen roller 21 that acts as a counter electrode that forms a predetermined electric field with a discharge electrode 0 described later and that conveys a recording paper P as a medium on which an image is formed is rotatably disposed. . The recording head 10 is mounted on the moving stage 11 so as to be movable in the axial direction of the platen roller 21, and is arranged at a predetermined angle toward the outer peripheral surface of the platen roller 21.

The ink supplied to the recording head 10 is stored in an ink reservoir 13. The recording head 10 and the ink reservoir 13 are connected via a supply pipe 15, and a supply pump 14 for pumping ink to the recording head 10 is provided in the supply pipe 15.
The supply pump 14 adjusts the supply amount and supply pressure of ink so that an ink meniscus (described later) formed at the tip of the recording head 10 is stabilized. In the ink reservoir 13, a propeller 18 for agitating the ink to uniformly disperse the toner in the ink and a density sensor 19 for detecting the toner density in the ink are provided.

The ink jet printer 1 has a transport mechanism 20 including a platen roller 21 for transporting the recording paper P on which an image is formed. The transport mechanism 20 includes a recording paper cassette 22 that stores the recording paper P before recording, a take-out roller 23 that intermittently takes out the recording paper P one by one from the recording paper cassette 22, and a platen roller 21 that takes out the taken-out recording paper P.
And a guide plate group 25 for guiding the recording paper P conveyed by the conveyance roller group 24, and the recording paper P while keeping the interval between the recording paper P and the recording head 10 constant. It has a platen roller 21 to be conveyed and a tray 26 for receiving the recording paper P after image formation from the platen roller 21.

A platen roller 21 is provided on the outer peripheral surface of the platen roller 21 substantially opposite to the recording head 10.
A cleaning roller 28 for removing excess ink adhered to the sheet is rolled. Cleaning roller 28
Is formed of felt or sponge. Also,
A control unit 30 for controlling each operation of the printer 1 such as driving of the recording head 10, supply of ink, conveyance of the recording paper P, and the like, and a high-voltage power supply are installed near the bottom in the housing 2.

The ink used in the ink jet printer 1 configured as described above is prepared by mixing toner as colorant particles charged to a predetermined polarity in a carrier liquid as an insulating liquid at a ratio of 10% by weight or less. It is configured to be distributed. The carrier liquid is composed of an isoparaffin-based solvent having an electric resistivity of at least 10 ⁹ ohm-cm or more, and preferably an insulating liquid (for example, Isopar G, H, and L having an electric resistance of 10 ¹² to 10 ¹³ or more). As a dispersion medium, the toner has a particle size of about 0.01 to 5 μm. In this embodiment, the toner is charged to a positive polarity in advance.

Next, a control system for controlling the operation of the ink jet printer 1 configured as described above will be described. As shown in FIG. 2, the control system of the ink jet printer 1 has a control unit 30 acting as control means. The control unit 30 includes a control panel 31 on which various operation inputs are performed by a user, a ROM 32 storing control data such as various operation programs of the printer 1, an external I / F 33 connected to an external device such as a scanner, and an external I / F. A RAM 34 for temporarily storing image data input via the F33, a high-voltage power supply 35 for generating a high voltage to be applied to the platen roller 21 and the recording head 10,
A density sensor 19 for detecting the toner density of the ink in the ink reservoir 13 is connected.

The control unit 30 includes a head movement controller 3 that drives the moving stage 11 on which the recording head 10 is mounted and slides the recording head 10 in a desired direction.
6. A transport motor 37 for driving the transport mechanism 20 for transporting the recording paper P, a motor 38 for rotating the cleaning roller 28, a platen roller drive circuit 4 for controlling the platen roller 21 to a predetermined potential, and recording via the high voltage power supply 35. A voltage is applied to each electrode of the head 10 described later, and the recording head 1
0, a supply pump 14 for pumping ink from the ink reservoir 13 to the recording head 10, a propeller 18 for stirring ink contained in the ink reservoir 13, and toner detected by the density sensor 19. A cartridge 39 for supplying high-density ink according to the density is connected.

Next, the operation of the ink jet printer 1 configured as described above will be described. The inkjet printer 1 operates according to a program stored in the ROM 32.

First, in accordance with an instruction input from the control panel 31 or the external I / F 33, image data is input via the external I / F.
4 is written once.

Then, the transport motor 37 of the transport mechanism 20 is rotated at a predetermined speed, and the recording paper P is taken out of the cassette 22. The taken out recording paper P is wound around the platen roller 21 and transported. At this time, the ink in the ink reservoir 13 is agitated by the propeller 18, and the ink is supplied to the recording head 10 via the supply pump 14. In addition, the toner concentration of the ink contained in the ink reservoir 13 is monitored by the concentration sensor 19, high-concentration ink is supplied via the cartridge 39, and the toner concentration is kept constant.

In this state, the recording head 10 is driven according to the image data stored in the RAM 34, and a predetermined electric field is formed between the recording head 10 and the platen roller 21. Then, ink droplets fly from the recording head 10 onto the recording paper P being conveyed via the platen roller 21, and a desired image is formed on the recording paper P.

The recording paper P on which the image is formed is transported by the transport mechanism 2
Further, the sheet is further conveyed by the “0” and discharged onto the sheet discharge tray 26. Next, the recording head 10 will be described in detail. As shown in FIG. 3, the recording head 10 has a rectangular plate-shaped base material 41 fixed at a predetermined angle with respect to the housing 2, and the upper surface of the base material 41 has a rectangular shape as shown in FIG. A film substrate 42 is attached. Film substrate 42
Is formed of a dielectric film, for example, a polyimide film having a thickness of 100 μm. The recording head 10
Is that the front end 42a of the film substrate 42 is
The front end 42a is inclined at a predetermined angle with respect to a horizontal plane so that the front end 42a faces upward toward the platen roller 21.

A plurality of discharge electrodes 44 are formed on the upper surface of the film substrate 42 and extend parallel to and away from the front end 42a of the film substrate 42 by a predetermined distance.
The tip of each ejection electrode 44 is the front end 42a of the film substrate 42.
And a rear end extends to a rear end 42b of the film substrate 42.

The front end 42a of the film substrate 42 is provided one-to-one with respect to each of the ejection electrodes 44.
A plurality of rectangular cutouts 45 extending from 2a to near the tip 44a of each ejection electrode 44 are formed. The width of each notch is set to 20 to 200 μm, and the portion of the notch 45 opened at the front end 42 a of the film substrate 42 forms an ink discharge point corresponding to each discharge electrode 44.

On the upper surface of the film substrate 42 near the front end 42a of the film substrate 42, a comb-shaped partition member 46 having a plurality of ink supply paths 48 divided for each discharge electrode 44 is formed.
Are arranged. A plurality of tips 46 a where the partition member 46 is located between the notches 45 are converged toward the open end of each notch 45 and are inclined toward the front end 42 a of the film substrate 42. That is, each ink supply path 48 is formed so as to become thinner toward the ink discharge point.

On the upper surface of the film substrate 42, a cover member 51 for covering the partition member 46 and forming an ink supply path in cooperation with the partition member 46 is provided. The cover member 51 includes a film substrate 42.
Has a common ink chamber 52 communicating with each ink supply path 48 in a state of being mounted on the upper surface (the partition member 46), and the supply pipe 15 led from the ink reservoir 13 is connected to the common ink chamber 52. ing.

The common ink chamber 52 is inclined at a predetermined angle downward toward the front end 42a of the film substrate 42 in a state where the recording head 10 is arranged to be inclined from the horizontal plane as described above. Thus, the ink supplied at a predetermined pressure via the supply pipe 15 is uniformly distributed to the respective ink supply paths 48 via the common ink chamber 52, and the ink of a predetermined shape is formed at the discharge point of each ink supply path 48. A meniscus is formed. At this time, the ink is sucked by the capillary action of the notch 45 formed at the front end 42a of the film substrate 42, and is guided to the discharge point.

The cover member 51 has an upper surface (inclined surface) 51a which is inclined at substantially the same angle along the common ink chamber, and a toner transport electrode 54 is provided on the inclined surface 51a. The toner transport electrode 54 extends over the entire width of the plurality of ink supply paths 48 formed on the film substrate 42, that is, the entire width of the common ink chamber 52, and transfers the toner contained in the ink flowing through the common ink chamber 52 to each ink. It is provided for efficiently leading to the supply path 48.

That is, the toner transport electrode 54 is connected to the opposite electrode (platen roller) 2 from the tip 44 a of each ejection electrode 44.
It is provided at a position retracted from 0, in other words, at a position upstream of the leading end 44a of each ejection electrode 44 with respect to the ink supply direction. Then, by controlling the potentials of the discharge electrode 44 and the toner transport electrode 54 so that the potential increases in the order of the counter electrode 20, the discharge electrode 44, and the toner transport electrode 54, the toner is efficiently transported to each ink supply path 48. You.

For example, the potential of the platen roller 21 is set to 0
V, the bias potential of each ejection electrode 44 is 1.2 KV, the recording voltage superimposed on each ejection electrode 44 is 400 V, and the potential of the toner transport electrode 54 is 2.4 KV (the recording voltage is superimposed on the bias voltage applied to the ejection electrodes). In this case, an electric field is formed in the vicinity of the leading end of the recording head 10 along the line of electric force as indicated by an arrow E in FIG.

When an electric field E as shown in FIG. 5 is formed in the vicinity of the discharge point, the common ink chamber 52 is influenced by the electric field component from the toner transport electrode 54 to each discharge electrode 44.
The electrostatic force is applied to the toner in the ink flowing through the ink, and the toner is urged toward each ejection electrode 44. As a result, the toner extruded from the common ink chamber 52 to each ink supply path 48 is discharged from the ejection electrode 44 to the platen roller 21.
Due to the influence of the electric field component toward the ink meniscus 56, the ink is moved in the direction toward the liquid surface of the ink meniscus 56, and is conveyed to each ejection point along the liquid surface of the ink meniscus 56 (FIG. 6).
reference).

By the way, the ink supply path 48 near each discharge point is formed by the partition member 46 so as to become thinner toward the discharge point. Therefore, the ink meniscus 56 formed at each ejection point is formed so as to be thinner and narrower toward the ejection point.
Therefore, the toner moved toward each discharge point due to the influence of the electric field E collides with the liquid surface of the thinned ink meniscus and migrates, and is efficiently aggregated at the discharge point by the action of the partition member 46. (See FIG. 7).

The operation in the case where ink droplets fly from the ejection point of the recording head 10 will be described below with reference to FIG. When a bias voltage is applied to each ejection electrode 44 in a state where ink is supplied to each ink supply path 48 of the recording head 10 and an ink meniscus is formed near each ejection point, as shown in FIG. Then, the toner is aggregated toward the discharge point, an electrostatic force is applied to the toner aggregate, and the ink meniscus 61 rises toward the platen roller 21. At this time, the magnitude of the bias voltage is set so that the electrostatic attraction force applied to the toner aggregate from the platen roller 21 does not break the surface tension of the ink meniscus 61.

As described above, when the recording voltage is applied to the ejection electrode 44 selected according to the image signal in a state where the toner is aggregated in the vicinity of each ejection point, as shown in FIG. Ink meniscus 6 formed at the ejection point
1 is further protruded toward the platen roller 21 to form a thread-shaped ink meniscus 61 having the width of the notch 45 as a base end.

Then, as shown in FIG. 8C, the electrostatic force applied to the toner aggregate agglomerated in the ink meniscus 61 overcomes the surface tension of the ink meniscus 61, and the opening end of the notch 45 is used as a node. The toner aggregate is separated from the ink meniscus and flies toward the platen roller 21.

In this case, since the dot diameter of the ink droplet flying from the ink meniscus 61 is determined by the opening width of the notch 45, the dot diameter can be made uniform by setting the width of the notch 45 to a predetermined value. Can be. If the dot diameter is made uniform, an image without roughness can be formed on the recording paper P, and high-quality image quality can be obtained. For example, when the opening width of the notch 45 was set to 60 μm, an ink droplet having a stable dot diameter of 50 μm was formed.

Further, since the dot diameter of the ink droplet is determined by the opening width of the notch 45, the width of the ink supply path can be made larger than the desired dot diameter. Thereby, even if the dot diameter is set small, the width of the ink supply path can be set large, and clogging of the ink can be prevented. Further, by reducing the width of the notch 45, the ink meniscus can be reduced, the surface tension for stopping the toner aggregate can be reduced, and the ink ejection frequency can be increased.

When the width of the ink supply path is made larger than the width of the notch 45 as described above, the interval between pixels becomes larger when multi-channeling is performed. For this reason, the recording head 10 is placed on the moving stage 11, and the recording head 10 is slid along the direction in which the pixels are arranged, that is, in the axial direction of the platen roller 21 for scanning.

Hereinafter, an appropriate mounting angle of the recording head 10 will be described. The shape of the ink meniscus formed at each ejection point of the recording head 10 is
It is determined by the wettability of the ink with respect to 2, the capillary action of the notch 45, the voltage applied to the ejection electrode 44 (the electric field formed by applying the voltage), gravity, and the like. Therefore, when the mounting angle of the recording head 10 is changed, the direction of gravity acting on the ink meniscus is changed, and the shape of the ink meniscus is changed.

For example, as shown in FIG. 9, when the arrangement angle of the recording head 10 with respect to the horizontal plane is set to 0 ° or less,
The thickness of the ink meniscus increases near the front end 42a of the film substrate 42. When a recording voltage is applied to the ejection electrode 44 in this state, the ink droplets fly before a sufficient amount of toner is collected, and the ink containing a large amount of the carrier liquid is transferred onto the recording paper P. As a result, bleeding occurs in the image on the recording paper P.

On the other hand, as shown in FIG. 10, when the recording head 10 is arranged at an angle of 60 degrees with respect to the horizontal plane, it is difficult for the ink to reach the front end 42a of the film substrate 42, and the ink meniscus near the discharge point is reduced. become thinner.
In this state, even if a recording voltage is applied to the ejection electrode 44, it is difficult for the toner to aggregate at the ejection point, it takes a long time to collect enough toner for flying, the ink ejection frequency decreases, and the ink ejection frequency decreases. The dot size of the drop is reduced.

The relationship between the inclination angle of the recording head 10 and the printing characteristics was examined. When the inclination angle of the recording head 10 was set to 0 ° or less, bleeding occurred in the image. Is 500 Hz or less. Therefore, it is determined that the appropriate tilt angle of the recording head 10 is 0 to 45 degrees, and the recording head 10
By setting the inclination angle of this range to within this range, it was possible to obtain a high-quality image without bleeding at an ejection frequency of 1 KHz.

Next, the recording operation of the recording head 10, particularly the cleaning operation of the ink staying at the discharge point after flying the toner aggregate, will be described with reference to FIG.
This will be described with reference to the timing charts shown in FIGS. Here, the potential of the discharge electrode 44 is shown by a solid line, and the potential of the platen roller 21 is shown by a broken line.

In the recording head 10, when the toner aggregate agglomerated at the discharge point is separated from the carrier liquid and flies, the remaining carrier liquid without flying stays near the discharge point. The carrier liquid retained near the discharge point in this way is changed in quality as the toner is consumed, and the resistance of the liquid surface is gradually reduced.

That is, when the carrier liquid stays in the vicinity of the discharge point, ions generated by air discharge adhere to the ink surface under the influence of the electric field, and positive ions other than the toner contained in the carrier liquid are affected by the electric field. Pressed to. In addition, the negative ions generated in the carrier liquid due to the mutual charging action with the toner increase as the toner is consumed, and the negative ions are charged to a positive polarity by charge injection from the electrodes, and are charged on the ink surface by the influence of the electric field. Pressed, the ink near the discharge point becomes conductive,
The liquid surface resistance of the ink surface is reduced.

As described above, when the liquid surface resistance of the ink surface is reduced, the amount of the carrier liquid that flies together with the toner aggregates increases, causing an image formed on the recording paper P to bleed, and Image cannot be formed.

For this reason, in the present embodiment, a predetermined potential difference is applied between each of the discharge electrodes 44 of the print head 10 and the platen roller 21 at the end of the printing operation, so that the print head 10 undesirably stays near the discharge point. The carrier liquid having a low liquid surface resistance flies toward the platen roller 21,
Instead, new ink with a high liquid surface resistance is supplied to the ejection point.

More specifically, as shown in FIG. 11A, the potential of the platen roller 21 is set to V0, the potential of each discharge electrode 44 is set to the bias potential Vb at which the toner does not fly, and the recording paper P is printed. In the transported state, the recording voltage Vp is applied to the ejection electrode 44 selected according to the image signal at a predetermined timing.
To cause ink droplets to fly toward the recording paper P. Although FIG. 11A shows a timing chart in which all the pixels are printed, it goes without saying that some pixels are not printed.

As described above, when the ink droplets are ejected and the recording operation for one recording sheet is completed, the recording sheet P is ejected onto the ejection tray 26 and the potentials of all the ejection electrodes 44 are reduced. The platen roller 21 is returned to the bias potential Vb.
Is controlled to the cleaning potential V1. In this case, the cleaning potential V1 is the potential difference VA between the discharge electrode 44 and the platen roller 21 when the ink droplet flies.
From (VP-V0), the potential difference VB (Vb) between the discharge electrode 44 and the platen roller 21 during the cleaning operation.
−V1) is set to be larger. That is, the relationship of VA <VB holds between the potential difference VA during the recording operation and the potential difference VB during the cleaning operation.

As described above, by applying a potential difference VB, which is larger than the potential difference VA during the recording operation, between each ejection electrode 44 and the platen roller 21 during the cleaning operation, a stronger electric field is formed at each ejection point than during the recording operation. In this way, the ink having a low liquid surface resistance that has stayed at each discharge point without flying during the printing operation can easily fly toward the platen roller 21.

The ink droplets flying by the cleaning operation and adhering to the platen roller 21 are transported with the rotation of the platen roller 21 and
8 removed.

The timing for performing the above-described cleaning operation can be set arbitrarily.
It is not necessary to limit the timing to each time the recording operation of a sheet is completed. The potential difference VB between each of the discharge electrodes 44 and the platen roller 21 during the cleaning operation is set to a range where no discharge occurs so that a discharge is not generated between the two and the electrodes are not damaged. .

As described above, by applying a potential difference between each of the discharge electrodes 44 and the platen roller 21 that is larger than that during the printing operation, undesired ink staying at the discharge point can be easily removed, and the density of the ink is always high. Ink can be supplied to the ejection points. Therefore, the amount of the carrier liquid that flies together with the toner aggregates can be kept low, and a high-quality image without bleeding can be formed.

As another embodiment, the discharge electrode 4
There is also a method in which a potential difference is applied between the roller 4 and the platen roller 21 at a timing as shown in FIG.

According to this method, when the recording operation is completed as described above, the potentials of all the ejection electrodes 44 are returned to the bias potential Vb, and the platen roller 2
The first cleaning potential is set to the first cleaning potential V2 and then to the second cleaning potential V3. The first and second cleaning potentials V2 and V3 each have a predetermined pulse width. Then, this operation is repeated a plurality of times as one cycle to clean the undesired ink.

The first cleaning potential V2 is set slightly higher than the recording potential Vp applied to the discharge electrode 44. When the platen roller 21 is set to the first cleaning potential V2, the first cleaning potential V2 The potential and the potential of the platen roller 21 are reversed. Therefore, in a state where the platen roller 21 is set to the first potential, the direction of the electric field is reversed, and the substance having the negative polarity flies toward the platen roller 21. Also, the platen roller 2
When 1 is set to the first cleaning potential V2, the nonpolar carrier liquid generated by the mutual charging action with the toner and the like also flies.

However, if the direction of the electric field is reversed for a long time as described above, a problem arises that the toner charged to the positive polarity due to the electric field in the opposite direction adheres to the discharge electrode 44. For this reason, the pulse width of the first cleaning potential V2 applied to the platen roller 21 is shortened to such an extent that the toner does not adhere to the first cleaning potential V2.
Immediately after the application of 2, the second cleaning potential V3 is applied.

The potential difference VD between the second cleaning potential V3 and the bias potential Vb applied to the ejection electrode 44 during the printing operation is determined by the difference between the printing potential Vp applied to the ejection electrode 44 during the printing operation and the potential V0 of the platen roller 21. Is set to be larger than the potential difference VA between the two. That is, the relationship VA <VD is established between the potential difference VA during the recording operation and the potential difference VD during the cleaning operation.

As described above, the potential difference VD larger than the potential difference VA during the recording operation is applied to each of the ejection electrodes 44 and the platen roller 2.
1, an electric field that is stronger than that during the printing operation is formed at each ejection point, and the ink having a low liquid surface resistance that stays at each ejection point without flying during the printing operation is easily directed to the platen roller 21. Can fly.

As described above, as the cleaning operation,
By applying a first cleaning potential higher than the recording potential of the discharge electrode 44 to the platen roller 21, the direction of the electric field can be reversed so that a non-polar substance or a carrier liquid can fly from the discharge point. Discharge electrode 4
By giving a potential difference between the platen 4 and the platen roller 21 larger than that during the printing operation, undesired ink staying at the ejection point can be easily removed, and ink with a high density can always be supplied to the ejection point. Therefore, the amount of the carrier liquid that flies together with the toner aggregates can be kept low, and a high-quality image without bleeding can be formed.

Also, as in the present embodiment, by alternately changing the potential of the platen roller 21 between the first cleaning potential V2 and the second cleaning potential V3, ink, particularly toner Can be applied to the toner to prevent the toner from adhering to the film substrate 42 and the like. Note that the present invention is not limited to the above-described embodiment, and can be variously modified within the scope of the present invention.

[0070]

As described above, since the image forming apparatus of the present invention has the above-described configuration and operation, it has a high ejection frequency, and can produce high-quality images with high density and no bleeding. Can be formed.

[Brief description of the drawings]

FIG. 1 is a schematic view showing an ink jet printer of the present invention.

FIG. 2 is a block diagram showing a control system for controlling the operation of the inkjet printer of FIG.

FIG. 3 is a sectional view showing a recording head incorporated in the ink jet printer of FIG.

4 is a film substrate incorporated in the recording head of FIG. 3,
FIG. 3 is a perspective view showing an ejection electrode and a partition member.

FIG. 5 is a diagram showing the direction of an electric field formed between a recording head and a platen roller by lines of electric force.

FIG. 6 is a schematic diagram illustrating a state of toner toward an ejection point at a leading end of a recording head.

FIG. 7 is a plan view of the recording head of FIG. 6;

FIG. 8 is an operation explanatory diagram illustrating an ink droplet flying operation by a recording head.

FIG. 9 is a schematic diagram illustrating the shape of an ink meniscus when the inclination angle of the recording head is set to 0 ° or less.

FIG. 10 is a schematic diagram showing the shape of an ink meniscus when the inclination angle of the recording head is set to 60 degrees.

FIG. 11 is a timing chart showing potentials applied to ejection electrodes and a platen roller during a recording operation and a cleaning operation.

DESCRIPTION OF SYMBOLS 1 ... Inkjet printer, 2 ... Housing, 10 ... Recording head, 11 ... Moving stage, 13 ... Ink reservoir, 20 ... Transport mechanism, 21 ... Platen roller, 28 ... Cleaning roller, 30 ... Control unit, 35 ... High voltage power supply, 42 ... Film substrate, 44 ... Ejection electrode, 45 ... Notch, 46 ... Partition member, 48 ... Ink supply path, 51 ... Cover member, 52 ... Common ink chamber, 54 ... Toner transport electrode, 56 ... Ink Meniscus, P: Recording paper.

Claims (8)

[Claims] A supply unit configured to supply a recording liquid formed by dispersing charged colorant particles in an insulating liquid to a discharge position separated from an image forming medium by a predetermined distance; and a first electric field is applied to the discharge position. Forming, aggregating the colorant particles contained in the recording liquid supplied to the discharge position by the supply means, the second electric field stronger than the first electric field at the discharge position.
A recording means for forming an electric field of the type described above and causing the aggregated colorant particles to fly toward the image forming medium; and forming a third electric field stronger than the second electric field at the discharge position and flying from the discharge position. An image forming apparatus comprising: a removing unit configured to fly a residue including an insulating liquid remaining without flying from the discharge position to remove the residue. 2. A conveying means for conveying an image forming medium to a predetermined transfer position, and a recording liquid, which is obtained by dispersing charged colorant particles in an insulating liquid, to a discharge position separated from the transfer position by a predetermined distance. A supply unit for supplying, and a first electric field from the discharge position to the transfer position is formed in a state where the image forming medium is transported by the transport unit, and the first electric field is supplied to the discharge position by the supply unit. The colorant particles contained in the recording liquid are aggregated to form a second electric field stronger than the first electric field from the discharge position to the transfer position, and the aggregated colorant particles fly toward the image forming medium. A recording unit for causing the image forming medium to be conveyed by the conveyance unit, and a third electric field stronger than the second electric field from the ejection position to the transfer position is formed from the ejection position. Remained without flying An image forming apparatus, comprising: a removing unit configured to fly a residue including an insulating liquid from the discharge position to remove the residue; and a collecting unit configured to collect the residue removed by the removing unit. . 3. A supply means for supplying a recording liquid obtained by dispersing charged colorant particles in an insulating liquid to a predetermined discharge position; a plurality of discharge electrodes having a tip extending to the discharge position; A counter electrode disposed at a predetermined distance from the discharge position; a transport unit that transports the image forming medium through a predetermined transfer position between the plurality of discharge electrodes and the counter electrode; In a state where the forming medium is transported, a first electric field is formed from the plurality of ejection electrodes to the counter electrode, and the plurality of colorant particles contained in the recording liquid supplied to the ejection position by the supply unit are removed. To form a second electric field stronger than the first electric field directed from the ejection electrode selected in accordance with an image signal to the counter electrode, and formed near the tip of the ejection electrode. Aggregated colorant particles A recording unit that flies toward the image forming medium; and a third unit that is stronger than the second electric field from the plurality of ejection electrodes to the counter electrode in a state where the image forming medium is not being conveyed by the conveying unit. A removing means for forming an electric field and flying a residue containing the insulating liquid remaining without flying near the tip of each of the ejection electrodes toward the counter electrode; and removing the residue fly by the removing means. An image forming apparatus, comprising: a collecting unit that collects from the counter electrode. 4. A supply means for supplying a recording liquid obtained by dispersing charged colorant particles in an insulating liquid to a predetermined discharge position, and a plurality of discharge electrodes having a tip extending to the discharge position. A recording head, a conductive platen roller disposed at a predetermined distance from the ejection position, and an image forming medium on a peripheral surface of the platen roller through a predetermined transfer position between the recording head and the platen roller. Transport means for transporting the image-forming medium along the transporting means, and applying a first potential difference between the plurality of discharge electrodes and the platen roller in a state in which the image forming medium is transported by the transport means. Forming a first electric field toward the roller, causing the colorant particles contained in the recording liquid supplied to the discharge position by the supply means to aggregate near the tips of the plurality of discharge electrodes; And applying a second potential difference larger than the first potential difference between the discharge electrode selected in accordance with the signal and the platen roller to be stronger than the first electric field from the selected discharge electrode toward the platen roller. A recording unit that forms a second electric field and causes the colorant particles aggregated near the tip of the discharge electrode to fly toward an image forming medium conveyed along the platen roller; In a state where the forming medium is not being conveyed, a third potential difference larger than the second potential difference is applied between the plurality of ejection electrodes and the platen roller, and the third potential difference from the plurality of ejection electrodes toward the platen roller is increased. 2
Removing means for forming a third electric field stronger than the electric field of the above, and causing the residue containing the insulating liquid remaining without flying near the tip of each of the discharge electrodes to fly toward the platen roller; An image forming apparatus, comprising: a collecting unit having a cleaning roller for collecting a residue that has been rolled and that has been flying on the outer peripheral surface of the platen roller by the removing unit. 5. A supply means for supplying a recording liquid formed by dispersing charged colorant particles in an insulating liquid to a discharge position separated from an image forming medium by a predetermined distance, and applying a first electric field to the discharge position. Forming, aggregating the colorant particles contained in the recording liquid supplied to the discharge position by the supply means, the second electric field stronger than the first electric field at the discharge position.
Recording means for forming an electric field of the type described above and causing the aggregated colorant particles to fly toward the image forming medium; a third electric field in the discharge position opposite to the first and second electric fields; A fourth electric field which is stronger than the electric field is alternately formed to vibrate the residue containing the insulating liquid which does not fly from the discharge position and remove the residue by flying from the discharge position. And an image forming apparatus. 6. A transporting means for transporting an image forming medium to a predetermined transfer position, and a recording liquid formed by dispersing charged colorant particles in an insulating liquid to a discharge position separated from the transfer position by a predetermined distance. A supply unit for supplying, and a first electric field from the discharge position to the transfer position is formed in a state where the image forming medium is transported by the transport unit, and the first electric field is supplied to the discharge position by the supply unit. The colorant particles contained in the recording liquid are aggregated to form a second electric field stronger than the first electric field from the discharge position to the transfer position, and the aggregated colorant particles fly toward the image forming medium. Recording means for causing the image forming medium to be conveyed by the conveying means, a third electric field opposite to the first and second electric fields at the ejection position, and the transfer from the ejection position to the ejection position. The second power Removing means for alternately forming a fourth electric field stronger than the field, vibrating the residue containing the insulating liquid remaining without flying from the discharge position, and removing the residue by flying from the discharge position An image forming apparatus comprising: a collecting unit configured to collect a residue removed by the removing unit. 7. A supply means for supplying a recording liquid formed by dispersing charged colorant particles in an insulating liquid to a predetermined discharge position; a plurality of discharge electrodes having a tip extending to the discharge position; A counter electrode disposed at a predetermined distance from the discharge position; a transport unit that transports the image forming medium through a predetermined transfer position between the plurality of discharge electrodes and the counter electrode; In a state where the forming medium is transported, a first electric field is formed from the plurality of ejection electrodes to the counter electrode, and the plurality of colorant particles contained in the recording liquid supplied to the ejection position by the supply unit are removed. To form a second electric field stronger than the first electric field directed from the ejection electrode selected in accordance with an image signal to the counter electrode, and formed near the tip of the ejection electrode. Aggregated colorant particles And recording means for flying toward the image forming medium, in a state where an image forming medium is not conveyed by the conveying means, third toward from the counter electrode to said plurality of ejection electrodes
And a fourth electric field stronger than the second electric field from the plurality of ejection electrodes to the counter electrode is formed alternately, and the insulating liquid remaining without flying near the tip of each ejection electrode is formed. Removing means for applying vibration to the containing residue and causing the residue to fly toward the counter electrode; and collecting means for collecting the residue flying by the removing means from the counter electrode. An image forming apparatus comprising: 8. A supply means for supplying a recording liquid formed by dispersing charged colorant particles in an insulating liquid to a predetermined discharge position, and a plurality of discharge electrodes having a tip extending to the discharge position. A recording head, a conductive platen roller disposed at a predetermined distance from the ejection position, and an image forming medium on a peripheral surface of the platen roller through a predetermined transfer position between the recording head and the platen roller. Transport means for transporting the image forming medium by the transport means, and setting the potential of the platen roller to a reference potential V0 and the potential of the plurality of ejection electrodes to a bias potential Vb while transporting the image forming medium. A first electric potential difference is applied between the discharge electrodes of the plurality of discharge electrodes and the platen roller to form a first electric field from the plurality of discharge electrodes toward the platen roller. The colorant particles contained in the recording liquid supplied to the ejection position are aggregated near the respective tips of the plurality of ejection electrodes, and in this state, the potential of the ejection electrode selected according to the image signal is changed from the bias potential Vb. A second potential difference V larger than the first potential difference between the platen roller and the platen roller at a high recording potential Vp.
A, forming a second electric field that is stronger than the first electric field from the selected ejection electrode toward the platen roller, and causing the colorant particles aggregated near the tip of the ejection electrode to travel along the platen roller. A recording unit that flies toward the image forming medium being conveyed; and a state in which the image forming medium is not conveyed by the conveying unit, the potentials of the plurality of ejection electrodes are set to the bias potential V.
b, the potential of the platen roller is set to a first cleaning potential higher than the recording potential, and a potential difference VD between the first potential and the bias potential Vb is lower than the bias potential Vb and larger than the second potential difference VA. A third electric field from the platen roller toward the plurality of ejection electrodes and a fourth electric field stronger than the second electric field from the plurality of ejection electrodes toward the platen roller alternately with the second cleaning potential. Removing means for forming an electric field alternately, vibrating the residue containing the insulating liquid remaining without flying near the tip of each of the discharge electrodes, and causing the residue to fly toward the platen roller; A cleaning roller that is rolled and contacted with a platen roller and collects a residue flying on the outer peripheral surface of the platen roller by the removing unit. It includes a collecting means having an image forming apparatus according to claim.